The Structure And Magnetic Properties Of R₂Fe_17-xM_x (M=Mn, Cr) Compounds

The crystal structure, magnetic properties and thermal expansion behaviors of Dy2AlFe16-xMnx (x= 1,2,3,4,6,8) and Tb2Fe17-xCrx (x=0,0.5,1.0,1.5,2.0,3.0) compounds have been studied by means of X-Ray diffraction and magnetization measurements. The effect of Mn and Cr substitution on the structure parameter, magnetic properties and thermal expansion behaviors of Dy2AlFe16-xMnx compounds are analyzed, and spontaneous magnetostriction of Dy2AlFe16-xMnx and Tb2Fe17-xCrx compounds is also discussed.The Dy2AlFe16-xMnx(x≤8) compounds have a hexagonal Th2Ni17-type structure. The unit-cell volumes and lattice constants of the Dy2AlFe16-xMnx compounds increase with the increasing Mn concentration. The manganese concentration dependence of the saturation magnetization is related to Mn-Fe antiferromagnetic interaction. The rapid drop at low x (x<6) and the small change at high x (x>6) of Tc, suggesting that magnetic interactions have changed enormously in the 3d sublattice since Mn atoms replace Fe atoms. Experiment results indicate that the great effect of spontaneous magnetostriction leads to the thermal expansion anomaly phenomenon in a state of magnetism and the negative thermal expansion phenomenon at near Curie temperature. It is found that Dy2AlFe16-xMnx compounds have great, anisotropic and positive spontaneous magnetostriction, and the spontaneous magnetostriction decreases with increasing manganese concentration.The Tb2Fe17-xCrx(x≤3.0) compounds have a hexagonal Th2Ni17-type structure. The unit-cell volumes and lattice constants of the Tb2Fe17-xCrx compounds decrease with the increasing Cr concentration. The unit-cell volumes of the Tb2Fe17-xCrx compounds have a small change as x< 1.5 but decrease rapidly as x≥ 1.5. The Curie temperature of the Tb2Fe17-xCrx compounds increases notably at low x. The saturation magnetization of the Tb2Fe17-xCrx compounds decreases rapidly with the increasing Cr concentration, which may be related to Cr-Fe antiferromagnetic interaction. The contributions of the phonon and magnetic order to thermal expansion leads to the...