Spin Dynamics and Ground State of the Frustrated Diamond Lattice Magnet CoAl<inf>2</inf>O<inf>4</inf> as seen by ²⁷Al NMR

Abstract

© 2016, Springer-Verlag Wien.We report an experimental study of the low-temperature dynamics of electron spin fluctuations in the magnetically frustrated spinel CoAl2O4 as revealed by 27Al nuclear magnetic relaxation measurements in a magnetic field of 7.7 T in the temperature range 4 < T < 240 K. With this local probe technique, we show that the dynamics of the correlated Co spins strongly depends on the frustration of spin interactions and on Co/Al site disorder. The anisotropy of the temperature dependences of the spin–lattice (T1−1) and spin–spin (T2−1) 27Al nuclear relaxation rates reveals a coexistence of the short-range Néel order below a characteristic temperature T* = 8 K and slow non-commensurate magnetic correlations below and above T*, in agreement with the results of neutron diffraction experiments and our previous NMR spectroscopy data.