Coercivity and squareness enhancement in ball-milled hard magnetic-antiferromagnetic composites

Abstract

The room-temperature coercivity, Hc, and squareness, MR/MS (remanence/saturation magnetizations), of permanent magnet, SmCo5 powders have been enhanced by ball milling with antiferromagnetic NiO (with Néel temperature, TN = 590 K). This enhancement is observed in the as-milled state. However, when the milling of SmCo5 is carried out with an antiferromagnet with TN below room temperature (e.g., for CoO, TN = 290 K), the coercivity enhancement is only observed at low temperatures after field cooling through TN. The ferromagnetic-antiferromagnetic exchange coupling induced either by local heating during milling (SmCo5 + NiO) or field cooling (SmCo5 + CoO) is shown to be the origin of the Hc increase. © 2001 American Institute of Physics.