Cluster-glass behavior in the two-dimensional triangular lattice Ising-spin compound Li₂Mn₃O₇

We present the detailed structural and magnetic properties of Li₂Mn₃O₇ using powder X-ray diffraction (XRD), dc susceptibility, heat capacity, ac susceptibility, thermoremanent magnetization, magnetic memory, and exchange bias effect. Rietveld refinement of XRD data reveals that this compound has a rhombohedral structure composed of a layered triangular lattice. The onset of spin-glass transition was confirmed by dc magnetization and ac susceptibility measurements. We have used various dynamic scaling laws were used to analyze and classify the glassy behavior of the compound. Magnetic field dependence of irreversible temperature follows the Almeida-Thouless line, which is characteristic of an Ising spin-glass system. Fitting of the frequency-dependent freezing temperature with a power-law result in zv = 4.06 ± 0.06, which indicates the critical exponent of the sluggish spin dynamics, and τ₀ = 4.2 × 10^-8 s is a characteristic time scale for a single spin-flip. Further evidence of cluster-glass behavior comes from the frequency dependence of the freezing temperature fitted with the Vogel-Fulcher law, which considers the interaction between bigger magnetic entities. The values of fitting parameters are E_a/k_B = 27.62 K and T₀ = 9.57 K, which confirm cluster-glass behavior. The presence of magnetic relaxation below freezing temperature and the magnetic memory effect confirm the nonequilibrium dynamics of the system through a number of metastable states. Moreover, observation of the exchange bias effect reflects the presence of intrinsic phase inhomogeneity. These results indicate that the triangular lattice causes a disordered ground state due to competing exchange interactions. (author)