Local electronic effects in the vicinity of an impurity provide pivotal insight into the origin of unconventional superconductivity, especially when the materials are located on the edge of magnetic instability. In high-temperature cuprate superconductors, a strong suppression of superconductivity and appearance of low-energy bound states are clearly observed near nonmagnetic impurities. However, whether these features are common to other strongly correlated superconductors has not been established experimentally. Here, we report the in situ scanning tunneling microscopy observation of electronic structure around a nonmagnetic Zn impurity in heavy-fermion CeCo(In1−xZnx)5 films, which are epitaxially grown by the state-of-the-art molecular beam epitaxy technique in ultrahigh vacuum. The films have very wide atomically flat terraces and Zn atoms residing on two different In sites are clearly resolved. Remarkably, no discernible change is observed for the superconducting gap at and around the Zn atoms. Moreover, the local density of states around Zn atoms shows little change inside the hybridization gap between f -and conduction electrons, which is consistent with calculations for a periodic Anderson model without local magnetic order. These results indicate that no nonsuperconducting region is induced around a Zn impurity and do not support the scenario of antiferromagnetic droplet formation suggested by indirect measurements in Cd-doped CeCoIn5. These results also highlight a significant difference of the impurity effect between cuprates and CeCoIn5, in both of which d-wave superconductivity arises from the non-Fermi liquid normal state near antiferromagnetic instabilities.

It is a long-standing important issue in heavy fermion physics whether f -electrons are itinerant or localized when the magnetic order occurs. Here we report the in situ scanning tunneling microscopy observation of the electronic structure in epitaxial thin films of CeRhIn5, a prototypical heavy fermion compound with antiferromagnetic ground state. The conductance spectra above the Néel temperature TN clearly resolve the energy gap due to the hybridization between local 4f electrons and conduction bands as well as the crystal electric field excitations. These structures persist even below TN . Moreover, an additional dip in the conductance spectra develops due to the antiferromagnetic order. These results provide direct evidence for the presence of itinerant heavy f -electrons participating in the Fermi surface even in the magnetically ordered state of CeRhIn5.

We studied Tb‐Fe‐Co giant magnetostrictive thin films and researched sputtering conditions to improve their magnetostrictive properties and investigated the possibility of their practical use. The sputtering Ar gas pressure influenced their inner stress and played a very important role for the determination of the magnetic easy axis. The largest magnetostriction was obtained when the Ar gas pressure was set at 0.7 Pa and the inner stress was controlled at a tensile stress of about 50 MPa. In the Tb‐Fe system, the Curie temperature is very low (about 140°C) compared with bulk materials, but the Curie temperature can be improved with increasing Co ratio. For films over 70% Co ratio, the Curie temperature was more than 250°C and the largest magnetostriction (1508 ppm) was obtained at 80.1% Co ratio. For almost all Tb‐Fe‐Co thin films, the values of magnetostriction were very high (over 1000 ppm), and the coercive forces were low (around 8 kA/m). Therefore, the Tb‐Fe‐Co giant magnetostrictive thin films are very appropriate materials for the applications in micro‐actuators and sensors. © 2008 Wiley Periodicals, Inc. Electron Comm Jpn, 91(5): 49– 55, 2008; Published online in Wiley InterScience (www.interscience.wiley.com). DOI 10.1002/ecj.10115

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