Anisotropic magnetothermoelectric power of ferromagnetic thin films

TL;DR

This study investigates the magnetothermoelectric power (MTEP) in ferromagnetic thin films of Ni80Fe20, Co, and CrO2, revealing distinct behaviors and field-dependent effects related to magnetic domains and electronic structure.

Contribution

It provides a comparative analysis of MTEP in different ferromagnetic thin films, highlighting novel observations of opposite MTEP behavior in Py and Co, and detailed field-dependent effects in CrO2.

Findings

Py and Co films show ~0.2% change in MTEP with magnetic field reversal.

CrO2 films exhibit up to 20% MTEP variation depending on the thermal gradient direction.

Low-field effects are due to magnetic domain switching; high-field effects relate to electronic structure.

Abstract

We compare the behavior of the magnetothermoelectric power (MTEP)in metallic ferromagnetic thin films of Ni80Fe20 (Permalloy; Py), Co and CrO2 at temperatures in the range of 100 K to 400 K. In 25 nm thick Py films and 50 nm thick Co films both the anisotropic magnetoresistance (AMR) and MTEP show a relative change in resistance and thermoelectric power (TEP) of the order of 0.2% when the magnetic field is reversed, and in both cases there is no significant change in AMR or MTEP any more after the saturation field has been reached. Surprisingly, both Py and Co films have opposite MTEP behavior although both have the same sign for AMR and TEP. The data on 100 nm films of fully spin-polarized CrO2, grown both on TiO2 and on sapphire, show a different picture. The MTEP behavior at low fields shows peaks similar to the AMR in these films, with variations up to 1%. With increasing field both the MR and the MTEP variations keeps growing, with MTEP showing relative changes of 1.5% with the thermal gradient along the b-axis and even 20% with the gradient along the c-axis, with an intermediate value of 3% for the film on sapphire. It appears that the low-field effects are due to magnetic domain switching, while the high-field effects are intrinsic to the electronic structure of CrO2.