FIELD-INDUCED NONCOLLINEAR MAGNETIC-STRUCTURES IN AL-STABILIZED RCO2 LAVES PHASES - STUDY OF THE LU1-YTMY(CO0.88AL0.12)2 SYSTEM

The magnetization of Lu1-yTmy(Co1-xAlx)2 cubic Laves-phase ferrimagnets, in which magnetism of the itinerant d-subsystem is stabilized by partial Al-substitution, has been measured in magnetic fields up to 38 T. Field-induced noncollinear magnetic structures are observed for Hc1 less-than-or-equal-to H less-than-or-equal-to Hc2 in compounds with Tm concentrations y less-than-or-equal-to 0.6. The intersublattice molecular-field coefficient, lambda(fd), is found to be equal to -(13.5 +/- 1)Tf.u./mu(B), and to be independent of the Tm concentration. At 4.2 K, the experimentally determined mu0H-y phase diagram can be described well, if we take into account the field dependence of the Tm moment.