LIFSHITZ POINT IN MnP: SPECIFIC HEAT EXPONENT AND CRITICAL AMPLITUDE RATIOŤ

摘要: MnP is the only magnetic system in which a Lifshitz point (LP) of the uniaxial type was identified, and for which the crossover exponent, 4, and the critical wavevector exponent, ẞx, have been measured. This LP arises in the T vs. Ho phase diagram, with the magnetic field H, applied along the orthorhombic b-axis (perpendicular to the ferromagnetic easy axis). According to generalized scaling theory, the isothermal susceptibility X as a function of H diverges with the specific heat exponent a at the paramagnetic-ferromagnetic (PF) A-line near the LP. We used this prediction to obtain a, and the corresponding critical amplitude ratio A+/A-, from the Xь vs. Hь data. At the LP temperature we found a between 0.4 and 0.5, in agreement with scaling estimates based on the experimentally known values of and ẞ. We found also A+/A-= 0.65 0.05. Crossover to a Ising-like critical behavior was observed from the temperature dependence of a along the PF phase boundary.