Ladislav R. Pust

Thermomechanical head performance

Mismatch of thermal expansion of various materials used in the transducer and slider of giant magnetoresistive (GMR) recording heads causes, at higher operating head temperature, mechanical stresses and, in particular, protrusion toward the media [thermal pole tip recession (T-PTR)]. Low T-PTR is necessary for low head-media spacing without mechanical contact. Impact of the magnitude of the Poissons ratio of a photoresist coil insulator on thermal protrusion is shown to be large, due to large variation of the volume compressibility. Three-dimensional FE (3-D FE) thermomechanical modeling shows that the distribution of thermal stress in shields caused by mismatch of coefficient of thermal expansion changes completely close to the air bearing surface due to protruded head surface. During head operation, the primary heat source arises from the writer coil. The maximum temperature and the particular temperature distribution depends on the ability of the head components to dissipate effectively the generated heat. As the transducer continues to scale down in size with increasing areal density and data rate, the power dissipated per unit volume grows due to the larger coil resistance in the core region.

Comparing theoretical demagnetizing factors with the observed saturation process in rectangular shields

An analytic expression is given for the ballisticdemagnetizing factors, D ′ , of the general rectangular prism, in which the field is averaged over the middle cross section of the prism, and for the “side” demagnetizing factor, D ″ , in which the averaging is over the edges of the prism. The demagnetizing fields are compared with the applied field values when a 250×95×2.35 μ m magnetic shield transfers into the saturated state. This shield was made of a Ni 80 Fe 20 film, with a small uniaxial magnetic anisotropy induced during the electroplating process. Domain structure and the process of magnetic saturation were imaged using wide-field Kerr microscopy in fields up to 400 Oe, both along the easy and the hard axes. The ballisticdemagnetizing field is found to be close to the external field necessary to align magnetically the central part of the shield, while the full shield saturation takes place at a field above the recently published magnetometric demagnetizing field. Saturation fields along the hard uniaxial anisotropy axis are larger, due to effective anisotropy fields.

Temperature dependence of the magnetization reversal in Co(fcc)–BN–Co(poly hcp) structures

The magnetic properties of multilayer structures with two magnetic layers of the same metal (Co) but with different crystallographic structures separated by an insulating BN layer have been studied. These structures were prepared on Si (001) substrates by a combination of molecular beam epitaxy (metallic layers) and electron cyclotron resonance-assisted sputtering (BN layer). An fcc Co single-crystal layer (60 A) was first stabilized by growing it on a copper fcc buffer layer and subsequently a polycrystalline Co layer (70 A) with hcp structure was grown on top of the insulating BN layer. A CoO antiferromagnetic layer, formed adjacent to this hcp Co layer, significantly influenced the magnetic behavior of the polycrystalline hcp Co layer. The magnetic hysteresis loops for these structures were measured at temperatures ranging from 5 to 350 K with the magnetic field applied along the easy (110) in-plane axis of the fcc Co. A very sharp flipping of the magnetization was found for the fcc Co layer with a nea...

Exchange tab stabilized readback transducers for areal densities exceeding 20 Gb/in/sup 2/

We present results from a high-density giant magnetoresistive magnetic recording reader using exchange bias stabilization. This novel reader design approach reduces the amount of parasitic resistance, as the sense current is not delivered through high resistivity permanent magnets. Heads were demonstrated to deliver areal densities in excess of 24 Gb/inch/sup 2/. The electrical performance of these heads, in particular, amplitude sensitivity, microtrack profiles and areal density capability are presented. Reader film properties and manufacturability of this approach are discussed in detail.

Domain control in magnetic shields using patterned permanent magnet underlayer

The domain state of a magnetic shield in a recording head can be controlled by an adjacent patterned permanent magnet layer. A 1.1-μm-thick electroplated Ni80Fe20 (NF) film with slight uniaxial magnetic anisotropy was patterned into rectangular magnetic shields with various dimensions over patterned thin film made from a 0.1-μm-thick CoCrPt permanent magnet (PM). The shape of the adjacent biasing PM layer should be the shape of a desired final domain in NF. Domain structure in the NF layer and the process of magnetic saturation were imaged using wide-field Kerr microscopy. The NF and PM layers are magnetically coupled and, therefore, a magnetic state with parallel magnetization is preferred. The PM direction of magnetization is set in high magnetic field and the final NF domain state is controlled by the shape of PM features. The simplest stable domain structure in a rectangular thin shield is of an “envelope” type. Using a PM underlayer, either clockwise or counterclockwise domain structure is preferred....

Exchange tab readback transducer using reactive ion etching to define the trackwidth

IrMn was used to stabilize the free layer in exchange tab type magnetic recording readback heads. These heads were fabricated using either reactive ion etching (RIE) or argon ion beam etching (IBE) to define the trackwidth. The two processes were used to eliminate the coupling between the exchange tab material (IrMn) and the free layer (NiFe), which creates a sensitive, nonhysteretic, linear, stable free layer. Wafer level test structures were measured during the head build process and results for the RIE and IBE processes are compared. Transmission electron micrographs were taken. Undercutting of the electrodes can be seen on the RIE processed heads. Spin-stand data for the read heads were compared and the RIE processed heads had a larger low frequency amplitude and sensitivity. Micro-track profiles and tack scans were also taken using the RIE processed heads. The increased process latitude that the RIE process has over the IBE process leads to, on average, overall better performing heads.