Effects of temperature on exchange coupled alloys of Ni80Fe20-FeMn, Ni80Fe20-αFe2O3, and Ni80Fe20-TbCo

Abstract

The effect of temperature on the exchange coupling at the interface of three different bilayered materials was studied with the objective of developing temperature-stable single-domain materials for magnetoresistive readback heads. Exchange field (HE) was measured from room temperature to 245 °C for NiFe films coupled to FeMn, αFe2O3, and TbCo. In the permalloy-FeMn system, the exchange field decreases linearly, and reaches zero at about 150 °C, which is close to the Neel temperature of the antiferromagnet. These results agree well with previous work [C. Tsang and Kenneth Lee, J. Appl. Phys. 53, 2605 (1982)]. HE also decreases linearly in the αFe2O3 system, from 6.8 Oe at room temperature to 1.8 Oe at 245 °C. While the αFe2O3 system offers greater temperature stability, the exchange field produced is not very large, and the coercivity is somewhat high. Changes in HE with variations in the thickness of the αFe2O3 layer were also noted. Results for permalloy coupled to ferrimagnetic amorphous TbCo indicate a finite exchange field to at least 250 °C, with samples deposited at 90-V substrate bias having exchange fields of 12 Oe at 250 °C. Room-temperature coercivities of some 400-Å NiFe films coupled to TbCo have been measured to be as low as 1 Oe. These results suggest that films that have a low coercivity and an exchange field large enough to bias a magnetoresistive head can be produced with good temperature stability up to 250 °C.