Temperature-driven band motion prior to the phase transition of an itinerant ferromagnet.

Tunneling magnetoresistance spectroscopy measurements have been performed on spin-valve magnetic tunnel junctions where the free magnetic electrode is a Cu38Ni62 alloy with a Curie temperature of around 240 K. These measurements allow us to follow the temperature dependence of the energy of the bottom of a minority-spin band close to the Fermi energy, which is partly responsible for the tunneling conductance. The temperature dependence of the tunneling spin polarization of the CuNi electrode has also been extracted using the Julliere formula. We show that the tunneling spin polarization as a function of temperature can be related to the temperature-dependent magnetization using an extension of the commonly applied Stearns model that incorporates the motion of the band close to the Fermi level. This model reproduces the nonlinear relation between tunneling spin polarization and magnetization obtained for Cu38Ni62. [ABSTRACT FROM AUTHOR]