Magnetocaloric effects in Ni-Mn-Ga-Fe alloys using Monte Carlo simulations
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abstract
Heusler alloys based on the Ni2MnGa system have been shown to exhibit strong magneto-thermo-structural couplings that make them very attractive multi-functional materials. In this work, first principles calculations combined with Monte Carlo simulations have been used to study the magnetocaloric effect (MCE) in Fe-doped Ni-Mn-Ga alloys. The first principles calculations have been used to determine the magnetic properties of the alloysspecifically, magnetic exchange couplingsand to construct a lattice-based Hamiltonian (q-state Pott's model) for the description of the magnetic transformations. The magnetic Hamiltonian is then coupled to a lattice description of the structural (martensitic) transformation, leading to the development of phenomenological models for the magneto-thermo-structural phase transformation. This model Hamiltonian is then investigated through a Monte Carlo framework to describe the coupled phase transformations as well as the magnetocaloric effect. The field-induced entropy change during the transformation is then calculated and used to estimate the adiabatic temperature change associated to switching of magnetic fields. These calculations are in good agreement with the experimental results with a near linear increase in inverse and conventional MCE as structural and magnetic transformation takes place.
