Svetlana Sofronova

Magnetization pole reversal of ferrimagnetic ludwigites Mn3−xNixBO5

The conditions for the flux growth of new Mn-Ni oxyborates with the ludwigite structure are reported. Magnetic measurement data for the samples with nickel and manganese predominance are presented. Diamagnetic anomalies of the antiferromagnetic phases are established and analyzed in the framework of a model comprising two antiferromagnetically interacting subsystems, each being antiferromagnetically ordered.

Magnetism and structure of Ni2MnBO5 ludwigite

Single crystals of ludwigite Ni2MnBO5 were synthesized by flux growth technique. The detailed structural and magnetic characterizations of the synthesized samples have been carried out. The cations composition of the studied crystal was determined using X-ray diffraction and EXAFS technique, the resulting composition is differ from the content of the initial Mn2O3 - CuO components of flux. Magnetic susceptibility measurements and the calculations of the exchange integrals in frameworks of indirect coupling model revealed strong antiferromagnetic interactions and appearance of magnetic ordering phase at the temperature T=85 K. The hypothesis of the existence of several magnetic subsystems was supposed.

Magnetic structure of Cu2MnBO5 ludwigite: thermodynamic, magnetic properties and neutron diffraction study

We report on the thermodynamic, magnetic properties and the magnetic structure of ludwigite-type Cu2MnBO5. The specific heat, low-field magnetization and paramagnetic susceptibility were studied on a single crystal and combined with powder neutron diffraction data. The temperature dependence of the specific heat and the neutron diffraction pattern reveal a single magnetic phase transition at T  =  92 K, which corresponds to the magnetic ordering into a ferrimagnetic phase. The cation distribution and the values and directions of magnetic moments of ions in different crystallographic sites are established. The magnetic moments of Cu2+ and Mn3+ ions occupying different magnetic sites in the ferrimagnetic phase are pairwise antiparallel and their directions do not coincide with the directions of the principal crystallographic axes. The small value of the magnetic moment of copper ions occupying site 2a is indicative of partial disordering of the magnetic moments on this site. The magnetization measurements show a strong temperature hysteresis of magnetization, which evidences for field-dependent transitions below the phase transition temperature.

Transformation of structure and magnetic properties of Cu 2 MnBO 5 under partial Mn 3+ → Fe 3+ substitution

Abstract Single crystals of Fe-substituted Cu2Mn1-xFexBO5 ludwigites have been synthesized using flux technique (x = 0.2, 0.4, 0.5 – in the initial flux system). Structural properties of the synthesized compounds were studied by the single crystal and powder X-ray diffraction analysis. Obtained results were analyzed in the relationship with parent compound Cu2MnBO5. It was revealed that the type of monoclinic distortions of Fe-substituted ludwigites is different from the structure of Cu2MnBO5. The real cation composition and local structure of Cu2Mn1-xFexBO5 ludwigites were studied using XANES and EXAFS techniques, respectively. Analysis of field and thermal dependencies of magnetization showed a high dependence of the magnetic properties of these ludwigites on x with changing the type of magnetic ordering.