| Budget Amount *help |
¥7,800,000 (Direct Cost: ¥7,800,000)
Fiscal Year 1997: ¥2,000,000 (Direct Cost: ¥2,000,000)
Fiscal Year 1996: ¥5,800,000 (Direct Cost: ¥5,800,000)
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| Research Abstract |
1. Magnetostriction of YbInCu_4, YbAgCu_4, and YbAuCu_4, We measured the temperature dependence of magnetostriction of YblnCu_4, which show the first-order valence transition, atypical dense Kondo compound YbAgCu_4 and antiferromagnetic heavy fermion compound YbAuCu_4, For all substances, we found the both volume and anisotropic magnetostriction is in proportion to the square of the external field. The volume magnetostriction has positive sign for all the materials but has markedly different magnitude depending on the Kondo temperature T_K. Applying a relation d V/V = C(XH)^2, we estimated large C values (-10^<-3>/mu_B^2) for the high-temperature state of YbInCu_4 and a low-temperature part of YbAgCu_4 (valence fluctuation regime), and much smaller C values (-10^4/mu_B^2) for the low-temperature state of YbInCu_4 and a high-temperature part of YbAgCu_4 (Kondo regime).
2. Magnetostriction of EuNi_2 (Si_<1-x> Ge_x)_2 The magnetostriction of EuNi_2(Si_<1-x> Ge_x)_2 was measured at ISSP, the University of Tokyo, using pulse field up to 40 T.We found that, except the compound with x=0.82, which shows a metamagenetic transition, the volume magnetostriction is in proportion to the square of the magnetization and that its sign is positive. The magnetovolume coupling constant was estimated to be C-10^<-5>/mu_B^2 for localized-moment antiferromagnetic region (x>0.85) and C-10^<-3>/mu_B^2 for the valence fluctuation regime (x<0.8).
In spite of the different microscopic origin of the valence instability in these Yb and Eu compounds, the magnetovolume effect seems to be dominated by the same factor. A theoretical approach to the magnetovolume effect seems to be helpful to understand the origin of the valence instability in the f-electron materials.
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