Parul Arora

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

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.

Magnetocaloric effect in MnSi

The temperature dependence of heat capacity of MnSi has been measured in the presence of different values of magnetic field. When the magnetic field is applied, an appreciable adiabatic temperature change is observed in the compound. The entropy change due to isothermal change of magnetic field is found to be significant well above the ordering temperature of the compound. This produces a large refrigerant capacity in MnSi, making it important for applications in refrigeration cycles.

The magnetotransport properties of the intermetallic compound GdCu6

We have studied the temperature and magnetic field dependence of the electrical resistivity of GdCu(6) and have co-related the results with the temperature dependence of heat capacity and magnetization. The magnetoresistance of GdCu(6) is found to be positive both in the paramagnetic and antiferromagnetic regimes. Within the antiferromagnetic regime, the magnetoresistance is very high and increases to still higher values both with increasing field and decreasing temperature. In the paramagnetic regime the magnetoresistance continues to exhibit a finite positive value up to temperatures much higher than that corresponding to the antiferromagnetic to paramagnetic phase transition. We have shown through quantitative analysis that both the temperature dependences of resistivity and heat capacity indicate the presence of spin fluctuations within the paramagnetic regime of GdCu(6). The field dependence of electrical resistivity indicates that the positive magnetoresistance in the paramagnetic phase is not related to the orbital motion of the conduction electrons in a magnetic field (the Kohler rule). In contrast, our analysis indicates that these spin fluctuations are responsible for the positive magnetoresistance observed within this paramagnetic regime. The nature of the field dependence of electrical resistivity is found to be qualitatively similar both in the antiferromagnetic and paramagnetic regimes, which probably indicates that spin fluctuations in the paramagnetic regime are of the antiferromagnetic type.

Magnetic properties and large magnetocaloric effect of DyPt2

We report the results of magnetization and heat capacity measurements on the rare-earth intermetallic compound DyPt2 as a function of temperature and magnetic field. These studies reveal the presence of short range magnetic correlations in DyPt2 above the Curie temperature, well inside the paramagnetic regime. This contributes appreciably to the magnetic entropy, which can be tuned with the help of applied magnetic field over a wide range of temperature. As a result, DyPt2 exhibits a large magnetocaloric effect that persists at temperatures much above the Curie temperature.

Multiple magnetic transitions in Ag-substituted DyPt2

We show that the partial substitution of Ag in place of Pt in the cubic Laves phase ferromagnetic (below 9.2 K) compound DyPt2 leads to multiple temperature and field induced magnetic phase transitions. We study these phase transitions in details in a Dy(Pt0.94Ag0.06)2 alloy with the help of magnetization and specific heat measurements. One of the magnetic transitions produces an unusually sharp peak in the temperature dependence of heat capacity of Dy(Pt0.94Ag0.06)2, which is not observed in either of the parent compounds DyPt2 or DyAg2. The shape of this peak resembles those observed in the temperature dependence of heat capacity of the rare earth elements and some rare-earth based alloys and compounds across first order magnetic transitions accompanied by magneto-elastic effects and structural changes. The magnetic properties of Dy(Pt0.94Ag0.06)2 are analyzed in terms of the enhancement of crystal field effect and quadrupolar interactions. Large magneto-elastic coupling resulting from these interaction...

Magnetic properties of the field-induced ferromagnetic state in MnSi.

We present results of dc magnetization measurements focusing on the magnetic properties of the field-induced ferromagnetic state in MnSi. The temperature dependence of saturation magnetization in this ferromagnetic state exhibits the signatures of both spin wave excitations and itinerant electron ferromagnetism. The Arrott plots obtained from the isothermal field dependence of magnetization, however, are found to be distinctly nonlinear and hence cannot be explained within a simple framework of itinerant electron magnetism.