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Co 2 MnGa is known as a Weyl semimetal exhibiting giant anomalous Hall and Nernst effects. However, the performance of Co 2 MnGa thin films grown on MgO(001) by the magnetron sputtering method is somewhat lower than that of the bulk crystals. Here, we attempted to improve the electrical transport properties by post-growth annealing at temperatures from 573 to 773 K. X-ray diffraction analysis indicated that the degree of long-range order changed from A 2 to B 2 plus L 2 1 upon annealing at 673 K or above. Positron annihilation spectroscopy revealed the presence of high-density (≳ 100 ppm) divacancies, which were absent in the bulk crystal, and their partial improvement near the Co 2 MnGa/MgO interface on annealing at 673 K or above. Accompanying these structural changes, the longitudinal and anomalous Hall conductivities increased considerably and the anomalous Hall angle reached a maximum value of 11.8%. These findings imply that the post-growth annealing improved the electrical transport properties of Co 2 MnGa films through the development of long-range crystal order and reduction of divacancies. However, the electrical performance achieved by thermal annealing was still insufficient in comparison with the bulk crystals, and hence for further improvement, alternative approaches may need to be considered. [ABSTRACT FROM AUTHOR]

Magnetic properties and stability of L21 and B2 phases in the Co2MnAl Heusler alloy were investigated. It was confirmed that the order-disorder transition from the B2 to L21 phase is located at about 950 K and that the Curie temperature TC of the L21 phase is 726 K which is about 50 K higher than that (TC=677 K) of the B2 phase. The difference in TC between the L21 and B2 phases is smaller than a theoretical prediction. On the other hand, the saturation magnetic moments Ms at 4.2 K for the L21 and B2 phases were estimated to be 4.07μB/f.u. and 4.16μB/f.u., respectively, comparable to the value Mt=4 expected from the generalized Slater–Pauling relation. [ABSTRACT FROM AUTHOR]

Concentration dependence of the magnetic and electrical properties of MnPt alloy system with a AuCu-I type crystal structure has been investigated in order to discuss the electronic state. Temperature dependence of the electrical resistivity shows a characteristic behavior of gap-type antiferromagnets and the electronic specific heat coefficient y is considerably small in consistent with the calculated band structure having a pseudo-gap around the Fermi level. In the vicinity of the equiatomic composition, the Néel temperature is highest, whereas the value of y is smallest and increases with decreasing the Néel temperature. From the present experimental results, a close relationship between the electronic state and the antiferromagnetic stability in this alloy system is revealed, in accord with the band calculations. [ABSTRACT FROM AUTHOR]

The martensitic transformation behavior in a Ni45Co5Mn36In14 was investigated at low temperatures. Almost perfect superelasticity was confirmed below 200 K. The reverse transformation finishing stress monotonically decreased with decreasing temperature and the forward transformation starting stress changed from a decrease to an increase at ∼125 K. The temperature dependence of equilibrium stress had the same tendency as that of equilibrium magnetic field, allowing the thermal transformation arrest temperature to be determined. The temperature dependence of hysteresis in stress-induced transformation was also similar to that in magnetic-field-induced transformation, and the levels of dissipation energy yielded by the stress and magnetic field were intrinsically equivalent. [ABSTRACT FROM AUTHOR]

Magnetic measurements and neutron powder diffraction experiments on Ni50Mn33Sn17 and Ni45Co5Mn33Sn17 alloys were performed in order to establish the magnetic structures and the effects of Co substitution on the magnetic properties. It was shown that the magnetic coupling between the Mn moments on the 4a and 4b sites changed from being antiferromagnetic to ferromagnetic by substitution of Co. As a result of the change in the magnetic structure due to the Co substitution, the ferromagnetic properties of Ni-Co-Mn-Sn are enhanced. These results have enabled the concentration dependence of the magnetic moment to be quantified. [ABSTRACT FROM AUTHOR]

Magnetic measurements and neutron powder diffraction experiments on Ni50Mn33Sn17 and Ni45Co5Mn33Sn17 alloys were performed in order to establish the magnetic structures and the effects of Co substitution on the magnetic properties. It was shown that the magnetic coupling between the Mn moments on the 4a and 4b sites changed from being antiferromagnetic to ferromagnetic by substitution of Co. As a result of the change in the magnetic structure due to the Co substitution, the ferromagnetic properties of Ni-Co-Mn-Sn are enhanced. These results have enabled the concentration dependence of the magnetic moment to be quantified. [ABSTRACT FROM AUTHOR]

The concentration dependence of magnetic properties in the austenite phase of NiCoMnIn and NiCoMnSn Heusler alloys was systematically investigated by the magnetization measurements. The TC for Ni(50-x)CoxMn(50-y)Sny alloys linearly increases with increasing the Co content and fixed Sn content. Although showing a concave curve for Ni50Mn(50-y)Sny ternary alloys, the Sn content-dependence of magnetic moment per formula unit changes from the concave curve to a straight line when Co is substituted for Ni. On the other hand, the In content-dependence of the magnetic moment for Ni45Co5Mn(50-y)Iny alloys is perfectly linear as is that in the Ni50Mn(50-y)Iny ternary alloys. [ABSTRACT FROM AUTHOR]

For the Co2Mn(Ga1-xZx) (Z=Si, Ge, and Sn) Heusler alloys, the L21/B2 order-disorder transition temperature TtL21/B2, the Curie temperature TC, and the saturation magnetization Ms were determined. The TtL21/B2 for all the systems linearly increases with increasing x. Although the TtL21/B2 was not determined in the high x region because of melting of alloys, those of Co2MnGe and Co2MnSn could be estimated by extrapolation from the quaternary data. The Ms at 4.2 K and the TC increase with x, and the Ms for all the systems is in good agreement with the Slater Pauling rule. [ABSTRACT FROM AUTHOR]

Martensitic and magnetic properties of Fe–Mn–Ga single and polycrystalline alloys were investigated. It was found that Fe–Mn–Ga alloys exhibit martensitic transformation from the paramagnetic L21 Heusler parent phase to the ferromagnetic L10 martensite phase. The martensitic transformation temperatures increased by about 20 K by the application of a magnetic field of 7 T, and a metamagnetic phase transition was observed. In addition, a magnetic field-induced strain of 0.6% associated with magnetic field-induced forward transformation was confirmed in an Fe43Mn28Ga29 single crystal. [ABSTRACT FROM AUTHOR]

The effects of chemical order on the phase stability and magnetic properties of the metamagnetic shape memory alloy Ni45Co5Mn36.7In13.3 were investigated. Alloys quenched from the B2 and L21 phase regions were found to transform to the L10 and 6M martensite phases, respectively. For alloys quenched from the B2 region the martensitic transformation starting temperature is about 80 K higher than that for alloys quenched from the L21 region. The Curie temperature of the parent phase and the magnetization of the martensite phase were both lower for the alloy quenched from the B2 region than those for the alloy quenched from L21 region. [ABSTRACT FROM AUTHOR]

Effects of the addition of Co to the NiMnAl alloy on the martensitic and magnetic properties were investigated. The magnetic properties of the parent (P) phase drastically changed from paramagnetic to ferromagnetic, while the magnetization in the martensite (M) phase slightly decreased with increasing Co composition. Consequently, in the Ni40Co10Mn33Al17 alloy with the B2 ordered structure, the martensitic transformation from a ferromagnetic P to a weak magnetic M phase was obtained. The martensitic transformation temperatures in this alloy decreased by about 30 K with the application of a magnetic field of 7 T and a metamagnetic phase transformation was confirmed. [ABSTRACT FROM AUTHOR]

Magnetic and differential scanning calorimetric measurements and Mössbauer examination were carried out to clarify the magnetic features of Ni50Mn36.557Fe0.5Sn13. The magnetic field cooling effects were observed in the thermomagnetization curves below 235 K and the Curie temperature of the parent phase was near the martensitic transformation temperature. The Mössbauer spectra taken from the parent+martensite two-phase state at 312 K and from the martensite single-phase state at 264 K were both singlets, showing a typical paramagnetic feature. On the other hand, the Mössbauer spectra taken from the martensite phase at 199 and 80 K were complicated, including some magnetic components. [ABSTRACT FROM AUTHOR]

Martensitic, magnetic transformations, and crystal structures in Pd–In–Fe alloys were investigated. It was confirmed that some Pd–In–Fe alloys show martensitic transformation from a Heusler-type (L21) ordered bcc phase to a 2M-type (DO22) structure and that an almost perfect superelastic effect accompany the transformation can be obtained. Furthermore, some alloys show transformation from the paramagnetic parent phase to the ferromagnetic martensite phase. [ABSTRACT FROM AUTHOR]

The theoretical calculations of magnetic anisotropy energy (MAE) for antiferromagnetic L10-type MnTM [transition metal (TM)=Ni, Pd, Pt, Rh, and Ir] alloys were carried out on the basis of the local spin-density approximation using linear muffin-tin orbital method with atomic sphere approximation including the spin-orbit interaction. It has been demonstrated that the magnitude of the MAE for L10-type MnIr alloy is highest, -20.77×106 J/m3, and the negative sign of the MAE is consistent with the reported spin structure. On the other hand, the sign of the MAE for L10-type MnPt alloy is positive in accordance with the spin structure. The MAE of the MnPt alloy is sensitive to the electron number, which would be correlated with the fact that only the MnPt alloy system exhibits a complicated magnetic phase diagram. [ABSTRACT FROM AUTHOR]

The saturation magnetic moment Ms and the Curie temperature TC of the half-metal-type Co2CrGa Heusler alloy have been investigated. The value of Ms at 4.2 K for the L21-type Co2CrGa alloy is 3.01 μB/f.u., in agreement with the generalized Slater-Pauling line and the theoretical calculation. The Curie temperature TC and the phase-transformation temperature Tt from the L21 to B2-type structure are 495 and 1050 K, respectively. The band calculations disclose that the spin polarization is also relatively high in the B2-type structure, although its estimated TC is about 100 K lower than that of the L21-type structure. [ABSTRACT FROM AUTHOR]

The concentration dependence of magnetic properties in the austenite phase of Ni50Mn50-xInx/2 Sbx/2 Heusler alloys was systematically investigated by magnetization measurements. The Curie temperature for Ni50Mn50-xInx/2Sbx/2 alloys is almost independent of content x. On the other hand, the concentration dependence on magnetic moment shows a concave curve similar to that of Ni50Mn50-xSnx alloys, which have the same number of valence electrons. This tendency suggests that the magnetic moment continues to increase with decreasing content x and reaches that of the metastable ferromagnetic NiMn-B2 phase. [ABSTRACT FROM AUTHOR]

Magnetic properties of the B2 phase in Co50-xNixMn25Al25 alloys were investigated. Spontaneous magnetization Ms measured at 4.2 K increases linearly with increasing x in the region of x ≤ 30 in accordance with following the generalized Slater-Pauling (GSP) line. However, Ms abruptly decreases with increasing x and deviates from the GSP line in the Ni-rich region of x > 30, suggesting a drastic change in the density of states at the Fermi energy. The Curie temperature TC decreases monotonically with increasing x and significantly decreases in the region of x > 30. Antiferromagnetic evidence is clearly observed at x > 45, and the Néel temperature TN increases with increasing x, in reaching the value of the B2 phase in Ni2MnAl. [ABSTRACT FROM AUTHOR]

By controlling the annealing temperature, single phase Fe2CrAl alloys with A2 (1573 K), B2 (873 K), and L21-type structures (673 K) can be obtained. [ABSTRACT FROM AUTHOR]

A powder sample of body-centered tetragonal Ni2N in a single phase was prepared by a high rate-type triode dc reactive sputtering and the magnetic properties have been reinvestigated. It is confirmed that Ni2N is not a ferromagnet. However, the material is not a simple paramagnet either and shows a weak spin-glass-like behavior at low temperatures with a freezing temperature of about 8K. Posible origins of the behavior are discussed. Band-structure calculations are reported to see the stability of the nonmagnetic ground state of bct Ni2N against lattice expansion and appearance of nitrogen vacancies. [ABSTRACT FROM AUTHOR]

Permeability, magnetization, and differential scanning calorimetry measurements are carried out on the ferromagnetic shape memory alloys Ni2MnGa1-xCox (0 ≼ x ≼ 0.20). On the basis of the experimental results, the phase diagram in the temperature-concentration plane is determined. The determined phase diagram is spanned by a paramagnetic austenite (Para-A) phase, paramagnetic martensite phase, ferromagnetic austenite phase, ferromagnetic martensite (Ferro-M) phase, and a premartensite phase. The measurements show that a magnetostructural transition between the Para-A and Ferro-M phases does not appear in this alloy system. The phase diagram is discussed using phenomenological Landau theory. [ABSTRACT FROM AUTHOR]

We have studied the electronic structure of ferrimagnetic Mn2 VAl single crystals by means of soft x-ray absorption spectroscopy (XAS), x-ray absorption magnetic circular dichroism (XMCD), and resonant soft x-ray inelastic scattering (RIXS). We have successfully observed the XMCD signals for all the constituent elements. The Mn L2 , 3 XAS and XMCD spectra are reproduced by spectral simulations based on density-functional theory, indicating the itinerant character of the Mn 3 d states. On the other hand, the V 3 d electrons are rather localized since the ionic model can qualitatively explain the V L2 , 3 XAS and XMCD spectra. This picture is consistent with local d d excitations revealed by the V L3 RIXS. [ABSTRACT FROM AUTHOR]

Co 2 MnGa is a Weyl semimetal exhibiting giant anomalous Hall and Nernst effects. Using spin-polarized positron annihilation spectroscopy, we examined a Bridgman-grown Co 2 MnGa single crystal with a nearly perfect L 2 1 -ordered structure and a reference Co 2 MnAl polycrystal with a Mn-Al-disordered B 2 structure. We found that a large amount of magnetic vacancies (more than 100 ppm) were included in the Co 2 MnGa crystal but not the Co 2 MnAl crystal. We discuss possible reasons for the inclusion of vacancies, the role of vacancies in the development of the ordered structure, and the electronic states associated with the vacancies. Toward the development of Co 2 MnGa-based devices, the manners for reducing vacancies as well as the influence of vacancies on the electrical transport properties should be considered., (© 2021 IOP Publishing Ltd.)

The magnetization distribution in Co2FeSi which has the largest moment per formula unit ∼6 μB of all Heusler alloys, has been determined using polarized neutron diffraction. The experimentally determined magnetization has been integrated over spheres centred on the three sites of the L12 structure giving μ Fe = 3.10(3) μB and μ Co = 1.43(2) μB, results which are slightly lower than the moments in atomic spheres of similar radii obtained in recent LDA + U band structure calculations (Li et al 2010 Chin. Phys. B 19 097102). Approximately 50% of the magnetic carriers at the Fe sites were found to be in orbitals with eg symmetry. This was higher, ≃65%, at the Co sites. Both Fe and Co were found to have orbital moments that are larger than those predicted. Comparison with similar results obtained for related alloys suggests that there must be a finite density of states in both spin bands at the Fermi energy indicating that Co2FeSi is not a perfect half-metallic ferromagnet.