Exchange anisotropy in amorphous Gd-Co films

Abstract

It was previously reported that multilayer samples of Co/GdCo2 annealed at 500 °C exhibited exchange anisotropy. One observes a B-H hysteresis loop centered at a finite field, the ‘‘exchange’’ field. To identify the ‘‘hard’’ magnetic phase(s) responsible for the shifted loops we have studied thin films of GdCox as well as multilayers of Co/GdCox, where x varies from 2 to 8.5. We saw shifted loops in two distinct groups of samples, neither of which is multilayered. The first group was GdCox in the composition range between GdCo3 and GdCo5. The loop displacement at room temperature is about 5 Oe. The coercivities of these samples are about 10 Oe. The second group of samples had a composition close to GdCo2. For these samples most of the B-H loop is centered at zero field with a coercivity of 1–2 Oe. However, at ±80 Oe there are small loops which account for about 20% of the total magnetization. X-ray measurements indicate that both groups of samples are microcrystalline or amorphous. The second set of samples discussed above exhibit a maximum in diffracted intensity at 2θ=36°, where GdCo2 has a strong (220) peak. The first group of samples have a broad maximum at 38°, where neither GdCo3 nor GdCo5 has peaks. Gd2Co7 has a very weak peak at this angle and Gd2Co17 has strong peaks but would have to be metastable.