Temperature and bias-assisted transport properties of LSMO/AlO/CoFeB magnetic tunnel junction

We have observed the transport properties in magnetic tunnel junction with the multilayered structure: La_0.67Sr_0.33MnO₃ (50 nm)/Al-O (1 nm)/CoFeB (5 nm)/Ta (10 nm)/Ru (10 nm). The maximum normal tunneling magnetoresistance (TMR) ratio was found to be 12.4% at a temperature range around 100 K, and the maximum inverse TMR ratio was observed to be ∼3% at a temperature of 5 K. The inverse TMR decreases with increasing temperature until it reaches a temperature range of around 50 K, whereby it switches to the normal TMR behavior. The appearance of inverse TMR at low temperatures is attributed to the presence of minority-spin density of states (DOS) of half-metal La_0.67Sr_0.33MnO₃ around the Fermi level present at the half-metal-insulator interface. The vanishing of inverse TMR and increase of normal TMR above certain temperature range is due to no contribution from the minority-spin DOS in the tunneling process. These results were found to be reproducible and the TMR ratio of more than 3% and 11% was obtained at room temperature before and after annealing at a temperature of 235 K for an annealing time of one hour, respectively.