Electrical properties of single crystal Yttrium Iron Garnet ultra-thin films at high temperatures

TL;DR

This study reveals that ultra-thin Yttrium Iron Garnet films exhibit semiconducting behavior with temperature-dependent resistivity and Hall effects, impacting their use in spintronic and magnetic devices at high temperatures.

Contribution

First detailed electrical characterization of 19 nm YIG films at high temperatures, showing semiconducting properties and Hall effects relevant for device applications.

Findings

Resistivity decreases exponentially with temperature, indicating a band gap of about 2 eV.

Hall mobility is positive and roughly temperature-independent at 5 cm²/(V·s).

Electrical properties cause offset voltages and magnetic field sensitivities in devices.

Abstract

We report a study on the electrical properties of 19 nm thick Yttrium Iron Garnet (YIG) films grown by liquid phase epitaxy. The electrical conductivity and Hall coefficient are measured in the high temperature range [300,400]~K using a Van der Pauw four-point probe technique. We find that the electrical resistivity decreases exponentially with increasing temperature following an activated behavior corresponding to a band-gap of $E_g\approx 2$ eV, indicating that epitaxial YIG ultra-thin films behave as large gap semiconductor, and not as electrical insulator. The resistivity drops to about $5\times 10^3$~$\Omega \cdot \text{cm}$ at $T=400$ K. We also infer the Hall mobility, which is found to be positive ($p$-type) at 5 cm$^2$/(V$\cdot$sec) and about independent of temperature. We discuss the consequence for non-local transport experiments performed on YIG at room temperature. These electrical properties are responsible for an offset voltage (independent of the in-plane field direction) whose amplitude, odd in current, grows exponentially with current due to Joule heating. These electrical properties also induce a sensitivity to the perpendicular component of the magnetic field through the Hall effect. In our lateral device, a thermoelectric offset voltage is produced by a temperature gradient along the wire direction proportional to the perpendicular component of the magnetic field (Righi-Leduc effects).