J.D. Jarratt

Hysteresis reduction in NiFeCo/Cu multilayers exhibiting large low‐field giant magnetoresistance

Giant magnetoresistance (GMR) has been observed in Ni66Fe16Co18/Cu multilayered uniaxial magnetic thin films prepared by dc magnetron sputtering. Both easy and hard axis loops saturate at very low applied fields. The MR ratio reaches ∼80% of its saturation value in less than 30 Oe. A maximum MR ratio of ∼10% has been observed in the as‐deposited state in a structure containing only ten bilayers. Typical hysteresis values for magnetoresistance loops are ∼4 Oe in the as‐deposited state. A gradual decrease of this hysteresis has been observed with annealing. An increase in the saturation field is also observed with annealing. Short‐term annealing increases the magnitude of the magnetoresistance ratio; prolonged annealing causes a decrease. A field sensitivity of about 0.3% per Oe has been observed and dc magnetoresistance minor loops exhibit no measurable decrease in sensitivity.

High coercivity nanostructured networks

Films of Fe, Co, and Co35Fe65 alloy have been sputter deposited onto the surface of porous nanochannel alumina substrates producing nanostructured contiguous magnetic “networks.” Large room temperature coercivities have been measured which approximately scale with the bulk saturation magnetization of the material used. In the as-deposited state the largest coercivities (e.g., >1000 Oe for Co35Fe65) are observed in ∼15-nm-thick networks deposited on the smallest commercially available pore size substrates (those having an average pore diameter of ∼20 nm and a wall thickness of ∼15 nm). Preliminary studies of the effects of annealing indicate that coercivities can be substantially increased (by as much as ∼50%) with an appropriate post-deposition thermal treatment.

Structural evolution in sputtered Co90Fe10/Ag giant magnetoresistance multilayers

The thermal evolution of structure, giant magnetoresistance (GMR), and magnetic properties in two sequences of sputtered (Co90Fe10/Ag) multilayers is presented. Granular‐type and ‘‘discontinuous’’ GMR is observed depending on layer thickness.

Artificially controlled stress anisotropy and magnetic properties of FeTaN thin films

This article presents a new method of investigating internal stress effects on thin film magnetic properties, in this case magnetically soft FeTaN sputtered films. The FeTaN films were deposited on a series of oxidized silicon (111) substrates prestressed to different degrees. During sputtering all the deposition conditions were kept exactly the same for all the samples. However, anisotropic stresses with different amplitudes are systematically introduced into the films when the prestressed wafers were released. In this way, FeTaN films with compressive stress varying from 80 to 608 MPa are produced. We found that the saturation magnetostriction (λs), anisotropy field (Hk), initial permeability (μi) as well as easy axis orientation of FeTaN thin films are strongly affected by the induced stress anisotropy. A stress ratio concept is proposed as a measure of the degree of the stress anisotropy. Models for easy-hard axis switching induced by stress for magnetic films with positive magnetostriction are discussed.

Electrical resistivity in sputtered Co90Fe10/Ag GMR multilayers

An analysis of room temperature electrical transport properties in sputtered (Co90Fe10/Ag) giant magnetoresistive multilayers is presented. The Co90Fe10 and Ag thickness ranges are both well below bulk electron mean free paths. Layer thickness dependent resistivity is observed and compared to resistivity measurements of single layer Co90Fe10 and Ag films.

Hybrid NiFeCo‐Ag/Cu multilayers: Giant magnetoresistance, structure, and magnetic studies

Giant magnetoresistance (GMR), crystal structure, and magnetic properties have been investigated in sputtered Ni66Fe16Co18‐Ag/Cu hybrid granular multilayer thin films. High angle x‐ray diffraction (HXRD) was used to reveal the overall film structure and growth texture and low angle XRD was used to investigate the periodicity and flatness of the multilayer structures. Hysteresis loops for the as‐deposited Ag‐rich films show superparamagnetic behavior (and conventional granular GMR) which does not saturate in 14 kOe. Very NiFeCo‐rich films are magnetically soft and exhibit induced in‐plane uniaxial anisotropy.

Microstructure In Sputtered Co/sub 90/Fe/sub 10/ Ag GMR Multilayers

The microstructure of Co/sub 90/Fe/sub 10//Ag GMR multilayer films has been investigated using X-ray diffraction (XRD) and cross-sectional transmission electron microscopy (XTEM). Columnar grain growth with a (111) fiber texture is observed. A direct correlation is made between superlattice satellite peak signals from selected area electron diffraction (SAD) and XRD.

Microstructural Studies of Sputtered Co 90 Fe 10 /Ag GMR Multilayers

The microstructure of Co 90 Feio/Ag giant magnetoresistive multilayer films has been investigated using x-ray diffraction (XRD) and cross-sectional transmission electron microscopy. Columnar grains with a (111) fiber growth texture is observed. A comparison is made between the observed layering structure and earlier multilayer schematics based on the literature and magnetic and magnetoresistive measurements as a function of layer thickness. A direct correlation is made between superlattice satellite peak signals from selected area electron diffraction patterns and XRD scans.