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)
(SrAl
TaO)
with 
伊藤 孝; 髭本 亘; 幸田 章宏*; 中村 惇平*; 下村 浩一郎*
Interactions (Internet), 245(1), p.25_1 - 25_7, 2024/12
We report on muon spin relaxation (
SR) measurements in a mixed perovskite compound, (LaAlO)
(SrAlTaO) with (LSAT), which is widely used as a single-crystalline substrate for thin film deposition. In zero applied field (ZF), muon depolarization due to the distribution of nuclear dipole fields was observed in the temperature range from 4 K to 270 K. Interestingly, SR time spectra in ZF maintained a Gaussian-like feature over the entire range, while the depolarization rate exhibited a monotonic decrease with increasing temperature. This behavior may be attributed to the thermally activated diffusion of muons between a few adjacent sites within a confined space of the angstrom scale, where the motionally averaged local field that each muon experiences can remain non-zero and result in maintaining the Gaussian-like line shape. The spatial distribution of electrostatic potential at lattice interstices evaluated via density functional theory calculations suggests that such a restriction of muon diffusion paths can be caused by the random distribution of cations with different nominal valences in the mixed perovskite lattice.
伊藤 孝; 門野 良典*
Journal of the Physical Society of Japan, 93(4), p.044602_1 - 044602_7, 2024/04
被引用回数：2 パーセンタイル：76.47(Physics, Multidisciplinary)We propose a model to describe the fluctuations in the internal magnetic field due to ion dynamics observed in muon spin relaxation (
SR) by an Edwards-Anderson-type autocorrelation function that separates the quasi-static and dynamic components of the correlation by the parameter 
(where 
). Our Monte Carlo simulations for this model showed that the time evolution of muon spin polarization deviates significantly from the Kubo-Toyabe function. To further validate the model, the results of simulations were compared with the SR spectra observed in a hybrid organic-inorganic perovskite FAPbI [with FA referring to HC(NH
)], where local field fluctuations associated with the rotational motion of FA molecules and quasi-static fields from the PbI lattice are presumed to coexist. The least-squares curve fitting showed reasonable agreement with the model with 
, and the fluctuation frequency of the dynamical component was obtained. This result opens the door to the possibility of experimentally distinguishing fluctuations due to the dynamics of ions around muons from those due to the self-diffusion of muons. On the other hand, it suggests the need to carefully consider the spin relaxation function when applying SR to the issue of ion dynamics.
伊藤 孝; 髭本 亘; 下村 浩一郎*
Physical Review B, 108(22), p.224301_1 - 224301_11, 2023/12
被引用回数：5 パーセンタイル：44.45(Materials Science, Multidisciplinary)In positive muon spin rotation and relaxation (SR) spectroscopy, positive muons () implanted into solid oxides are conventionally treated as immobile spin-probes at interstitial sites below room temperature. This is because each is thought to be tightly bound to an oxygen atom in the host lattice to form a muonic analogue of the hydroxy group. On the basis of this concept, anomalies in SR spectra observed in oxides have been attributed in most cases to the intrinsic properties of host materials. On the other hand, global diffusion with an activation energy of 
0.1~eV has been reported in some chemically-substituted perovskite oxides at cryogenic temperatures, although the reason for the small activation energy despite the formation of the strong O bond has not yet been quantitatively understood. In this study, we investigated interstitial diffusion in the perovskite oxide lattice using KTaO cubic perovskite as a model system. We used the SR method and density functional theory calculations along with the harmonic transition state theory to study this phenomenon both experimentally and theoretically. Experimental activation energies for global diffusion obtained below room temperature were less than a quarter of the calculated classical potential barrier height for a bottleneck transfer path. The reduction in the effective barrier height could be explained by the harmonic transition state theory with a zero-point energy correction; a significant difference in zero-point energies for at the positions in the O bonding equilibrium state and a bond-breaking transition state was the primary cause of the reduction. This suggests that the assumption of immobile in solid oxides is not always satisfied since such a significant decrease in diffusion barrier height can also occur in other oxides.
