Synthesis and magnetoelectric properties of single crystals of metastable KCOPO₄

Abstract

Single crystals of the metastable phase of KCOPO₄ (α-KCP) have been synthesized in a gel of tetra-methoxysilane. The crystals have a hexagonal symmetry which belongs to space group P6₃ (cell parameters a = 18.206(1), c = 8.5135(8) [Å] and Z = 24). The crystals have been characterized by x-ray diffraction and by polarized light microscopy. The magnetoelectric properties of this compound have been studied at 4.4 K. No linear magnetoelectric effect has been detected and all coefficients of the tensor corresponding to the quadratic magnetoelectric effect (ME)_H, have been determined at 4.4 K: β₁₂₃ = -β₂₁₃ = 2.3 10⁻¹⁸, β₁₁₃ = β₂₂₃ = 7.1 10⁻¹⁸, β₃₁₁ = β₃₂₂ = 12.2 10⁻¹⁸ and β₃₃₃ = 7.2 10⁻¹⁸ in [s A⁻¹] (estimated error less than 5%). The absence of a linear magnetoelectric effect and the form of the tensor of the quadratic effect indicate that the magnetic symmetry of the crystal at this temperature must belong either to the antiferromagnetic magnetic point group 6′ or to the paramagnetic one 61′. The pyroelectric effect was also measured confirming polar character of the structure.

Key Words:

• Quadratic magnetoelectric effect
• KCoPO₄
• pyroelectric effect
• metastable phase.