Magnetic nature of the austenite–martensite phase transition and spin glass behaviour in nanostructured Mn₂Ni_1.6Sn_0.4 melt-spun ribbons

Abstract

Nanocrystalline ribbons of inverse Heusler alloy Mn₂Ni_1.6Sn_0.4 have been synthesised by melt spinning of the arc-melted bulk precursor. The single-phase ribbons crystallize into a cubic structure and exhibit very fine crystallite size of <2 nm. Temperature-dependent magnetization (M–T) measurements reveal ferromagnetic–austenite (FM-A)–antiferromagnetic–martensite (AFM-M) phase transition that begins at M _S ≈ 249 K and finishes at M _f ≈ 224 K. During warming, the reverse AFM-M to FM-A transitions begins at A _s ≈ 240 K and finishes at A _f ≈ 261 K. A re-entrant FM transition is observed in the M-phase at $T_{\text{CM}}$ ≈ 145 K. These transitions are also confirmed by temperature-dependent resistivity (ρ–T) measurements. The hysteretic behaviour of M–T and ρ–T in the temperature regime spanned by the A-M transition is a manifestation of the first-order phase transition. M–T and ρ–T data also provide unambiguous evidence in favour of spin glass at $T < T_{\text{CM}}$. The scaling of the glass freezing temperature (T _f) with frequency, extracted from the frequency-dependent AC susceptibility measurements, confirms the existence of canonical spin glass at $T < T_{\text{CM}}$ ≈ 145 K. The occurrence of canonical spin glass has been explained in terms of the nanostructuring modified interactions between the coexisting FM and AFM correlations in the martensitic phase.