Thermal deterioration mechanism of CoFeB/PdPtMn spin valves

We clarified the mechanism of thermal deterioration that occurs in the CoFeB/PdPtMn spin-valve films at temperatures above 310 degrees C. Two kinds of CoFeB spin-valve film, Ta/NiFe/CoFeB/Cu/CoFeB/PdPtMn/Ta (B:0-3 at. %) and Ta/NiFe/CoFeB/Cu/CoFeB/FeMn/Ta (B:2 at. %), were prepared and annealed in a magnetic field. For the PdPtMn spin-valve samples, the magnetoresistance (MR) output decreased after annealing at a temperature above 330 degrees C and there was an increase in the interlayer coupling field of free and pin layers (Hin). There was no large change in the sheet resistance for annealing below 330 degrees C. For CoFe/PdPtMn(no B) spin valves, the MR output decreased during annealing at more than 310 degrees C and there was an increase of Hin. An addition of only 1 at. % of boron into the free and pinned layers is sufficient to obtain thermal stability. For the CoFeB/FeMn spin-valve samples, the MR output decreased for annealing above 280 degrees, the sheet resistance increased, and the Hin value did not change for annealing below 300 degrees C. The interface properties of PdPtMn spin valves were examined using high resolution scanning transmission electron microscopy with energy dispersive spectroscopy. We observed the connection between the free and the pinned layers through Cu pinholes and reduced Mn inter diffusion for the deteriorated sample. The increase of Hin can be explained by the pinholes of the Cu layer which result in a connection between the free and pinned layers. Boron in the free and pinned layer has the effect of blocking diffusion, thereby preventing a connection of the free and pinned layers. (C) 1999 American Institute of Physics. [S0021-8979(99)35508-0].