Meghmalhar Manekar

First-order transition from antiferromagnetism to ferromagnetism inCe(Fe0.96Al0.04)2

Results of dc magnetization study are presented showing interesting thermomagnetic history effects across the antiferromagnetic to ferromagnetic transition in Ce(Fe

Reproducible room temperature giant magnetocaloric effect in Fe?Rh

_{0.96}

Magnetocaloric effect in CeFe2 and Ru-doped CeFe2 alloys

Al

Metamagnetic transition in Ce(Fe0.96Al0.04)2: a dc magnetization study

_{0.04})_2

Very large refrigerant capacity at room temperature with reproducible magnetocaloric effect in Fe0.975Ni0.025Rh

. 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.

Contrasting magnetic behavior of Ni50Mn35In15 and Ni50Mn34.5In15.5 alloys

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.

Magnetic and transport properties of (β+γ) Ni35Co35Al30 ferromagnetic shape memory alloy across the martensitic transition

The magnetocaloric effect (MCE) is studied in CeFe2 and Ru-doped CeFe2 alloys with dc magnetization measurements. The pure CeFe2 compound shows a distinct peak in MCE around the paramagnetic to ferromagnetic transition. In Ru-doped CeFe2 alloys there is a further transition from the ferromagnetic to antiferromagnetic state at low temperatures. This latter magnetic transition gives rise to a relatively large inverse MCE. A comparative study of the MCE associated with two different magnetic transitions is made and the possible role of a structural transition in the inverse MCE is discussed.

Training effects in Gd5Ge4: role of microstructure

We present results of a dc magnetization study which show interesting thermomagnetic history effects across the antiferromagnetic-to-ferromagnetic transition in Ce(Fe 0.96 Al 0.04 ) 2 pseudobinary alloy. Specifically, we observe (i) the degree of ZFC/FC irreversibility rising with increasing field; (ii) the virgin curve lying outside the envelope M-H curve. Some of the key results are supported by magneto-transport measurements. We argue that these effects are quite different from the characteristics seen in spin glasses or in hard ferromagnets. They can be understood in terms of kinetic arrest of a first-order transition.

Glassy dynamics in magnetization across the first order ferromagnetic to antiferromagnetic transition in Fe0.955Ni0.045Rh.

We present the results of magnetocaloric effect (MCE) measurements on Fe0.975Ni0.025Rh. The MCE is estimated using both the isothermal field-dependent magnetization and the temperature-dependent magnetization in constant magnetic fields. We find a very large effective refrigerant capacity of nearly 492.8 J kg−1, with the hot end at about 307 K, which is reproducible over many field cycles. We compare this refrigerant capacity with those of two well known systems, namely Gd5Ge1.9Si2Fe0.1 and MnFeP0.45As0.55, which show a large MCE near room temperature, and also with our earlier results on the parent Fe–Rh alloy. The large effective refrigerant capacity in our sample is one of the largest achieved yet at room temperature with a significant improvement over the parent Fe–Rh system.

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

We have studied the electrical resistivity, magnetization, and heat capacity of the off-stoichiometric Heusler alloys Ni50Mn35In15 and Ni50Mn34.5In15.5 as functions of temperature and magnetic field. The results show that the alloy system is more sensitive to the composition than what is apparent from the established phase diagram. We have found that the ground states as well as the nature of phase transitions strongly depend on concentration differences as low as 0.5 at. %. While in the case of Ni50Mn34.5In15.5 we do observe a magnetic field induced martensite to austenite phase transition, there is no detectable signature of any field induced transition in the Ni50Mn35In15 alloy even up to fields as high as 80 kOe. Accordingly, the functional properties of these two alloys are also drastically different.