MAGNETIC PHASE-TRANSITIONS, MAGNETOCRYSTALLINE ANISOTROPY, AND CRYSTAL-FIELD INTERACTIONS IN THE RFE11TI SERIES (WHERE R = Y, PR, ND, SM, GD, TB, DY, HO, ER, OR TM)

A systematic investigation of the intrinsic magnetic properties of RFe11Ti compounds with R=Y, Pr, Nd, Sm, Gd, Th, Dy, Ho, Er, and Tm has been performed by means of ac susceptibility measurements, singular-point-detection techniques, and high-field magnetization measurements. Spin-reorientation transitions were observed in RFe11Ti with R=Nd (T(SR)=189 K), Tb (T(SR)=339 K), Dy (T(SR1)=214 K and T(SR2)=98 K), and Er (T(SR)=48 K). First-order magnetization processes of type I for R=Nd and Er and of type II for R=Ho and Tm were detected at low temperatures. The uniaxial magnetocrystalline anisotropy fields of the whole RFe11Ti series have been determined in a wide temperature interval from 4.2 K to the Curie temperatures. It is deduced that the ''anomalous increase'' in the magnetization curve of SmFe11Ti for the external field perpendicular to the c axis is not a first-order magnetization process, but a continuous rotation of the magnetic moment under the action of the external field. The observed magnetic phase transitions, the spin-reorientation transitions, and the first-order magnetization processes in the RFe11Ti compounds are well described in terms of a crystal-field description in which the rare-earth sublattice (R) and transition-metal sublattice (T) exchange interaction is included. A set of crystalline-electric-field parameters as well as the values for the R-T exchange field are deduced for the whole RFe11Ti series from fitting the experimentally obtained values of the anisotropy field, the critical field for the first-order magnetization process, and the spin-reorientation temperature with the calculations in the present systematic study. Magnetic anomalies are observed in the temperature dependence of the ac susceptibility of the RFe11Ti compounds with R=Nd, Sm, Er, and Tm. They are shown to be connected with domain-wall motion.