Field Tuning and Quantum Criticality in Ytterbium Based Heavy Electron Compounds

We review here the results of magnetization, specific heat, and inelastic neutron scattering measurements conducted on Yb3Pt4, Yb2Pt2Pb, Yb5Pt9, and YbRh2Pb, which indicate that the Yb moments in these heavy electron compounds are appreciably localized, at least in their paramagnetic states. The magnetic ground states in each are isolated magnetic doublets, and we show that magnetic fields suppress long ranged magnetic order and lead to a characteristic magnetic field-temperature phase diagram where order vanishes suddenly above a critical value for the field. We argue that the stability of magnetic order in these compounds arises from the competition between the Zeeman splitting g mu (B) H of the ground state doublet, which favors a spin polarized state with minimal entropy and without long range order, and the exchange splitting Delta of the doublet, which enables long ranged magnetic order.