Crystal structure and magnetic ordering in magnetoelectric KNiPO₄ investigated by means of X-ray and neutron diffraction

Abstract

The crystal structure of magnetoelectric KNiPO₄ was refined by single crystal X-ray diffraction methods at room temperature confirming orthorhombic space group Pna2₁. Powder neutron diffraction investigations showed that the room temperature structure is preserved down to 30 K. Consistent with magnetic susceptibility measurements, long-range antiferromagnetic ordering according to K = 0 and Shubnikov space group Pna2₁ is established by neutron diffraction at temperatures below T _N = (25.5 ± 0.5) K. The ordered magnetic moments of (3.00 ± 0.04) μ_g, oriented along [1, 0, 0], indicate large orbital contributions to the magnetic moment of Ni²⁺. DTA studies in the temperature range from 100–1000°C, showed two phase transitions, at 486.5°C and at 581.3°C.

Key Words:

• magnetic ordering
• crystal structure
• KNiPO₄
• phase transitions