Annealing temperature dependance of magnetic properties and magneto-impedance effect in CoZrB alloys

The influence of conventional annealing on the magnetic properties and the magneto-impedance (MI) effect of Co72Zr8B20 alloys has been intensively studied in this paper. The as-quenched Co72Zr8B20 ribbon is identified to be amorphous alloy. After Co72Zr8B20 being annealed at 495 °C for 10 min, there is almost no change in the XRD pattern. When the annealing temperature (Ta) reaches 540 °C, a diffraction peak representing some crystalline phase appears. After the sample being annealed at 630 °C, Co, Zr and B12Zr crystalline phase are formed in the alloy. Magnetic measurements reveal that the as-quenched Co72Zr8B20 possesses smaller coercivity, higher permeability and larger saturation magnetization. With the increasing annealing temperature, the soft magnetic properties of the sample greatly deteriorate. The study on the MI ratio (ΔZ/Z(%)) versus external magnetic field curves indicates that the MI behavior changes from single-peak to double-peak shape when Ta increases from 495 to 540 °C. The most drastic MI ratio about 90% is obtained in the as-quenched Co72Zr8B20 at 1110 kHz. The mechanism of thermal treatment affecting the magnetic properties and the MI effect in Co72Zr8B20 alloys will be discussed in this paper.