Field-Temperature Evolution of Antiferromagnetic Phases in Ludvigites Ni3-xMnxBO5

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.