Magnetic structures of geometrically frustrated SrGd$_2$O$_4$ derived from powder and single-crystal neutron diffraction

TL;DR

This study uncovers two distinct low-temperature magnetic phases in SrGd$_2$O$_4$, revealing complex magnetic ordering and anisotropy through neutron diffraction on both powder and single crystals.

Contribution

First detailed neutron diffraction analysis of SrGd$_2$O$_4$ revealing two magnetic phases and their structures, highlighting complex anisotropy and site-specific magnetic order.

Findings

Identification of a ferromagnetic chain order below 2.73 K.

Discovery of an incommensurate fan-like magnetic phase below 0.48 K.

Analysis of crystal field effects clarifies Gd site-specific magnetic behavior.

Abstract

We present the low-temperature magnetic structures of SrGd$_2$O$_4$ combining neutron diffraction methods on polycrystalline and single-crystal samples containing the $^{160}$Gd isotope. In contrast to other members of the Sr$Ln_2$O$_4$ family ($Ln$ = lanthanide) this system reveals two long-range ordered magnetic phases, which our diffraction data unambiguously identify. Below $T_{\rm N1}$ = 2.73~K, a $\mathbf{q}_1$ = (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 $T_{\rm N2}$ = 0.48~K, an additional incommensurate component modulated by $\mathbf{q}_2$ = (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.