Investigation of magnetic structure and phase transitions in Co₃¹¹B₇O₁₃Br boracite by neutron diffraction

Abstract

Neutron diffraction investigations of orthorhombic Co₃ ¹¹B₇O₁₃Br at 293 K and in the temperature range 1.5–30 K reveal a two step onset of magnetic ordering, starting at the the second order transition to a weakly ferromagnetic phase at T _N = 17.5 K (Néel type) and followed at about T _t = 10.5 K, by a smooth transformation to a three-dimensional canted magnetic structure (magnetic space group Pc′a2₁′ (Sh₂₉ ¹⁰¹), magnetic modes C _x(+ + − −), F _y(+ + + +), A _z(+ − − +). The three Co sites display completely different moment values and directions, arising from frustration effects associated with the formation of isolated Co₃Br groups with a triangular arrangement of the three Co sites.

Key Words:

• Bozacite
• neutron diffraction
• magnetic structure
• ferroelectric
• ferromagnetic
• ferroelastic.