Temperature and Thickness Dependent Spin Current Transmission through Epitaxial Antiferromagnetic alpha-Fe2O3

Antiferromagnetic insulator α-Fe2O3 is a potential medium for coherent motion of spin waves over relatively large distances, allowing non-dissipative transfer of information between circuit elements. However, the structural defects and temperature dependent spin reorientations in this oxide impact the propagation. Understanding how the magnetic state of an antiferromagnetic insulator affects spin-current transmission is therefore important for elucidating the mechanisms governing spin transport. Here, we report spin-current transmission through epitaxial α-Fe2O3 thin films sandwiched between Permalloy and Pt. Using spin pumping and inverse spin Hall effect, we observe a finite symmetric dc voltage across the Pt layer over the temperature range 1.6 to 300 K for alpha-Fe2O3 thicknesses of 0, 30, 40, and 100 nm. The symmetric voltage coefficient Ks exhibits two approximately linear temperature regimes, separated by a characteristic temperature T* whose value depends on the thickness of the α-Fe2O3 layer. Further, the dc magnetization measurements on some of the samples suggest that the T* is correlated with the spin reorientation transition (Morin transition) in α-Fe2O3. Interestingly, a significantly larger magnitude of dKs/dT is noted below the characteristic temperature T*. The observed thickness and temperature dependent spin-current transmission indicates a sensitivity to the magnetic state of the insulating hematite layer.