The authors report the observation of large magnetoresistance in Ni50Mn34In16 alloy. This alloy undergoes an austenite-martensite phase transformation which can be strongly affected by the applied magnetic field. This latter effect produces very large magnetoresistance at relatively high temperatures (e.g., 250K). Signature of field induced shape memory effect is also observed in the magnetoresistance results. Above 225K, the field induced shape memory effect is found to be affected by the path traversed in the H-T phase space to reach the target temperature.

Results of dc magnetization study are presented showing interesting thermomagnetic history effects across the antiferromagnetic to ferromagnetic transition in Ce(Fe 0.96 Al 0.04 ) 2 . Specifically, we observe (i)ZFC/FC irreversibility rising with increasing field; (ii) virgin curve lying outside the envelope M-H curve. We argue that these effects are quite different from the characteristics seen in spin-glasses or in hard ferromagnets; they can be understood as metastabilities associated with a first order magnetic phase transition.

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We report a study of the magnetocaloric effect in the ternary alloy system Ni50Mn34In16. This system undergoes an austenite–martensite phase transition, and the change in magnetic entropy is found to be quite large across this martensitic transition. This entropy change is due to an increase in entropy induced by the application of an external magnetic field and can lead to a large inverse magnetocaloric effect. Isothermal magnetic field variation of magnetization exhibits field hysteresis in Ni50Mn34In16 across the martensitic transition. But in spite of the hysteresis losses, a large effective refrigerant capacity can be obtained in this material over a wide temperature interval.

First order ferromagnetic (FM) to antiferromagnetic (AFM) phase transition in doped CeFe2 alloys is studied with the micro-Hall probe technique. Clear visual evidence of magnetic phase coexistence on micrometer scales and the evolution of this phase coexistence as a function of temperature, magnetic field, and time across the first order FM-AFM transition is presented. Such phase coexistence and metastability arise as a natural consequence of an intrinsic disorder-influenced first order transition. The generality of these phenomena involving other classes of materials is discussed.

Experimental results of magnetization measurements of first-order ferromagnetic-antiferromagnetic transitions in Ce(Fe 0.96 Ru 0.04 ) 2 alloy are presented. The metastability of states in the transition region gives rise to large relaxation and lack of end-point-memory effect in the magnetization. Traditional phenomenological asymmetry between the extent of supercooling and superheating is observed in the temperature and magnetic field variation of the magnetization and is also confirmed in relaxation results. Nonuniform variation of the relaxation rate with magnetic field gives a clear picture of the nucleation and growth of phases.

We present results of detailed ac susceptibility, magnetization and specific heat measurements in Heusler alloys Ni50Mn34In16 and Ni50Mn34Sn16. These alloys undergo a paramagnetic to ferromagnetic transition around 305 K, which is followed by a martensitic transition in the temperature regime around 220 K. Inside the martensite phase both the alloys show signatures of field-induced transition from martensite to austenite phase. Both field- and temperature-induced martensite–austenite transitions are relatively sharp in Ni50Mn34In16. We estimate the isothermal magnetic entropy change and adiabatic temperature change across the various phase transitions in these alloys and investigate the possible influence of these transitions on the estimated magnetocaloric effect. The sharp martensitic transition in Ni50Mn34In16 gives rise to a comparatively large inverse magnetocaloric effect across this transition. On the other hand the magnitudes of the conventional magnetocaloric effect associated with the paramagnetic to ferromagnetic transition are quite comparable in these alloys.