Low-temperature phonon, magnon and exciton effects on the polarization of BaXF4

Studies of the polarization deviation ΔP and of the dynamic pyroelectric response (I/cρ) (dP/dT) at low temperatures of the family of barium-transition metal-fluorides BaXF4, for X = Mg, Zn, Mn, Ni and Co are reported. The various effects of acoustic and optic phonon excitation, 2D and 3D antiferromagnetic ordering in the Ni and Co salts. Frenkel excitons in the Mn salt and the subtle structural transition in the Mn salt are demonstrated.