Probing phase transition and anisotropy in magnetic insulator based heterostructures employing magnon spin currents

Many reports have explored the temperature dependence of Longitudinal Spin Seebeck Effect (LSSE) in insulating magnets. However, there has been a longstanding disparity between theory and experimental evidence with regards to the nature of power law decay of the LSSE while approaching the ferromagnetic phase transition temperature (T_C). We investigate bilayers of Pt/La₂NiMnO₆ (LNMO) and Pt/EuO_1-X, both predicted to be promising candidates for spintronics. Our findings reveal that the signal near T_C can be fitted to a power law of the form (T_C-T)^P. We explain our results based on the magnon-driven thermal spin pumping theory. We comprehensively demonstrate correlation between the critical exponents of LSSE and magnetization for both FMs. Interestingly, the exponent, P, remained invariant upon varying the crystallinity in LNMO. In contrast, Spin Hall Magnetoresistance (SMR) measurements on epitaxial LNMO, exhibit distinctly different features. The observed behavior in epitaxial films appears to be dominated by the interface magnetic anisotropy. In addition, we observe SMR and Anisotropic Magnetoresistance (AMR) in Pt/EuO_1−X thin films. We deduce possible explanations based on the temperature dependence of EuO_1−X bandstructure and spin mixing conductance of the Pt/EuO_1−X interface.