Novel Magnetism in New Heavy Electron Compounds

Meigan Aronson
Stony Brook University and Brookhaven National Laboratory


Unconventional superconductivity has been observed in heavy electron compounds and 
in complex oxides near their `quantum critical points, where  magnetic order only occurs 
at the lowest temperatures. The small energy scales characteristic of the heavy electron 
compounds and their separability allows us to conveniently study the full range of 
pertinent behaviors, from the physics of individual moments to their collective 
phenomena as the quantum critical point is approached.  In order to understand the full 
range of conditions which favor heavy electron superconductivity, we are searching for 
new systems which can be tuned continuously and without compositional variation to the 
quantum critical point.  One newly discovered system is Yb3Pt4, which makes a first 
order transition from a paramagnetic state with localized Yb moments into an ordered 
state where the moment is fully itinerant,  best described as a Fermi Liquid with strong 
ferromagnetic correlations. Magnetic fields can be used to tune the magnetic ordering 
transition to a critical endpoint, accompanied by the suppression of both the paramagnetic 
moment above the transition and the temperature independent susceptibility below the 
transition.  Unlike the general case in heavy electron systems, the ordered state in Yb3Pt4 
seems to have a large Fermi surface, while the moments are localized and not 
participating in the Fermi surface in the paramagnetic state.