Magnetic tunnel junctions thermally stable to above 300°C

Magnetic tunnel junctions formed from sandwiches of magnetically hard Co₇₅Pt₁₂Cr₁₃ and magnetically soft Co₈₈Pt₁₂ ferromagnetic layers separated by thin alumina tunnel barriers are shown to be thermally stable to temperatures in excess of 300°C. A comparison of cross-section transmission electron micrographs of an untreated sample and a similar one annealed at 350°C indicates that the thickness of the amorphous tunnel barrier is slightly decreased after annealing. The resistance and magnetoresistance are only slightly affected by annealing at temperatures of up to ∼300°C but then decrease monotonically at higher annealing temperatures. Interaction of the alumina layer with the adjacent ferromagnetic layers is the likely cause of this decrease.