Spin-flop transition in Gd₅Ge₄ observed by x-ray resonant magnetic scattering and first-principles calculations of magnetic anisotropy

X-ray resonant magnetic scattering was employed to study a fully reversible spin-flop transition in orthorhombic Gd₅Ge₄ and to elucidate details of the magnetic structure in the spin-flop phase. The orientation of the moments at the three Gd sites flop 90° from the c axis to the a axis when a magnetic field, H_sf=9 kOe, is applied along the c axis at T=9 K. The magnetic space group changes from Pnm^′a to Pn^′m^′a^′ for all three Gd sublattices. The magnetic anisotropy energy determined from experimental measurements is in good agreement with the calculations of the magnetic anisotropy based on the spin-orbit coupling of the conduction electrons and an estimation of the dipolar interactions anisotropy. No significant magnetostriction effects were observed at the spin-flop transition.