Magnetic properties and heat capacity of the three-dimensional frustrated S=1/2 antiferromagnet PbCuTe2O6

We report magnetic susceptibility (chi) and heat capacity (C-p) measurements along with ab initio electronic structure calculations on PbCuTe2O6, a compound made up of a three-dimensional (3D) network of corner-shared triangular units. The presence of antiferromagnetic interactions is inferred from a Curie-Weiss temperature (theta(CW)) of about -22 K from the chi(T) data. The magnetic heat capacity C-m data show a broad maximum at T-max similar or equal to 1.15 K (i.e., T-max/theta(CW) similar or equal to 0.05), which is analogous to the the observed broad maximum in the C-m/T data of a hyper-kagome system, Na4Ir3O8. In addition, C-m data exhibit a weak kink at T* similar or equal to 0.87 K. While the T-max is nearly unchanged, the T* is systematically suppressed in an increasing magnetic field (H) up to 80 kOe. For H >= 80 kOe, the C-m data at low temperatures exhibit a characteristic power-law (T-alpha) behavior with an exponent alpha slightly less than 2. Hopping integrals obtained from the electronic structure calculations show the presence of strongly frustrated 3D spin interactions along with non-negligible unfrustrated couplings. Our results suggest that PbCuTe2O6 is a candidate material for realizing a 3D quantum spin liquid state at high magnetic fields.