Site Preferences of Pr and Co in(Nd,Pr)_2(Fe,Co)_(14)B Compounds

The Curie temperature of(Nd_(1-x)Pr_x)_2Fe_(14)Co_yB compounds(x=0,0.2,…,1.0 and y=O,2,4,6,14)has been determined with AC initial susceptibility measurement.It was found that the variations of Curie tempera- ture with x is not linear for y=0 and 14,whereas it is linear for other values of y.The lattice constants of (Nd_(1-x)Pr_x)_2Fet_(14)B were determined by using X-ray diffraction.The lattice expansion was mostly along the c axis,whereas that along the a-axis remained practically zero for the whole series.It is suggested that Pr atoms may show site preference in R_2M_(14)B compounds(M=Fe or Co).Due to the substitution of Co for Fe.the tendency of site preference of Pr becomes less pronounced,which may be attributed to the decrease of differ- ence of crystal electric field(CEF)acting on the two rare earth sites with the introduction of Co or Fe.In con- trast to that of the Pr atoms,the site preference of Co iu(Nd(1-x)Pr_x)_2Fe(14-y)Co_yB compounds does not depend on the composition of the rare earth sublattice(R=N d or Pr).

Spontaneous Magnetic Transitions and Corresponding Magnetoelastic Properties of Intermetallic Compounds RMn_2Ge_2(R=Gd, Tb and Dy)

The spontaneous magnetic transitions and corresponding magnetoelastic properties of intermetallic compounds RMn2Ge2（R=Gd, Tb and Dy） were investigated by using the X-ray diffraction method and magnetic measurement. The results showed that the compounds experience two magnetic transitions, namely the second-order paramagnetic to antiferromagnetic transition at temperature TN（TN=368, 423 and 443 K for Gd Mn2 Ge2, Tb Mn2 Ge2 and Dy Mn2 Ge2, respectively） and the first-order antiferromagnetic-ferrimagnetic transition at temperature Tt（Tt=96, 80 and 40 K for Gd Mn2 Ge2, Tb Mn2 Ge2 and Dy Mn2 Ge2, respectively） as the temperature decreases. The temperature dependence of the lattice constant a（T） displays a negative magnetoelastic anomaly at the second-order transition point TN and, at the first-order transition Tt, a increases abruptly for Gd Mn2 Ge2 and Tb Mn2 Ge2, Da/a about 10^（-3）. Nevertheless, the lattice constant c almost does not change at these transition points indicating that such magnetoelastic anomalies are mainly contributed by the Mn-sublattice. The transitions of the magnetoelastic properties are also evidenced on the temperature dependence of magnetic susceptibility χ. The first-order transition behavior at Tt is explained by the Kittel mode of exchange inversion.

Effects of combined substitution of Dy and Mo or Si on the crystal structures and magnetic properties of Nd_(1-y)Dy_yFe_(11-x)TiM_x(M=Mo,Si) compounds

A series of Nd1-yDyyFe11-xTiMx(M=Mo,Si) alloys have been prepared by arc melting and studied by X-ray diffraction and neutron diffraction.All samples are found to crystallize in the ThMn12-type structure.The lattice parameters a and c and unit cell volume V of Nd0.5Dy0.5Fe11-xTiMox alloys increase linearly with increasing content of Mo(x),while the lattice parameters a and c and unit cell volume V of Nd0.5Dy0.5Fe11-xTiSix alloys decrease linearly with increasing content of Si(x).In NdyDy1-yFe11-xTiMx(M=Mo,Si) compounds,Ti and Mo atoms preferentially occupy the 8i sites and Si atoms preferentially occupy the 8j and 8f sites.Magnetic measurements show that the substitution of Fe by either Mo or Si leads to a decrease in the Curie temperature.