Exchange coupled NiFe-TbCo thin films for use in self-biased magnetoresistive heads

It is found that the exchange field produced at the NiFe-TbCo interface has a maximum value at a TbCo layer composition of 27.5%. When proper sputtering conditions are used, this deposited composition produces an exchange field as large as 500 Oe when the layer is coupled to a 370-Å Permalloy layer. Torque and VSM data indicate that the TbCo layers have both in-plane and perpendicular anisotropy components and that the in-plane M-H loops of films that produce the maximum exchange field are square. A linear decrease in exchange field is observed as the NiFe layer thickness increases. The exchange field is independent of the TbCo layer thickness in the range of 1000-4000 Å. Films with a 500-Å layer of TbCo exhibited a greatly reduced exchange effect. A preliminary 500-Å-thick 128-μm×20-μm permalloy head biased with 2000 Å of TbCo exhibited at ΔR/R of 1.45%. The hard-axis coercivity is negligibly small (<0.5 Oe) in the range of 1 Hz to >1 MHz