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.
In Fe 0.75 Mn 1.35 As compound, a metamagnetic transition from an antiferromagnetic phase to a ferrimagnetic phase can be induced above its phase transition temperature T s = 165 K by an external magnetic field, which leads to large magnetocaloric effects around T s . The sign of the magnetic entropy change DS M in the Fe 0.75 Mn 1.35 As compound is negative, not as expected as an inverse magnetocaloric effect, and the maximum value of DS M is 4.2 J/kg K at 167.5 K for a magnetic field change of 5 T. Although it induces an irreversible lattice expansion, the cycling of a magnetic field does not induce an irreversible change in the magnetic transitions and magnetocaloric behaviors. The antiferromagnetism-related metamagnetic transitions with a large magnetic entropy change may provide with an opportunity in searching novel materials for magnetic refrigeration.
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