We have succeeded in growing single crystals of the heavy-fermion superconductor CeCo(In1-xZnx)5 with x<=0.07. Measurements of specific heat, electrical resistivity, dc magnetization and ac susceptibility revealed that the superconducting (SC) transi
tion temperature Tc decreases from 2.25 K (x=0) to 1.8 K (x=0.05) by doping Zn into CeCoIn5. Furthermore, these measurements indicate a development of a new ordered phase below T_o ~ 2.2 K for x=>0.05, characterized by the reduced magnetization and electrical resistivity in the ordered phase, and the enhancement of specific heat at T_o. This phase transition can be also recognized by the shoulder-like anomaly seen at H_o ~ 55 kOe in the field variations of the magnetization at low temperatures, which is clearly distinguished from the superconducting critical fields Hc2=49 kOe for x=0.05 and 42 kOe for x=0.07. We suggest from these results that the antiferromagnetic (AFM) order is generated by doping Zn, and the interplay between the SC and AFM orders is realized in CeCo(In1-xZnx)5.
The magnetic and electronic properties of Sr1-xLaxRuO3 were studied by means of dc-magnetization, ac-susceptibility, specific heat, and electrical resistivity measurements. The dc-magnetization and ac-susceptibility measurements have revealed that th
e transition temperature and the ordered moment of the ferromagnetic order are strongly suppressed as La is substituted for Sr. The ac-susceptibility exhibits a peak at T* due to the occurrence of spontaneous spin polarization. Furthermore, we observed that T* shows clear frequency variations for x>= 0.3. The magnitude of the frequency shifts of T* is comparable to that of cluster-glass systems, and the frequency dependence is well described in terms of the Vogel-Fulcher law. On the other hand, it is found that the linear specific heat coefficient gamma enhances with the suppression of the ferromagnetic order. The relatively large gamma values reflect the presence of the Ru 4d state at Fermi level, and hence, the magnetism of this system is considered to be tightly coupled with the itinerant characteristics of the Ru 4d electrons. The present experimental results and analyses suggest that the intrinsic coexistence of the spatially inhomogeneous magnetic state and the itinerant nature of the Ru 4d electrons is realized in this system, and such a feature may be commonly involved in La- and Ca-doped SrRuO3.
