Magnetocaloric and magnetotransport properties of R2 Ni2 Sn compounds (R=Ce, Nd, Sm, Gd, and Tb)

We report a detailed magnetic, magnetocaloric, and magnetotransport study on R2 Ni2 Sn compounds with different rare earths. The magnetic state of these compounds is found to be complex because of the coexistence of ferromagnetic and antiferromagnetic components. These compounds show phenomena such as multiple magnetic transitions, nonsaturation of magnetization, and metamagnetic transitions. Analysis of the zero-field heat capacity data shows that the magnetic entropy is less than the theoretical value, indicating the presence of some moment on Ni. Schottky anomaly is present in the magnetic heat capacity data of Sm2 Ni2 Sn. The temperature variation of magnetocaloric effect reflects the magnetization behavior. Tb2 Ni2 Sn and to a less extent Gd2 Ni2 Sn show oscillatory magnetocaloric effect. The variation of magnetocaloric effect is correlated with the ferromagnetic-antiferromagnetic phase coexistence. The electrical resistivity analysis has shown that the electron-magnon scattering is prominent at low temperature, while phonon scattering modified by the s-d interaction is crucial at high temperatures. The magnetoresistance is very large in Ce2 Ni2 Sn and shows a quadratic dependence on the field, implying the role of spin fluctuations in determining the transport behavior. Large magnetoresistance has been observed in other compounds as well.