EFFECT OF HEAT-TREATMENT ON THE MICROSTRUCTURE AND MAGNETIC-PROPERTIES OF POLYCRYSTALLINE MNZN FERRITES

The effect of heat treatment of commercially available polycrystalline MnZn ferrite slabs was studied for temperatures near typical recordin g head glassing temperatures. Toroid-shaped specimens were heated in a tmospheres of varying levels of oxygen and the deterioration in magnet ic properties was measured. The surfaces of the exposed specimens were inspected by means of optical and electron microscopy and the occurre nce of ferrite instabilities such as grain growth, segregation of seco ndary phases etc were observed. The degradation also appeared to be su rface-driven. To investigate this further, some samples were heat trea ted in highly oxidizing and reducing atmospheres to induce gross ferri te instabilities. The near surface regions of these samples were then characterized by x-ray diffraction, x-ray photoelectron spectroscopy ( XPS) and conversion electron and conversion x-ray Mossbauer spectrosco py (CEMS and CXMS). In addition to grain growth and other structural c hanges, the precipitation of extraneous phases appears to be a major m ode of ferrite failure during such annealing.