Jacobus Josephus Maria Ruigrok

Disk recording beyond 100 Gb/in.2: Hybrid recording? (invited)

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 ...

The initial permeability of polycrystalline MnZn ferrites : the influence of domain and microstructure

The validity of nonmagnetic grain‐boundary (NMGB) models for the initial permeability of polycrystalline ferrites is examined. The domain size in a series of wet‐chemically prepared polycrystalline MnZn ferrites, in the demagnetized state, has been determined by neutron depolarization. A transition in the intragranular domain structure from mono‐ to two domain is observed at grain size D≊4 μm. An expression for this transition has been derived for a dense magnetic material. The grain size dependence of the initial permeability of the ferrites studied, particularly for monodomain grains, is consistent with the NMGB model. The grain‐boundary width and composition have been determined with a nanoprobe (1.5 nm resolution). Composition variations extend ≊10 nm into the grain. The findings suggest that, although the NMGB model considers ‘‘nonmagnetic’’ grain boundaries, in practice the grain boundary may be hard magnetic.

Application of giant magnetoresistive elements in thin film tape heads

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. >

The electrical and magnetic response of yoke-type read heads based on a magnetic tunnel junction

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 junctions tunnel resistance is not drastically reduced below R=1 k/spl Omega/.

Performance of yoke type GMR heads

Yoke type spin valve giant magnetoresistive (GMR) heads with a track width of 70 and 10 /spl mu/m are studied. The head design has the sensor on top. The output of the heads is found to be up to 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 /spl mu//sub 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/spl deg/C.

Design and fabrication of thin film heads for the digital compact cassette audio system

The digital compact cassette (DCC) system requires a multitrack recording head which can handle the digital multitrack format but can also playback standard analog compact cassette tapes. The layout and design of a recently developed thin film DCC head are discussed. An analysis of design parameters is presented, which shows why a small throat height of only 3 mu m has been chosen. In order to insure sufficient lifetime of the head, a CrN coating on the tape bearing surface is applied. >

Permalloy/Sendust metal-in-gap head

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 SiO/sub 2//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. >

Design and performance of magnetic heads for magneto‐optic recording with magnetic field modulation

In magneto‐optic recording, the most direct way to overwrite stored information is to switch the magnetization in a laser‐heated region of the magneto‐optic layer by means of an alternating magnetic field generated by a magnetic head. The heat dissipation in the head and the necessary voltage and current amplitude associated with fast switching, the desired high field, and a large head‐to‐medium distance make high demands upon the head design and the current source, respectively. Design criteria and numerical and experimental results for some circularly symmetric head configurations are presented.

NEW OPTIONS IN THIN FILM RECORDING HEADS THROUGH FERRITE LAYERS

Abstract 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.

TRENDS IN DIGITAL MAGNETIC RECORDING; THE APPLICATION OF THIN-FILM HEADS FOR TAPE RECORDING

Abstract 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.