Pinholes and spin transfer effect in magnetic tunnel junction heads

Spin-transfer-induced microwave excitations in magnetic tunnel junction (MTJ) read heads have been investigated via spin-torque-modified micromagnetic modeling. This study focuses on the effect of possible pinholes in the barrier layer for a MTJ read head with permanent magnet stabilization. It is found that the critical current threshold for the spin-transfer-excited microwaves is significantly reduced if small pinholes exist in the tunnel barrier layer. The smaller effective conductive area, the smaller the current threshold. For a single small pinhole in the center of the barrier surface, the resulted spin-transfer-excited microwaves are chaotic in nature, yielding a significant 1/f noise below 1 GHz. The,microwave excitation also strongly depends on the exact location of the pinhole(s). The study suggests that by studying the spin-transfer-excited microwaves, one can obtain a good knowledge about the possible existence of pinholes as well as their spatial distributions for the magnetic tunnel junction read heads. (c) 2005 American Institute of Physics.