Magnetic Ground States of the Rare-Earth Tripod Kagome LatticeMg2RE3Sb3

Abstract

We present the structural and magnetic properties of a new compound family, Mg2RE3Sb3O14 (RE = Gd, Dy, Er), with a hitherto unstudied frustrating lattice, the "tripod kagome" structure. Susceptibility (ac, dc) and specific heat exhibit features that are understood within a simple Luttinger-Tisza type theory. For RE = Gd, we found long ranged order (LRO) at 1.65 K, which is consistent with a 120• structure, demonstrating the importance of diople interactions for this 2D Heisenberg system. For RE = Dy, LRO at 0.37 K is related to the "kagome spin ice (KSI)" physics for a 2D system. This result shows that the tripod kagome structure accelerates the transition to LRO predicted for the related pyrochlore systems. For RE = Er, two transitions, at 80 mK and 2.1 K are observed, suggesting the importance of quantum fluctuations for this putative XY system. Introduction.-The two-dimensional (2D) kagome lattice magnet (KLM) has been a favorite in the theoretical condensed matter community since the experimental work on SCGO [1], due to the strong frustration associated with its network of corner-shared triangles. [15]. From a materials standpoint, however, these two systems are limited by (i) known defect prone structures [14,16], and (ii) the inability to substitute facilely on the magnetic site (e.g with non-Heisenberg spins) to realize states other than the QSL. Clearly then, finding new KLM-containing compounds with spin-type variability is a challenge of the highest order.Intriguingly, a 2D KLM is naturally contained in the frustrated 3D pyrochlore structure. In pyrochlores RE 2 X 2 O 7 (RE = rare earth element, X = transition metal element), both the RE 3+ and X 4+ sublattices form alternating kagome and triangular layers along the [111] axis as a result of corner-shared tetrahedrons ( Fig. 1(a)) [17]. However, the strong inter-layer interaction enforces three-dimensionality. An exception is found in studies of Dy 2 Ti 2 O 7 in a [111] magnetic field, which polarizes the triangular layer spins, effectively decoupling the kagome planes, leading to a KSI state [17].Obviously, if one can remove the magnetic moment of the triangular layers in the pyrochlore lattice, a RE-kagome-

Realization of the kagome spin ice state in a frustrated intermetallic compound

“…Because the CEF Hamiltonian does not include the effect of exchange coupling between Ho moments, which is of similar size to the separation between the lower CEF levels, it may not fully account for the anisotropy of the moments, especially at low temperatures. Dy3Mg2Sb3O14 (22,23) where they are comparable. This is likely a result of the relatively strong RKKY-type interaction between Ho moments (27).…”

Emergent order in the kagome Ising magnet Dy3Mg2Sb3O14

“…20) is an ideal candidate for an ECO state. The material crystallizes in a variant of the pyrochlore structure (space group R m 20) in which kagome planes of magnetic Dy 3+ alternate with triangular layers of non-magnetic Mg 2+ (Fig. 1c).…”

“…1d) yield a Curie-Weiss constant θ CW =−0.1(2) K for fitting range 5≤ T ≤50 K, consistent with ref. 20 (however, the value depends strongly on fitting range). Demagnetization effects may also be significant—increasing θ CW by 1.4 K in spin-ice materials21—but cannot be quantitatively determined for a powder sample.…”

“…Whether the predicted spin-ordering8 eventually occurs in Dy 3 Mg 2 Sb 3 O 14 remains to be seen: spin freezing3637 or site disorder may prevent its onset. We expect physical and/or chemical perturbations to control the properties of Dy 3 Mg 2 Sb 3 O 14 ; for example, application of magnetic field slightly tilted from the c -axis should drive a Kastelyn transition towards spin-ordering1516; modified synthesis conditions may allow the degree of site mixing to be controlled20; and application of chemical pressure may alter the spin-canting angle and/or the distance between kagome layers, potentially generating a novel spin-ordering phase instead of ECO for sufficiently large canting28. Substitution of Dy 3+ by other lanthanide ions20383940 may increase the ratio of exchange to dipolar interactions, offering promising routes towards exotic spin-liquid behaviour: dimensionality reduction by effective layer decoupling (when exchange dominates over dipolar interactions), and realization of quantum kagome systems with local spin anisotropies.…”

“…20). Our experimental evidence derives from neutron-scattering and thermodynamic measurements, while Monte Carlo (MC) simulations reveal that this ECO state is stabilized by a combination of interactions between kagome layers, spin canting out of kagome layers and chemical disorder.…”