Investigating the nature of magnetic correlations in the anti-ferromagnetic hyper-kagome material, Yb$_3$Ga$_5$O$_{12}$

The magnetic Yb$^{3+}$ ions in Yb$_3$Ga$_5$O$_{12}$ (YbGG) reside on a hyper-kagome lattice, which has the same connectivity as the planar kagome lattice but in higher dimensions. For anti-ferromagnetically (AFM) coupled spins the hyper-kagome lattice provides a highly-frustrated geometry in three-dimensions. YbGG is isostructural with the well-studied Gd$_3$Ga$_5$O$_{12}$ (GGG), which enjoys an exotic magnetic phase diagram. In GGG, the effects of geometric frustration manifest as a disordered, partial spin-glass ground state down to 25mK in zero-field. The application of an external magnetic field first induces an intermediate spin liquid state, then a long range AFM ordered phase. Much less is known about YbGG, though all experimental evidence indicates a lack of LRO in zero-field down to 30mK. We have recently produced single crystals of YbGG and have performed neutron scattering experiments over a range of temperatures (80mK - 10K) and magnetic field strengths (0T - 8T). The results indicate low-energy, fluctuating spin correlations at 80mK, 0T, as well as a dramatic response to an applied magnetic field. At zero-field, we also observe a low-energy dispersionless spin excitation that softens as the temperature is increased above the Schottky anomaly in the specific heat.