ABSTRACT
In this work the magnetocaloric effect is theoretically investigated considering a microscopic model Hamiltonian, which describes a magnetic system formed by two sublattices of different magnetic ions coupled by exchange and magnetoelastic interactions. We analyze systematically several profiles of the ferrimagnetic arrangements that were studied earlier without the magnetoelastic interaction. The influence of changing the magnetoelastic parameters on the magnetization, isothermal entropy change and adiabatic temperature change curves are investigated. Depending on the model parameters, the magnetic system shows a first-order magnetic phase transition leading to high direct and inverse magnetocaloric effect, besides two simultaneous first-order magnetic phase transitions which were predicted. A constant ΔS(T) = 0.4 J mol(-1) K(-1) is obtained in the simulated system in a temperature interval of 50 K, around 110 K.
ABSTRACT
To present day, the maximum magnetocaloric effect (MCE) at room temperature for a magnetic field change of 5 T is 40 J/(kg K) for MnAs. In this Letter we present colossal MCE measurements on MnAs under pressure, reaching values up to 267 J/(kg K), far greater than the magnetic limit arising from the assumption of magnetic field independence of the lattice and electronic entropy contributions. The origin of the effect is the contribution to the entropy variation coming from the lattice through the magnetoelastic coupling.