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- Timopheev, A. A., et al.
(författare)
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Effect of interaction in the magnetization reversal relaxation of superparamagnetic granulaR CoFeB -SiO2 FILMS
- 2009
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Ingår i: Magnetism and Magnetic Materials. - : Scientific.Net. ; , s. 213-216
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Konferensbidrag (refereegranskat)abstract
- In order to study the magnetic interactions influence on the relaxation processes in superparamagnetic media, the magnetostatic measurements were carried out for the granular (CoFeB)x-(SiO2)1-x films with x values near percolation threshold. The observed temperature dependences of the coercivity for the samples magnetized along in-plane easy axis have shown two parts linear on √T with different inclination angles, which cross each other at the blocking temperature (Tb). The first part of the curve, which corresponds to the temperature range below T b, depends on the measuring time and is related to the thermal activation nature of magnetization reversal process in the blocked superparamagnetic state. Second part of the curve, which corresponds to the temperature range above Tb, is practically independent on the measuring time and is related to existence of correlated state of superparamagnetic grains moments, i.e. to superferromagnetic state. The method of the magnetization reversal curves simulation based on the numerical solving of kinetic equation has been applied to explain the experimental results.
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- Timopheev, A. A., et al.
(författare)
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The influence of intergranular interaction on the magnetization of the ensemble of oriented Stoner-Wohlfarth nanoparticles
- 2009
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Ingår i: Journal of Applied Physics. - : AIP Publishing. - 0021-8979 .- 1089-7550. ; 105:8
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Tidskriftsartikel (refereegranskat)abstract
- The influence of interparticle interaction on the processes of magnetization reversal is considered for an ensemble of oriented Stoner-Wohlfarth nanoparticles. This is done through a solution of a kinetic equation describing the relaxation of the total magnetization to its equilibrium value in an effective mean field which includes a term proportional to the instantaneous value of the magnetization. It is shown that the interparticle interaction influences the temperature dependence of a coercive field. Under certain conditions, the presence of the interparticle interaction can lead to the formation of the so-called superferromagnetic state with the correlated directions of the magnetic moments of the particles. If the system is unable to come to the equilibrium during the time interval necessary to perform measurements, some measured quantities become dependent on the measurement time. It is shown that the blocking temperature T-b and the temperature dependence of coercive field at T < T-b are strongly dependent on a measurement time. At T>T-b, however, the coercivity, if exists, does not depend on the measurement time. The data of magnetostatic measurements, carried out on the (CoFeB)(x)-(SiO2)(1-x) nanogranular films with the concentration of ferromagnetic particles slightly lower than a percolation threshold, are in compliance with the results of the calculations.
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- Johnsson, P., et al.
(författare)
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Transport anisotropy in hetero-amorphous (CoFeB)-SiO2 thin films
- 2003
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Ingår i: Journal of Applied Physics. - : AIP Publishing. - 0021-8979 .- 1089-7550. ; 93:10, s. 8101-8103
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Tidskriftsartikel (refereegranskat)abstract
- We here present resisitivity and magnetoresistance measurements of two granular (CoFeB)-SiO2 amorphous thin films, with a different amount of metallic content. The films were deposited onto substrates sitting on a rotating cylinder. This induces anisotropy in the film plane, which is higher for the sample with less metallic content. This film exhibits typical isotropic giant magnetoresistance (GMR), while the film with higher-metallic content has less anisotropic resistivity, and shows a mixture of GMR and anisotropic magnetoresistance (AMR). The AMR appears at fields below 500 Oe. We believe that this has not been observed before in amorphous samples.
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- Manuilov, Sergey. A., et al.
(författare)
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Ferromagnetic resonance, magnetic susceptibility, and transformation of domain structure in CoFeB film with growth induced anisotropy
- 2011
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Ingår i: Journal of Applied Physics. - : AIP Publishing. - 0021-8979 .- 1089-7550. ; 109:8, s. 083926-
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Tidskriftsartikel (refereegranskat)abstract
- Field dependence of magnetic susceptibility in nanocrystalline CoFeB film was studied in a wide frequency range from 500 kHz to 15 GHz. Anomalies of the susceptibility were detected exciting CoFeB film with a solenoidal coil, microwave strip line, in the tunable microwave cavity as well as employing magneto-optical domains imaging. Critical spin fluctuations in the form of "soft" modes were observed in a whole range of orientations of magnetic field perpendicular to the "easy" magnetic axis. A sequence of domain structure transformations was extensively examined in a "hard" direction in in-plane magnetic field reduced below the field of uniaxial anisotropy H-p = 535Oe. At first, uniformly magnetized state in CoFeB film transforms to stripe domains separated by low angle Neel domain walls (DWs) parallel to the "hard"-axis. Then, at critical field H-cr = 232 Oe, Neel DWs gradually convert to the"easy"-axis oriented Bloch DWs loaded with vertical Bloch lines (VBLs). After field reversal at H = H-cr, backward conversion of VBL-loaded Bloch DWs to Neel DWs results in instantaneous energy release and sharp anomaly of magnetic susceptibility. Appearance of critical spin fluctuations accomplishes domains transformation to the uniformly magnetized state at H = 535 Oe.
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