Magnetostriction in some amorphous Fe-Co-Ni-P alloys

Amorphous bulk samples of Fe-Co-Ni-P were prepared by continuous electroless deposition in the form of hollow cylinders 6mm diameter, 20mm length and with a uniform thickness of the order 0.2mm. The specimens had a general formula NiwCoxFeyPz, with a range of compositions given by 0< w< 0.81; 0 < x < 0.92; 0 < y < 0.10; 0.06 < z < 0.25. The room temperature magnetostriction and the temperature dependence of the saturation magnetisation of the amorphous samples were measured. A number of the samples were heat treated to obtain a single phase crystalline material, the heat treatment conditions being determined by differential scanning calorimetry. The magnetisation values showed a composition dependence similar to that of crystalline alloys of Ni-Co and Ni-Fe. The magnetostriction coefficients, however, were all negative in sign, unlike the behaviour observed in polycrystalline alloys of Ni-Co and Ni-Fe. The magnetostriction values for the amorphous samples were found to be roughly twice the magnitude of those for the crystallised samples. A qualitative explanation of this phenomenon is given based on the lower value of Young's modulus which has been observed in amorphous materials.