Mark E. Re

High‐frequency permeability of laminated and unlaminated, narrow, thin‐film magnetic stripes (invited)

The permeability of the magnetic material in a thin‐film magnetic head is an important, but hard to characterize, parameter since the magnetic permeability depends on the head domain structure, the drive frequency, and the shape and size of the head. We have measured the high‐frequency permeability from 1 MHz to 300 MHz, hysteresis loops, and domain structure of unlaminated and multilayer magnetic thin‐films as a function of stripe width for arrays of long narrow stripes. Monolithic permalloy films and permalloy films laminated with SiO2 have been photolithographically patterned and ion‐milled to create 3 to 1000 μm wide rectangles, 1 cm long, with the hard axis oriented along the long axis of the rectangles. The high‐frequency permeability of each array of a given width is measured by the signal detected by a nonresonant butterfly‐coil pickup loop when the film is driven by a uniform radio‐frequency magnetic field generated by a strip‐line waveguide. The changes in domain pattern as the film structure an...

Magnetic and structural characterization of sputtered FeN multilayer films

The magnetic and structural properties of ferromagnetic FeN thin films, FeN/FeN (ferromagnetic/paramagnetic), and FeN/SiO2 multilayers deposited in a rotational dc magnetron sputter system were investigated. Monolithic films containing ≂2 at. % N2 had 4πMs values ≂25 kG. The Fe16N2 phase has been identified by electron microdiffraction in these films. Saturation magnetostriction (λs) has been related to N2 content and can be varied from −3×10−6 to 5×10−6 in a range of compositions where 4πMs is ≳22 kG. Lamination reduced easy and hard axis coercivity to <1 Oe and produced single domain configurations in yoke‐shaped structures. Lorentz microscopy indicated that the ferromagnetic FeN layers in the FeN/FeN films were exchanged coupled while those in the FeN/SiO2 films were magnetostatically coupled.

Structure and orientation of films prepared by reactive sputtering of Ni, Fe, and NiFe in Ar/N2 mixtures

Using controlled N2/Ar sputtering gas mixtures, rf‐sputtered films were prepared from Fe, Ni, and Ni81Fe19 targets, and their structure and orientation were studied by x‐ray diffraction. When no N2 was introduced during sputtering, all the films were oriented in the highest density planes; i.e., in (110), (111), and (111) for α‐Fe, Ni, and γ‐Ni81Fe19, respectively. With increasing N2 introduction, however, the orientation shifted to lower density planes, and eventually nitrides were formed. Multilayer films of metal and nitride were prepared with the Ni81Fe19 target by repetitive supply of N2 for short periods during sputtering. Strong orientation effects were observed depending on the number of layers grown. In addition, the x‐ray diffraction of these films presented evidence of epitaxial growth of the nitrides (Ni,Fe)4N on the alloy layers.

Interference resonances in the permeability of laminated magnetic thin films

In high‐frequency magnetic structures (like thin‐film magnetic heads) which have been laminated to avoid eddy current loss, it is standard to assume that electromagnetic coupling across the dielectric separating the magnetic layers is small. We show that for macroscopic films with insulating interlayers, the laminated structure is better modeled by an anisotropic effective medium with a magnetic permeability of around 3000 but an insulating dielectric function perpendicular to the lamination plane, while still metallic parallel to the lamination plane. Electromagnetic waves can propagate parallel to the lamination direction but with 1/100 of the free‐space wavelength. The electromagnetic (capacitive) coupling between the layers can lead to radically altered propagation of magnetic flux and generate novel permeance resonances caused by interference effects across the width of the film. A Fourier series solution constructed with a mean‐field theory for the wave equation for laminated slab geometries predict...

Bloch line influence on wall motion response in thin‐film heads

We describe a new dynamic response behavior of domain walls in the permalloy of thin‐film inductive heads. A laser magneto‐optic microscope (LAMOM) which enhances the longitudinal Kerr effect, is used to image Bloch lines (BLs) within the 180° walls by aligning the optical plane of incidence perpendicular to these walls. BLs are visible due to the reversal in the Neel‐type surface components of the wall magnetization at the BL position. Current pulses with fast transition times and ac currents within the frequency range of 1–10 MHz are applied to the integrated coil windings. Continuous excitation induces either a continuous flowing of the wall network or a temporary displacement. When individual pulses are applied, displacements of BLs are observed. Correlation of wall displacements with the BL displacements is demonstrated for some pulsed excitations.

The high field, high frequency permeability of narrow, thin-film magnetic stripes

The authors report measurements of the magnetic response of arrays of narrow Permalloy stripes using a high field permeameter. The permeameter operates in a swept frequency mode from 300 KHz to 30 MHz with a field amplitude of up to 5 Oe. Using this device, two modes of flux conduction, rotation and wall motion, can be observed in narrow Permalloy stripes. The low field-amplitude permeability of narrow unlaminated Permalloy stripes is frequency independent except for eddy current losses as expected for magnetization rotation. At higher fields the magnetic response increases at frequencies below 10 MHz with increasing drive amplitude as domain wall motion becomes significant. Results are consistent with the expected domain wall mobility (around 2*10/sup 3/ cm/(s-Oe) for 2- mu m-thick films). Because of the high density of wall in microscopic structures, wall motion is the dominant flux conduction mechanism below 30 MHz at high drive fields. >

Signal to noise ratio of thin film disks with various orientation ratios

Thin-film disks with various orientation ratios (OR) ranging from 0.5 to 4.3 were fabricated by sputter deposition of CoPtCr with Cr underlayers onto preheated NiP/Al-Mg disks. The recording characteristics of these disks were investigated using a thin-film head. The isolated pulse signal amplitude-to-media noise ratio (So/N) increased when OR was increased from 0.5 to 1 and then remained relatively constant for OR>or=1. An improvement of about 10 dB in overwrite of the disks with OR>1 was observed. >

Magnetics and microstructure of sputtered Ni/sub 80/Fe/sub 20//SiO/sub 2/ multilayer films

Multilayered Ni/sub 80/Fe/sub 20//SiO/sub 2/ films have been produced by sputter deposition. The effects of lamination on the bulk magnetic properties, microstructure, and high-frequency permeability of stacks with various Ni/sub 80/Fe/sub 20/ and SiO/sub 2/ thicknesses were investigated. In general, laminated films with a total magnetic thickness of 1.5 mu m had significantly lower H/sub c/ and extended frequency response, compared to unlaminated films of the same magnetic thickness. In addition, the impact of lamination on domain configuration of yoke-shaped structures was determined, and excellent agreement with micromagnetic theoretical prediction was obtained. >

Fe/Fe‐N multilayer films with low coercivity zero magnetostriction and high saturation magnetization

A method of fabricating of Fe/Fe‐N multilayer films in the form of alternating thin films of Fe separated by very thin interlayers of Fe‐N sputtered in the presence of nitrogen is described. It was found that the properties of these films depended on the thickness of Fe and Fe‐N layers and the bias voltage. There is a region where the composite films have coercivity less than 1 Oe, with zero or near‐zero magnetostriction. The normally high saturation magnetization of Fe with value of 20 kG was preserved.

High frequency characterization and recording performance of NiFe and laminated FeN heads

A simple high frequency characterization technique extended from DC disk erasure is presented to measure the write field degradation for frequencies up to 500 Mfc/s (250 MHz) on plated NiFe and sputtered laminated FeN heads. The results show that eddy currents appear to be the main cause for high frequency write field degradation. Overwrite recording measurements, which may be used to approximate the non-linear write effects, also indicate that FeN heads, despite low efficiency, may be adequate for writing up to 100 MHz on a disk with a coercivity of 2500 Oe. This disk is capable of supporting 5-10 Gb/in/sup 2/ densities.