Spin Dynamics and Ground State of the Frustrated Diamond Lattice Magnet CoAl2O4 as seen by 27Al NMR

Abstract

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.