Structural origin of coercivity enhancement and exchange-bias field in double antiferromagnet/ferromagnet bilayers

An experimental method to identify the structural origins of the coercivity enhancement and the exchange-bias field of polycrystalline ferro-antiferromagnetic (F/AF) coupled systems is proposed. The exchange-bias field and the coercivity of the F-I layer of the samples of the structure F-I/AF(I) are compared with those of the F-II layer of the samples of the structure F-II/AF(II)/F-III/AF(III). It is concluded that, for a given temperature, it is those AF grains which stop their growth at a critical thickness that contribute to the coercivity enhancement, and those which grow over the critical thickness that contribute to the exchange-bias field. Meanwhile the effective magnetic surface anisotropy introduced to the top surface of the AF(II) layer by the F-III layer can increase the exchange-bias field of the F-II layer when the AF(II) layer is thin. (C) 2000 American Institute of Physics. [S0003-6951(00)04726-4].