Magnetic properties of ludwigite Mn2.25Co0.75BO5

Abstract Needle-shape single crystals of Mn2.25Co0.75BO5 ludwigite were synthesized by the flux technique and investigated by means of X-ray diffraction, static magnetic susceptibility and specific heat measurements. Magnetization and specific heat experiments showed the presence of ferrimagnetic ordering near T N ≃ 61 K. Below this temperature the magnetic properties demonstrated the angular dependence and the high magnetic hardness in a magnetic field applied perpendicular to the crystallographic c axis, which is similar to other cobalt-containing ludwigites. The effective magnetic moment per magnetic ion 4 . 8 μ B was calculated from the paramagnetic data. Analysis of the phonon contribution to the specific heat allowed to distinguish the magnetic contribution C M , which has two features. One of which was observed at T N and can be attributed to strong exchange interactions between spins of magnetic ions. The second one at T  =  11.6 K is due to the effect of the ligands crystal field on a magnetic ion with S > 1 ∕ 2 .