Electrical and thermal transport coefficients of CoFe thin films deposited on a microcalorimeter

Sasmita Srichandan
Interaction of spin, charge and heat currents in micro/nano structures opens opportunities for improving the performance of thermoelectric devices and future generation memory devices. For example, in magnetic insulators, coupled interaction of magnons with heat current generates the so called spin-Seebeck effect while magnon degree of freedom is utilized to transmit and process information in the sub-field of magnonics. In parallel, in magnetic metals, the charge carrying electrons interact
more » ... h magnons and phonons to generate effects such as spin transfer torque and spin-dependent Seebeck effect. In the heart of the research on future generation thermoelectric and memory devices, lies the interplay of electrons, phonons and magnons along with external parameters of magnetization and thermal current. In this thesis, the roles played by the electrons, phonons and magnons in generating various electrical, thermal and magneto-thermal transport properties has been studied in ferromagnetic alloy thin films. Emphasis has been given to the development and utilization of SiN membrane based suspended microcalorimeter. In CoFe thin films, resistivity, thermopower and thermal conductivity were measured in the temperature range of 25 K-296 K. Contribution of electron scattering from phonons and magnons to these transport coefficients has been separated. The change of sign of the magnon drag contribution to thermopower from Co-rich to Fe-rich side of the material has been discussed. Additionally simultaneous measurement of resistivity and thermal conductivity has facilitated studying the validity of Wiedemann-Franz law in these films. In a second alloy of Permalloy, observation of transverse magneto-thermoelectric effects in the presence of in-plane temperature gradient and magnetization has been discussed. Various competing effects have been separated depending on their angular dependencies. Together with the results from bulk substrates (see PhD thesis by M. Schmid), the existence of transverse spin Seebeck effect has been [...]
doi:10.5283/epub.35254 fatcat:oq6i63x5jvdr5da6i6okxtxq3e