Magnetic properties of ludwigite Mn<inf>2.25</inf>Co<inf>0.75</inf>BO<inf>5</inf>

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 TN≃61K. 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 4.8μB was calculated from the paramagnetic data. Analysis of the phonon contribution to the specific heat allowed to distinguish the magnetic contribution CM, which has two features. One of which was observed at TN 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.