The variation of resistance with applied magnetic field for an epitaxial NiMnSb/Al₂O₃/Ni_0.8Fe_0.2/CoO tunnel junction. An ultrathin layer of CoO was used to bias the permalloy (Ni_0.8Fe_0.2) film at an angle of 22° from one of the [100] cubic NiMnSb axes along which its magnetic moment normally points. The labels 1 to 4 correspond to the four crystalline [100] directions in the NiMnSb film. When the magnetization of NiMnSb and permalloy are nearly parallel (H along direction 4) the lower resistance state is achieved. With the field reversed (H along direction 1), the resistance is highest. Depending on how the field is reduced, two additional, intermediate resistance levels can be reached. These resistance states, reflecting NiMnSb's cubic magnetocrystalline isotropy directions, illustrate the principle of a four-state spin tunneling nonvolatile memory element. These data were taken at 77 K. Room-temperature operation can be achieved by using an exchange biasing material such as FeMn or IrMn instead of CoO. (Adapted from C. Tanaka, J. Nowak, J. S. Moodera, Journal of Applied Physics, volume 86, page 6239, 1999).

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© 2001 American Institute of Physics