Magnetic properties of ThFe11Cx compounds (x=1.5, 1.8)

Magnetic measurements are carried out on polycrystalline ThFe11Cx (x = 1.5,1.8) samples between 4 and 900 K and magnetic field up to 7 T. This wide temperature range covers both the ferromagnetically ordered region and the paramagnetic region. Not only the ordering temperature, but also the magnetisation are found to be very sensitive to the carbon concentration. The evolution of the magnetic properties versus the carbon content is discussed. The Curie temperature and the Fe-Fe exchange interactions increase when the carbon concentration increases. The mean ordered iron magnetic moment deduced from saturation magnetisation is also found to depend upon the carbon concentration but in the opposite direction. Mean magnetic moment values of 2.00 and 1.88 mu(B) per iron atom are observed for ThFe11C1.5 and ThFe11C1.8, respectively. The effective magnetic moment is found to decrease from 3.91 to 3.73 mu(B) per iron atom for ThFe11C1.5 and ThFe11C1.8, respectively. The evolution of the effective magnetic moment is discussed on the basis of the spin fluctuations theory. The iron magnetic state in the ThFe11C1.5 and ThFe11C1.8 present similarities with that reported for the Fe3C compound. (C) 2002 Elsevier Science B.V. All rights reserved.