Muon SR study of the longitudinal fluctuation of f-electron moment in CeRh2Si2

Abstract

CeRh2Si2 shows two successive antiferromagnetic phase transitions with different magnetic wave vectors and has relatively high ordering temperatures (T(sub N1) = 36 K and T(sub N2) = 25 K) among other Ce-based heavy fermion compounds. The muon SR (Spin Relaxation) experiments were performed at pi 1A surface muon port in the temperature range from 2 K to 50 K using He-4 gas flow cryostat, and time evolution of the asymmetries was shown at various temperatures. The ZF (Zero Field)-muon SR time spectra showed an exponential relaxation without any precession even in the ordered state between T(sub N1) and T(sub N2), although the LF (Longitudinal Field)-muon SR experiment proved the static nature of the relaxation. With further decreasing temperature, a spontaneous precession signal was observed in ZF-muon SR spectra below T(sub N2). The amplitude of precession component increased as decreasing temperature, although its precession frequency did not change so much. The muon-stopping site was studied in detail by considering the crystal symmetry with a help of the neutron diffraction results and found to be (1/2,0,0). The actual ground magnetic structure could not be determined, however the ordered moment of 1.46 mu(sub B) was deduced for either multi-domain or superimposed structure cases. This value showed good agreement with that in the neutron diffraction result.

CeRh2Si2は異なる磁気波動ベクトルをもつ2つの連続反強磁性相転移を示し、他の重いフェルミオンCe化合物の中では比較的高い秩序温度(T(sub N1)=36KとT(sub N2)=25K)をもつ。He-4気体流クライオスタットを用いて2-50Kの温度範囲におけるπ1A表面ミューオンポートでμSR(ミューオンスピン緩和)実験を行い、非対称時間発展を示した。LF(縦磁場)-μSR実験は静的緩和を示したが、ZF(ゼロ磁場)-μSR時間スペクトルはT(sub N1)とT(sub N2)間の秩序状態においていかなる歳差もない指数形緩和を示した。さらに温度を下げると自発歳差信号がT(sub N2)以下でZF-μSRスペクトルに観測された。歳差成分の振幅は温度減少とともに増加したが、歳差周波数はそれほど変化しなかった。中性子回折の結果を用いて結晶対称性を考慮することによりミューオン阻止サイトを詳細に調べ、(1/2, 0, 0)であることがわかった。実際の基底磁気構造は決定できないが、多磁区か重ね合わせ構造のどちらかで秩序モーメントは1.46μ(sub B)と推測した。この値は中性子回折の結果とよく一致した。