Abstract
The magnetic nature of the CaFe 2 O 4 -type NaMn 2 O 4 and Li 0.92 Mn 2 O 4 , 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 NaMn 2 O 4 at T N =39 K and for Li 0.92 Mn 2 O 4 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 0.92 Mn 2 O 4 was found to be dynamic, whereas that in NaMn 2 O 4 was almost static. This implies the diffusive motion of Li + ions in Li 0.92 Mn 2 O 4 even below 250 K.
Published Version
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