The magnetocaloric effect associated with magnetic phase transitions in ␤-Co͑OH͒ 2 nanoparticles has been investigated. A sign change in the magnetocaloric effect is induced by a magnetic field, which is related to a field-induced transition from the antiferromagnetic to the ferromagnetic state below the Néel temperature. The large reversible magnetic-entropy change −⌬S m ͑20.9 J / kg K at 15 K for a field change of 7 T͒ indicates that ␤-Co͑OH͒ 2 is a potential candidate for application in magnetic refrigeration in the low-temperature range.

Strong effects of ferromagnetic ͑FM͒ materials on the exchange coupling are observed at different temperatures in FM 1 ͑3 nm͒ / Cr 2 O 3 ͑6 nm͒ / FM 2 ͑10 nm͒ trilayers with FMϵ Co, Fe, or Ni 80 Fe 20. Changes of the anisotropy of FM and spin-asymmetry of the reflection coefficients for spin-up and spin-down electrons of FM contacted the antiferromagnetic layer influence the strength of interfacial and interlayer coupling of the trilayers. Thus, the reduction of the interfacial coupling and the enhancement of the interlayer coupling with increasing temperature result in quite different magnetic behavior of different trilayers.

The exchange coupling in textured HM/NM/α-Fe/NM/HM multilayer films (HM = NdFeB or PrFeB hard magnetic layers; NM = nonmagnetic Mo, Cu, and Cr layer) is shown to be indirect and long-range. The influences of thickness of NM spacer layer and HM layer, the material of HM phase and NM spacer layers, and the texture of HM layer, on the effective critical correlation length (Lexeff) and exchange-coupling between soft-magnetic (SM) and HM layers are investigated. A non-linear dependence of Lexeff on the thickness of NM spacer layer is observed. Magnetostatic interaction may lead to the observed non-linear dependence.