Spin-Valve-Like Magnetoresistance inMn2NiGaat Room Temperature

Abstract

Spin valves have revolutionized the field of magnetic recording and memory devices. Spin valves are generally realized in thin film heterostructures, where two ferromagnetic (FM) layers are separated by a nonmagnetic conducting layer. Here, we demonstrate spin-valve-like magnetoresistance at room temperature in a bulk ferrimagnetic material that exhibits a magnetic shape memory effect. The origin of this unexpected behavior in Mn(2)NiGa has been investigated by neutron diffraction, magnetization, and ab initio theoretical calculations. The refinement of the neutron diffraction pattern shows the presence of antisite disorder where about 13% of the Ga sites are occupied by Mn atoms. On the basis of the magnetic structure obtained from neutron diffraction and theoretical calculations, we establish that these antisite defects cause the formation of FM nanoclusters with parallel alignment of Mn spin moments in a Mn(2)NiGa bulk lattice that has antiparallel Mn spin moments. The direction of the Mn moments in the soft FM cluster reverses with the external magnetic field. This causes a rotation or tilt in the antiparallel Mn moments at the cluster-lattice interface resulting in the observed asymmetry in magnetoresistance.

Negative to positive magnetoresistance and magnetocaloric effect in Pr0.6Er0.4Al2

“…4f shows an interesting behavior, an asymmetric MR around H = 0, which is similar to that observed in spin-valve-like MR effect in other systems, e.g. Mn 2 NiGa [25], where the mechanism was explained by antisite disorder, in which Ga atom sites are partially occupied by Mn atoms forming FM nanoclusters coupled antiparallel to the other Mn atoms. The observed negative but asymmetrical MR in low magnetic field shown in Fig.…”

Residual stress induced stabilization of martensite phase and its effect on the magnetostructural transition in Mn-rich Ni-Mn-In/Ga magnetic shape-memory alloys

“…The M(T ) plot in a low applied magnetic field of 50 Oe for annealed bulk samples shown in Fig. 5(a) reveals M s , M f , A s , and A f for Mn 1.75 Ni 1.25 Ga as 139, 134, 160, and 175 K, respectively, whereas the corresponding temperatures for Mn 1.9 Ni 1.1 Ga are 264, 160, 230, and 315 K. The drop at M s is related to the large magnetocrystalline anisotropy and lower magnetization of the martensite phase in these MSMAs [10,18,24]. A comparison of x-ray powder-diffraction profiles of the as-ground powder samples and the same powder after it was annealed at 773 K for 10 h (Fig.…”

“…The austenite phase of Mn excess Ni-Mn-In alloys is known to be ferromagnetic whereas the martensite phase is generally believed to be nonmagnetic (either paramagnetic or antiferromagnetic) [6,8,11], whereas in the Mn excess Ni-Mn-Ga alloys, both the austenite and the martensite phases are reported to be ferrimagnetic [10,[16][17][18]. Using high-resolution synchrotron and laboratory x-ray powder-diffraction (XRD) data, it is shown that the martensite structure can be stabilized by residual stresses over a wide temperature range well above A f in both alloy systems.…”

Asymmetric switchinglike behavior in the magnetoresistance at low fields in bulk metamagnetic Heusler alloys

“…A different mechanism was responsible for the spin-valve-like MR observed in bulk Mn 2 NiGa Heusler alloys; this was explained as a result of antisite coupling of Mn atoms located in the Ga positions, forming ferromagnetic nanoclusters coupled antiferromagnetically to the other Mn atoms [8].…”