Muon-spin relaxation and heat capacity measurements on the magnetoelectric and multiferroic pyroxenesLiFeSi2O6andNaFeSi

Abstract

The results of muon-spin relaxation and heat capacity measurements on two pyroxene compounds LiFeSi2O6 and NaFeSi2O6 demonstrate that despite their underlying structural similarity the magnetic ordering is considerably different. In LiFeSi2O6 a single muon precession frequency is observed below TN, consistent with a single peak at TN in the heat capacity and a commensurate magnetic structure. In applied magnetic fields the heat capacity peak splits in two. In contrast, for natural NaFeSi2O6, where multiferroicity has been observed in zero-magnetic-field, a rapid Gaussian depolarization is observed showing that the magnetic structure is more complex. Synthetic NaFeSi2O6 shows a single muon precession frequency but with a far larger damping rate than in the lithium compound. Heat capacity measurements reproduce the phase diagrams previously derived from other techniques and demonstrate that the magnetic entropy is mostly associated with the build up of correlations in the quasi-one-dimensional Fe 3+ chains.

One-dimensional short-range magnetic correlations in the magnetoelectric pyroxeneCaMnGe2O6

“…The former phenomenon corresponds to a considerable entropy release; indeed, about half of the magnetic entropy (51%) is released above T N . A similar phenomenon occurs in NaMnGe 2 O 6 , LiFeSi 2 O 6 , and NaFeSi 2 O 6 [21,22], which was suggested to be the signature of short-range magnetic correlations within chains far above the long-range-ordering temperature.…”

Magnetic structure and multiferroic coupling in pyroxeneNaFeSi2O6

“…Muon-spin relaxation experiments on synthetic and natural samples of NaFeSi 2 O 6 yield a different behavior for the two samples. In the synthetic sample, a single muon-oscillation frequency indicates commensurate order, while the natural sample exhibits more complex magnetic order [23]. The symmetry breaking in NaFeSi 2 O 6 was studied theoretically by Mettout et al [24] who propose the replication of a single-order parameter as the origin of the two transitions.…”

Anisotropy study of multiferroicity in the pyroxene NaFeGe2O6

“…The mineral aegirine of the composition Na 1.04 Fe 0.83 Ca 0.04 Mn 0.02 Al 0.01 Ti 0.08 Si 2 O 6 was identified as multiferroic a few years ago, while LiFeSi 2 O 6 and LiCrSi 2 O 6 were found to be linear magnetoelectrics [18]. Interestingly, synthetic NaFeSi 2 O 6 apparently has a modified magnetic structure compared to natural aegirine, indicating that it is probably only a linear magnetoelectric [19]. In the years after the pioneering work of Jodlauk et al [18], intense research activities set in to find more multiferroic materials within the pyroxene family [20,[22][23][24][25]; however, to date only one further multiferroic compound has been identified, namely NaFeGe 2 O 6 [26].…”