Guoke Li

Anomalous magnetic configuration of Mn2NiAl ribbon and the role of hybridization in the martensitic transformation of Mn50Ni50−xAlx ribbons

The magnetic configuration of Mn2NiAl ribbon has been investigated. In contrast to Ni2MnAl, the compound Mn2NiAl with considerable disorder does exhibit ferromagnetism and, due to exchange interaction competition, both ferromagnetic and antiferromagnetic moment orientations can coexist between nearest neighbor Mn atoms. This is unexpected in Heusler alloys. Regarding the mechanism of the martensitic transformation in Mn50Ni50−xAlx, it is found that increasing the Al content results in an unusual change in the lattice constant, a decrease of the transformation entropy change, and enhancement of the calculated electron localization. These results indicate that the p-d covalent hybridization between Mn (or Ni) and Al atoms gradually increases at the expense of the d-d hybridization between Ni and Mn atoms. This leads to an increased stability of the austenite phase and a decrease of the martensitic transformation temperature. For 11 ≤ x ≤ 14, Mn50Ni50−xAlx ferromagnetic shape memory alloys are obtained.

Tuning exchange bias by Co doping in Mn50Ni41−xSn9Cox melt-spun ribbons

In Mn50Ni41−xSn9Cox ribbons, the exchange bias field is very sensitive to the Co content. Based on both theoretical and experimental studies, it has been found that with increasing Co content, the pinned phase (ferromagnetic phase) remains almost unchanged while the pinning phase is changed from a canonical spin glass to a cluster spin glass and finally to a ferromagnetic phase. Changing the Co content in Mn50Ni41−xSn9Cox alloys has been proven to be an effective way of tuning the magnetic anisotropy and the phase structure of the pinning phase. With different Co contents, a continuous tuning of the exchange bias field from 345 Oe to 3154 Oe is realized.

Magnetization jumps and exchange bias induced by a partially disordered antiferromagnetic state in (FeTiO3)0.9-(Fe2O3)0.1

Magnetization jumps (MJs) and the exchange bias (EB) effect are simultaneously observed in the mixed-spin oxide (FeTiO3)0.9-(Fe2O3)0.1 at 2.0 K. Dc and ac susceptibility measurements confirm a reentrant spin glass phase with a partially disordered antiferromagnetic (PDA) state below the irreversibility temperature (Tir = 60 K). Antiferromagnetic (AFM) Fe3+ clusters are nested in AFM Fe2+ lattices forming a triangular lattice, in which 2/3 of the magnetic moments order antiferromagnetically with each other leaving the remaining 1/3 “confused.” This geometric frustration in the triangular lattice leads to a PDA state that is the ground state of the AFM triangular configuration. The PDA state, in the presence of a critical trigger field, evolves into a ferromagnetic (FM) state, and induces the AFM spins of the Fe2+ ions to enter a FM state, resulting in the MJs. Meanwhile, the FM spins of Fe2+ can serve as the pinned phase, and the AFM spins of Fe3+ can serve as the pinning phase, resulting in the EB effect....

ε-iron nitrides: Intrinsic anomalous Hall ferromagnets

The anomalous Hall effect in e-iron nitrides (e-Fe3-xN, 0 ≤ x ≤ 1) has been systematically investigated taking advantage of the fact that the exchange splitting of e-Fe3-xN can be continuously tuned through the nitrogen concentration. It has been found that the anomalous Hall conductivity, σxyAH, is proportional to the saturation magnetization MS, i.e., σxyAH=SHMS, across significant variations in the saturation magnetization (96–1146 emu/cc). This relationship is in excellent agreement with the intrinsic mechanism as well as with the unified theory of AHE. Our results also demonstrate that the anomalous Hall conductivity is sensitive to the exchange splitting of the band structure.