Comparative Muon-Spin Rotation and Relaxation Study on the Zigzag Chain Compounds NaMn2O4 and Li0.92Mn2O4

Sugiyama Jun, Ikedo Yutaka, Ofer Oren, Månsson Martin, Ansaldo Eduardo J., Brewer Jess H., Chow Kim H., Sakurai Hiroya, Takayama-Muromachi Eiji

doi:10.1143/jpsj.78.084715

The magnetic nature of the CaFe₂O₄-type NaMn₂O₄ and Li_0.92Mn₂O₄, in which Mn ions form a zigzag chain along the b-axis, have been investigated by muon-spin rotation and relaxation (μ⁺SR) and susceptibility (χ) measurements in the temperature range between 1.9 and 250 K using polycrystalline samples. Weak transverse-field μ⁺SR measurements revealed the existence of a bulk antiferromagnetic (AF) transition for NaMn₂O₄ at T_N=39 K and for Li_0.92Mn₂O₄ at T_N=44 K, although the χ(T) curve did not exhibit a clear anomaly around T_N for either compound. Below T_N, however, the zero-field μ⁺SR spectra in both samples did not show the oscillatory signal characteristic of long range magnetic order. Instead, a slowly relaxing tail is observed. Comparisons with the calculated internal magnetic field for the AF ordered phase suggests that the AF spin structure is disordered and/or rapidly fluctuating. In the paramagnetic region above 100 K, a nuclear magnetic field in Li_0.92Mn₂O₄ was found to be dynamic, whereas that in NaMn₂O₄ was almost static. This implies the diffusive motion of Li⁺ ions in Li_0.92Mn₂O₄ even below 250 K.

Comparative Muon-Spin Rotation and Relaxation Study on the Zigzag Chain Compounds NaMn<SUB>2</SUB>O<SUB>4</SUB> and Li<SUB>0.92</SUB>Mn<SUB>2</SUB>O<SUB>4</SUB>

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