According to conventional theories of strongly correlated electron systems, the natural consequence of strong hybridization between f-electrons and conduction electrons is the opening of a gap in both charge and spin channels. Despite their importance, there are few experimental observations of such gaps in real materials.
Recently, the opening of a spin gap has been reported in the intermetallic compounds CeT2Al10 (T = Ru and Os) below TN = 27-29 K through heat capacity and magnetic susceptibility measurements as well as in the paramagnetic state of CeFe2Al10 through resistivity and NMR measurements. Various theoretical models have been proposed to explain the spin gap formation, for example a spin-Peierls model of Hanzawa for CeRu2Al10.
To understand the nature of the spin gap formation in these compounds, we have carried out neutron diffraction, inelastic neutron scattering, and mSR studies of these three compounds. Our neutron diffraction and mSR studies reveal a clear sign of long-range magnetic ordering in CeRu2Al10 and CeOs2Al10, while CeFe2Al10 does not order magnetically down to 50mK. We have found a clear evidence of spin gap formation in the inelastic response of the Ru and Os compounds below their magnetic ordering temperatures as well as in the paramagnetic state of CeFe2Al10. We will present the inelastic neutron scattering measurements on CeT2Al10 (T=Ru and Os) single crystals that unravel the true nature of the spin gap formation in these compounds. We will discuss the effect of La and Fe substitution in CeRu2Al10 on the spin gap formation. Further we will compare the spin gap formation in CeT2Al10 with that observed in the dimerised ground state of YbAl3C3 and mixed valence compounds CeRhAs and CeRu4Sb12.
ISIS Facility, Rutherford Appleton Laboratory, Chilton, OX11 0QX, UK