Low-field magnetization of ludwigites Co3O2BO3 and Co3-x Fe x O2BO3 (x aparts per thousand 0.14)

Ludwigite single crystals of compositions Co3O2BO3 and Co3 - x Fe (x) O2BO3 (x a parts per thousand 0.14) have been synthesized. The crystal structure is investigated at room temperature, and the magnetization is studied in the temperature range T = 4.2-100 K in magnetic fields of up to 600 Oe. The orthorhombic symmetry is revealed, and the unit cell parameters are determined. A number of features are established for the temperature dependence of the magnetization. In unsubstituted Co3O2BO3, two magnetic transitions are found at T (C1) = 43 K and T (C2) = 15 K. At temperatures below 40 K, spin-glass state is revealed. Substitution of iron ions for cobalt ions leads to a noticeable shift in the magnetic transitions toward the high-temperature range: T (C1) = 83 K and T (C2) = 74 K. A ferromagnetic ordering of the P type is found in the Co3 - x Fe (x) O2BO3 (x a parts per thousand 0.14) compound.