Effects of carbon on magnetic properties and magnetic entropy change of the LaFe11.5Si1.5 compound

Effects of the interstitial carbon atoms on the magnetic properties, especially on the magnetic entropy change, of the LaFe11.5Si1.5 compound, have been studied. X-ray diffraction patterns reveal a monotonous increase of the lattice constant with the concentration of carbon, while the cubic NaZn13-type structure remains unchanged. The Curie temperatures T-C of LaFe11.5Si1.5Cy are similar to195, 225, and 241 K for y=0, 0.2, and 0.5, respectively, increasing with the increase of carbon concentration. The maximal magnetic entropy changes \DeltaS\ of LaFe11.5Si1.5Cy at the respective T-C under a magnetic field change of 0-5 T are similar to24.6, similar to22.8, and similar to12.7 J/kg K for y=0, 0.2, and 0.5, respectively, notably exceeding that of Gd (\DeltaS\ similar to9.8 J/kg K at T-C=293 K). The \DeltaS\ of LaFe11.5Si1.5C0.2 is nearly as giant as that of the parent alloy LaFe11.5Si1.5 due to the first-order field-induced itinerant-electron metamagnetic transition that occurs in both compounds clearly observed for the LaFe11.5Si1.5C0.5 compound. With the increase of carbon concentration, the nature of magnetic transition has been changed from first order to second order, which results in the significant decrease of the magnetic entropy change. The large \DeltaS\, convenient adjustment of T-C and relatively low cost make the LaFe11.5Si1.5Cy interstitial compounds promising candidates for magnetic refrigerants in the corresponding temperature range. (C) 2003 American Institute of Physics.