FeCo Layer Thickness Research Articles

Influence of the Substrate on the Exchange Coupling of NiO/FeCo Bilayers

Antiferromagnetic/ferromagnetic (AF/F) systems have been extensively investigated due to the importance that interfacial exchange coupling effects have in the development of magnetic storage technologies. Recently, these systems have garnered interest for the potential they have to imprint the magnetic moments of the AF into an F layer, offering the possibility of using it as a read-out mechanism in antiferromagnetic spintronics. In this study, we explored the importance of crystalline orientation and strains induced by the substrate in the exchange coupling properties of NiO/FeCo AF/F bilayers. For that, we have grown NiO/FeCo bilayers on MgO (001) and Al2O3 (0001) substrates varying the FeCo layer thickness. In addition, we have analyzed both deposited samples and those with induced interfacial unidirectional anisotropy. For inducing such interfacial anisotropy, we used a field cooling procedure, heating the bilayers to 650 K and subsequently cooling down to room temperature under the presence of an external magnetic field of 300 mT. We have investigated the effect of the substrate in terms of crystalline orientation and lattice mismatching on the AF/F exchange coupling as well as the dependence of the coercivity and exchange bias on the inverse F layer thickness that is consistent with the interfacial origin of the AF/F exchange coupling. Moreover, the angular dependence of the magnetic properties was explored by using vectorial Kerr magnetometry, confirming the presence of both magnetocrystalline anisotropy, arising from the epitaxial character of the growing process mainly when the bilayer is grown on MgO (001) substrates, and the field cooling (FC)-induced unidirectional anisotropy.

Influence of FeCo layer thickness on the interfacial asymmetry of FeCo/Si multilayers fabricated by direct current magnetron sputtering.

FeCo/Si is a promising material combination for polarized neutron supermirrors because of its appropriate optical constants. Five FeCo/Si multilayers with monotonically increasing FeCo layer thicknesses were fabricated. Grazing incidence x-ray reflectometry and high-resolution transmission electron microscopy were performed to characterize the interdiffusion and asymmetry of the interfaces. Selected area electron diffraction was used to determine the crystalline states of FeCo layers. It was found that the asymmetric interface diffusion layers existed in FeCo/Si multilayers. Furthermore, the FeCo layer started the transition from amorphous to crystalline when the thickness of the FeCo layer reached 4.0nm.

In-situ investigation of exchange bias property in FePt (L10)/FeCo bilayer with increasing FeCo thickness

Magnetization reversal of soft ferromagnetic (FM) FeCo layer coupled to hard FM FePt (L10) layer in FePt (L10)/FeCo) bilayer has been studied in-situ with increasing thickness of FeCo layer. During FePt(L10) phase formation, an in-plane magnetic saturation field (HMAX) is applied to keep the hard FePt(L10) layer in its remanent state. Magneto-optical Kerr effect measurements reveal the absence of hysteresis loops initially up to 4.8 nm thickness of FeCo layer while loops with significant shift, i.e. exchange bias (EB) opposite to the HMAX direction, were observed on further deposition. The EB is found to decrease with the increasing thickness of the FeCo layer. It is due to the combined effect of both magnetostatic coupling and interfacial exchange interaction, where the contribution of magnetostatic interaction to EB is almost constant, and interfacial exchange coupling exhibits an inverse relation. Furthermore, different nucleation mechanisms during magnetization reversal in the descending and ascending branches of hysteresis loops lead to asymmetry in magnetization reversal at the lower thickness of the FeCo layer. This asymmetry decreases with the decrease in the interfacial coupling as the thickness increases. Azimuthal angle dependence of exchange shift with respect to the direction of HMAX further revealed the unidirectional character of the EB.

Synthesis and characterization of magnetically exchange coupled Zr2Co11/MgO/FeCo thin films with MgO as diffusion barrier

Zr2Co11 thin films were deposited by sputtering. MgO thin film was deposited on the top of Zr2Co11, followed by FeCo thin film deposition and post-annealing, to have magnetic exchange coupling between Zr2Co11 and FeCo. MgO thin film worked as a diffusion barrier between Zr2Co11 and FeCo during post-annealing. The thickness of FeCo layer was controlled as 4, 8 and 12 nm, respectively. The results showed that when the FeCo thickness was 8 nm, the Zr2Co11/MgO/FeCo showed the optimum magnetic properties, with 58% increased of (BH)max over Zr2Co11, which could be attributed to the effective exchange coupling between Zr2Co11 and FeCo. The exchange coupling between Zr2Co11 and FeCo thin film was investigated by Henkel plots.

Magnetically exchange coupled MnBi/FeCo thin film composites with enhanced maximum energy products

MnBi/FeCo thin film composites are synthesized by magnetron sputtering, the physical and crystal structures are confirmed by SEM and XRD. The magnetic properties are characterized by VSM. When the FeCo layer thickness is 2 and 4nm, magnetic exchange coupling between MnBi and FeCo is demonstrated by enhanced maximum energy product in MnBi/FeCo thin films from the single hard phase of MnBi. When the FeCo thickness is further increased to 6nm, the exchange coupling between MnBi and FeCo is destroyed in MnBi/FeCo thin films. This research explored a possible way to increase the maximum energy product of MnBi thin films.

High-frequency magnetic properties of [FeCo/FeCo-SiO2]n multilayered films deposited on flexible substrate

A series of 120 nm [FeCo/FeCo-SiO2]n multilayer thin films with different FeCo layer thicknesses (T = 10–40 nm) and fixed FeCo-SiO2 layer thickness (20 nm) were deposited on flexible substrate (Mylar) by controlling the sputtering time under applied magnetic field. The magnetic properties of the multilayer thin films were investigated. The experimental results showed that the multilayer thin films had obvious in-plane uniaxial magnetic anisotropy, which can be adjusted in a broad range by changing the thickness of FeCo layer. In addition, good soft magnetic performance was obtained. The coercivity in the easy axis Hce of the multilayer films with the T = 10 nm, 20 nm, 30 nm, and 40 nm was 5 Oe, 25 Oe, 10 Oe, and 8 Oe, respectively. In frequency-dependent permeability spectra measurement, two resonance peaks of complex permeability spectrum were observed, especially for T = 20 nm, which can be attributed to the complicated magnetic structure of FeCo and FeCo-SiO2 layer. By introducing multilayers with different effect anisotropy field, one can broaden the absorption peak while maintaining the high permeability, which would open the way for their potential applications as wide-band microwave absorber.

The investigation of interface properties of FeCo/Bepp2 heterostructures

The interface has become an important issue in organic magnetic spin-valves. In this work, Si/FeCo/Ta, Si/FeCo/Bepp2/Ta, and Si/Bepp2/FeCo/Ta samples with the variation of the FeCo layer thickness were fabricated by direct-current magnetron sputtering for FeCo layers and the thermal evaporation method for Bepp2 layers. The interaction at the interfaces between the FeCo magnetic layer and Bepp2 organic layer was investigated by the traditional magnetic properties measurement and X-ray photoelectron spectroscopy with the Argon ion etching technique. The experimental results show that the interfacial reaction is strong when sputtering FeCo on Bepp2 layer due to the high energy of sputtered FeCo atoms in contrast with the weak interfacial reaction when evaporating Bepp2 on FeCo layer. Moreover, the capping layer of Ta is quite important to protect FeCo layer against oxidation from air either by direct contact or through Bepp2 layer. Our experiment is very helpful for fabricating organic spin-valves with high-spin injection efficiency.

Nanostructure and hard magnetic properties of exchange coupled Nd-Fe-B/FeCo multilayer films

The nanocomposite Nd-Fe-B/FeCo mutilayer films have been prepared by rf sputtering. XRD results and HRTEM observation showed that as-deposited films deposited at substrate temperature of 300K were amorphous. The columnar grains of Nd2Fe14B phase with the c-axis perpendicular to the film plane developed after annealing at 923 K for 15 min. Nd2Fe14B grain size was about 10 nm in average and Nd-O particles of about 7 nm were dispersed within the grains and along the grain boundaries. The magnetization of these samples is found to increase with increasing FeCo layer thickness (tFeCo) and the coercivity decreases with increasing tFeCo. The multilayer films of maximum energy product is 200 kJ/m3 for tFeCo=5 nm at room temperature. The enhancement of the remanence and energy product in nanocomposite films is attributed to the exchange coupling between the magnetically hard and soft phases.

Exchange coupling and remanence enhancement in nanocomposite Nd–Fe–B/FeCo multilayer films

Nd–Fe–B-type hard phase single layer films and nanocomposite Nd 28Fe 66B 6/Fe 50Co 50 multilayer films with Mo underlayers and overlayers have been fabricated on Si substrates by rf sputtering. The hysteresis loops of all films indicated simple single loops for fixed Nd–Fe–B layer thickness (10 nm) and different FeCo layer thickness ( d FeCo=1–50 nm). The remanence of these films is found to increase with increasing d FeCo and the coercivity decrease with increasing d FeCo. It is shown that high remanence is achieved in the nanocomposite multilayer films consisting of the hard magnetic Nd–Fe–B-type phase and soft magnetic phase FeCo with 20 nm⩾ d FeCo⩾3 nm. The sample of maximum energy product is 27 MG Oe for d FeCo=5 nm at room temperature. The enhancement of the remanence and energy products in nanocomposite multilayer films is attributed to the exchange coupling between the magnetically soft and hard phases.

Perpendicular magnetic anisotropy in nanocomposite Nd?Fe?B/FeCo bilayer films

Abstract Nd–Fe–B/FeCo bilayer films with Mo underlayers and overlayers have been investigated. All the samples have perpendicular anisotropy and the magnetization is found to increase with increasing FeCo layer thickness ( d FeCo ) and the coercivity decreases with increasing d FeCo . The maximum energy-product is 20 MGOe for d FeCo = 5 nm. The enhancement of the remanence and energy products in the bilayer films is attributed to the exchange coupling between the magnetically soft and hard phases.

Preparation and magnetic properties of nanocomposite Nd28Fe66B6 /Fe50Co50 bilayer films

The nanocomposite Nd28Fe66B6/Fe50Co50 bilayer films with Mo underlayer and overlayer have been fabricated on Si substrates. All the samples prepared have perpendicular anisotropy and th e hysteresis loops are simple single loops for fixed Nd-Fe-B layer thickness (10 nm) and different FeCo layer thickness (dFeCo =1—100nm). The shape a nd the behavior of the initial loops and the minor loops suggest that wall pinni ng is the dominant coercivity mechanism in these films. The magnetization of the se samples is found to increase with increasing FeCo layer thickness for a fixed Nd-Fe-B layer thickness and the coercivity of films decrease with increasing Fe Co layer thickness. The sample of maximum energy product is 160×１０３A/m for dFeCo =5nm at room temperature. The enhancement of the rema nence and energy products in nanocomposite bilayer films is attributed to the ex change coupling between the magnetically soft and hard phases.

Combinatorial fabrication of magnetic multilayer films

Magnetic multilayer thin films are promising for applications in micro-sensor and high-frequency devices. To accelerate the materials development, nanoscale Fe 50Co 50/Co 80B 20 multilayers were fabricated in combinatorial deposition experiments: magnetron sputtering and photolithographic lift-off was used to generate discrete libraries of multilayers on 6 in. Si wafers such that the thickness of the constituent layers varied continuously across one direction of the wafer, remaining about constant in the perpendicular direction, i.e. wedge type films were fabricated. This was realized by moving the substrate from one side into and out of the sputtering plasma using a turntable and fixed shutters. Wedge type films composed of layers of one material were deposited to investigate their thickness distribution. Multilayers were fabricated by depositing thin wedge layers from two targets such that the increasing thickness of one material matched the decreasing thickness of the other. Film thickness, chemical composition, crystallinity, as well as static and dynamic magnetic properties were measured, partly automated. The multilayer properties across the wafer varied as intended, e.g. individual layer thickness from about 0.3–1.6 nm, saturation magnetization μ 0 M S from 1 to 1.8 T, coercive field μ 0 H C from 0.024 to 0.25 mT, anisotropy field μ 0 H K from 2 to 12 mT, and ferromagnetic resonance frequency f R from 2 to 4.7 GHz. Furthermore, non-linear dependencies of H C, H K and f R on the FeCo layer thickness were found.

The structure of FeCo/Ag multilayers

Abstract Field emission gun transmission electron microscopy and electron spectroscopy imaging have been used to determine the structure of the interface between FeCo and Ag, the local crystallographic texture and the distribution of the Ag in magnetostrictive Fe50Co50/Ag multilayers. These are correlated with the coercivity and magnetostriction of the multilayers, for FeCo layer thickness in the range 3.5—17.5 nm with constant Ag thickness of 2.2 nm. A significant texture exists in the films with preferential {110}FeCo and {111}Ag parallel to the growth direction. Where the local orientation of the film coincides with the texture, partial coherency exists between {110}FeCo and {111}Ag. Electron spectroscopy imaging indicates that the Ag layer is not continuous and provides a rough interface between the FeCo and Ag. The manner in which the microstructure determines magnetic properties is discussed.

The structure of FeCo/Ag multilayers

Abstract Field emission gun transmission electron microscopy and electron spectroscopy imaging have been used to determine the structure of the interface between FeCo and Ag, the local crystallographic texture and the distribution of the Ag in magnetostrictive Fe50Co50/Ag multilayers. These are correlated with the coercivity and magnetostriction of the multilayers, for FeCo layer thickness in the range 3.5—17.5 nm with constant Ag thickness of 2.2 nm. A significant texture exists in the films with preferential {110}FeCo and {111}Ag parallel to the growth direction. Where the local orientation of the film coincides with the texture, partial coherency exists between {110}FeCo and {111}Ag. Electron spectroscopy imaging indicates that the Ag layer is not continuous and provides a rough interface between the FeCo and Ag. The manner in which the microstructure determines magnetic properties is discussed.

Magnetic properties of nanostructured CoSm/FeCo films.

${\mathrm{Co}}_{80}$${\mathrm{Sm}}_{20}$/${\mathrm{Fe}}_{65}$${\mathrm{Co}}_{35}$ bilayer and multilayer films with Cr underlayers and overlayers have been fabricated and studied. All the samples prepared have in-plane anisotropy and the hysteresis loops were simple single loops for ${\mathit{t}}_{\mathrm{FeCo}}$\ensuremath{\le}300 \AA{} indicating that the two phases are strongly exchange coupled. The magnetization of these samples is found to increase with increasing FeCo layer thickness for a fixed CoSm layer thickness. The coercivity, anisotropy constant, and anisotropy field for films with fixed CoSm layer thickness were found to decrease with increasing FeCo layer thickness. The magnetization squareness values of the hysteresis loops in the direction parallel to the film plane, for different CoSm and FeCo layer thicknesses, were found to be close to S\ensuremath{\approxeq}0.75. The energy products for these samples vary from about 6 MG Oe at room temperature to 26 MG Oe at 30 K. The shape and the behavior of the initial loops and the minor loops suggest that wall pinning is the dominant coercivity mechanism in these films. Reversible demagnetization curves were measured and found to be consistent with the behavior expected for ``exchange-spring'' magnets.