Spin Seebeck effect in ɛ-Fe2O3 thin films with high coercive field

Abstract

We present the experimental observation of the spin Seebeck effect in ε-Fe2−xAlxO3 (x=0 and 0.3) thin films with Pt detection layer. The films with 40–70 nm thicknesses were deposited by a spin-coating method on Y:ZrO2(100) substrates. The prepared films are highly oriented with the easy magnetic a-axis parallel to the film surface. The magnetic hysteresis loops measured for x=0 at room temperature with the magnetic field parallel to the surface exhibit coercive fields up to 11.6 kOe, which is so far the highest value of ε-Fe2O3 thin films. The spin Seebeck signal for x=0 increases proportionally to the film's thickness, which means that the critical thickness corresponding to the magnon propagation length is greater than 70 nm. Al substitution enhances the spin Seebeck signal, while it reduces the coercive field. The shape and coercive field of the spin Seebeck hysteresis loops closely resemble magnetization loops for single phase samples. A difference is encountered in the case of films with a small amount (1–2 vol. %) of secondary soft ferrimagnetic phase, where their presence is revealed in the magnetization loops by a constricted shape, in contrast to the spin Seebeck loops, where no constriction is observed. The large coercive field makes doped ε-Fe2O3 a suitable material for applications of the spin Seebeck effect without an external magnetic field.