William C. Cain

Investigation of the exchange mechanism in NiFe-TbCo bilayers

The origin of the interfacial exchange coupling that exists in NiFe‐TbCo bilayer thin films has been investigated through high resolution Kerr microscopy and VSM studies. Based on these experimental observations, a new model of the exchange mechanism for in‐plane, ferromagnetic‐perpendicular ferrimagnetic materials is developed. It is proposed that the local anisotropy in the TbCo layer varies from in‐plane at the interface to perpendicular at the top surface. The relative magnitude of the exchange effect calculated with average TbCo Ku values, agrees with experimental data. The predicted dependence of the exchange field on NiFe and TbCo layer thickness also fit the experimental data.

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

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 ...

Micromagnetic model of an exchange coupled NiFe‐TbCo bilayer

We present a micromagnetic model for NiFe‐TbCo exchange coupled bilayers that can quantitatively predict and explain the major macroscopic features observed in measured M‐H characteristics. Comparison of theoretical and experimental results shows conclusively that the strong interfacial exchange coupling in NiFe‐TbCo is essentially indistinguishable from that of a perfect, homogeneous interface. Commonly invoked assumptions concerning the existence or origin of a grossly weakened exchange coupling at a highly imperfect interface are neither necessary nor consistent with experimental measurements. The mechanism of the unidirectional exchange anisotropy is the formation of Bloch‐type domain walls in a ≂0.08‐μm‐thick TbCo sublayer of uniaxial, in‐plane anisotropy adjacent to the NiFe interface. The manner in which the observable magnetic behavior of NiFe‐TbCo bilayers depends on film thicknesses, TbCo anisotropy, interfacial exchange coupling strength, as well as the previously unconsidered large hysteretic ...

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-AA 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 AA. Films with a 500-AA layer of TbCo exhibited a greatly reduced exchange effect. A preliminary 500-AA-thick 128- mu m*20- mu m permalloy head biased with 2000 AA of TbCo exhibited at Delta R/R of 1.45%. The hard-axis coercivity is negligibly small ( 1 MHz. >

Dual exchange biased NiFe-TbCo unshielded MR heads for high density recording

Narrow-trackwidth unshielded MR (magnetoresistive) heads with both longitudinal and transverse bias supplied by a single TbCo exchange-bias layer were constructed. These preliminary dual-biased NiFe-TbCo MR heads exhibit Barkhausen-noise-free, low-distortion response characteristics over a wide range of recording densities (up to 80 kFCI). A 64- mu m track width, 7- mu m height dual-exchange-biased element exhibited a phase margin of 50% at a raw bit error rate of 10/sup -5/ in a recording channel reproducing

Improved bias and stability in dual-exchange-biased unshielded magnetoresistive heads

Data are presented on dual-exchange-biased NiFe-TbCo UMR (unshielded magnetoresistive) tape heads with improved signal response and process stability. It was found that a Si/sub 3/N/sub 4/ passivation layer offered better stability of the exchange bias through head processing than SiO/sub 2/. In order to improve sensor sensitivity, the longitudinal component of the exchange bias was reduced by increasing the exchange angle to 75 degrees from the sense current direction. This resulted in a +6-dB improvement in signal over previous heads without sacrificing Barkhausen-noise-free operation in narrow trackwidths. Heads with trackwidths as narrow as 8 mu m were shown to operate at linear densities of up to 50 kFCI with excellent signal-to-noise ratios (>45 dB). Investigations of different passivation materials showed Si/sub 3/N/sub 4/ to provide the best protection against environmental corrosion and thermally induced oxidation of the TbCo layer. >

Modeling of various magnetoresistive head designs for contact recording

As areal density increases demand magnetoresistive (MR) sensors and contact limited spacing, recessed MR designs will be needed for system robustness. In this study, two dimensional reciprocity modeling is used to evaluate the relative performance of various MR designs for both longitudinal and perpendicular recording in contact. Shielded designs offer large signals but are not robust enough for sliding contact applications. Of the recessed sensor designs, longitudinal yokes tend to have low efficiency, while a perpendicular pole MR head offers excellent efficiency, but reduced resolution.

Exchange anisotropy for providing dual bias in magnetoresistive heads

The large bias field produced by exchange anisotropy at the interface of NiFe-TbCo thin films is considered for providing dual bias in magnetoresistive (MR) heads. Exchange-biased NiFe-TbCo MR heads that exhibit a linear response (applied field range: +or-50 Oe) and greatly reduced Barkhausen noise have been produced. Dual exchange bias is accomplished by directing a component of the exchange field along the longitudinal direction for domain stabilization and directing another component of exchange field along the transverse direction for linearization. >

Achieving 1 Gbit/in/sup 2/ with inductive recording heads

By using a planar inductive head run in continuous contact with the media surface we have demonstrated an areal recording density of 1 Gb/in/sup 2/ This was achieved by first recognizing several fundamental limits on the areal density performance of inductive heads, then by developing a new transducer capable of overcoming these limitations. This paper describes a contact planar thin film head capable of a 1 Gb/in/sup 2/ areal density with a robust off-track error rate.

Micromagnetic model of an exchange‐coupled NiFe‐TbCo bilayer (abstract)

A micromagnetic model for NiFe‐TbCo exchange‐coupled bilayers which can quantitatively predict and explain the major macroscopic features observed in measured M‐H characteristics is presented. Comparison of theoretical and experimental results shows conclusively that the strong interfacial exchange coupling in NiFe‐TbCo is essentially indistinguishable from that of a perfect, homogeneous interface. Commonly invoked assumptions concerning the existence or origin of a substantially weakened exchange coupling at a highly imperfect interface are neither necessary, nor even consistant with experimental measurements. The mechanism of the unidirectional exchange anisotropy is the formation of Bloch‐type domain walls in an ≂0.08‐μm‐thick TbCo sublayer of uniaxial, in‐plane anisotropy adjacent to the NiFe interface. The manner in which the observable magnetic behavior of NiFe‐TbCo bilayers depends on film thicknesses, TbCo anisotropy, interfacial exchange coupling strength, as well as the previously unconsidered l...