X-Ray Diffraction and Magnetic Measurements of the Fe-Cr Spinels

X-ray diffraction intensity measurements and magnetic moment measurements were made on the spinel system FeFe_2-xCrₓO₄, 0≤x≤2, for the purpose of finding structural details in this system which were unknown. The x-ray measurements covered the entire composition range, and the magnetic measurements covered the range from $x=0$ to $x=1.2$. From the x-ray measurements the oxygen parameter of each sample was deduced. These parameters indicated inverse spinels for low values of x, partially inverse spinels for intermediate values of x, and normal spinels for $x=1.3$ to $x=2$.The magnetic measurements indicated inverse spinels for $x=0$ to $x=0.3$. It was inferred from the magnetic measurements that the spins of cations on the B sites are not all parallel, at least for large x and probably for $x>0.5$. Hence, the arrangement of cations on the A and B sites for a spinel in this composition range could not be deduced from its saturation magnetic moment. Estimates of the relative strengths of the magnetic interactions in various composition ranges and a prediction of the variation in saturation magnetic moment with composition in the range $x=1.3$ to $x=2$ were made.