Magnetic phase transitions, magnetocrystalline anisotropy, and crystal-field interactions in theRFe11Ti series (whereR=Y, Pr, Nd, Sm, Gd, Tb, Dy, Ho, Er, or Tm)

A systematic investigation of the intrinsic magnetic properties of R${\mathrm{Fe}}_{11}$Ti compounds with R=Y, Pr, Nd, Sm, Gd, Tb, 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 R${\mathrm{Fe}}_{11}$Ti with R=Nd (${\mathit{T}}_{\mathrm{SR}}$=189 K), Tb (${\mathit{T}}_{\mathrm{SR}}$=339 K), Dy (${\mathit{T}}_{\mathrm{SR}1\mathrm{}}$=214 K and ${\mathit{T}}_{\mathrm{SR}2\mathrm{}}$=98 K), and Er (${\mathit{T}}_{\mathrm{SR}}$=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 R${\mathrm{Fe}}_{11}$Ti 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 ${\mathrm{SmFe}}_{11}$Ti 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 R${\mathrm{Fe}}_{11}$Ti 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 R${\mathrm{Fe}}_{11}$Ti 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 R${\mathrm{Fe}}_{11}$Ti compounds with R=Nd, Sm, Er, and Tm. They are shown to be connected with domain-wall motion.