The interaction between the local 4f electrons and the conduction electrons, namely c-f hybridization, brings about various physical properties such as Kondo semiconductor and long range order (LRO). Kondo semiconductor and LRO are incompatible with each other. The former happens in the 4f itinerant-electrons system and the latter happens in the 4f localized-electrons system.

Fig. 1. Temperature dependence of Hall coefficient R_H on CeRu₂Al₁₀ under pressure.

Fig. 2. Temperature dependence of Hall coefficient R_H on 
Ce(Ru_1-xFe_x)₂Al₁₀.

CeT₂Al₁₀ (T=Fe, Ru, Os) system is attracted much attention because of their unusual features such as unusual long range order (LRO) appeared in CeRu₂Al₁₀ at T₀ ~ 27 K [1] or in CeOs₂Al₁₀ [2] at T₀ ~ 29 K and Kondo semiconducting behavior appeared in CeFe₂Al₁₀[3] or in CeOs₂Al₁₀. LRO and Kondo semiconductor may coexist in the same system. In addition, the temperature of LRO of CeRu₂Al₁₀ is extremely high in comparison with antiferromagnetic ordering temperature T_N = 16.5 K on GdRu₂Al₁₀ or T_N = 2.4 K on NdRu₂Al₁₀ which expected much higher than TN of CeRu₂Al₁₀. In spite of high ordering temperature, magnetic moment in the ordered phase is reduced to 0.34μ_B/Ce[4]. One of the key mechanisms behind this long range order is the gap open at T₀. Hall coefficient R_H on CeRu₂Al₁₀ increases by nearly two orders of magnitude below T₀ before saturating towards low temperatures. In order to investigate the gap open at T₀ on CeRu₂Al₁₀ or Kondo semiconducting gap open on CeFe₂Al₁₀ from the viewpoint of physical pressure and chemical pressure, we measured Hall Resistivity on CeRu₂Al₁₀ under pressure and of Ce(Ru_1-xFe_x)₂Al₁₀.

Figure 1 shows temperature dependence of Hall coefficient on R_H on CeRu₂Al₁₀ under pressure. The magnitude of R_H at lowest temperatures decreases with increasing pressure, which indicates that the gap open at T₀ shallows with pressure. Figure 2 the temperature dependence of Hall coefficient R_H on Ce(Ru_1-xFe_x)₂Al₁₀. For x=0.375 and x=0.625, R_H increases abruptly below T₀ and become negative value at low temperatures, which indicates the gap open at T₀ in CeRu₂Al₁₀ exhibit as positive value of R_H and the c-f hybridization gap proposed in CeFe₂Al₁₀ exhibit as negative value. In addition, the reversal of the sign indicates that Ce(Ru_1-xFe_x)₂Al₁₀ is in a multi-carrier system. The R_H of CeRu₂Al₁₀ are suppressed by pressure and the R_H of Ce(Ru_1-xFe_x)₂Al₁₀ are suppressed by Fe substitution. The consistency of chemical pressure and physical pressure is observed in the Hall Effect measurement.

References

• [1] A. M. Strydom, Physica B 404, 2981 (2009).
• [2] Y. Muro et al., J. Phys. Soc. Jpn. 78, 083707 (2009).
• [3] T. Nishioka et al., J. Phys. Soc. Jpn. 78, 123705 (2009).
• [4] D. D. Khalyavin et al., Phys. Rev. B 82, 100405 (2010).

Authors

• Y. Kawamura^a, D. Hirai^b, T. Nishioka^b, D. Tanaka^c, H. Tanida^c, M. Sera^c, M. Matsubayashi, Y. Uwatoko
• ^aMuroran Institute of Technology
• ^bKochi University
• ^cHiroshima University