Tunneling magnetoresistance spectroscopy: Temperature dependent spin-polarized band structure inCu38Ni62

Abstract

Tunneling magnetoresistance spectroscopy measurements have been performed on spin-valve magnetic tunnel junctions where the free magnetic electrode is a ${\mathrm{Cu}}_{38}{\mathrm{Ni}}_{62}$ alloy with a Curie temperature of around $240\phantom{\rule{0.3em}{0ex}}\mathrm{K}$. Measurement of the asymmetry in the tunneling magnetoresistance as a function of applied bias allows information on the spin-polarized electronic band structure to be gained. We have tracked the temperature dependence of the energy of the bottom of a minority-spin band close to the Fermi energy that is partly responsible for the tunneling conductance. The band minimum remains fixed slightly above the Fermi level until the temperature is raised to around $190\phantom{\rule{0.3em}{0ex}}\mathrm{K}$, at which point it abruptly drops below the Fermi level. This temperature dependence is shown to be consistent with a Stoner-like collapse of the effective exchange splitting of energy bands responsible for tunneling with increasing temperature.