Ground state and low-energy magnetic dynamics in the frustrated magnet CoAl<inf>2</inf>O<inf>4</inf> as revealed by local spin probes

Abstract

© 2015 American Physical Society. We report a combined experimental study of magnetic properties of a single crystal of the frustrated diamond lattice antiferromagnet CoAl<inf>2</inf>O<inf>4</inf> with Co²⁺ electron spin resonance, ²⁷Al nuclear magnetic resonance, and muon spin rotation/relaxation techniques. With our local probes, we show that the frustration of spin interactions and the Co/Al site disorder strongly affect the spin dynamics. The experimental results evidence inhomogeneous and slow magnetic fluctuations and the occurrence of short-range electron spin correlations far above a characteristic temperature T∗=8 K at which the spin system turns into in a quasistatic state. Our data indicate that this spin order is likely short range and unconventional with spin fluctuations persistent even at T 蠐 T∗. The results of three spectroscopy techniques highlight a nontrivial role of structural disorder for the magnetism of a frustrated diamond spin lattice at the proximity to the critical point.