Magnetovolume effect in intermetallicsLaFe13−xSix

Abstract

Based on the Bean–Rodbell model, which assumes a linear variationof exchange coupling with atom spacing, the magnetovolume effects inLaFe13−xSix (x = 1.2–2.0) have been systematically studied. A relation between phase volume andmagnetization is first obtained by comparing the structural and magnetic datacollected at various temperatures. The maximum spontaneous magnetostrictionthus derived is dependent on the content of Si, linearly decreasing from∼2.15% for x = 1.2 to ∼1.12% for x = 2. Based on these results and limited experimental data, theparameters involved in the Bean–Rodbell model are determined for theLaFe13−xSix compounds. Further analysis indicates that the Bean–Rodbell model equipped with these parametersgives a satisfactory description of the magnetovolume effects produced by interstitial hydrogen forthe LaFe11.44Si1.56 hydride. To explain the pressure effects, in contrast, changes of the parameters underpressure, which are a result of the enhancement of the first-order character of the phasetransition, have to be taken into account. These results indicate that either theincrease or the decrease of the Curie temperature is simply a consequence of thevariation of the phase volume due to the introduction of interstitial atoms or theapplication of a high pressure, and can be described well by the Bean–Rodbell model.