Effect of disorder on the magnetic and electronic structure of a prospective spin-gapless semiconductor MnCrVAl

Recent discovery of a new class of materials, spin-gapless semiconductors (SGS), has attracted considerable attention in the last few years, primarily due to potential applications in the emerging field of spin-based electronics (spintronics). Here, we investigate structural, electronic, and magnetic properties of one potential SGS compound, MnCr-VAl, using various experimental and theoretical techniques. Our calculations show that this material exhibits ≈ 0.5 eV band gap for the majority-spin states, while for the minority-spin it is nearly gapless. The calculated magnetic moment for the com- pletely ordered structure is 2.9 μB/f.u., which is different from our experimentally measured value of almost zero. This discrepancy is explained by the structural disorder. In particular, A2 type disorder, where Mn or Cr atoms exchange their positions with Al atoms, results in induced antiferromagnetic exchange coupling, which, at a certain level of disorder, effectively reduces the total magnetic moment to zero. This is consistent with our x-ray diffraction measurements which indicate the presence of A2 disorder in all of our samples. In addition, we also show that B2 disorder does not result in antiferromagnetic exchange coupling and therefore does not significantly reduce the total magnetic moment

Effect of Fe substitution on the structural, magnetic and electron-transport properties of half-metallic Co2TiSi

The structural, magnetic and electron-transport properties of Co2Ti1-xFexSi (x = 0, 0.25, 0.5) ribbons prepared by arc-melting and melt-spinning were investigated. The rapidly quenched Co2Ti0.5Fe0.5Si crystallized in the cubic L21 structure whereas Co2Ti0.75Fe0.25Si and Co2TiFe0Si showed various degrees of B2-type disorder. At room temperature, all the samples are ferromagnetic, and the Curie temperature increased from 360 K for Co2TiSi to about 800 K for Co2Ti0.5Fe0.5Si. The measured magnetization also increased due to partial substitution of Fe for Ti atoms. The ribbons are moderately conducting and show positive temperature coefficient of resistivity with the room temperature resistivity being between 360 µΩcm and 440 µΩcm. The experimentally observed structural and magnetic properties are consistent with the results of first-principle calculations. Our calculations also indicate that the Co2Ti1-xFexSi compound remains nearly half-metallic for x ≤ 0.5. The predicted large band gaps and high Curie temperatures much above room temperature make these materials promising for room temperature spintronic and magnetic applications

Magnetic and magnetocaloric properties of Co2-xFexVGa Heusler alloys

The magnetic and magnetocaloric properties of iron-substituted Co2VGa alloys, Co2-xFexVGa (x = 0, 0.1, 0.15, 0.2, 0.3), were investigated. The Fe-substituted samples, prepared by arc melting, melt spinning, and annealing, crystallized in the L2(1) Heusler structure, without any secondary phases. The Curie temperature and high-field magnetization at 50 K decreased from 345 K and 44 emu/g (1.90 mu(B)/f.u.) for Co2VGa to 275 K and 39 emu/g (1.66 mu(B)/f.u.) for Co1.7Fe0.3VGa, respectively, but the maximum entropy change remained almost insensitive to Fe concentration for x 1.85Fe0.15VGa. First-principle calculations show that Co2VGa retains its half-metallic band structure until at least 30% of the cobalt atoms are replaced by Fe atoms. The wide operating temperature window near room temperature and the lack of thermal and magnetic hysteresis are the interesting features of these materials for application in room-temperature magnetic refrigeration. (c) 2018 Author(s). All article content, except where otherwise noted, is licensed under a Creative Commons Attribution (CC BY) license (http://creativecommons.org/licenses/by/4.0/). https://doi.org/10.1063/1.500664

Effect of disorder on the magnetic and electronic structure of a prospective spin-gapless semiconductor MnCrVAl

Recent discovery of a new class of materials, spin-gapless semiconductors (SGS), has attracted considerable attention in the last few years, primarily due to potential applications in the emerging field of spin-based electronics (spintronics). Here, we investigate structural, electronic, and magnetic properties of one potential SGS compound, MnCrVAl, using various experimental and theoretical techniques. Our calculations show that this material exhibits ≈ 0.5 eV band gap for the majority-spin states, while for the minority-spin it is nearly gapless. The calculated magnetic moment for the completely ordered structure is 2.9 µB/f.u., which is different from our experimentally measured value of almost zero. This discrepancy is explained by the structural disorder. In particular, A2 type disorder, where Mn or Cr atoms exchange their positions with Al atoms, results in induced antiferromagnetic exchange coupling, which, at a certain level of disorder, effectively reduces the total magnetic moment to zero. This is consistent with our x-ray diffraction measurements which indicate the presence of A2 disorder in all of our samples. In addition, we also show that B2 disorder does not result in antiferromagnetic exchange coupling and therefore does not significantly reduce the total magnetic moment

Effect of Fe substitution on the structural, magnetic and electron-transport properties of half-metallic Co2TiSi

The structural, magnetic and electron-transport properties of Co2Ti1-xFexSi (x = 0, 0.25, 0.5) ribbons prepared by arc-melting and melt-spinning were investi- gated. The rapidly quenched Co2Ti0.5Fe0.5Si crystallized in the cubic L21 structure whereas Co2Ti0.75Fe0.25Si and Co2TiFe0Si showed various degrees of B2-type disorder. At room temperature, all the samples are ferromagnetic, and the Curie tem- perature increased from 360 K for Co2TiSi to about 800 K for Co2Ti0.5Fe0.5Si. The measured magnetization also increased due to partial substitution of Fe for Ti atoms. The ribbons are moderately conducting and show positive tempera- ture coefficient of resistivity with the room temperature resistivity being between 360 μΩcm and 440 μΩcm. The experimentally observed structural and magnetic prop- erties are consistent with the results of first-principle calculations. Our calculations also indicate that the Co2Ti1-xFexSi compound remains nearly half-metallic for x ≤ 0.5. The predicted large band gaps and high Curie temperatures much above room temperature make these materials promising for room temperature spintronic and magnetic applications

Effect of disorder on the magnetic and electronic structure of a prospective spin-gapless semiconductor MnCrVAl

Recent discovery of a new class of materials, spin-gapless semiconductors (SGS), has attracted considerable attention in the last few years, primarily due to potential applications in the emerging field of spin-based electronics (spintronics). Here, we investigate structural, electronic, and magnetic properties of one potential SGS compound, MnCr-VAl, using various experimental and theoretical techniques. Our calculations show that this material exhibits ≈ 0.5 eV band gap for the majority-spin states, while for the minority-spin it is nearly gapless. The calculated magnetic moment for the com- pletely ordered structure is 2.9 μB/f.u., which is different from our experimentally measured value of almost zero. This discrepancy is explained by the structural disorder. In particular, A2 type disorder, where Mn or Cr atoms exchange their positions with Al atoms, results in induced antiferromagnetic exchange coupling, which, at a certain level of disorder, effectively reduces the total magnetic moment to zero. This is consistent with our x-ray diffraction measurements which indicate the presence of A2 disorder in all of our samples. In addition, we also show that B2 disorder does not result in antiferromagnetic exchange coupling and therefore does not significantly reduce the total magnetic moment

Comparative study of topological Hall effect and skyrmions in NiMnIn and NiMnGa

A nonequilibrium rapid-quenching method has been used to fabricate NiMnIn and NiMnGa alloys that are chemically and morphologically similar but crystallographically and physically very different. NiMnGa crystallizes in a Ni2In-type hexagonal structure, whereas NiMnIn is a cubic Heusler alloy. Both alloys yield a topological Hall effect contribution corresponding to bubble-type skyrmion spin structures, but it occurs in much lower magnetic fields in NiMnIn as compared to NiMnGa. The effect is unrelated to net Dzyaloshinskii-Moriya interactions, which are absent in both alloys due to their inversion-symmetric crystal structures. Based on magnetic-force microscopy, we explain the difference between the two alloys by magnetocrystalline anisotropy and uniaxial and cubic anisotropies yielding full-fledged and reduced topological Hall effects, respectively. Since NiMnIn involves small magnetic fields (0.02–0.3 kOe) at and above room temperature, it is of potential interest in spin electronics