Intrinsic coercivity in [formula omitted]-[formula omitted] intermetallic magnets with valence fluctuations

Abstract

Temperature dependence of magnetization curves of well homogenized samples of Ce(Co1−xCux)5 (0≤x≤0.7), a family of representative 4f-3d intermetallic magnets found in rare-earth permanent magnets, is measured. A remarkable enhancement of intrinsic coercivity is observed with x=0.3 and x=0.4, persisting to higher temperatures. We argue that this experimental observation can be attributed to an effect of electronic correlation among 4f-electrons. That is, an intrinsic pinning seems to happen originating in an anomalously enhanced magnetic anisotropy energy contributed by a charge-transfer process between 4f-electrons and 3d-electrons, of which energy scale is stronger than the conventional crystal field effects by an order of magnitude. It is demonstrated that the dominance of the 4f-3d charge-transfer process depends on the direction of magnetization in the middle of a crossover of the valence state of Ce between the localized 4f-electron state in CeCu5 and relatively delocalized 4f-electron state in CeCo5.