Random singlets in the s=5/2 coupled frustrated cubic lattice Lu3Sb3Mn2O14

We combine thermodynamic, electron spin resonance (ESR), and muon spin-relaxation (mu SR) measurements with density functional theory (DFT) and classical Monte Carlo calculations toward understanding a disorderdriven behavior of the 3D coupled frustrated cubic lattice Lu3Sb3Mn2O14 with s = 5/2. The classical Monte Carlo calculations based on exchange interactions extracted from DFT predict that Lu3Sb3Mn2O14 undergoes a transition to magnetic ordering. In sharp contrast, our specific heat measurements evince a weak magnetic anomaly at 0.5 K while mu SR detects neither long-range magnetic order nor spin freezing down to 0.3 K. For temperatures above 2 K, our ac susceptibility, magnetization, and specific heat data obey temperature-magnetic field scalings, indicative of the formation of 3D random singlets. The development of multiple ESR lines with decreasing temperature below 80 K supports the notion of inhomogeneous magnetism. Our results extend random-singlet physics to 3D frustrated classical magnets with a large spin number s = 5/2.