Measurement of the transport spin polarization of doped strontium ruthenates using point contact Andreev reflection

Electrical conductivity, magnetic susceptibility, and point contact Andreev reflection (PCAR) studies were done on bulk, polycrystalline Sr Ru 1 − x ( TM ) x O 3 ( TM = Cr , Mn, Ti) and Sr Ru 0.92 O 3 with a high degree of disorder. Fits of the temperature dependence of the latter using the Curie-Weiss law yielded values for the Curie-Weiss temperature, Θ . Furthermore, the values of the Curie temperature, T C were identified by determining the maximum susceptibility as a function of temperature. PCAR measurements were done to determine the transport spin polarization, P t ( 0 ⩽ P t ⩽ 1.0 ) . Pure Sr Ru O 3 undergoes ferromagnetic ordering at a Curie temperature of T C ∼ 160 K and has a relatively high spin polarization ( ∼ 0.6 ) . Our results indicate that when the lattice is disordered from either the presence of Ru lattice site defects or the substitution of a transition metal for the Ru, T C changes by a factor of 2, and Θ by a factor of 1.7. By contrast, the spin polarization is unchanged for both Sr Ru 0.94 Ti 0.06 O 3 and Sr Ru 0.9 Mn 0.1 O 3 , while it is barely changed ( P = 0.5 ) for Sr Ru 0.9 Cr 0.1 O 3 .