Abstract
The N$\acute{\rm e}$el temperature of the new frustrated family of Sr\emph{RE}$_2$O$_4$ (\emph{RE} = rare earth) compounds is yet limited to $\sim$ 0.9 K, which more or less hampers a complete understanding of the relevant magnetic frustrations and spin interactions. Here we report on a new frustrated member to the family, SrTb$_2$O$_4$ with a record $T_{\rm N}$ = 4.28(2) K, and an experimental study of the magnetic interacting and frustrating mechanisms by polarized and unpolarized neutron scattering. The compound SrTb$_2$O$_4$ displays an incommensurate antiferromagnetic (AFM) order with a transverse wave vector \textbf{Q}$^{\rm 0.5 K}_{\rm AFM}$ = (0.5924(1), 0.0059(1), 0) albeit with partially-ordered moments, 1.92(6) $\mu_{\rm B}$ at 0.5 K, stemming from only one of the two inequivalent Tb sites mainly by virtue of their different octahedral distortions. The localized moments are confined to the \emph{bc} plane, 11.9(66)$^\circ$ away from the \emph{b} axis probably by single-ion anisotropy. We reveal that this AFM order is dominated mainly by dipole-dipole interactions and disclose that the octahedral distortion, nearest-neighbour (NN) ferromagnetic (FM) arrangement, different next NN FM and AFM configurations, and in-plane anisotropic spin correlations are vital to the magnetic structure and associated multiple frustrations. The discovery of the thus far highest AFM transition temperature renders SrTb$_2$O$_4$ a new friendly frustrated platform in the family for exploring the nature of magnetic interactions and frustrations.
Highlights
Revealing the magnetic coupling mechanism is often a critical step toward understanding the role of magnetism in intriguing phenomena such as colossal magnetoresistance (CMR), high TC superconductivity, multiferroicity or frustration in correlated electron materials [1,2,3,4,5]
Similar inplane anisotropic magnetic correlations were observed in the iron-based superconductors [49,50,51,52,53] that are highly frustrated, too, where its microscopic origin, from the ellipticity of the electron pockets or the competing exchange interactions associated with the local-moment picture, is still highly debated
We tentatively estimate the compatibility between ordered magnetic and nuclear crystalline domains based on the non-deconvoluted full width at half maximum (FWHM) (κ) of the Bragg (1.6, 1, 0) (κm = 0.0300(7) Å−1) and (2, 0, 0) (κn = 0.0238(2) Å−1) peaks, i.e., κn/κm = 79(2)%, which implies that the incommensurate AFM structure orders in a long-range fashion relative to the underlying lattice of the single crystal
Summary
Revealing the magnetic coupling mechanism is often a critical step toward understanding the role of magnetism in intriguing phenomena such as colossal magnetoresistance (CMR), high TC superconductivity, multiferroicity or frustration in correlated electron materials [1,2,3,4,5]. Without detailed knowledge of the structural and magnetic parameters, it is hard to uniquely determine which interaction acts as the major exchange mechanism [8]. The competition between spin-orbital coupling and crystal electric field (CEF) at low temperatures largely affects the highly-degenerate Hund’s rule ground state, and besides the anisotropic dipolar and DM interactions, determine the magnitude of the magnetic anisotropy [9, 10]. This anisotropy strongly influences the degree of magnetic www.frontiersin.org
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