The effects of 0.01 and 0.1 mol B2O3 addition to the microstructure and magnetic properties of a Ni-Zn ferrite composition expressed by a molecular formula of Ni0.4Zn0.6Fe2O4 were investigated. The toroid-shaped samples prepared by pressing the milled raw materials used in the preparation of the composition were sintered in the range of 1000-1300 degrees C. The addition of 0.01 mol B2O3 increased the grain growth and densification giving rise to reduced intergranular and intragranular porosity due to liquid-phase sintering. The sintered toroid sample at 1300 degrees C gave the optimum magnetic properties of B-r = 170 mT, H-c = 0.025 kA/m and a high initial permeability value of mu(i) = 4000. The increment of the B2O3 content to 0.1 mol resulted in a pronounced grain growth and also gave rise to large porosity due to the evaporation of B2O3 at higher sintering temperatures. Hence, it resulted in an air-gap effect in the hysteresis curves of these samples. (C) 2007 Elsevier B.V. All rights reserved.