X-ray diffraction analysis of the magnetoelastic phase transition in the Mn-Fe-P-Si magnetocaloric alloy

Abstract

Structural characterization of the Mn1.3Fe0.65P0.5Si0.5 powder is reported. The rare-earth-free magnetocaloric material was prepared by ball milling and solid-state synthesis. X-ray diffraction data were collected in a wide temperature range across the magnetoelastic phase transition. The lattice parameters and volume fractions of the paramagnetic and ferromagnetic phases were determined as functions of temperature using Rietveld fitting. The virgin effect (a delay of the phase transition on first cooling) and associated variation of lattice parameters are analyzed on the assumption of elastic constraints imposed on the paramagnetic phase by the defect structure. A simple Landau model with magnetoelastic coupling illustrates the observed first-order behavior.

First- Versus Second-Order Magnetocaloric Material for Thermomagnetic Energy Conversion

“…Because of design constraints, a thermodynamic cycle composed by two isofield and two adiabatic processes (Brayton cycle) is a common choice for systems of the latter class. Here we compute the thermodynamic cycle following [3], namely using an equation of state deduced from a phenomenological Landau model with magnetoelastic coupling [12] (for a review of similar approaches see also [11]). This model was developed to describe the first order phase transition in the Mn1.3Fe0.65P0.5Si0.5 magnetocaloric compound.…”

Enhanced reversibility of the magnetoelastic transition in (Mn,Fe)2(P,Si) alloys via minimizing the transition-induced elastic strain energy

“…Taking the elastic constants reported by Roy et al [58] and the elastic strain ( a / a and c / c values at T C ) from Refs. [59][60][61][62][63][64] , we can calculate the elastic strain energy U e at T C of the (Mn,Fe) 2 (P,Si) alloys with different compositions based on Eq. (3) .…”

Numerical study of thermomagnetic cycle

“…However hysteresis has been drastically reduced in many alloys using composition and annealing [8], so here we prefer to focus our attention on an ideal material where hysteresis has been mastered. We try to estimate the potential benefits of first order materials using an equilibrium Landau model where the transition is driven by magneto-elastic coupling between two order parameters (magnetic and elastic) as described in [9,10]. The parameters of the model are adjusted using a set of measurements on Mn1.3Fe0.65P0.5Si0.5 [10].…”

“…We try to estimate the potential benefits of first order materials using an equilibrium Landau model where the transition is driven by magneto-elastic coupling between two order parameters (magnetic and elastic) as described in [9,10]. The parameters of the model are adjusted using a set of measurements on Mn1.3Fe0.65P0.5Si0.5 [10]. Because the model does not fit the thermal capacity at high temperature, a term ln( ) is added to the entropy to introduce a constant in the thermal capacity.…”