Study of magnetic properties of Ce and Yb strongly correlated electron systems with the CaCu5 structure

Among the Rare Earths elements, Ce and Yb present the largest variety of physical phenomena due to the instability of their 4f orbital occupation. Depending on their chemical environment, magnetic order, heavy fermion behaviour, valence instability and/or superconductivity may be observed. Different environmental effects (like electronic density variation) can be compared when some parameters (like the crystalline structure) are fixed. The CaCU5 (Haucke) type of structure is one of the richest families in Ce and Yb intermetallics, including binary: Ce(Yb)M 5 and ternary compounds: Ce(Yb)M jXk (j+k=5), where M are transition or platinum group metals and X p-type ones. Within the joint project intensive research in the above mentioned subject - involving various studies of magnetic, transport and thermal properties of Ce and Yb Haucke-type of intermetallic compounds - has revealed an enormous variety of physical properties of alloy systems based on the hexagonal CaCu 5 type structure. Although some of the results have already been presented in a series of joint scientific contributions, the wealth of newly accumulated information requests prior to publication additional detailed and sophisticated studies in all the co- operating laboratories involved. In order to thoroughly complete the interesting and diverse research subject described in detail in the main part of the proposal, it would thus be highly desirable for both project partners of the bilateral project to prolong the original project period by one more year. A corresponding application for prolongation of the project has been simultaneously submitted to CONICET by our project partner in Argentina, Prof. J. Sereni. For such a purpose different complementary measurements are foreseen: 1) a.c. and d.c. magnetic susceptibility between 0.4K and 300K and isothermal magnetization up to 8 Tesla. 2) Electrical resistivity, thermal conductivity and thermopower between 0.3K and 300K, under magnetic fields up to 14 Tesla and hydrostatic pressure up to about 100kbar. 3) Specific heat from 0.4K to 30K under magnetic fields of 4 Tesla. The samples will be prepared in polycrystalline and partly single-crystal form. Investigations will be carried out in the Austrian and/or Argentinian laboratories, depending on the type of measurements and range of temperature, field and pressure to be covered. For the prolongation of project the schedule will be the following: i) Preparation of selected additional samples, e.g., a Rh/Pd substitution in CeRh 3 B2 and characterization, measurements and comparison of results among samples of different composition. ii) Evaluation of their main physical characteristics (magnetic order, heavy fermion and non-Feremi-liquid- behaviour, valence instabilities, etc.). iii) Discussion of the final results and preparation of joint publications. For such a purpose, particularly the visit of one of the counterparts is required during this period. iv)The selected alloys will be intensively investigated and eventual correlations among different physical properties will be analyzed. The final results will be published in international journals with peer review, which will guarantee the quality of the work.