Value Of Exchange Bias Field Research Articles

Analytical solutions for exchange bias and coercivity in ferromagnetic/antiferromagnetic bilayers

Analytical expressions have been derived for the exchange bias field, coercivity, and effective anisotropy field in ferromagnetic/antiferromagnetic bilayers in the framework of a model assuming the formation of a planar domain wall at the antiferromagnetic side of the interface with the reversal of the ferromagnetic orientation. It is shown that there are five different sets of analytical expressions for the hysteresis loop displacement and coercivity, which depend on the interfacial exchange coupling strength and ferromagnetic anisotropy, and only one expression for the effective anisotropy field. These expressions are compared with the previously reported theoretical results, and the validity of the latter is discussed. It is shown that in the framework of the present model, the hysteresis loop, ac susceptibility, and ferromagnetic resonance measurements of exchange anisotropy should give the same values for the exchange bias field. The difference between the exchange bias field values, estimated experimentally by ac susceptibility and through hysteresis loop measurements for Co/CoO bilayers, is explained as well.

Exchange biasing and thermal stability of CoFe/PtPdMn films

Two sets of PtPdMn exchange biased films Ta 50 Å/CoFe 100 Å/PtPdMn (tAF) Å/Ta 50 Å, with PtPdMn thickness, tAF=350, 600 Å, were deposited on Si substrates by dc magnetron sputtering techniques. After magnetic annealing, these two sets of films exhibited values of exchange bias field, Hex=229 and 254 Oe, respectively. The PtPdMn layer was then thinned to various thicknesses from 600 down to 50 Å by ion beam etching. Hex does not retain its original value. It decreases with decreasing tAF and becomes zero at tAF∼75 Å. In addition, we have observed that the training effect or the anomalous hysteresis loss becomes more pronounced with decreasing tAF. This confirms that not only face-centered-tetragonal phase but, more critically, tAF plays role in determining exchange biasing and its thermal stability. The blocking temperature, TB, appears unaffected by the thinning of the PtPdMn layer, and no apparent change occurs in the local blocking temperature distribution, as suggested by the finite size effect.