Structure formation and magnetiec .properties of Co-Fe-Ni-Si-B films, obtained by the splat-quenching

Abstract

Purpose. The new metastable phases (including amorphous state), that are characterised unique physical properties, can be obtained by the quenching from the melt. The practical use of amorphous materials is restricted by the thermal interval of amorphous state stability. Study of influence of cooling rate on the films structure, as well as the effect of thermal treatments on the phase transformations occurred in solid states are very important. Methodology. The structure details of initial and treated films are determined by means of X-ray diffraction and metallographic methods. Magnetic properties were investigated by the vibration magnetometer. Findings. It has been found, that the change from crystalline structure (mixture of phases р-Со(В) и (Co,Si>B) to amorphous one is observed in Co67.2Fe6.1Ni10Si11B15.9 films with increase of cooling rate from 104 K/s to 106 K/s. Size of the coherently diffracting domains was approx. 2 nm. The structure change and formation of amorphous phase leads to the drastic decrease of initial films coercivity from 4000 A/m to 80 A/m. The crystallisation of amorphous films occurs in temperature range 480 - 510 оС (5 min). In the first stage, only primary р-Со(В) crystals appears in residual amorphous matrix. The annealing at the temperature 550 оС (5 min) leads to the decomposition of residual amorphous phase. In the second one, metastable phase (Co,Si)3B (structure type Fe3C) is formed. Coercivity of treated films increased to 24 000 A/m. It connected with crystallisation processes and the formation of multiphase structure. The annealing under tensile stress in this temperature interval 480 - 570 oC (5 min) did not alter the films structure. Size of the coherently diffracting domains increased up to 3 nm. Coercivity of treated films under tensile stress was 80 A/m. Originality. Annealing under tensile stress increased the thermal stability of amorphous phase. The crystallisation processes begins at temperature up to 570 oC, that expands the thermal interval stability of amorphous phase on 80-100 oC. It is possible that stress annealing stimulates the processes of amorphous phase separation into two phase with different short order and following formation of the phase mixture (Р-Со(В) и (Co,Si)3B) through eutectic crystallization. Practical value. Increase the thermal interval stability of amorphous phase will expand practical use in devices and precized apparatures.