Magnetism and superconductivity of rare earth borides

Abstract

Rare earth (RE) borides have yielded systems exhibiting interesting and varied magnetic behaviors. The electron deficient boron atomic frameworks are a good combination with rare earth atoms, which are relatively localized and contribute outer shell electrons to stabilize the various structures formed. At the same time, the variations in the boron network structure and the arrangement of the rare earth atoms occupying the voids, have resulted in a variety of interesting geometric magnetic behavior, from frustration derived from the Shastry-Sutherland lattice in REB4, to 1D, 2D, 3D behavior in the boron icosahedral compounds. The rare earth borides have also yielded systems with particularly fascinating physical properties, e.g. heavy fermions, Kondo insulators, controversial topological insulators, magnetic polaron-induced ferromagnetism, magnetic quadrupole ordering, etc. as described in detail in this review. On the other hand, it is peculiar that in the presence of rich phonon modes, which mainly originate from the light atomic weight boron framework, superconductivity occurs in RE borides only at rather low temperature (∼0.4 K) in LuB12 and the origins of this behavior are also discussed in detail.