Nucleation and growth dynamics across the antiferromagnetic to ferromagnetic transition in (Fe0.975Ni0.025)50Rh50: analogy with crystallization

We present the results of ac susceptibility and dc magnetization measurements on polycrystalline (Fe0.975Ni0.025)50Rh50. The sample undergoes a first order antiferromagnetic to ferromagnetic transition both as a function of temperature and magnetic field. The presence of phase coexistence and metastable states across the transition is highlighted through the observation of minor hysteresis loops and magnetic relaxation respectively. The magnetic relaxation follows a power law which can arise due to long-range dipolar interaction between the ferromagnetic clusters in the phase coexistent state. The non-monotonic behaviour of the power law exponent as a function of temperature and magnetic field suggests a nucleation and growth behaviour very similar to crystallization of solids. The area of minor hysteresis loops is conjectured to be related to the phase fraction of one of the phases involved in the transition. The temperature and field dependent phase fraction is shown to follow the well known Avrami law of transformation kinetics.