Structural and magnetic properties of the RFe11-xCoxTi compounds with
R = Y and Er have been investigated. X-ray diffraction patterns and
thermomagnetic curves show that all the synthesized compounds with x ranging
from 0 to 11.0 are almost single phase and crystallize in the ThMn12-type
structure. Substitution of Co for Fe leads to a monotonic decrease of lattice
constants and unit-cell volume and a clear increase of the Curie temperature.
The saturation moments increase with increasing Co content, going through a
maximum at around x = 2.5, and then decrease with further increasing Co
content. The easy magnetization direction (EMD) at room temperature for
ErFe11-xCoxTi compounds is along the c-axis for x⩽4,
perpendicular to the c-axis for 6⩽x⩽9 and then back to the c-axis
for further increasing x. The anisotropy of the YFe11-xCoxTi
compounds shows a similar behaviour. This concentration dependence of the
magnetocrystalline anisotropy in the YFe11-xCoxTi and
ErFe11-xCoxTi compounds results from the different contributions to
the magnetocrystalline anisotropy from various transition-metal sites and the
preferential occupation of Co atoms. A spin reorientation occurs below the
Curie temperature for all ErFe11-xCoxTi compounds. Spin reorientation
temperatures as a function of Co concentration were derived. A tentative spin
phase diagram is given for ErFe11-xCoxTi compounds and can be
understood in terms of crystal field theory.
The magnetic properties of RFe12−xNbx and R(Fe1−yCoy)11.3Nb0.7 compounds with R=Y, Tb, and Dy have been investigated in the concentration region defined by 0.6<x<0.8 and y⩽0.3, where the compounds are single phase with the ThMn12-type of structure. The Curie temperature TC of the RFe12−xNbx compounds is almost independent of the Nb content whereas the saturation magnetization Ms decreases with increasing Nb content. The spin-reorientation temperature Tsr of the TbFe12−xNbx and DyFe12−xNbx compounds decreases monotonically with increasing x. Substitution of Co for Fe in RFe11.3Nb0.7 leads to a remarkable increase of TC and the appearance of a maximum in the Co-concentration dependence of Ms. In contrast, Tsr decreases monotonically with increasing Co content for both R=Tb and Dy. The modification of T- and R-sublattice anisotropy originating from a change of the Nb content and from substitution of Co for Fe was analyzed by combining crystalline electric field theory and the individual-site model.
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