Magnetic structures and excitations in rare-earth metals

摘要

The recent development within the studies of magnetic structures and excitations in the rare-earth metals is reviewed. The fine resolution obtainable in x-ray synchrotron experiments led to the discovery of a number of commensurable magnetic structures in Ho and Er which helped renew interest in these long-period helically or cycloidally modulated structures. Shortly after, the helifan phases in Ho were established and effects due to trigonal couplings were detected in Er and Ho. The development of the technique of molecular-beam epitaxy has allowed the fabriction of superlattices and alloys of rare-earth metals. One of the important discoveries made possible by the use of this technique is the isolation of a pentacritical point in the magnetic phase diagram of the Ho-Er and Ho-Tm alloys. The investigation of the magnetic structures in the two light rare-earth metals Nd and Pr gives rise to a number of challenging problems, because of the complexity of the different structures and, in Pr, because of the low value of the Neel temperature (50 mK). The extra excitation branch observed a couple of years ago, in the paramagnetic phase of the singlet-ground-state system Pr at small wave vectors, still awaits a full explanation.