Ground state and low-energy magnetic dynamics in the frustrated magnetCoAl2O4as revealed by local spin probes

Abstract

We report a combined experimental study of magnetic properties of a single crystal of the frustrated diamond lattice antiferromagnet CoAl 2 O 4 with Co 2+ electron spin resonance, 27 Al 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 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.

Dynamic spin fluctuations in the frustrated A -site spinel CuAl2O4

“…In the case of 27 Al with I=5/2, the Zeeman splitting and the first-order nuclear quadrupolar interactions [24] produce four additional satellite peaks, coming from the transitions between Iz=±1/2 to ±3/2 and ±3/2 to ±5/2 states, around the central peak at ω0 (transition between Iz=±1/2). The NMR spectra of other spinel compound CoAl2O4 shows a five-peak structure, and the detailed feature changes depending on the direction of the external magnetic field B0 [25]. The minimum width of the spectra coincides with the angular factor of the quadrupolar interactions (3cos 2 θ−1)/2 (where θ is the angle between B0 and the three-fold rotational symmetry (C3) axis of the B-site) becoming zero, which occurs, B0∥[0 0 1].…”

Molecular diamond lattice antiferromagnet as a Dirac semimetal candidate

“…In the counterpart insulating system, the frustrated local moment on the diamond lattice has been extensively studied as a spin liquid candidate [7][8][9]. A typical example is the magnetic spinel (AB 2 C 4 ) with the A site diamond lattice [10][11][12][13][14][15][16][17][18], where the properties of the disordered state are under intense debate. A (topological) Mott transition is expected to occur from a spin disordered phase to a Dirac semimetal phase by tuning the electron correlation [2,7].Organic molecular compounds have provided the platform for investigating the pressure-tuned Mott transition for the soft crystal.…”

Linear magnetoelectric effect as a signature of long-range collinear antiferromagnetic ordering in the frustrated spinel CoAl2O4

“…On the other hand, it has been shown that these properties are anisotropic microscopically as inferred from neutron diffraction experiments under magnetic fields [10]. On the same sample, using local spin probe techniques such as electron spin resonance, nuclear magnetic resonance and muon spin relaxation, Iakovleva et al emphasize the role of structural disorder and suggest the slowing down of spin dynamics below 100 K with a gradual crossover to a quasistatic regime below 8 K, where a short -range spin fluctuation persists [11]. In contrast, Gregory J. MacDougall et al, using single crystal neutron diffraction experiments on CAO:0.02, reported that CoAl 2 O 4 exhibits a first order magnetic phase transition; however a true longrange order is inhibited by the frozen magnetic domain walls, which cannot grow even at lowest temperature [12].…”