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.

Results of isothermal magnetization and magnetic relaxation measurements are presented probing the nature of the magnetic-field-induced magnetostructural transition in the intermetallic compound Gd 5 Ge 4 . This transition shows the characteristics of a disorder-influenced first order transition including distinct metastable behavior. Below approximately 21 K, the transition from the magnetic-field-induced ferromagnetic state back to the antiferromagnetic state shows additional interesting features. Similarities with other classes of magnetic systems exhibiting magnetostructural transitions are pointed out.

We present the results of magnetocaloric effect (MCE) studies in polycrystalline Fe–Rh alloy over a temperature range of 250–345 K across the first order antiferromagnetic to ferromagnetic transition. By measuring the MCE under various thermomagnetic histories, contrary to the long held belief, we show here explicitly that the giant MCE in Fe–Rh near room temperature does not vanish after the first field cycle. In spite of the fact that the virgin magnetization curve is lost after the first field cycle near room temperature, reproducibility in the MCE under multiple field cycles can be achieved by properly choosing a combination of isothermal and adiabatic field variation cycles in the field-temperature phase space. This reproducible MCE leads to a large effective refrigerant capacity of 324.42 J kg−1, which is larger than that of the well-known magnetocaloric material Gd5Si2Ge2. This information could be important as Fe–Rh has the advantage of having a working temperature of around 300 K, which can be used for room temperature magnetic refrigeration.

We present results of ac susceptibility measurements highlighting the presence of thermal hysteresis and phase coexistence across the ferro-to antiferromagnetic transition in various CeFe 2 based pseudobinary systems. These results indicate that the ferro-to antiferromagnetic transition in these systems is first order in nature.

Magnetotransport behavior is investigated in detail across a first-order magnetic phase transition from a ferromagnetic state to an antiferromagnetic state in a polycrystalline Ce(Fe 0.96 Al 0.04 ) 2 sample. The study clearly brings out various generic features associated with a first-order transition, viz., hysteresis, phase coexistence, supercooling and superheating, and the presence and limits of the metastable regimes. These magnetotransport study results exhibit and support all the interesting thermomagnetic history effects that were observed in our earlier dc magnetization study on the same sample. Most notable here is the initial ͑or virgin͒ resistivity vs field curve lying outside the hysteretic ''butterfly-shaped'' magnetoresistivity loops obtained on cycling the magnetic field between high enough positive and negative strengths. These findings, bearing a one-to-one similarity with the data obtained in their magnetic counterpart ͑i.e., dc magnetization͒, are ascribed an origin due to the arresting of this first-order transition kinetics at low temperature and high magnetic field.