Search

A Mn-based Heusler alloy Mn2NiSb has been synthesized. First-principles calculations and experimental measurements were employed to investigate its electronic structure and magnetism. Theoretical calculation indicates a ferromagnetic coupling in Mn2NiSb and a total spin moment of 4.21μB/f.u., which agrees quite well with the saturation moment at 5 K. This ferromagnetic coupling arises from the larger lattice constant and more valence electrons compared with other Mn-based Heusler alloys. The partial spin moments for Mn (A), Mn (B), and Ni are 0.6, 3.30, and 0.3μB, respectively. The Curie temperature of Mn2NiSb is 647 K, indicating a strong exchange interaction between Mn atoms. [ABSTRACT FROM AUTHOR]

Mn2NiSb can exist in both ferromagnetic and antiferromagnetic states because there is only a small total energy difference between the two states. In its electronic structure, two different types of energy gaps exist and are close to the Fermi level. The relative position of the Fermi level to the gap determines the ferromagnetic or antiferromagnetic state. That is the origin of the magnetic instability in Mn2NiSb. A 70% decrease of the total moment is predicted between the ferromagnetic and antiferromagnetic Mn2NiSb. [Copyright &y& Elsevier]

The effect of boron substitution for Sb in the Heusler alloys Ni50Mn36.5Sb13.5− x B x (x =0, 0.5, 1.0, 1.5) has been studied. The substitution with B reduces the Curie temperature of both the martensite and austenite phases. The saturation magnetization M s decreases monotonically with increasing B content. The doping of B increases the martensitic transformation temperature effectively. When x =1.0 and 1.5, an orthorhombic four-layered (4O) martensite is observed at room temperature. [Copyright &y& Elsevier]

Abstract: The effect of Fe substitution for the vacant site in half-Heusler alloy CoCrAl is studied. A series of single phase CoFe x CrAl (x=0.0, 0.25, 0.5, 0.75 and 1.0) alloys has been successfully synthesized. The lattice constant is found to increase almost linearly with increasing Fe content, indicating Fe atoms enter the lattice of CoCrAl instead of existing as a secondary phase. When Fe entering the vacant site, spin polarization occurs and the alloy turns from a semimetal in CoCrAl to a half-metallic ferromagnet (HMF) in CoFeCrAl. This is due to the reconstruction of the energy band with Fe substitution. The Curie temperature and saturation magnetic moments are enhanced and increase monotonically with increasing Fe content. The variation of the spin moment follows the Slater–Pauling curve and agrees with the theoretical calculation as well. [Copyright &y& Elsevier]

Abstract: The effect of doping with Cr on the electronic structure and magnetism of Co3Al has been studied by density functional calculations. It has been found that the Cr atom has a strong site preference for the B-site in Co3Al. With the substitution of Cr for Co, the total densities of states (DOS) change obviously: A DOS peak appears at E F in the majority spin states and an energy gap is opened in the minority spin states. The effect of Cr in Co3Al is mainly to push the antibonding peak of the Co (A,C) atoms high on the energy scale and to form the energy gap around E F, and also to contribute to the large DOS peak at E F in the majority spin direction. The calculations indicate a ferromagnetic alignment between the Co and Cr spin moments. The calculated total magnetic moment decreases and becomes closer to the Slater–Pauling curve with increasing Cr content. This is mainly due to the decrease of the Co (A,C) spin moments. At the same time, the moments of Co (B) and Cr (B) only change slightly. [Copyright &y& Elsevier]

C-doped Fe 2 MnGaC x (x = 0, 0.05, 0.1 and 0.2) alloys have been synthesized and the influence of carbon on the structure and magnetic properties of Fe 2 MnGa has been investigated. The doping of C can expand the lattice of Fe 2 MnGa, suggesting that it enters the interstitial site of FCC lattice. The ferromagnetic coupling in Fe 2 MnGaC x can be strongly enhanced with increasing C content. The ferromagnetic to antiferromagnetic transition in undoped Fe 2 MnGa is suppressed by C-doping and disappears when x = 0.1 and 0.2. The saturation magnetization M s and Curie temperature T C also increase with C-doping. Large coercivity and exchange bias can be observed in the magnetic hysteresis loops of Fe 2 MnGa, due to the coexistence of FM and AFM states. But in Fe 2 MnGaC 0.2 , both of them disappear and a pure ferromagnetic character is observed. All this suggests that C-doping can be a possible way to adjust the magnetic properties of Fe 2 MnGa and other related alloys. • Fe 2 MnGaC x alloys were synthesized successfully. • Effect of C-doping on structure and magnetism of Fe 2 MnGa was studied. • Ferromagnetic state in Fe 2 MnGa can be strongly enhanced by C-doping. • A possible way to adjust the magnetic structure of Fe 2 MnGa is proposed. [ABSTRACT FROM AUTHOR]

The site preference, electronic structure, magnetic properties and martensitic transformation in Heusler alloys Ni 2 CoZ (Z = Al, Ga, In, Si, Ge, Sn, Sb) have been investigated by first-principles calculations. Different from literature, it is found that these Ni 2 CoZ alloys tend to form XA structure (Hg 2 CuTi-type), except for Ni 2 CoIn, in which L2 1 (Cu 2 MnAl-type) structure is preferable. Theoretical calculation reveals that the tetragonal martensitic phase has a lower total energy compared with the cubic austenitic phase, therefore, a structural transition from cubic to tetragonal is likely to happen in these Ni 2 CoZ alloys. The largest energy difference is observed in Ni 2 CoIn. It is interesting that Ni 2 CoSi is paramagnetic in austenitic state, while is ferromagnetic in martensitic state. This leads to a large change in the total moment, which is meaningful for the realization of magnetic field-induced martensitic transformation in this alloy. [ABSTRACT FROM AUTHOR]