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| 2. |
- Dey, J., et al.
(författare)
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Helical magnetic structure of epitaxial films of nanolaminated Mn2GaC MAX phase
- 2023
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Ingår i: Physical Review B. - : AMER PHYSICAL SOC. - 2469-9950 .- 2469-9969. ; 108:5
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Tidskriftsartikel (refereegranskat)abstract
- Nanolaminated Mn2GaC epitaxial films crystallizing in the hexagonal structure belong to the family of MAX phase compounds and display complex magnetic interactions. While the critical temperature of the order-disorder transition is 507 K, at around 214 K this compound undergoes a first-order phase transition with the magnetic structure below the transition point not being fully resolved. Previous studies indicated a noncollinear spin arrangement, but a specific magnetic structure could not be defined. In this work we present the results of 69Ga, 71Ga, and 55Mn NMR experiments performed at 4.2 K in an external in-plane magnetic field up to 1 T. The in-depth analysis of the experimental results shows a helical magnetic structure consisting of the ferromagnetically coupled Mn-C-Mn slabs that are twisted across the Ga layer by 167.2 degrees with respect to the next Mn-C-Mn slab. As a result, the magnetic structure presents a spiral propagating along the out-of-plane direction (hexagonal c axis) with a pitch of around 14 lattice constants.
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| 3. |
- Dey, J., et al.
(författare)
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Non-collinear magnetic structure of the MAX phase Mn2GaC epitaxial films inferred from zero-field NMR study (CE-5:L05)
- 2023
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Ingår i: Ceramics International. - : ELSEVIER SCI LTD. - 0272-8842 .- 1873-3956. ; 49:14, s. 24235-24238
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Tidskriftsartikel (refereegranskat)abstract
- Zero-field NMR investigations on the 69Ga, 71Ga, and 55Mn nuclei have been performed at 4.2 K on a 100 nm thick epitaxial Mn2GaC(0001) MAX phase film grown on a MgO(111) substrate. This nano-laminated structure consists of ferromagnetic Mn-C-Mn stacks interleaved with monolayers of gallium. A resolved quadrupolar structure of the observed gallium resonances is a fingerprint of a well-defined crystal field confirming high crystal quality. The nuclei of non-magnetic gallium atoms are shown to experience the transferred hyperfine magnetic field of 15.75 T (& PLUSMN;0.05 T), which is due to polarization of their 4s electron shell by the magnetic moments of manganese neighbors, evidencing the presence of an uncompensated ferromagnetic moment within the manganese sublattice. The average magnetic moment of manganese was found to be around 2 & mu;B, strongly contrasting with the reported remnant magnetization of only 0.3 & mu;B. Moreover, the 55Mn NMR spectrum in-dicates the presence of magnetically non-equivalent manganese sites within this structure. The observed features of the 69,71Ga and 55Mn NMR spectra cannot be reconciled with any of the hitherto proposed collinear ar-rangements of manganese moments and suggest their non-collinear arrangement across a gallium layer. Nevertheless a more advanced study is required to elucidate the detailed nature of magnetic structure in this material.
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| 5. |
- Salikhov, R., et al.
(författare)
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Enhanced spin-orbit coupling in tetragonally strained Fe-Co-B films
- 2017
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Ingår i: Journal of Physics. - : Institute of Physics Publishing (IOPP). - 0953-8984 .- 1361-648X. ; 29:27
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Tidskriftsartikel (refereegranskat)abstract
- Tetragonally strained interstitial Fe-Co-B alloys were synthesized as epitaxial films grown on a 20 nm thick Au0.55Cu0.45 buffer layer. Different ratios of the perpendicular to in-plane lattice constant c/a = 1.013, 1.034 and 1.02 were stabilized by adding interstitial boron with different concentrations 0, 4, and 10 at.%, respectively. Using ferromagnetic resonance (FMR) and x-ray magnetic circular dichroism (XMCD) we found that the total orbital magnetic moment significantly increases with increasing c/a ratio, indicating that reduced crystal symmetry and interstitial B leads to a noticeable enhancement of the effect of spin-orbit coupling (SOC) in the Fe-Co-B alloys. First-principles calculations reveal that the increase in orbital magnetic moment mainly originates from B impurities in octahedral position and the reduced symmetry around B atoms. These findings offer the possibility to enhance SOC phenomena - namely the magnetocrystalline anisotropy and the orbital moment - by stabilizing anisotropic strain by doping 4 at.% B. Results on the influence of B doping on the Fe-Co film microstructure, their coercive field and magnetic relaxation are also presented.
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| 6. |
- Salikhov, R., et al.
(författare)
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Magnetic properties of nanolaminated (Mo0.5Mn0.5)(2)GaC MAX phase
- 2017
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Ingår i: Journal of Applied Physics. - : AMER INST PHYSICS. - 0021-8979 .- 1089-7550. ; 121:16
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Tidskriftsartikel (refereegranskat)abstract
- The magnetic properties of hexagonal (Mo0.5Mn0.5)(2)GaC MAX phase synthesized as epitaxial films on MgO (111) substrates with the c-axis perpendicular to the film plane are presented. The analysis of temperature-dependent ferromagnetic resonance (FMR) and magnetometry data reveals a ferro-to paramagnetic phase transition at 220 K. The electrical transport measurements at 5K show a negative magnetoresistance of 6% in a magnetic field of 9 T. Further analysis confirms the spin-dependent scattering of charge carriers in this layered material. A small perpendicular (c-axis) magnetocrystalline anisotropy energy density (MAE) of 4.5 kJ/m(3) at 100K was found using FMR. Accordingly, (Mo0.5Mn0.5)(2)GaC behaves similar to the (Cr0.5Mn0.5)(2)GaC MAX phase as a soft magnetic material. The density functional theory calculations reveal that the sign and the amplitude of the MAE can be very sensitive to (Mo0.5Mn0.5)(2)GaC lattice parameters, which may explain the measured soft magnetic properties. Published by AIP Publishing.
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| 7. |
- Seidel, Y. E., et al.
(författare)
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Nanostructured Pt/GC model electrodes prepared by the deposition of metal-salt-loaded micelles
- 2007
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Ingår i: Langmuir. - : American Chemical Society (ACS). - 0743-7463 .- 1520-5827. ; 23:10, s. 5795-5801
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Tidskriftsartikel (refereegranskat)abstract
- Novel, nanostructured, carbon-supported Pt model electrodes with homogeneously distributed Pt nanoparticles of uniform size were fabricated and analyzed with respect to their electrochemical properties. For this purpose, Pt-salt-loaded micelles were deposited on a glassy carbon substrate and subsequently exposed to an oxygen plasma and a H-2 atmosphere for removal of the polymer carriers and reduction of the Pt salt. The morphology of the resulting nanoparticles and their electrochemical/electrocatalytic properties were characterized by high-resolution scanning electron microscopy, X-ray photoelectron spectroscopy, cyclic voltammetry, and differential electrochemical mass spectrometry for CO electrooxidation. The data demonstrate that this method is generally suited to the production of nanostructured model electrodes with well-defined and independently adjustable particle size and interparticle distance distributions, which are specifically suited for quantitative studies of transport processes in electrocatalytic reactions.
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| 8. |
- Tao, Quanzheng, et al.
(författare)
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Thin film synthesis and characterization of a chemically ordered magnetic nanolaminate (V,Mn)(3)GaC2
- 2016
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Ingår i: APL Materials. - : AMER INST PHYSICS. - 2166-532X. ; 4:8
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Tidskriftsartikel (refereegranskat)abstract
- We report on synthesis and characterization of a new magnetic nanolaminate (V,Mn)(3)GaC2, which is the first magnetic MAX phase of a 312 stoichiometry. Atomically resolved energy dispersive X-ray mapping of epitaxial thin films reveals a tendency of alternate chemical ordering between V and Mn, with atomic layers composed of primarily one element only. Magnetometry measurements reveal a ferromagnetic response between 50 K and 300 K, with indication of a magnetic ordering temperature well above room temperature. (C) 2016 Author(s).
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