Evidence for the Ising-Lifshitz crossover in MnP

Manganese phosphide (MnP) is one of the few magnetic systems in which a uniaxial Lifshitz point (LP) has been identified. For the external magnetic field applied along the crystallographic b axis, the LP occurs at TL=121±1K and Hb=16.4kOe, at the confluence of modulated, ferromagnetic (F), and paramagnetic (P) phases. It has been shown that the magnetic susceptibility at fixed temperature ({χ}) as a function of Hb diverges at the F-P phase boundary with the specific heat exponent {α}. In this work χ×Hb was measured across the F-P phase boundary from T≈200K down to T=121K. From the analysis of the divergence, {α} was evaluated at different temperatures. For T well above TL, α≈0.12, a value close to the prediction for the three-dimensional Ising model. As T is lowered, the divergence gets sharper and {α} increases, reaching α=0.44 at TL, in agreement with predictions for this uniaxial LP.