Crystal structure and magnetic properties of Gd1+nFe12-x-yMox□y solid solution

A ternary ferromagnetic phase of the ThMn12 structure type (S.G. 14/mmm) is formed in the Gd-Fe-Mo system like in other rare earth - iron - transition metal systems. The phase exhibits in this case a homogeneity range between 83... 80 and 63... 60 at% iron and 10 and 30 at% molybdenum, respectively. The crystal structure and its composition dependence was determined by X-ray powder diffraction and Rietveld analysis. Our structural results - lattice constants and site occupancies versus chemical composition - point to an extended homogeneity region of the ThMn12-type phase which can be expressed as Gd(1+n)Fe(12-x-y)Mo(x)rectangle (y) ( rectangle is a vacancy, 0 less than or equal to n less than or equal to 0.2. 1.3 less than or equal to x less than or equal to 3.7, 0.6 less than or equal to y less than or equal to 0.90). The 8f and 8j positions are only partly occupied by iron (site occupancy : 92-94%). The 8i crystallographic site of the ThMn12 structure is always completely filled and occupied by iron as well as by molybdenum. The magnetic properties Curie temperature and magnetic moment of the ThMn12-type phase vary with molybdenum content and are correlated to the behaviour of some interatomic distances within the unit cell. The temperature dependence of the demagnetisation curves shows composition dependent transition in the magnetic structure at low temperature. Highly resolved X-ray diffraction measurements at temperatures between 10 K and 300 K exhibit no structural transition. The thermal expansion of the lattice is isotropic. The linear expansion coefficients increases with temperature with a transition between 200 and 250 K.