boron silicon alloy yields an optimum coupling k 0 90 when cross field annealed at 400 u00b0 c for 30 minutes this anneal yields an optimum resonant frequency range with the bias field centered around 1 oe for alloys having the compositions specified hereinabove the annealing temperature ranges from about 300 u00b0 to 450 u00b0 c and the annealing time ranges from about 7 to 120 min the anneal also affects the bias field required to optimize k for a given amorphous metal with a given anneal the coupling depends strongly on the bias field at zero and saturating fields the coupling is zero no resonant and anti resonant phenomena for a given alloy an optimum bias field exists which yields a maximum k for alloys having the compositions specified herein the bias field required to optimize k ranges from about 0 1 to 20 oe even though most magnetostrictive materials will exhibit some mmc amorphous metal yield extremely high coupling factors and are therefore highly preferred as cast amorphous metals yield higher k than most other magnetostrictive materials no material has higher k than amorphous metals when cross field annealed amorphous metals have high k because they have a low magnetic losses no grain boundaries high resistivity b low structural and stress anisotropy c reasonable magnetostriction and d an ability to be given a beneficial magnetic anisotropy amorphous metal alloys make good targets because a they have high.