Interpretation of the Magnetic Properties of LaCoO3

Abstract

Susceptibility measurements have been carried out on single-crystal LaCoO3 in the temperature range of 4.2° to 300°K. We find an effective magnetic moment squared that agrees with Heikes et al. at 300°K, but which falls more rapidly with decreasing temperature. Paramagnetic resonance measurements at 4.2°, 77°, and 300°K have ruled out the presence of modest quantities of paramagnetic cobalt, leaving only the possibilities of diamagnetic or highly concentrated paramagnetic Co+3. (Large concentrations of other cobalt valencies are ruled out for chemical reasons.) Using a model found successful by Goodenough, we assume that Co+3 is near the crossover point, with the 1A1 state lowest. A calculation including spin-orbit effects, but assuming cubic symmetry for the 300° to 4.2°K range, gives essentially a linear variation for the energy difference between the 1A1 and the center of gravity of the 5T2 states, opposite to that expected for a cubic variation. This effect can be explained by including a lower symmetry distortion (probably trigonal) which increases with decreasing temperature, similar to that found in LaAlO3:Cr.

Structural phenomena associated with the spin-state transition inLaCoO3

“…The lattice, electronic and magnetic properties of LaCoO 3 have been the subject of continuing interest since the fifties [1][2][3][4][5][6][7] . The core of the debate is the interpretation of two broad transitions in the magnetic susceptibility, occurring near 100 and 500 K. The effective bulk magnetic moment, which is zero at low temperatures once the effect of magnetic impurities and the surface is subtracted, increases rapidly to about 2.5 m B at the first transition, followed by a broad plateau.…”

Role of entropy and structural parameters in the spin-state transition of LaCoO3

“…[1][2][3] This compound is established to be a narrow bandgap insulator at low temperature with Pauli-like magnetic susceptibility. However between 90-150 K, it transitions to a local moment phase with a Curie-Weiss like susceptibility which reaches its peak around 150K.…”

Electronic structure and electrical transport properties of LaCo1−xNixO3 (0 ≤ x ≤0.5)

“…Among LaMO 3 compounds (M ¼ Ti, V, Cr, Mn, Fe, Ni) which are well known as strongly correlated systems, LaCoO 3 has been extensively studied; it exhibits the characteristic behaviour associated with the metal-insulator transition (MIT) as well as with magnetic properties due to a change in the spin state of the Co ion. [1][2][3][4][5][6][7] This spin state transition and properties can be controlled by substitution either at the La or Co cation sites. LaCoO 3 has already been reported by introducing different cations both in the La (e.g., Sr 2þ , Ca 2þ ) and Co (e.g., Mg 2þ ) perovskite sublattices.…”