Anisotropic spin form factor of SmAl2 -: art. no. 054406

The spin moment associated with the 4f unpaired electrons of Sm3+ in the cubic Laves phase compound SmAl2 has been selectively measured by the nonresonant coherent elastic scattering (diffraction) of the white synchrotron-radiation x rays. The results have reasonably shown that the spin moment negatively contributes to the sample magnetization and reduces with rising temperature. In addition, it has also been found that the form factor is more contracted than the isotropic case and that the zero-crossing position observed in the form factor varies with temperature. The mean-field analysis with the operator-equivalent technique has adequately described this contraction of the form factor, due to the prolate distribution of the scatterers along the quantization axis, and suggested two possible causes for the thermal shift of the zero-crossing position: the thermal variation of the aspherical 4f spin density through the J-mixing effect, characteristic to Sm3+, and that of the aspherical 4f charge density rather than the spin one concomitant with the magnetic ordering.