Magnetic order in intermetallic compounds studied by nuclear methods

This project proposed to the Austrian Science Foundation is intended to support on the one side laboratory experiments which need financial sources exceeding the regular institute budget and, on the other hand, to facilitate experiments on international research facilities which, in the past, were already carried out successfully. Both, techniques and materials shall be used, where the project collaborators have gained international reputation. The aims of the present project are threefold: 1) Hyperfine interaction studies using Mössbauer spectroscopy have a long tradition at the Institute for Experimental Physics and much experience was gained so far. In order to run the Mössbauer spectrometers reasonably weil, however, a periodic support for supplying the sources is necessary (half life time of the parent isotope 57Co is only 272 days). The prices have reached a level which makes it impossible to cover such costs from the regular Institute budget. Furthermore, for studying compounds which do not contain a sultable Mössbauer isotope the possibillty exists of doping with small amounts (<1%) of an enriched isotope, thus, leaving the properties of the original compound essentially unchanged. In the present case it concerns 57Fe which, again, due to its high costs can not be supplied via the institute budget. Since it is of considerabli interest and simultaneously prepared and studied by our French collaborators from structural points of view, the system SmFe 2 Dx is given the highest priority, followed by 57Fe doped RMn12 andYC0 2 . 2) For the first time in Austria activities in the field of muon spin rotation/relaxation (SR) were initiated in 1992 and since then carried out within the frame of the Austrian Science Foundation (procect S 5604 which currently expires). Quite some effort was necessary to eventually become fully independent from the collaborators (A. Schenck et al. from whom much knowledge could be gained). Computer programmes had to be installed at the VAX cluster of the TU Vienna computing centre and some time passed, since enough experience was achieved to fully use the entire facilities for analysing the data. Since this local probe technique proved to be utmost valuable at the search for ultra small quasistatic (in view of the muon life time 2,2 s) magnetic moments or the study of dynamic properties of a given material, the activities on this field are intended to be continued, in order to support the remaining groups at the institute with results obtained from a further microscopic method. Since some highly correlated electron- and spin fluctuation systems could successfully be studied by this particular method already, further members of these families shall be investigated again (i.e. GdNi 2 Ga and YCo 2 , respectively). 3) The neutron scattering activities performed so far by the different members of the institute are intended to be concentrated as much as possible and to be carried out within a single project. Since intensive studies are currently carried out on the rare earth-manganese system, compounds of the type RMn12 were chosen as suitable candidates for future elastic neutron scattering activities.

It was the essential aim of the project, to complete the bulk studies at the Institute of Solid State Physics in the field of electronic properties/magnetism/superconductivity by experiments using local probe hyperfine techniques. These methods act - expressed in an oversimplified way - like a microscope yielding a detailed information about a crystal from an atomistic point of view. In the frame of the project three techniques were applied. First, the laboratory methode 57Fe Mößbauer spectroscopy. Furthermore, muon spin rotation/relaxation (muSR) and neutron diffraction experiments were carried out on several international research facilities (ILL Grenoble, PSI Villigen/Switzerland, ISIS Didcot/UK). Due to the structure of the project several topics had to be treated simutaneously. Thanks to several national and international cooperations the aims of the project could almost completely be gained. Via a cooperation with the CNRS in Thiais/France rare earth metal hydrides were studied, a material which is already in use as a battery material. It can, however, still be improved. Furthermore, with a french company and two groups from french universities, a new type of ferrites was investigated. Since decades this kind of material is used as low cost permanent magnet. Quite recently, however, a method was developed for improving the permanent magnetic properties, which is currently tested. Muon spin rotation/relaxation (muSR) is successfully used when small magnetic moments are studied. Thus, it is particuparly well suited for studies of systems which are close to the dissappearance of long range magnetic order. In the present case the enhanced paramagnetic system YCo 2 was studied, in order to search for slow spin fluctuations. Moreover, the system Ce(Rh, Ru)3 B2 was investigated, the main reason being the complex magnetic phase diagram accompanied by the existence of small moments. The question concerning the magnetic order of SmAl 2 is a long story which still is not completely solved. Thus, neutron diffraction studies were carried out at the ILL using the hot source. Unfortunately, after a few experiments, a malfunction occurred in the reactor leading to a shut down of the hot source. Consequently, further experiments had to be postponed. In the course of a second set of neutron scattering experiments, a sample of Ce(Rh, Ru)3 B2 in the concentration range exhibiting complex magnetic order was studied at the spallation source at the PSI, the reason being the need for additional information to the muSR results. Due to the low magnetic scattering contribution, however, no clear cut result about the magnetic structure is available up to now. Finally, in the frame of the traditional collaboration with the institute of inorganic chemistry several spin cross over complexes were studied. This kind of material is in a state close to be applied technilogically, e.g. as optical switches. Since by using Mößbauer spectroscopy, high spin and low spin compounds can easily be distinguished, HS - LS transition can readily be monitored. Concluding, it should be noted that by applying local probe hyperfine techniques valuable completions could be achieved to bulk studies, yielding a more reliable physical interpretation regarding given samples, important for both basic research and application.