Cluster spin glass in off-stoichiometric Ni2.01Mn1.58Sn0.41 alloy

Abstract

The Ni2.01Mn1.58Sn0.41 alloy is a member of the Heusler material family which undergoes diffusionless structural transition from cubic austenite to orthorhombic martensite during its cooling. The transition was observed at temperature 398 K from paramagnetic austenite to martensite with complex magnetic structure. The measurement of AC magnetic susceptibility of the alloy confirmed spin-glass state at temperatures below 155 K and from the frequency dependence of the cups in AC susceptibility, a presence of clusters (11 nm3 in size) with strong interaction is deduced. The alloy shows anomalous Hall effect (AHE) of the order of 0.051 μΩ cm at 2 K in the spin-glass state of the alloy and its sign changes at around 140 K. The ordinary Hall coefficient of the metallic alloy is strikingly positive in the whole studied temperature region, and it points to complex magnetic and electronic structure of the alloy. The electrical resistance of the sample shows a flat maximum of 220 μΩ cm at spin-glass transition temperature. The magnetoresistance is of the order of 1% and is negative in the whole temperature region which points to a standard scattering of charge carriers on magnetic fluctuations. Quantum-mechanical calculations of supercells with compositions Ni32Mn25Sn7, Ni32Mn26Sn6 and Ni32Mn24Sn8 simulated different arrangement of Mn and Sn atoms. Ni32Mn25Sn7 composition is thermodynamically the most stable, although its magnetic moment is 1.67 μB/f.u., twice higher than the measured value. The combination of the latter two states, with additional Mn–Sn swaps, provides the magnetic moments matching the experimental value at a very small energy cost. Theoretical results then indicate that a scenario of local chemical variations and clustering is likely in the studied alloy.