We report two developments in the emerging technique of recording head characterization by Magnetic Force Microscopy (MFM). The MFM signal amplitude was used to measure the field magnitude at the single pole tip of a vertical high-M(s) FeAlN/NiFe write head as a function of input current, This method enabled us to observe directly the onset of saturation in a high-M(s) write head. Scans over the pole tips of a longitudinal NiFe head, on the other hand, revealed features asymmetric across the gap and of identical sense upon current reversal, These features constitute possible evidence for magnetization rotation of the nominally ''hard'' Co-alloy MFM tip as a function of down-track position.

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.

The effects of pole trimming on the recording performance of thin film heads is investigated through experiment and modeling. Three dimensional head fields are computed numerically for various pole geometries, and are used by a simple two dimensional recording simulation to determine written width, erase width, read width and isolated pulse response. These parameters are then compared to experimental values measured on trimmed and untrimmed heads. Both modeled and experimental parameters are then used as input to a system error rate simulation to determine the effects of pole trimming on system error rate as a function of track density. Good agreement is found between model and experimental parameters. The error rate results suggest that in a system with a reasonable track misregistration (TMR), a track density increase of 7 to 9% can be obtained by trimming the inductive head poles. >

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 large hysteretic effects due to the small net magnetization in ferrimagnetic TbCo, are discussed in detail. It is demonstrated, for a strongly coupled system such as NiFe-TbCo, that the often used single parameter ‘‘exchange field’’ description of a shifted NiFe M-H loop is inadequate. A quantitatively accurate description requires that one take into account the spatial variations in the micromagnetic magnetization distributions of both layers.

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.

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.< >

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-μm track width, 7-μm height dual-exchange-biased element exhibited a phase margin of 50% at a raw bit error rate of 10-5 in a recording channel reproducing (1,7)-coded data written at 40 kFCI (54 kbPI) using compact spectrum write equalization. These exchange-biased head response data compare favorably to data obtained from an unshielded MR head biased by external permanent magnets. The dual-exchange-biased NiFe-TbCo MR heads exhibit a small dependence of bias on temperature (0.3% reduction per °C) and a small reduction in signal (1.3 dB) due to the shunting effect of the TbCo

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.

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 ...

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.

We have used ferromagnetic resonance (FMR) to investigate magnetic anisotropy in bilayer exchange-coupled thin films. Experiments, using both our 9 and 33 GHz FMR spectrometers, were done on two systems: NiFe/FeMn and NiFe/α-Fe2O3. In some of the NiFe/α-Fe2O3specimens an additional response was detected at 33 GHz. We attribute this additional resonance to a region formed by interdiffusion of NiFe and α-Fe2O3at their common interface. Effective anisotropy field, g-value and the relative volume have been determined for each ferromagnetic region. Auger profile, TEM and CBED (convergent beam electron diffraction) cross-section examinations were performed for an interdiffused specimen, the results are consistent with the presence of a layer containing Fe and Fe3O4located between the NiFe and α-Fe2O3regions. A memory effect, due presumably to irreversible spin reorientation at the interface, was observed in some of the NiFe/α-Fe2O3specimens.

Exchange coupled thin films of a soft magnetic film and an anti-ferromagnet are of interest as a way of providing bias for magneto-resistive recording heads. In this paper the influence of magnetic and geometrical parameters of the soft magnetic film on the magnetization curve and the permeability were derived from micromagnetic theory. A comparison with experimental data showed, that the exchange...