Technical Report of ISSP Ser. A: Number 2866

Abstract

Pressure effects on crystal electric field excitations in ultra-low carrier Kondo systems CeP and CeAs have been studied from ambient pressure to 2.8 GPa. There are two critical pressures P(sub c) and P(sub B). The critical pressures, P(sub c) and P(sub B) are 0.25 GPa and 1.1 GPa for CeP, while they are 1.3 GPa and 2.5 GPa for CeAs, respectively. For P being less than P(sub c), both CeP and CeAs exhibit a type one Antiferromagnetic (AF) structure in the low temperature phase. For P being greater than P(sub c) and less than P(sub B), they show the intermediate phase and the low temperature phase. Finally, for P less than P(sub B), they show only the low temperature phase. Crystal Electric Field (CEF) excitations are well-defined for P less than P(sub B), and in particular, there is no anomaly at the onset pressure of the ferromagnetic order, P(sub c). In contrast, striking anomalies have been observed in a CEF splitting at around P(sub B). For CeP, the CEF excitation decreases to 12 meV and a new CEF excitation appears at 9 meV near P(sub B), then it gradually replaces the first one above P(sub B). On the other hand, for CeAs, a CEF excitation exhibits strong softening as well as broadening near P(sub B). Although there remains a possibility of changeover of two CEF excitations in CeAs, It could not be confirmed due to broadening of the CEF excitations. Finally, the CEF spectra exhibit strong broadening at elevating temperature around 40 K in the low temperature phase near and above P(sub B).

極低担体近藤系CePおよびCeAsにおける結晶電場励起に対する圧力効果を大気圧から2.8GPaまで調べた。2種類の臨界圧力PCおよびPBが存在する。CePの場合は臨界圧力PCおよびPBは0.25GPaおよび1.1GPaであり、一方CeAsでは1.3GPaと2.5GPaであった。P<PCの場合、CePおよびCeAsは両方とも低温相でタイプ1の反強磁性構造を示す。PC<P<PBの場合、CePとCeAsは中間相と低温相を示す。P>PBの場合はCePとCeAsは低温相のみを示す。結晶電場(CEF)励起はP<PBでよく確定され、とくに強磁性オーダーの初期圧力PCで異常性がない。逆に、PB辺りのCEF分岐には異常性が見られた。CePの場合、CEF励起は12meVまで減少し、新しいCEF励起がPB近くの9meVで出現し、そしてそれはPB以上で最初のものに入れ替わる。一方、CeAsの場合、CEF励起はPB近くで強い軟化並びに広がりを示す。CeAsにおける2つのCEF励起の入れ替わりの可能性があるが、CEF励起の広がりのためにそれを確認することができない。CEFスペクトルはPB以上の低温相における40Kの温度で強い広がりを示す。