Magnetic-entropy change in Mn1.1Fe0.9P0.7As0.3-xGex

We have studied the magnetic properties and magnetic-entropy changes of Mn(1.1)Fe(0.9)P(0.7)AS(0.3-x)Ge(x) compounds with x = 0, 0.05, 0.1, 0.15 and 0.3. X-ray diffraction (XRD) study shows all the compounds crystallize in the Fe2P-type structure. Magnetic measurements show that the Curie temperature increases from 150 K for Mn1.1Fe0.9P0.7As0.3 to 380 K for Mn1.1Fe0.9P0.7Ge0.3. A field-induced first-order magnetic phase transition is observed above the Curie temperature for the compounds with x up to 0.15. There exists an optimal composition in which the first-order phase transition is the sharpest. The optimal composition for this system is x = 0.1. The maximal magnetic-entropy change derived from the magnetization data is about 40 J/(kg K) for a field change from 0 to 3 T. (c) 2004 Elsevier B.V. All rights reserved.