Evidence of the existence of a line of multicritical Lifshitz points in the phase diagram of manganese phosphide (abstract)

Abstract

Experimentally pure Lifshitz critical behavior has only been reported in the orthorhombic magnetic system MnP which exhibits uniaxial Ising-type Lifshitz points LP (d=3, n=1, m=1). Two LPs have been previously identified in MnP.1,2 One when the external magnetic field H was applied along the intermediate b axis, the other when H was along the hard anisotropy axis a. Both LPs occur roughly at the same temperature (T1∼121 K) but at different values of H due to the difference in anisotropy. In this work we report on measurements made with H applied within the ab plane. The observed phase diagram obtained using an ac susceptibility technique shows, near the confluence of the modulated and ferromagnetic phases with the paramagnetic phase the same characteristics of the phase boundaries found for H along a and b. The temperature at the multicritical point is ∼121 K. A preliminary analysis of the crossover exponent φ, obtained from the shape of the phase boundaries give φ≂0.6, a value that is consistent with that found for H along the a and the b axes. These data suggest that there is a line of LPs connecting the multicritical points found when H is along the b and a axes.<ks>