| 1. |
- Hudl, Matthias, et al.
(författare)
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Nonlinear Magnetization Dynamics Driven by Strong Terahertz Fields
- 2019
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Ingår i: Physical Review Letters. - : AMER PHYSICAL SOC. - 0031-9007 .- 1079-7114. ; 123:19
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Tidskriftsartikel (refereegranskat)abstract
- We present a comprehensive experimental and numerical study of magnetization dynamics in a thin metallic film triggered by single-cycle terahertz pulses of ∼20 MV/m electric field amplitude and ∼1 ps duration. The experimental dynamics is probed using the femtosecond magneto-optical Kerr effect, and it is reproduced numerically using macrospin simulations. The magnetization dynamics can be decomposed in three distinct processes: a coherent precession of the magnetization around the terahertz magnetic field, an ultrafast demagnetization that suddenly changes the anisotropy of the film, and a uniform precession around the equilibrium effective field that is relaxed on the nanosecond time scale, consistent with a Gilbert damping process. Macrospin simulations quantitatively reproduce the observed dynamics, and allow us to predict that novel nonlinear magnetization dynamics regimes can be attained with existing tabletop terahertz sources.
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| 2. |
- Pancaldi, Matteo, et al.
(författare)
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Anti-reflection coating design for metallic terahertz meta-materials
- 2018
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Ingår i: Optics Express. - 1094-4087. ; 26:3, s. 2917-2927
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Tidskriftsartikel (refereegranskat)abstract
- We demonstrate a silicon-based, single-layer anti-reflection coating that suppresses the reflectivity of metals at near-infrared frequencies, enabling optical probing of nano-scale structures embedded in highly reflective surroundings. Our design does not affect the interaction of terahertz radiation with metallic structures that can be used to achieve terahertz near-field enhancement. We have verified the functionality of the design by calculating and measuring the reflectivity of both infrared and terahertz radiation from a silicon/gold double layer as a function of the silicon thickness. We have also fabricated the unit cell of a terahertz meta-material, a dipole antenna comprising two 20-nm thick extended gold plates separated by a 2 mu m gap, where the terahertz field is locally enhanced. We used the time-domain finite element method to demonstrate that such near-field enhancement is preserved in the presence of the anti-reflection coating. Finally, we performed magneto-optical Kerr effect measurements on a single 3-nm thick, 1-mu m wide magnetic wire placed in the gap of such a dipole antenna. The wire only occupies 2% of the area probed by the laser beam, but its magneto-optical response can be clearly detected. Our design paves the way for ultrafast time-resolved studies, using table-top femtosecond near-infrared lasers, of dynamics in nano-structures driven by strong terahertz radiation.
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| 3. |
- Akhter, Shahida, et al.
(författare)
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Magnetic and magnetocaloric properties of Cu1-xZnxFe2O4 (x=0.6, 0.7, 0.8) ferrites
- 2014
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Ingår i: Journal of Magnetism and Magnetic Materials. - : Elsevier BV. - 0304-8853 .- 1873-4766. ; 367, s. 75-80
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Tidskriftsartikel (refereegranskat)abstract
- The effect of Zn substitution on the magnetic and magnetocaloric properties of Cu1-xZnxFe2O4 (x=0.6, 0.7, 0.8) ferrites over a wide temperature range has been investigated. The polycrystalline samples were synthesized using the solid-state reaction at sintering temperature 1050 degrees C (1323 K) for 2 h and has been characterized by SQUID magnetometry. Magnetization versus temperature showed that all samples exhibit a paramagnetic to ferromagnetic transition with decreasing temperature. The Curie temperature T-c is found to decrease from 373 K for x=0.6 to 140 K for x=0.8 as well as the saturation magnetization Ms which shifts from 100 to 44 emu/gm. The magnetocaloric effect was obtained by measuring a family of M-I1 curves at set temperature intervals and calculating the entropy change, LIS for this system using the Maxwell relation. The AS of all samples increased with increasing applied field and showed a maximum around their respective 'Fe. The entropy change (Delta S) decreased with increasing Zn content, whereas the relative cooling power (RCP) slightly increased. The large RCP and Delta S found in Zn substitution Cu-Zn ferrites will be interesting for magnetic refrigeration near room temperature.
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| 4. |
- Bran, Cristina, et al.
(författare)
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Magnetic Properties of Fe/WRe (001) Multilayers
- 2014
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Ingår i: Journal of Surfaces and Interfaces of Materials. - : American Scientific Publishers. - 2164-7542. ; 2:1, s. 33-39
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Tidskriftsartikel (refereegranskat)abstract
- Following recent theoretical predictions on perpendicular uniaxial magnetocrystalline anisotropy in multilayers of 5 monolayers of Fe and 2 monolayers of W x Re100–x with tetragonally strained components, we have measured the magnetization and detailed atomic structure in a series of such samples with x = 20–80 at%. Although the achieved strain in the WRe layers is smaller than in the modelled case, we do observe a positive uniaxial magnetocrystalline anisotropy of around 0.6 MJ/m3 at 40 K, after accounting for the in-plane shape anisotropy. This causes the out-of-plane saturation field to be reduced considerably compared to a pure Fe thin film, while the saturation magnetization is maintained at a value which is enhanced by at least 30% from what would be expected from the multilayer composition alone. The coercivity is low, on the order of 6 kA/m in all samples.
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| 5. |
- Hudl, Matthias, et al.
(författare)
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Investigation of the magnetic phase transition and magnetocaloric properties of the Mn2FeSbO6 ilmenite
- 2013
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Ingår i: Journal of Magnetism and Magnetic Materials. - : Elsevier BV. - 0304-8853 .- 1873-4766. ; 331, s. 193-197
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Tidskriftsartikel (refereegranskat)abstract
- The magnetic phase transition and magnetocaloric properties of both mineral and synthetic melanostibite Mn2FeSbO6 with ilmenite-type structure have been studied. Mn2FeSbO6 orders ferrimagnetically below 270 K and is found to undergo a second-order magnetic phase transition. The associated magnetic entropy change was found to be 1.7 J/kg K for the mineral and 1.8 J/kg K for the synthetic melanostibite for 5 T field change. For the synthetic Mn2FeSbO6 the adiabatic temperature change was estimated from magnetic- and specific heat measurements and amounts to 0.2 K in 1 T field change. Perspectives of the functional properties of Mn2FeSbO6-based materials are discussed.
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| 6. |
- Hudl, Matthias, 1981-
(författare)
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Magnetic materials with tunable thermal, electrical, and dynamic properties : An experimental study of magnetocaloric, multiferroic, and spin-glass materials
- 2012
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- This thesis concerns and combines the results of experimental studies of magnetocaloric, multiferroic and spin-glass materials, using SQUID magnetometry as the main characteriza-tion technique. The magnetocaloric effect offers an interesting new technology for cooling and heating applications. The studies of magnetocaloric materials in this thesis are focused on experimen-tal characterization of fundamental magnetic properties of Fe2P-based materials. These are promising magnetocaloric materials with potential industrial use. It is found that the magneto-caloric properties of Fe2P can be optimally tuned by substitution of manganese for iron and silicon for phosphorus. Furthermore, a simple device to measure the magnetocaloric effect in terms of the adiabatic temperature change was constructed. Materials that simultaneously exhibit different types of ferroic order, for example magnetic and electrical order, are rare in nature. Among these multiferroic materials, those in which the ferroelectricity is magnetically-induced, or vice versa the magnetism is electrically-induced, are intensively studied due to a need for new functionalities in future data storage and logic devices. This thesis presents results on two materials: Co3TeO6 and Ba3NbFe3Si2O14, which belong to the group of magnetically-induced ferroelectrics and exhibit strong coupling be-tween the magnetic and the electrical order parameter. Their ordering properties were studied using magnetic and electrical measurement techniques. The coupling between the magnetic and electronic degrees of freedom was investigated using high-field and low-temperature Raman spectroscopy. Spin-glass materials exhibit complex magnetism and disorder. The influence of the spin dimensionality on the low and high magnetic field properties of spin glasses was investigated by studying model Heisenberg, XY and Ising spin-glass systems. Significant differences were found between the non-equilibrium dynamics and the hysteresis behavior of Heisenberg systems compared to those of XY and Ising spin glasses.
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| 7. |
- Hudl, Matthias, et al.
(författare)
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Order–disorder induced magnetic structures of FeMnP0.75Si0.25
- 2011
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Ingår i: Physical Review B. Condensed Matter and Materials Physics. - 1098-0121 .- 1550-235X. ; 83:13, s. 134420-
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Tidskriftsartikel (refereegranskat)abstract
- We report on the synthesis and structural characterization of the magnetocaloric FeMnP0.75Si0.25 compound. Two types of samples (as quenched and annealed) were synthesized and characterized structurally and magnetically. We have found that minute changes in the degree of crystallographic order causes a large change in the magnetic properties. The annealed sample, with higher degree of order is antiferromagnetic with a zero net moment. The as-quenched sample has a net moment of 1.26 μB /f.u. and ferrimagnetic-like behavior. Theoretical calculations give rather large values for the Fe and Mn magnetic moments, both when occupied on the tetrahedral and pyramidal lattice site. The largest being the Mn moment for the pyramidal site reaches values as high as 2.8 μB /atom.
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| 8. |
- Hudl, Matthias, et al.
(författare)
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PPMS-based set-up for Raman and luminescence spectroscopy at high magnetic field, high pressure and low temperature
- 2015
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Ingår i: EPJ Techniques and Instrumentation. - : Springer Science and Business Media LLC. - 2195-7045. ; 2:1
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Tidskriftsartikel (refereegranskat)abstract
- We present an experimental set-up permitting Raman and luminescence spectroscopy studies in a commercial Physical Properties Measurement System (PPMS) from Quantum Design. Using this experimental set-up, gaseous, liquid and solid materials, in bulk or thin film form, may be investigated. The set-up is particularly suitable for the study of the spin-lattice coupling in strongly correlated oxide materials utilizing several different stimuli, e.g. magnetic and electric fields, high pressure and low temperatures. Details for the Raman extension, sample holder assembly and optical design, as well as data acquisition and measurement routine are described. Finally, we present exemplary results collected using the set-up, measured on reference materials, as well as on a correlated transition metal oxide.
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| 9. |
- Hudl, Matthias, et al.
(författare)
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Strongly enhanced magnetic moments in ferromagnetic FeMnP0.5Si0.5
- 2011
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Ingår i: Applied Physics Letters. - : AIP Publishing. - 0003-6951 .- 1077-3118. ; 99:15, s. 152502-
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Tidskriftsartikel (refereegranskat)abstract
- The compound FeMnP(0.5)Si(0.5) has been studied by magnetic measurements, Mossbauer spectroscopy, and electronic structure and total energy calculations. An unexpectedly high magnetic hyperfine field for Fe atoms located at the tetrahedral Me(1) site in the Fe(2)P structure is found, The saturation moment derived from magnetic measurements corresponds to 4.4 mu(B)/f.u. at low temperatures, a value substantially higher than previously reported, but in accordance with the results from our electron structure calculations, This high saturation moment and the tunable first order ferromagnetic transition make the Fe(2-x)Mn(x)P(1-y)Si(y), system promising for magnetocaloric applications.
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| 10. |
- Hudl, Matthias, et al.
(författare)
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Thermodynamics around the first-order ferromagnetic phase transition of Fe2P single crystals
- 2014
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Ingår i: Physical Review B. Condensed Matter and Materials Physics. - 1098-0121 .- 1550-235X. ; 90:14, s. 144432-
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Tidskriftsartikel (refereegranskat)abstract
- The specific heat and thermodynamics of Fe2P single crystals around the first-order paramagnetic to ferromagnetic (FM) phase transition at T-C similar or equal to 217 K are empirically investigated. The magnitude and direction of the magnetic field relative to the crystal axes govern the derived H-T phase diagram. Strikingly different phase contours are obtained for fields applied parallel and perpendicular to the c axis of the crystal. In parallel fields, the FM state is stabilized, while in perpendicular fields the phase transition is split into two sections, with an intermediate FM phase where there is no spontaneous magnetization along the c axis. The zero-field transition displays a textbook example of a first-order transition with different phase stability limits on heating and cooling. The results have special significance since Fe2P is the parent material to a family of compounds with outstanding magnetocaloric properties.
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