Successive phase transitions and incommensurate magnetic ordering in a triangular-lattice antiferromagnet

The triangular-lattice antiferromagnet (TLAF) has attracted a lot of attention in the past several decades as a prototypical two-dimensional (2D) frustrated magnet for which quantum fluctuations may stabilize unconventional ground-states such as the novel up-up-down (UUD) ground state. We have conducted a systematic study on a new TLAF compound with perfect equilateral triangular lattice Na2BaMn(PO4)2 with DC and AC susceptibilities and neutron scattering measurements. DC susceptibility measurements show the saturation field to be around 7 T. AC susceptibility measurements on single-crystal samples have confirmed a long-range magnetic ordering below 1.1 K under zero field and two critical fields at 1.6 T and 2.9 T with the magnetic field applied along the c axis, which also indicates an easy-axis anisotropy. Neutron scattering measurements were conducted on powder sample. The results suggest a novel incommensurate ordering in this compound under zero and finite fields, which is seldom to be observed in TLAF. More work will be done to solve the exact magnetic structure in different magnetic phases. And specific heat measurements will be conducted to map out a complete phase diagram.