Magnetic structures of geometrically frustrated SrGd2O4 derived from powder and single-crystal neutron diffraction
Abstract
We present the low-temperature magnetic structures of SrGd2O4 combining neutron diffraction methods on polycrystalline and single-crystal samples containing the 160Gd isotope. In contrast to other members of the SrLn2O4 family (Ln = lanthanide) this system reveals two long-range ordered magnetic phases, which our diffraction data unambiguously identify. Below T N1 = 2.73~K, a q1 = (0 0 0) magnetic structure is stabilized where ferromagnetic chains along the c~axis (space group Pnam) are coupled antiferromagnetically with neighboring chains. On cooling below T N2 = 0.48~K, an additional incommensurate component modulated by q2 = (0~0~0.42) evolves and aligned along either of the perpendicular axes for the two different Gd sites, resulting in a fan-like magnetic structure. The identification of the particular Gd sites with the magnetic order observed with neutron diffraction is facilitated by a detailed analysis of the crystal fields acting on the sites. The observed ordering phenomena underline the complex multiaxial anisotropy in this system.