5% negative magnetoresistance (MR) at room temperature has been observed in bulk Ni2+xMn1−xGa. This indicates the possibility of using Ni2+xMn1−xGa as magnetic sensors. We have measured MR in the ferromagnetic state for different compositions (x=0–0.2) in the austenitic, premartensitic, and martensitic phases. MR is found to increase with x. While MR for x=0 varies almost linearly in the austenitic and premartensitic phases, in the martensitic phase it shows a cusplike shape. This has been explained by the changes in twin and domain structures in the martensitic phase. In the austenitic phase, which does not have twin structure, MR agrees with theory based on s-d scattering model.

A detailed investigation of the first order antiferromagnetic insulator (AFI) to ferromagnetic metal (FMM) transition in N d 0.5 Sr 0.5 M nO 3 is carried out by resistivity and magnetization measurements. These studies reveal several anomalous features of thermomagnetic irreversibility across the first order transition. We show that these anomalous features can not be explained in terms of supercooling effect alone and H-T diagram based on isothermal MH or RH measurement alone do not reflect true nature of the first order transition in this compound. Our investigations reveal glass-like arrest of kinetics at low temperature which plays a dominant role in the anomalous thermomagnetic irreversibility observed in this system. The interplay between kinetic arrest and supercooling is investigated by following novel paths in the H-T space. It is shown that coexisting FMM and AFI phases can be tuned in a number of ways at low temperature. These measurements also show that kinetic arrest temperature and supercooling temperature are anti-correlated i.e. regions which are arrested at low temperature have higher supercooling temperature and vice versa.

A detailed investigation of the first-order ferrimagnetic (FRI) to antiferromagnetic (AFM) transition in Mn1.85Co0.15Sb is carried out. These measurements demonstrate anomalous thermomagnetic irreversibility and a glass-like frozen FRI phase at low temperatures. The irreversibility arising between the supercooling and superheating spinodals is distinguished in an ingenious way from the irreversibility arising due to kinetic arrest. Field annealing measurements show a re-entrant FRI–AFM–FRI transition with increasing temperature. In this system the kinetic arrest band and supercooling band are also shown to be anticorrelated (i.e. the regions which are kinetically arrested at higher temperature have lower supercooling temperature and vice versa), which has been a universal feature of the AFM/ferromagnetic transition so far.

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The first-order antiferromagnetic ͑AFM͒ to ferromagnetic ͑FM͒ transition in the functional material Fe 49 ͑Rh 0.93 Pd 0.07 ͒ 51 has been studied at low temperatures and high magnetic fields. We have addressed the nonmonotonic variation in lower critical field required for FM to AFM transition. It is shown that critically slow dynamics of the transition dominates below 50 K. At low temperature and high magnetic field, state of the system depends on the measurement history resulting in tunable coexistence of AFM and FM phases. By following cooling and heating in unequal magnetic field protocol it is shown that equilibrium state at 6 T magnetic field is AFM state. Glasslike FM state at 6 T ͑obtained after cooling in 8 T͒ shows reentrant transition with increasing temperature; viz., devitrification to AFM state followed by melting to FM state.