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.

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We report high-field magnetization, high-frequency electron spin resonance (ESR), and 77 Se nuclear magnetic resonance (NMR) measurements on the linear spin tetramer system CuSeO 3 , consisting of strongly interacting Cu(1) dimers and weakly coupled Cu(2) spins. The magnetization exhibits anisotropic half-step magnetization plateaux at µ 0 H = 45 T, depending on a crystallographic orientation. A temperature dependence of the ESR linewidth ∆H pp in a paramagnetic phase points towards the significance of anisotropic exchange interactions. Below T N = 9 − 10 K long-range magnetic order is evidenced by the observation of a critical divergence of both ∆H pp (T ) and the nuclear spin-lattice relaxation rate 1/T 1 . In addition, we identify a magnetic anomaly at T * = 6.0(5) K below T N , which is caused by a spin reorientation. The nuclear spin-spin relaxation rate 1/T 2 unveils the development of site-specific spin correlations. The intriguing magnetism of CuSeO 3 is discussed in terms of the energy hierarchy of Cu(1) and Cu(2) spins in concert with additional intertetramer interactions.

We report on thermodynamic, magnetization, and muon spin relaxation measurements of the strong spin-orbit coupled iridate Ba3IrTi2O9, which constitutes a new frustration motif made up a mixture of edge-and corner-sharing triangles. In spite of strong antiferromagnetic exchange interaction of the order of 100 K, we find no hint for long-range magnetic order down to 23 mK. The magnetic specific heat data unveil the T -linear and -squared dependences at low temperatures below 1 K. At the respective temperatures, the zero-field muon spin relaxation features a persistent spin dynamics, indicative of unconventional low-energy excitations. A comparison to the 4d isostructural compound Ba3RuTi2O9 suggests that a concerted interplay of compass-like magnetic interactions and frustrated geometry promotes a dynamically fluctuating state in a triangle-based iridate.