Localized magnetic modification of permalloy using Cr⁺ ion implantation

Doping ferromagnetic nickel–iron alloys with chromium causes the Curie temperature to be reduced. We have demonstrated that solid state solutions of Ni–Fe–Cr can be formed by implanting Cr ions into ferromagnetic NiFe alloy films, thus creating paramagnetic films. We find that the magnetic moment and coercivity decrease steadily with Cr⁺ dose, reaching zero at room temperature with the onset of paramagnetism. Using Cr⁺ implantation in conjunction with a lithographic mask we have patterned continuous Ni₈₀Fe₂₀ films into separate regions that are ferromagnetic and paramagnetic at room temperature. This magnetic patterning process may have applications for the manufacture of magnetic write heads, such as for the notching process used to constrain the stray field from the write gap.