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1.
  • Chung, J. -H, et al. (författare)
  • Carrier-mediated antiferromagnetic interlayer exchange coupling in diluted magnetic semiconductor multilayers Ga1-xMnxAs/GaAs:Be
  • 2008
  • Ingår i: Physical Review Letters. - 0031-9007 .- 1079-7114. ; 101:23
  • Tidskriftsartikel (refereegranskat)abstract
    • We report the antiferromagnetic (AFM) interlayer exchange coupling between Ga0.97Mn0.03As ferromagnetic semiconductor layers separated by Be-doped GaAs spacers. Polarized neutron reflectivity reveals a characteristic splitting at the wave vector corresponding to twice the multilayer period, indicating that the coupling between the ferromagnetic layers is AFM. When the applied field is increased to above the saturation field, this AFM coupling is suppressed. This behavior is not observed when the spacers are undoped, suggesting that the observed AFM coupling is mediated by doped charge carriers. © 2008 The American Physical Society.
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2.
  • Chung, J. -H, et al. (författare)
  • Investigation of weak interlayer exchange coupling in GaMnAs/GaAs superlattices with insulating nonmagnetic spacers
  • 2011
  • Ingår i: Journal of Applied Physics. - : AIP Publishing. - 0021-8979 .- 1089-7550. ; 110:1
  • Tidskriftsartikel (refereegranskat)abstract
    • A robust long-range antiferromagnetic coupling between ferromagnetic Ga 0.97Mn 0.03As layers has previously been realized via insertion of nonmagnetic Be-doped GaAs spacers between the magnetic layers. In this paper we report the observation of weak antiferromagnetic coupling between Ga 0.97Mn 0.03As layers through undoped GaAs spacers with thicknesses as large as 25 monolayers. The field and the temperature dependences of the sample magnetization suggest that the interlayer coupling in these systems substantially deviates from typical ferromagnetic behavior. Polarized neutron reflectivity measurements reveal antiferromagnetic alignment between Ga 0.97Mn 0.03As layers when a weak field is applied perpendicular to the magnetic easy axis during cooling below T C. The strength of the observed coupling between the magnetic layers is estimated to be weaker than 0.05 mT.
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3.
  • Yoon, Y. J., et al. (författare)
  • Effect of p-type buffer layer on the properties of GaMnAs ferromagnetic semiconductors
  • 2004
  • Ingår i: Journal of the Korean Physical Society. - 0374-4884 .- 1976-8524. ; 45:SUPPL., s. S720-S723
  • Tidskriftsartikel (refereegranskat)abstract
    • We have studied the magnetic and transport properties of Ga 1-xMn xAs epilayers grown either on undoped or on p-type doped GaAs buffer layer. The temperature dependence of the resistivity at zero magnetic field reveals that the Curie temperature (T C) in the Ga 1-xMn xAs layer grown on p-type doped GaAs buffer is slightly higher than that observed in the layer grown on undoped GaAs buffer. The magnetic and transport properties of the two samples show significant differences when they are placed in a magnetic field. In SQUID measurements, the Ga 1-xMn xAs layer grown on p-type buffer shows a larger coercive field and much slower decay of remanent magnetization than the layer grown on undoped buffer. This robust magnetic behavior observed in the doped sample is discussed in terms of the increase of free carrier concentration in the system arising from p-type doping in the buffer layer.
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4.
  • Kim, H., et al. (författare)
  • Magneto-transport properties of GaMnAs:Si ferromagnetic semiconductors
  • 2009
  • Ingår i: Journal of the Korean Physical Society. - : Korean Physical Society. - 0374-4884 .- 1976-8524. ; 55:1, s. 304-308
  • Tidskriftsartikel (refereegranskat)abstract
    • The magnetic properties of a series of GaMnAs:Si ferromagnetic semiconductor films, in which the Mn concentration ranges from 7% to 10%, were investigated by using magneto-transport measurements. The temperature dependence of the resistivity revealed a systematic increase in the Curie temperature (T c) with increasing Mn concentration in the series. Since the T0 of the undoped GaMnAs ferromagnetic semiconductor decreases with increasing Mn concentration above 6%, the observation of a systematic increase of T c with increasing Mn concentration in our GaMnAs:Si series indicates the effectiveness of our counter doping for the incorporation of a a large amount of 7% Mn in the system. The field scan of the planar Hall effect (PHE) showed a typical two-step switching behavior at low temperatures, indicating the presence of a strong cubic anisotropy. The switching fields, however, systematically decreased with increasing Mn concentration in the series. The angular dependences of the switching fields were fitted by using the magnetic free energy and Cowburn's model to obtained the domain pinning energy, which showed systematically smaller values as the Mn concentration of the sample was increased. The temperature dependences of the pinning energies indicated a change in the uniaxial anisotropy from the [110] to the [110] direction with increasing Mn concentration in the series.
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5.
  • Chung, S., et al. (författare)
  • Giant magnetoresistance and long-range antiferromagnetic interlayer exchange coupling in (Ga,Mn)As/GaAs:Be multilayers
  • 2010
  • Ingår i: Physical Review B. Condensed Matter and Materials Physics. - 1098-0121 .- 1550-235X. ; 82:5
  • Tidskriftsartikel (refereegranskat)abstract
    • We report the observation of the giant magnetoresistance effect in semiconductor-based GaMnAs/GaAs:Be multilayers. Clear transitions between low-field-high-resistance and high-field-low-resistance states are observed in selected samples with Be-doped nonmagnetic spacers. These samples also show negative coercive fields in their magnetic hysteresis and antiferromagnetic (AFM) splittings in polarized neutron reflectivity. Our data indicate that the AFM interlayer exchange couplings in this system occur over much longer periods than predicted by current theories, strongly suggesting that the coupling in III-V semiconductor-based magnetic multilayers is significantly longer ranged than in metallic systems.
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6.
  • Chung, S. J., et al. (författare)
  • Effect of low temperature annealing on the magnetic properties of Ga 1-xMn xAs/GaAs superlattices
  • 2005
  • Ingår i: Journal of Superconductivity and Novel Magnetism. - : Springer Science and Business Media LLC. - 1557-1939. ; 18:1, s. 93-96
  • Tidskriftsartikel (refereegranskat)abstract
    • We have studied the effect of low-temperature (LT) annealing on the properties of Ga 1-xMn xAs/GaAs superlattices (SLs). One SL contained GaAs layers doped by Be (which acts as a p-type dopant), while the GaAs layers of the other SL were undoped. The Be-doped SL exhibited a coercive field (H C) three times larger than the undoped SL, and showed a much more robust remanent magnetization (M r). While the effect of LT annealing on the undoped SL was relatively minor, magnetic properties of the Be-doped SL changed significantly after annealing. The coercive field of the Be-doped SL was reduced about three times, becoming comparable to that of the undoped SL. After annealing the temperature dependence of M r in the Be-doped SL also became similar to the undoped SL. We discuss the effect of LT annealing on the magnetic properties of the two SL systems in terms of inter-diffusion of carriers, and of the reduced sensitivity to annealing characteristic of capped structures. © 2005 Springer Science+Business Media, Inc.
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7.
  • Chung, S. J., et al. (författare)
  • Magneto-transport properties of a GaMnAs-based ferromagnetic semiconductor trilayer structure grown on a ZnMnSe buffer
  • 2008
  • Ingår i: Journal of Electronic Materials. - : Springer Science and Business Media LLC. - 0361-5235 .- 1543-186X. ; 37:6, s. 912-916
  • Tidskriftsartikel (refereegranskat)abstract
    • Magneto-transport properties have been investigated in a ferromagnetic GaMnAs/GaAlAs/GaMnAs semiconductor trilayer structure grown on a ZnMnSe buffer layer. The presence of the ZnMnSe buffer leads to the formation of a spin-valve-like structure, which provides the opportunity to investigate spin scattering effects by Hall resistance and magnetoresistance (MR) measurements in the current-in-plane (CIP) configuration. The Curie temperature (T c) and coercivity of the bottom GaMnAs layer are observed to be different from those of the top GaMnAs layer due to the proximity effect between the ferromagnetic GaMnAs and paramagnetic ZnMnSe layers. A two-step behavior is observed in the hysteresis loops of the Hall resistance, indicating that the coercive fields are different in the two GaMnAs layers in the trilayer structure. The magnetoresistance (MR) measured simultaneously with the Hall resistance shows a sudden increase in the field region where the magnetization of the two GaMnAs layers is different. Although the MR ratio was observed to be only 0.04% in our trilayer structure (due to the experimental CIP configuration), the study clearly demonstrates the presence of spin scattering in a trilayer ferromagnetic semiconductor structure grown on a ZnMnSe buffer. © 2008 TMS.
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8.
  • Chung, S. J., et al. (författare)
  • Possible indication of interlayer exchange coupling in GaMnAs/GaAs ferromagnetic semiconductor superlattices
  • 2004
  • Ingår i: Journal of Applied Physics. - : AIP Publishing. - 0021-8979 .- 1089-7550. ; 95:11, s. 7402-7404
  • Tidskriftsartikel (refereegranskat)abstract
    • The effects of free carriers in the nonmagnetic spacer layer on the magnetic properties of GaMnAs/GaAs ferromagnetic semiconductor superlattices (SL) were investigated. In the SL system, one of the SL structures was doped with Be in the GaAs spacer layers, and the GaAs layer of the other SL were undoped in order to investigate the effects of carriers. The remanent magnetization of the two SL were calculated in order to analyze the robustness of the SL systems. The hardness of the magnetization in the SL with Be-doped GaAs layer was found to be related to interlayer coupling which was introduced by doping of the nonmagnetic layers.
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9.
  • Chung, S. J., et al. (författare)
  • Time stability of multi-domain states formed in the magnetization reversal process of GaMnAs film
  • 2007
  • Ingår i: Solid State Communications. - : Elsevier BV. - 0038-1098 .- 1879-2766. ; 143:4-5, s. 232-235
  • Tidskriftsartikel (refereegranskat)abstract
    • The magnetization reversal process of ferromagnetic GaMnAs epilayers has been systematically investigated using the planar Hall effect (PHE) and magnetoresistance (MR). We have observed non-abrupt transitions between two orientations of magnetization in PHE and striking resistance dips at the second switching in MR. The observed behaviors indicate that multi-domain structures are formed as magnetization undergoes a reorientation. An asymmetric PHE hysteresis loop was obtained when the range of the field scan was restricted to fields below the final magnetization transition. This indicates that the domain structure formed at the moment of magnetization reorientation remains stable even after the magnetic field is removed. The time stability of the multi-domain structure was further tested by monitoring the change in the planar Hall resistance value for more than 24 h.
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10.
  • Kim, J., et al. (författare)
  • Quantitative analysis of the angle dependence of planar Hall effect observed in ferromagnetic GaMnAs film
  • 2009
  • Ingår i: Journal of Applied Physics. - : AIP Publishing. - 0021-8979 .- 1089-7550. ; 105:7
  • Tidskriftsartikel (refereegranskat)abstract
    • The angle dependence of the planar Hall effect has been analyzed based on the magnetic free energy including the magnetic anisotropy and the Zeeman effects. The Zeeman effect dominated the magnetic anisotropy in high field and only a single energy minimum is shown in free energy over entire field angle, which leads to the coherent rotation of the magnetization in the form of a single domain state. When the field strength is reduced below 300 Oe, multiple energy minima appear in the angle dependence of free energy due to the increase in the relative importance of magnetic anisotropy. In the low field region, reorientation of magnetization experiences abrupt transition between the free energy minima. The pinning fields obtained from the analysis showed systematic dependence on the strength of external field, which was used to rotate magnetization. We understood such pinning energy dependence in terms of the difference in the free energy density profile for the different field strengths. © 2009 American Institute of Physics.
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11.
  • Kim, T., et al. (författare)
  • Strain-engineered magnetic anisotropy of GaMnAs ferromagnetic semiconductors
  • 2007
  • Ingår i: Journal of the Korean Physical Society. - : Korean Physical Society. - 0374-4884 .- 1976-8524. ; 50:3, s. 829-833
  • Tidskriftsartikel (refereegranskat)abstract
    • A series of GaMnAs epilayers grown on GaInAs buffer layers have been investigated. The concentrations of Mn in the GaMnAs layer and In in the GaInAs layer were varied in the series, for which the tensile strain condition for the GaMnAs layer are systematically changed. The X-ray measurement provided the lattice constants of the layers, from which the stain of the GaMnAs layer was determined. The magneto-transport data revealed in-plane anisotropy in the GaMnAs sample grown on a GaInAs buffer with a low concentration of In. Such in-plan magnetic anisotropy of the GaMnAs layer continuously changed to a vertical magnetic anisotropy when the tensile strain was increased in the sample grown on the GaInAs buffer with a higher In concentration. This experiment clearly demonstrated that the magnetic anisotropy of GaMnAs could be continuously engineered by using the strain introduced by the GaInAs buffer layers.
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12.
  • Lee, S., et al. (författare)
  • Doping effect on the properties of III-V ferromagnetic semiconductor GaMnAs epilayers and their superlattices
  • 2005
  • Ingår i: Journal of the Korean Physical Society. - 0374-4884 .- 1976-8524. ; 47:3, s. 444-447
  • Tidskriftsartikel (refereegranskat)abstract
    • We present a systematic study on the properties of the ferromagnetic (FM) III-V-based semiconductor GaMnAs, including extrinsically doped GaMnAs: Be and its heterostructures in the form of superlattices. In an attempt to further improve the Curie temperature T c of GaMnAs, we have undertaken a systematic program of extrinsic p-doping of this material. In GaMnAs with low x (x = 0.03), T c is, indeed, seen to increase monotonically with increasing Be doping. We also studied the effect of p-doping of non-magnetic spacer layers on the magnetic properties of GaMnAs/GaAs superlattices (SLs). While Be-doped SLs exhibited relatively robust remanent magnetization and a larger coercivity over a broad temperature range, undoped SLs showed a fast decrease in the remanent magnetization with temperature, and a rather small coercivity. We propose that the observed hardness of the magnetization in SLs with Be-doped GaAs layers is related to the interlayer coupling introduced by the doping of the non-magnetic layers.
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13.
  • Lee, S., et al. (författare)
  • Effect of be doping on the properties of GaMnAs ferromagnetic semiconductors
  • 2003
  • Ingår i: Journal of Applied Physics. - : AIP Publishing. - 0021-8979 .- 1089-7550. ; 93:10 3, s. 8307-8309
  • Tidskriftsartikel (refereegranskat)abstract
    • The effect of Be doping on the properties of GaMnAs ferromagnetic semiconductors was analyzed. The samples were characterized using SQUID and magnetotransport measurements. The observed increase in the critical temperature in Ga 1-xMn xAs for the low range of x can be explained by the increase of free carrier concentrations in the system arising from Be doping.
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14.
  • Lee, S., et al. (författare)
  • Tunable quaternary states in ferromagnetic semiconductor GaMnAs single layer for memory devices
  • 2007
  • Ingår i: Applied Physics Letters. - : AIP Publishing. - 0003-6951 .- 1077-3118. ; 90:15
  • Tidskriftsartikel (refereegranskat)abstract
    • The authors show that staggered asymmetric planar Hall resistance (PHR) loops observed in GaMnAs ferromagnetic semiconductor films with biaxial in-plane magnetic anisotropy result in four stable resistance states at zero magnetic field owing to the formation of a stable multidomain structure during magnetization reversal. The values of PHR can be systematically controlled by changing the direction and the scanning range of the applied magnetic field. The possibility of a quaternary memory device based on the observed four PHR states is demonstrated by obtaining consistent results in the writing process using appropriate sequences of magnetic field pulses. © 2007 American Institute of Physics.
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15.
  • Shin, D. Y., et al. (författare)
  • Precise investigation of domain pinning energy in GaMnAs using planar hall effect and magnetoresistance measurements
  • 2007
  • Ingår i: IEEE transactions on magnetics. - 0018-9464 .- 1941-0069. ; 43:6, s. 3025-3027
  • Tidskriftsartikel (refereegranskat)abstract
    • The planar Hall effect (PHE) and magnetoresistance (MR) measurements have been carried out on a GaMnAs ferromagnetic semiconductor. The PHE and MR spectra exhibit interesting two-step magnetization switching behavior arising from the magnetic anisotropy properties of the system. By fitting the angle-dependent planar Hall resistance (PHR) data taken at 5 kG with the Stoner-Wohlfarth model, the cubic and uniaxial anisotropy constants were independently obtained. The anisotropy constants lead to the precise determination of easy axis direction, which turns out to be in good agreement with the easy axis determined from the angular plot of the switching field. The domain pinning energies were further obtained by fitting the angle dependence of the switching field, including the effect of uniaxial anisotropy. © 2007 IEEE.
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16.
  • Shin, D. Y., et al. (författare)
  • Stable multidomain structures formed in the process of magnetization reversal in GaMnAs ferromagnetic semiconductor thin films
  • 2007
  • Ingår i: Physical Review Letters. - 0031-9007 .- 1079-7114. ; 98:4
  • Tidskriftsartikel (refereegranskat)abstract
    • The process of magnetization reversal in ferromagnetic Ga(1-x)MnxAs epilayers has been systematically investigated using the planar Hall effect (PHE). Interestingly, we have observed a pronounced asymmetry in the PHE hysteresis when the range of the field scan is restricted to fields below the final magnetization transition. The observed behavior indicates that (a)A multidomain structures are formed as M undergoes a reorientation, (b) the domain landscape formed in this way remains stable even after the magnetic field is switched off, and (c) the reorientation of magnetization directions corresponding to the transition points in PHE takes place separately within each domain. © 2007 The American Physical Society.
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17.
  • Shin, D. Y., et al. (författare)
  • Temperature dependence of magnetic anisotropy in ferromagnetic (Ga,Mn)As films : Investigation by the planar Hall effect
  • 2007
  • Ingår i: Physical Review B. Condensed Matter and Materials Physics. - 1098-0121 .- 1550-235X. ; 76:3
  • Tidskriftsartikel (refereegranskat)abstract
    • We carried out systematic planar Hall effect (PHE) measurements of GaMnAs ferromagnetic semiconductor film as a function of temperature. The two-step switching of the PHE occurring in the magnetization-reversal process was observed to change significantly as the temperature was increased. To investigate the mechanism responsible for such behavior, the temperature dependence of the PHE was continuously measured (with and without an external magnetic field) after the sample was first magnetized along one of the easy axes to produce an initial single-domain state at 3 K. A detailed temperature dependence of the magnetization direction was then obtained by taking the ratio of the planar Hall resistance measured with and without a magnetic field. As the temperature was increased, the direction of the easy axis of magnetization was observed to change from the [010] crystallographic direction to [110]. This reorientation of the easy axis direction can be understood in terms of the temperature dependence of the relative strengths of the magnetic anisotropy constants (i.e., of the ratio of uniaxial-to-cubic anisotropy) of the GaMnAs film. © 2007 The American Physical Society.
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18.
  • Son, H., et al. (författare)
  • Quantitative investigation of the magnetic anisotropy in GaMnAs film by using Hall measurement
  • 2008
  • Ingår i: Journal of Applied Physics. - : AIP Publishing. - 0021-8979 .- 1089-7550. ; 103:7
  • Tidskriftsartikel (refereegranskat)abstract
    • We have performed a systematic Hall measurement on the GaMnAs ferromagnetic films. The angular dependences of the Hall effects were obtained by changing the magnetic field angle in two different crystal planes [i.e., (001) and (110)]. The in-plane and out-of-plane anisotropy fields were obtained by analyzing the angular dependence of planar Hall resistance and anomalous Hall resistance based on the magnetic free energy model. While the cubic anisotropy fields both for in-plane and out-of-plane showed strong temperature dependence, the uniaxial anisotropy fields were insensitive to the temperature. © 2008 American Institute of Physics.
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19.
  • Yea, S.-y., et al. (författare)
  • Effect of chemical etching on magnetic anisotropy of ferromagnetic GaMnAs films studied by planar Hall effect
  • 2008
  • Ingår i: Solid State Communications. - : Elsevier BV. - 0038-1098 .- 1879-2766. ; 147:7-8, s. 309-312
  • Tidskriftsartikel (refereegranskat)abstract
    • We have investigated the effect of chemical etching on magnetic anisotropy of ferromagnetic GaMnAs film using the planar Hall effect (PHE). Different thicknesses were obtained on a single GaMnAs specimen by using different etching times on selected areas, and the PHE was then measured using the Hall bar configurations patterned on the area. Cubic and uniaxial anisotropy fields were obtained for the films by fitting the angular dependence of the PHE data to the Stoner-Wohlfarth model. The results exhibited a very systematic dependence on the etched thickness, demonstrating that the chemical etching process significantly affects the magnetic anisotropy of ferromagnetic GaMnAs films.
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20.
  • Yea, S. -Y, et al. (författare)
  • Thickness dependence of magnetic domain pinning energy in GaMnAs ferromagnetic semiconductor films
  • 2008
  • Ingår i: Journal of Applied Physics. - : AIP Publishing. - 0021-8979 .- 1089-7550. ; 103:7
  • Tidskriftsartikel (refereegranskat)abstract
    • Magnetotransport measurements were performed on GaMnAs films with four different thicknesses. The process of magnetization reorientation was investigated by planar Hall effect, from which the magnetization switching fields were determined for each film thickness. Domain pinning energies were then obtained for the films by fitting the angular dependence of the switching fields using the model developed by Cowburn [J. Appl. Phys. 78, 7210 (1995)]. The results show a systematic increase of domain pinning energies as the thickness of the film decreases. Such dependence of domain pinning can be understood in terms of the carrier dependence of magnetic anisotropy in GaMnAs films on the concentration of carriers. © 2008 American Institute of Physics.
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21.
  • Chung, Sunjae, et al. (författare)
  • Investigation of superlattices based on ferromagnetic semiconductor GaMnAs by planar Hall effect
  • 2012
  • Ingår i: Journal of Applied Physics. - : AIP Publishing. - 0021-8979 .- 1089-7550. ; 111:7, s. 07D310-1-07D310-3
  • Tidskriftsartikel (refereegranskat)abstract
    • Two ferromagnetic semiconductor GaMnAs-based superlattices (SLs) were investigated by measuring the planar Hall effect (PHE) with the external magnetic field applied in the plane of the sample. The two GaMnAs/GaAs SLs differed only by the Be doping of the nonmagnetic GaAs spacer layers. Both SLs showed a typical two-step transition behavior in PHE field scans at 4.0 K, essentially the same as that normally observed on single GaMnAs ferromagnetic layers with two in-plane magnetic easy axes. As the temperature increased to 30 K, the behaviors of the PHE changed differently in the two SL samples. The PHE in the undoped SL can be described simply by the temperature dependence of the magnetic anisotropy within the film plane of a GaMnAs film. However, the Be-doped SL revealed a completely different behavior, showing a transition of magnetization with a negative coercive field. The observation of this feature in a ferromagnetic multilayer indicates the presence of spontaneous anti-parallel interlayer exchange coupling between the GaMnAs magnetic layers.
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22.
  • Chung, S., et al. (författare)
  • Magnetization reorientation in Gax Mn1-x As films : Planar Hall effect measurements
  • 2010
  • Ingår i: Physical Review B. Condensed Matter and Materials Physics. - 1098-0121 .- 1550-235X. ; 81:15
  • Tidskriftsartikel (refereegranskat)abstract
    • The process of magnetization reorientation in a ferromagnetic semiconductor GaMnAs films was investigated using planar Hall effect measurements. In addition to the well-known two-step switching behavior that occurs during this process, we have observed two additional distinct features in field scan data of the planar Hall resistance (PHR). First, the region of the external field required to begin and complete the reorientation of magnetization from one easy axis to another strongly depends on the direction of the applied field. And second, the maximum amplitude of PHR is significantly reduced during magnetization reversal when the applied field is oriented near one of the easy axes of the GaMnAs film. We provide an explanation of these phenomena using the magnetic field dependence of the free-energy density and assuming the coexistence of multiple domains with three different directions of magnetization in the sample. 
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23.
  • Chung, S., et al. (författare)
  • The effect of carrier density on magnetic anisotropy of the ferromagnetic semiconductor (Ga, Mn)As
  • 2009
  • Ingår i: Solid State Communications. - : Elsevier BV. - 0038-1098 .- 1879-2766. ; 149:41-42, s. 1739-1742
  • Tidskriftsartikel (refereegranskat)abstract
    • Planar Hall effect (PHE) measurements are used to investigate magnetic anisotropy in two (Ga, Mn)As samples which differ by the hole concentration, but are otherwise identical. The difference in the hole density is controlled via modulation doping by Be. Angular dependence of PHE measured at 13 K reveals that the uniaxial easy axis in the sample with a lower hole concentration lies along the [110] direction, and along [over(1, ̄) 10] in the sample with higher doping. This difference in the orientation of uniaxial easy axes in the two samples demonstrates that the magnetization of GaMnAs can be manipulated just by varying the carrier density.
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24.
  • Kim, Y., et al. (författare)
  • Asymmetry in the reorientation process of magnetization for crossing the [1 1- 0] and the [110] directions in Ga1-x Mnx As epilayers
  • 2010
  • Ingår i: Journal of Applied Physics. - : AIP Publishing. - 0021-8979 .- 1089-7550. ; 107:9
  • Tidskriftsartikel (refereegranskat)abstract
    • The magnetization reversal processes of ferromagnetic Ga 1-xMnx As films with different Mn concentrations have been investigated using the planar Hall effect. The field scan of the planar Hall resistance (PHR) showed an asymmetric behavior for the reorientation of magnetization crossing the [1 1- 0] and the [110] directions. The magnetic anisotropy fields and the domain pinning field distributions of the films are obtained from the angle dependence of the PHR measurements. The magnetic anisotropy and pinning field distribution in the samples provided explanation for the observed asymmetric behavior in the magnetization reorientation process of Ga1-xMnx As film.
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25.
  • Lee, H., et al. (författare)
  • Magnetotransport properties of GaMnAs based trilayer structures with different thicknesses of InGaAs spacer layer
  • 2009
  • Ingår i: Journal of Applied Physics. - : AIP Publishing. - 0021-8979 .- 1089-7550. ; 105:7
  • Tidskriftsartikel (refereegranskat)abstract
    • Magnetotransport properties of GaMnAsInGaAsGaMnAs trilayer structures have been investigated by Hall measurements. The samples in the series are identical except for the InGaAs spacer thickness, which varies from 5 to 50 nm. The Hall measurements revealed the systematic change of magnetic easy axes from in-plane to out-of plane with increasing InGaAs spacer thickness. Such dependence of magnetic easy axes of the trilayer systems was understood in terms of the magnetic anisotropy change with spacer thickness. In the magnetization reversal process, various configurations of magnetization between the two GaMnAs layers were observed both in in-plane and out-of plane samples by the planar and the anomalous Hall effects. © 2009 American Institute of Physics.
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26.
  • Lee, H., et al. (författare)
  • Temperature dependence of magnetization in GaMnAs film with critical strain
  • 2009
  • Ingår i: Solid State Communications. - : Elsevier BV. - 0038-1098 .- 1879-2766. ; 149:31-32, s. 1300-1303
  • Tidskriftsartikel (refereegranskat)abstract
    • The temperature dependence of the magnetization properties of GaMnAs film, in which the strain was controlled to be in a critical condition by inserting a thin InGaAs layer, has been investigated by Hall measurements. The Hall resistance obtained with the magnetic fields perpendicular to the sample plane showed a slanted hysteresis, indicating the coexistence of in-plane and out-of-plane components of magnetization. The magnetic anisotropy fields of the sample were obtained from the angle dependence of the Hall resistance measurements. Using the magnetic anisotropy fields, the three-dimensional magnetic free energy diagrams were constructed for several temperatures. All energy diagrams show six energy minima along or near 〈 100 〉 directions, implying the possibility of magnetization within the plane and/or along out-of-plane directions in the system. Though the energy minima presented in the film plane (i.e., within the (001) plane) are deeper than those appeared along the out-of-plane direction (i.e., along the [001] direction) at 10 K, the situation is reversed as the temperature increases. This change of free energy density results in the temperature dependence of the magnetization directions in GaMnAs film with critical strain condition.
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27.
  • Lee, Sanghoon, et al. (författare)
  • Magnetotransport properties of ferromagnetic semiconductor GaMnAs-based superlattices
  • 2012
  • Ingår i: Current applied physics. - : Elsevier BV. - 1567-1739 .- 1878-1675. ; 12:SUPPL. 2, s. S31-S36
  • Tidskriftsartikel (refereegranskat)abstract
    • Two series of GaMnAs/GaAs superlattices (SSs) comprised of ferromagnetic semiconductor GaMnAs layers and non-magnetic GaAs spacers were investigated by the electronic transport measurements with an external magnetic field applied in the plane of the sample. The two SL series consisted of specimens that were structurally the same, but the GaAs spacers layers of one series were doped by Be, while in the second series the spacers were undoped. Although in field scans taken at 4 K all SLs showed a typical anisotropic magnetoresistance (MR) behavior dominated by magnetic anisotropy, similar to that normally observed in single GaMnAs ferromagnetic layers grown on GaAs (001) substrates, some of the SLs showed signatures of interaction between the GaMnAs layers in the form of broadening of the MR hysteresis. The effect of inter-layer exchange coupling (IEC) between the GaMnAs magnetic layers became clear in the MR data taken at 30 K, where the strength of the magnetic anisotropy was reduced to the level of the inter-layer interaction. Specifically, MR measurements on two of the Be-doped SLs (BD2 and BD3) exhibited conspicuously large values of resistance at zero field, along with transitions of magnetization with negative coercive fields. The observation of these features in GaMnAs/GaAs SLs indicates the presence of spontaneous antiferromagnetic (AFM) inter-layer exchange coupling (IEC) between the GaMnAs magnetic layers. The study further revealed that the IEC in the GaMnAs multilayers strongly depended on the properties of the non-magnetic GaAs spacers, such as their thickness and the density of carriers in the layers. Importantly, these IEC effects occurred on a longer range than that expected from current theoretical studies.
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28.
  • Son, H., et al. (författare)
  • Vertical gradient of magnetic anisotropy in the ferromagnetic semiconductor (Ga,Mn)As film
  • 2010
  • Ingår i: Applied Physics Letters. - : AIP Publishing. - 0003-6951 .- 1077-3118. ; 96:9
  • Tidskriftsartikel (refereegranskat)abstract
    • The properties of magnetic anisotropy of GaMnAs films along the growth direction were studied by Hall effect measurements. The magnetic anisotropy fields were obtained by analyzing the angular dependence of the planar Hall resistance and the anomalous Hall resistance for in-plane and out-of plane components of the Hall signal, respectively. The magnetic anisotropy fields obtained by this process were used to construct a three-dimensional magnetic free energy diagram, which clearly shows that the out-of-plane characteristics of magnetic anisotropy become more pronounced as we approach the bottom part of the film.
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29.
  • Yoo, T., et al. (författare)
  • Asymmetry in the planar Hall resistance of Fe films grown on vicinal GaAs substrates
  • 2010
  • Ingår i: Journal of Applied Physics. - : AIP Publishing. - 0021-8979 .- 1089-7550. ; 107:9
  • Tidskriftsartikel (refereegranskat)abstract
    • We have investigated the Hall effects of the ferromagnetic Fe films grown on standard (001) and on vicinal (i.e., slightly tilted toward the [1 1- 0] direction) GaAs substrates at room temperature. While the symmetric hysteresis in the planar Hall resistance (PHR) is obtained from Fe film grown nominal (001) substrate, a significant asymmetry appeared in the Fe films grown on vicinal GaAs substrates. The asymmetry in the hysteresis of the PHR observed in the Fe film grown on vicinal surface originates from the switching of magnetization M between two easy axes while it is confined to the (001) crystal plane rather than to the film plane, thus involves both the planar Hall effect (PHE) and the anomalous Hall effect (AHE). The contribution of the AHE systematically increases as the tilted angle of the substrate increases. The asymmetric hysteresis of the PHR in the Fe films grown on the tilted substrate provides four distinct resistance states, which can be used for quaternary memory devices. 
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30.
  • Yoo, T., et al. (författare)
  • Four discrete Hall resistance states in single-layer Fe film for quaternary memory devices
  • 2009
  • Ingår i: Applied Physics Letters. - : AIP Publishing. - 0003-6951 .- 1077-3118. ; 95:20
  • Tidskriftsartikel (refereegranskat)abstract
    • We report the realization of four distinct magnetic states using single layers of Fe at room temperature. When the Fe film was grown on the vicinal surface of GaAs, the fourfold-symmetric magnetization along crystallographic direction give rise to four distinct Hall resistance values due to the different combination of planar and anomalous Hall effects for the given direction. Each Hall resistance state can be written reproducibly by the sequence of field pulses and was remained constant at the written state for more than 2 h, which brings the idea of a quaternary memory device much closer to practical implementation. © 2009 American Institute of Physics.
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