Multistage symmetry breaking in the breathing pyrochlore latticeLi(Ga,In)Cr4O8

Abstract

We present magnetic susceptibility, dielectric constant, high-frequency electron spin resonance, 7 Li nuclear magnetic resonance, and zero-field muon spin relaxation measurements of LiACr 4 O 8 (A=Ga, In), towards realizing a breathing pyrochlore lattice. Unlike the uniform pyrochlore ZnCr 2 O 4 lattice, both the In and Ga compounds feature two-stage symmetry breaking: a magnetostructural phase transition with subsequent antiferromagnetic ordering. We find a disparate symmetry breaking process between the In and Ga compounds, having different degrees of bond alternation. Our data reveal that the Ga compound with moderate bond alternation shows the concomitant structural and magnetic transition at T S = 15.2 K, followed by the magnetic ordering at T m = 12.9 K. In contrast, the In compound with strong bond alternation undergoes a thermal crossover at T * ≈ 20.1 K from a tetramer singlet to a dimer singlet or a correlated paramagnet and a separate weak magnetostructural transition at T S = 17.6 K and the second antiferromagnetic ordering at T m = 13.7 K. This suggests that the magnetic phases and correlations of the breathing pyrochlore lattice can be determined from the competition between the bond alternation and spin-lattice coupling, thus stabilizing long-range magnetic ordering against a nonmagnetic singlet.

Behavior of the breathing pyrochlore lattice Ba3Yb2Zn5O11 in applied magnetic field

“…[5] found J = +0.587 meV, K = −0.014 meV, Γ = −0.011 meV, D = −0.165 meV. (6) with g z = 3.07 and g ± = 2.36. The results of Refs.…”

Quantum and Classical Phases of the Pyrochlore Heisenberg Model with Competing Interactions

“…From a material perspective, the isotropic version of the model, i.e., ϕ = π/4, proves to be of relevance in understanding the low-temperature dynamics in chromium spinels [57,115]. On the other hand, the spatially anisotropic version of the model, wherein the up and down tetrahedra feature different exchange couplings, i.e., J down /J up = 1, the so-called breathing pyrochlore is realized in the recently synthesized spinels LiGaCr 4 [116][117][118][119][120][121][122][123][124][125][126][127][128][129][130] and in a pseudospin S = 1/2 Yb-based compound Ba 3 Yb 2 Zn 5 O 11 [131][132][133]. In these compounds, the magnetic Cr 3+ (Yb 3+ ) ions, which carry S = 3/2 (S = 1/2), form an alternating array of small and large tetrahedra, resulting in different exchange couplings for the two sets of tetrahedra.…”

Emergent spin-liquid-like state in the bond-disordered breathing pyrochlore

“…At high temperatures, the NMR spectrum exhibits a single sharp line with no quadrupolar splitting, similarly observed in LiInCr4O8. 20,28 As the temperature is lowered, the NMR spectra show a continuous broadening and a shift to higher magnetic fields, emulating the development of magnetic correlations and internal fields down to T = 2.7 K. We observe neither a structured broadening of the NMR spectrum nor a sharp peak in 1/T1, further confirming the absence of long-range magnetic ordering and structural phase transition.…”

“…Despite the large difference in Bf, both the LiACr4O8 compounds show commonly two-stage symmetry breaking: a magnetostructural phase transition at TS=16 (17) K with subsequent antiferromagnetic ordering at TM=13 (14) K for A=In (Ga). 20 The lasting magnetic orders suggest that the bond alternation alone is not sufficient to repress the effect of spin-lattice coupling that induces a cubic-to-tetragonal transition. In this situation, bond randomness can counteract the detrimental impact of the magnetoelastic transition.…”