Pr- and La-doping effects on the magnetic anisotropy in the antiferromagnetic phase of Kondo semiconductorCeRu2Al10

Abstract

We have studied the Pr-and La-doping effects on the magnetic anisotropy in the antiferro-magnetic (AFM) phase of CeRu 2 Al 10 . The crystalline electric field (CEF) splitting in PrRu 2 Al 10 was found to be as large as ∼800 K with a singlet ground state. In Ce 1−x Pr x Ru 2 Al 10 , the CEF level scheme of the Pr ion is not changed with x. The AFM moment (m AF ) is rotated from c to b axis in both systems at x sr c ∼ 0.03 and ∼0.07 for Ln=Pr and La, respectively. As the ionic radius of La and Pr is larger and smaller than that of Ce, respectively, these results indicate that the chemical pressure effect is not associated with the rotation of m AF , but is caused by the suppression of the c-f hybridization originating from the decrease of 4f electrons of Ce ions by Ce-site substitution. Since a small amount of Pr or La doping changes easily the magnetization easy axis of all the moments on Ce sites, the origin of the magnetic anisotropy is not the local single ion effect but the bandlike effect through the anisotropic c-f hybridization. The magnetic phase diagrams of Ce 1−x Ln x Ru 2 Al 10 indicate that above x sr c , the AFM order with m AF b continues to exist up to x c , which is ∼0.4 and ∼0.6 in Ln=Pr and Ln=La, respectively. This indicates that even in the sample with an AFM transition temperature (T 0 ) near x c , the anisotropic c-f hybridization dominates the AFM order. A large positive transverse magnetoresistance is seen below T 0 , but a very small one above T 0 . Together with the results of Hall resistivity and the observation of Shubnikov-de Haas oscillation, we propose that there exist large Fermi surfaces above T 0 and small ones below T 0 . A gap is opened by the AFM order on almost the area of the large Fermi surface, and small Fermi surfaces are constructed below T 0 , although we do not know the mechanism, which might be specific to the AFM order in Kondo semiconductors. The largest suppression of the magnetic scattering below T 0 is observed for the current I a and the smallest one for I b. This anisotropy may be associated with the anisotropic c-f hybridization, which may contribute to the anisotropic magnetic scattering of the conduction electron below T 0 .

Dilution effects on the antiferromagnetic Kondo semiconductor CeOs2Al10

“…The absolute values of the paramagnetic Curie temperature p stays at 22 -30 K, as is shown in the inset of figure 1. Both eff and p are insensitive to the La substitution, which are in common with those observed for Ce1-zLazRu2Al10 [9][10][11]. This result indicates that the 4f hole doping does not alter the c-f hybridization at high temperatures.…”

“…We note that the M(B) curves for B//a and B//b did not show any anomaly up to 14 T (not shown). Figure 5 shows the variations of TN and the  value as a function of doping amount for the three systems: 4f hole doped systems Ce1-zLazOs2Al10 and Ce1-zLazRu2Al10 [9][10][11] and 5d hole doped system Ce(Os1-yRey)2Al10 [5]. Between the two La substituted systems, the degree of suppression of TN for the Os compound is stronger than that for the Ru compound.…”

“…In order to understand the contrasting responses to the substitution in the T sublattice and that in the Ce sublattice, we have studied the dilution effect on the AFM order in Ce1-zLazOs2Al10. Another issue in Ce1-zLazRu2Al10 is the reorientation of the ordered magnetic moment AF from //c to //b, which occurs at z  0.07 [11]. In this work, we have examined whether such reorientation occurs in the Os system Ce1-zLazOs2Al10.…”

“…The effect of dilution of the Ce 4f sublattice on the physical properties of CeRu2Al10 was studied by substituting La for Ce [9][10][11]. It was expected that the La substitution expands the lattice and therefore the 4f state would be more localized.…”

Incommensurate-commensurate magnetic phase transition inSmRu2Al10

“…Although this could provide valuable information on the Fermi surface structure, further study is necessary to extract an interpretation from this result, such as measuring ρ(T ) for the three field directions and the three current directions as performed in Ref. 25. Finally, we note that the transition temperatures are hardly affected by the field.…”