Magnetic nature of the austenite-martensite phase transition and spin glass behaviour in nanostructured Mn_2Ni_(1.6)Sn_(0.4) melt-spun ribbons

摘要

Nanocrystalline ribbons of inverse Heusler alloy Mn_2Ni_(1.6)Sn_(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_(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_(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_(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.