Multipolar ordering in PrB₆

We investigate the mechanism how the complex magnetic structure is stabilized in PrB₆,paying attention to similarity to and difference from the case of OeB₆. A Ginzburg-Landau-typexpansion of the free energy is obtained with account of the γ₅-triplet crystalline electric field (CEF) ground state in PrB₆- It is found in the γ₅ model that combination of the nearest- neighbor dipole interaction and the next-nearest neighbor pseudo-dipole-type one reproduces the successive magnetic transitions observed in PrB₆: Incommensurate phase followed by a commensurate non-collinear structure with further decreasing of temperature. Inclusion of the quadrupolar interaction modifies the second-order transition to the IC phase into first order by enhancing the mode-coupling of dipole and quadrupole degrees of freedom.