The dependence of the antiferromagnet/ferromagnet blocking temperature on antiferromagnet thickness and deposition conditions

The blocking temperature was measured for several exchange biasing materials as a function of the antiferromagnet thickness and deposition conditions. For the oxide materials Co0.5Ni0.5O and NiO and for IrMn, the blocking temperature was found to decrease from the bulk values of 150, 190, and 250 degrees C, respectively, with decreasing thickness of the antiferromagnet. The minimum thickness needed in order to maintain a blocking temperature within 25% of the bulk value was 125, 145, and 140 Angstrom for Co0.5Ni0.5O, NiO, and IrMn, respectively. The functional dependence with thickness was found to follow a power law relationship, which is consistent with the finite size scaling phenomenon. The shift exponent for scaling obtained by curve fitting the experimental data was 1.65, 1.40, and 1.52 for the three materials, respectively. These values were in good agreement with the theoretical values of 1.4-1.6, as calculated for idealized antiferromagnets. The corresponding values for the correlation length at 0 K were 22, 19, and 30 Angstrom, respectively. For Co0.5Ni0.5O, the blocking temperature was also found to vary with deposition conditions, with high negative substrate biases and low pressures yielding the largest blocking temperatures. These trends were also found to follow a power-law relation. (C) 1999 American Institute of Physics. [S0021-8979(99)71208-9].