Dependence of Magnetostriction and Coercivity on Process Variables for Rolled 4–79 Molybdenum Permalloy Tape

In certain device applications, it is necessary to obtain cold‐rolled Permalloy tape having a high squareness ratio, a very low magnetostriction, and a low coercive force. These properties have been achieved in 4–79 molybdenum Permalloy by discrete variations in processing. A wire is first annealed at a selected diameter, and then cold‐drawn to a final diameter followed by roll‐flattening. Increasing the anneal temperature (in the 650°–950°C range) and the extent of cold drawing (prior to flattening) by increasing the anneal diameter, generally results in lower tape $H_c$ . However, as the extent of cold‐drawing is increased beyond about 75% area reduction, increased anneal temperatures cause a slight increase in tape $H_c$ . Further, the discrete process variations bring about an optimum two‐component tape texture ($\text{〈111〉+〈100〉}$ along tape axis) for zero magnetostriction. However, this optimum texture also depends critically on composition. Compositional deviations of 1% (well within commerical tolerances for 4–79 molybdenum Permalloy) have been found unacceptable in device applications.