Abstract
We have studied the structural and magnetic properties of enhanced-permeability-dielectric FeCo/Al2O3-multilayer thin films deposited on 8"-Si wafers in an industrial magnetron sputtering system. The EPD-multilayers consist of 25 periods of alternating nanometer-thick FeCo-layers deposited by DC sputtering from a Fe60Co40 target and Al2O3-interlayers deposited by RF sputtering from an Al2O3 target. We tuned the magnetic properties of these thin films by varying the thickness of FeCo-layers from 1.1nm to 2.1nm, while the thickness of Al2O3-interlayers remained unchanged (3.5nm). The formation of layers of disconnected FeCo-nanoparticles separated by an Al2O3-matrix was revealed by grazing incidence small angle X-ray-scattering. Further insight into the microstructure of these layers was obtained from X-ray-reflectivity, highly asymmetric-X-ray-diffraction and non-coplanar grazing-incidence-diffraction. The Fe/Co ratio in the FeCo-layers obtained from X-ray-fluorescence measurements was (59±1)/(41±1), which is in very good agreement with the nominal value in the Fe60Co40 target. Using the standing wave technique we found that most of the Fe and Co atoms were located inside the polycrystalline grains, except for a small fraction that diffused into the Al2O3-matrix, and that the thinner the FeCo-layers thickness the higher the fraction of diffused atoms with respect to those in the grains. Zero-field-cooled, field-cooled, and hysteresis (B-H) and (M-H) measurements showed that the FeCo/Al2O3-multilayers with FeCo-layers thinner than 1.7–1.8 nm exhibit superparamagnetic behavior (no coercivity and remanence) at room temperature with peak relative low-field permeability up to 887. By exceeding this critical thickness, the neighboring FeCo-aggregates started to coalesce, and this led to the ferromagnetic behavior revealed by a finite coercivity and remanence in the hysteresis loops.
Highlights
Nanoscale magnetic materials have received wide-spread interest in recent years due to their great potential for the development of new generation devices combining the advantages of semiconductor electronics with the spin-selective transport, e.g.magneto-resistive sensors, ultrahigh density memory cells and highfrequency programmable logic systems.1–3 In particular, discontinuous ferromagnetic-insulator multilayers consisting of separated layers of closely spaced ferromagnetic nanoparticles embedded in an insulating matrix have received special attention because the magnetic and transport properties of these structures can be accurately scitation.org/journal/adv tuned within a wide range by changing the thickness of the ferromagnetic layer.4–12Enhanced-permeability-dielectrics (EPD) are a particular class of discontinuous ferromagnetic-insulator multilayers13 where the magnetic nanoparticles are smaller than the superparamagnetic (SP) limit
We have studied the structural and magnetic properties of enhanced-permeability-dielectric FeCo/Al2O3-multilayer thin films deposited on 8"-Si wafers in an industrial magnetron sputtering system
By exceeding this critical thickness, the neighboring FeCo-aggregates started to coalesce, and this led to the ferromagnetic behavior revealed by a finite coercivity and remanence in the hysteresis loops
Summary
Discontinuous ferromagnetic-insulator multilayers consisting of separated layers of closely spaced ferromagnetic nanoparticles embedded in an insulating matrix have received special attention because the magnetic and transport properties of these structures can be accurately scitation.org/journal/adv tuned within a wide range by changing the thickness of the ferromagnetic layer.. Enhanced-permeability-dielectrics (EPD) are a particular class of discontinuous ferromagnetic-insulator multilayers where the magnetic nanoparticles are smaller than the superparamagnetic (SP) limit. These materials have been introduced to reduce the switching field in arrays of single-layer magnetoresistive-random-accessmemory (MRAM) bits and the nulling clock field in nanomagnetic logic (NML) systems by increasing the magnetic flux density in the EPD material surrounding these devices. Our objective is to fabricate EPD thin films with high magnetic permeability (μr ≫ 1), no hysteresis, and no remanence, while still retaining their insulating properties
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