Epitaxial Cr: An Electrically Conductive Transverse-Spin-Current Reflector

Electrically conductive metals are typically good spin conductors (e.g., Cu) or spin absorbers (e.g., Pt). We report evidence of conductive epitaxial (epi-) Cr (resistivity ~ 30 µΩ*cm) acting as a reflector of transverse spin current. Ferromagnetic resonance spin pumping measurements, performed on spin-valve-like stacks of epi-CoFe/epi-Cr/Cu/NiFe, indicate that epi-Cr blocks (reflects) an AC spin current that is polarized transverse to the CoFe and NiFe magnetization. Epi-Cr is a transverse spin-current reflector both at room temperature (where it is likely paramagnetic) and low temperature (where it is likely antiferromagnetic). The onset of this spin reflection behavior is also accompanied by a suppression of current-in-plane giant magnetoresistance. However, spin pumping measurements suggest polycrystalline Cr to be a good transverse-spin-current conductor. Our results thus suggest that the crystal structure of Cr plays a crucial role in its peculiar spin transport properties.