Magnetic susceptibility measurements on K₂Pt(CN)₄Br_0.3 · nH₂O single crystals

Static magnetic susceptibilities of single crystals of the mixed-valence platinum compound K₂Pt(CN)₄Br_0.3 · nH₂O (KCP) are reported exemplifying the difficulties encountered at the measurements. The measurements have been carried out by means of a vacuum microbalance following the Faraday method at temperatures between 4 and 148 K and at field strengths between 6 and 20 kOe. The difficulties relate to: (1) the possible contamination by ferromagnetic impurities; (2) the non-cylindrical symmetry of the field around the axis of rotation of the magnet and the off-axis location of the sample holder; (3) the occurrence of free radicals after degradation of the material; (4) the parasitic effect of microgram quantities of oxygen adsorbed on the samples below 50 K; (5) the determination of the weak Pauli paramagnetism of the "quasi one-dimensional metallic" conductor above 65 K; and (6) the need for more accurate susceptibility references for the determination of n, the water content, by susceptibility measurements. The gram-susceptibility of KCP at 65 K, for which n is estimated to be 1.5, is analysed to be - 3.60 × 10^-7 emu g^-1 and - 3.83 × 10^-7 emu g^-1 for the magnetic field vector being respectively parallel and perpendicular to the c-axis of the crystals. The 6 percent anisotropy is mainly attributed to the triple bond in the CN group.