Magnetic structures of geometrically frustrated SrGd2 O4 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 Gd160 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 TN1=2.73 K, a q1=(000) magnetic structure is stabilized where ferromagnetic chains along the c axis (space group Pnam) are coupled antiferromagnetically with neighboring chains. On cooling below TN2=0.48 K, an additional incommensurate component modulated by q2=(000.42) evolves and is aligned along either of the perpendicular axes for the two different Gd sites, resulting in a fanlike 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.