Observation of giant exchange anisotropy

Exchange anisotropy, an interface phenomena in layered magnetic films that produces a hysteresis loop centered at a finite field, has been observed in multilayered films of GdCo₂ and Co. It is found that the effective bias field diverges at the compensation temperature of the film. The data reported were for films with single-layer thicknesses of 35 AA. Multilayered films are deposited at room temperature and are, therefore, highly disordered or amorphous. To induce exchange anisotropy in these films, they were heated rapidly (<1 min) to 500 degrees C, well above the ordering temperature of the GdCo₂, and allowed to cool quickly (<3 min to 200 degrees C). The resulting hysteresis loop is shown. Even in the absence of an applied field, this annealing induces exchange anisotropy, presumably due to the presence of a stray magnetic field.