Effect of magnetism on lattice dynamics in SrFeAs using high-resolution inelastic X-ray scattering

高エネルギー分解能非弾性X線散乱法を使ったSrFeAsの格子振動への磁性の影響の研究

村井 直樹*; 福田 竜生  ; 小林 達也*; 中島 正道*; 内山 裕士*; 石川 大介*; 筒井 智嗣*; 中村 博樹  ; 町田 昌彦  ; 宮坂 茂樹*; 田島 節子*; Baron, A. Q. R.*

Murai, Naoki*; Fukuda, Tatsuo; Kobayashi, Tatsuya*; Nakajima, Masamichi*; Uchiyama, Hiroshi*; Ishikawa, Daisuke*; Tsutsui, Satoshi*; Nakamura, Hiroki; Machida, Masahiko; Miyasaka, Shigeki*; Tajima, Setsuko*; Baron, A. Q. R.*

Phonon spectra of detwinned SrFeAs crystals, as measured by inelastic X-ray scattering, show clear anisotropyaccompanying the magnetostructural transition at 200 K. We model the mode splitting using magnetic DFT calculations, including a phenomenological reduction in force-constant anisotropy that can be attributed to magnetic fluctuations. This serves as a starting point for a general model of phonons in this material applicable to both the antiferromagnetically ordered phase and the paramagnetic phase. Using this model, the measured splitting in the magnetic phase below T, and the measured phonon linewidth, we set a lower bound on the mean magnetic fluctuation frequency above T at 210 K.