A new method for recording above 100 Gb/in.2 is discussed. We call this method “hybrid recording,” a form of thermally-assisted recording that combines thermo-magnetic writing and magnetic reading. In order to increase the stability of the recorded information, writing is carried out at an elevated temperature on a medium with a very high coercivity at room temperature. In our proposal write and read heads with extremely narrow trackwidths are used, so the trackwidth is not determined by the optical spot size and the written bits have a rectangular shape, in contrast to the schemes proposed by others. Preliminary experiments are shown. The applicability of today’s granular and MO type media for hybrid recording is discussed. It is calculated that hybrid recording on optimized media can give an increase of the areal density of a factor 2.9 in areal density or 7 dB (2.2×) medium SNR improvement in case of Poisson noise and 11 dB (3.4×) in case of transition noise. Practically a factor of about 2 in density is more realistic, pushing limiting densities for longitudinal recording to 100–200 Gb/in.2. Typical limitations at very high densities arise from heat dissipation in the head and thermal instability of the medium. Based on simplified model calculations including realistic limitations on medium, head and leads, and today’s practical limitations on electronics, comparisons are made between read heads containing a tunnel junction magnetoresistive (TMR) element and containing a giant magnetoresistive element with sense current in the plane (CIP-GMR) or perpendicular to the plane (CPP-GMR) of the sensor films. They show that the signal-to-noise ratio of TMR sensors for areal densities above 15 Gb/in.2 is not advantageous over GMR sensors with sense current in the plane as long as the junction’s tunnel resistance is not drastically reduced to below 10 Ω μm2. The CPP-GMR heads are disadvantageous with respect to CIP-GMR heads until the highest densities, 300 Gb/in.2, considered.

Based on model calculations a comparison is made between yoke-type read heads containing a tunnel junction magnetoresistive element (TMRE) and containing a giant magnetoresistive element (GMRE). For typical head design parameters, TMR-based heads are 3-5 times more flux-efficient than GMR-based heads. However, for approximately 1/spl times/1 /spl mu/m/sup 2/ elements, the SNR of TMRE-based heads is not advantageous as long as the junction's tunnel resistance is not drastically reduced below R=1 k/spl Omega/.

Digital tape recording systems show the same trend as hard-disk drives: a large increase of storage density with time. The use of advanced media and highly sensitive thin-film heads with magnetoresistive (MR) readout will increase the storage density dramatically. Key improvements are narrower tracks, more sensitive MR elements attained by applying the giant magnetoresistance effect, high-saturation flux density pole materials, advanced metal powder tape, intimate head-to-tape contact, and accurate tracking. By increasing the number of channels in the multitrack thin-film head, high data rates can be obtained as well. The basics of digital magnetic recording are discussed and a short historical overview is given of the Philips activities on thin-film heads for tape recording. An outlook on future improvements is given.

An outlook is given on how the efficiency of future generation yoke-type magneto-resistive read heads may be improved through the use of oxidic layers. The effect of ferrite separation oxides, ferrite fluxguides and superconducting gap-oxides is discussed.

In this paper tools to handle the magnetostatic aspects of thin-film tape head design are reviewed. Some illustrative results from transmission-line calculations on inductive write heads and yoke-type magnetoresistive read heads are shown. New is the application to nonlinear saturation effects in write heads. The design of an emboss head for writing servo tracks on tape is described. Finally, a new type of read head is discussed that utilizes anisotropy of the permeability instead of structuring of the fluxguides for obtaining very small track widths.

The multichannel servo writer and the data read/write heads of the new DigaMaxTM tape storage system are discussed. These heads enable a storage capacity of 13 GB (uncompressed) on 300 m of 72 kA/m tape using prerecorded buried servo information for dynamic track following during reading and writing of data

Multitrack yoke-type MR readout heads having a single shared front fluxguide with a highly anisotropic permeability, have been designed and evaluated. The well defined microtrack response profiles of these heads show that the anisotropy of the permeability confines the flux-detection to the area on tape in between the contact leads of the MR element. This can be exploited in “full-density” tape recording heads which read directly a number of adjacent tracks

Magnetoresistive elements (MRE's) containing exchange-biased spin valve multilayers as the magnetoresistive material have been fabricated, Their electrical response has been measured using an integrated test coil, Both parallel and crossed arrangements of the easy axes of the free and biased layers have been studied, Output voltage levels of these elements in response to an ac magnetic field are typically a factor of 7-10 higher than those obtained in similar elements based on a conventional, 30 nm thick anisotropic magnetoresistive (AMR) Ni80Fe20 film linearized by the ''barber-pole'' method, The parallel arrangement is found to result in a switching behavior which is characteristic of domain wall movement and contains hysteresis, Barkhausen noise, and strong harmonic distortion, The arrangement with crossed anisotropies is found to display a behavior characteristic of switching by magnetization rotation as evidenced by a strong reduction of hysteresis, Barkhausen noise, and harmonic distortion. Demagnetization effects are calculated in order to quantitatively explain the shape of the response curve and the difference in output voltage when compared to AMR-based MRE's.

Yoke type spin valve giant-magnetoresistive (GMR) heads with a track width of 70 and 10 mu m ale studied. The head design has the sensor on tap. The output of the heads is found to be upto 10 times larger than similar heads with a 30 nm Ni-Fe MRE linearized using a barberpole. The crucial role of the free layer permeability mu(r) and the ferromagnetic interlayer coupling with respect to the head performance is analysed This is argued to give design rules for the GMR material. The applied FeMn exchange biasing is shown to become unreliable above T=105 degrees C.

We studied the applicability of Ni/sub 80/Fe/sub 20//Cu/Ni/sub 80/Fe/sub 20//Fe/sub 50/Mn/sub 50/ GMR multilayers for thin film tape heads. A method involving crossed anisotropies is applied for avoiding noise in the GMR response. We compare and analyse the sensitivities of AMR and GMR heads. >

A rule of thumb is given for determining the sufficient thickness, t, of the metal layer in any MIG head. It is shown that for small track width heads a high efficiency is easily obtained.

Very-small-track-width ferrite and Metal-In-Gap (MIG) video heads were manufactured with the help of reactive-ion etching. Electrical measurements show very good read and write performance, as expected from theories.

By first depositing a thin films of Permalloy on a recording head no pseudogaps occur. At the gap the relative wear is slight, due to the presence of the Sendust. The gap cladding has minimal residual stress to avoid a decrease of head efficiency due to induced stress in the ferrite. The SiO2/Mo/Au gap is prepared by low-temperature thermodiffusion. This results in a magnetically sharp gap with a reproducible length. With this Permalloy/Sendust metal-in-gap head, a high-density recording head for in-contact recording has been realized.

In this paper some improvements are proposed for one-sided probe heads, used for perpendicular recording on double-layer media. Two-dimensional lumped reluctance modelling shows that the read efficiency of the well-known W-shaped single-pole head, or WSP, is very low, but can be improved by more than 10 dB by designing a new triangular coil-chamber geometry. The model also indicates that narrowing the track width with respect to the core width results in a further 5 dB increase in output. Furthermore, a new head design, the V-shaped singIe-pole head (VSP), which shows some distinct advantages with respect to manufacturability, has also been modelled. The experimental results obtained from measurements on VSPs are in good agreement with the model calculations. Despite its somewhat lower efficiency (compared to a WSP with the same triangular coil chamber), this VSP yields > 12 dB output improvement compared to a conventional WSP with a rectangular coil chamber and a wider track.

A description is given of how to separately the recording and playback performance of an inductive head relative to that of a "reference" head. The resulting relative recording and relative playback figures are completely insensitive to azimuthal differences between recording and playback head and are independent of errors in track adjustment. Second order effects can now be measured. In addition,...

This paper describes some anomalous effects in the recording and playback performance of heads with thin metal layers on one or both gap surfaces. The most apparent effect, bumps in the output spectrum while reading with this metal-in-gap head, is discussed in detail. Under normal recording conditions no bumps are observed when another head is used for playback. The magnetic behaviour of the inter...

The magnetoresistance effect at room temperature of thin NiFe films can be used in a reproducing head for magnetic recording systems. Different head configurations are possible: unshielded magnetoresistive element (MRE), MRE between magnetic shields and MRE in the yoke of a head. Unshielded heads can be used when long wavelength information has to be detected. Shielded- and yoke magnetoresistive heads can also reproduce short wavelength information. Some applications in audio recording systems are discussed.