Thickness Of Magnetic Dead Layer Research Articles

Enhancement of magnetization and optical properties of CuFe2O4/ZnFe2O4 core/shell nanostructure

In this work, core/shell of CuFe2O4/ZnFe2O4 nanostructure composite was prepared by hydrothermal method. X-ray diffraction (XRD) analysis, transmission electron microscope imaging, energy dispersive X-ray (EDX), and Fourier transform infrared techniques were used to prove the phase formation, morphology, elemental analysis, and cation distribution of core/shell structure, respectively. Furthermore, measurement of the optical properties proved the decrease of photoluminescence (PL) efficiency. The magnetic measurements showed an enhancement of the magnetization by about 63% relative to pure Cu ferrite, and the magnetization curve exhibited superparamagnetic behavior. These results were explained in terms of the depression of the magnetic dead layer thickness in the core/shell structure. The results unleash the promising applications of the prepared samples as transformer cores in the high frequency range and as a photocatalytic agent for water purification and hydrogen production.

Magnetic properties of Pt/Co/Pt trilayers with W insert layer

The results of magnetic investigations of epitaxial trilayers Pt/Co/Pt asymmetrically modified by inserting W layer at the bottom or top Co interfaces in the wide ranges of Co and W layer thicknesses are reported. The samples were epitaxially grown on Pt buffer in double wedge geometry: the dCo thickness gradient of the continuous Co wedge was orthogonal to the dW thickness gradient of non-magnetic W underlayer (overlayer) deposited either as step-like or continuous wedge. Resulting samples have Pt/W/Co/Pt (Pt/Co/W/Pt) stacking sequences. The influence of (dCo, dW) on static magnetization reversal processes were studied using magnetooptical Kerr effect; Brillouin light scattering (BLS) method was applied for dynamical characterization. The magnetic dead layer thickness d0 abruptly increases until dW reaches ∼ 0.5 nm for both orderings. Then its value saturates for Pt/Co/W/Pt, while for Pt/W/Co/Pt samples a slow growth is observed. For dCo corresponding to out-of-plane magnetization the inserting of W layer leads to the strong reduction in coercivity (two orders of magnitude) and transition to in-plane magnetization in the case of Pt/W/Co/Pt ordering, while the Pt/Co/W/Pt samples demonstrates weak changes of coercivity with small change in magnetic anisotropy. The strength of interfacial Dzyaloshinskii-Moriya interaction (iDMI) and spin wave damping for selected dCo thicknesses as a function of dW were derived from BLS measurements. Inserting W with thickness dW ∼ 0.1 nm induces significant iDMI changes, iDMI saturates for dW > 0.4 nm. Our findings demonstrate the efficiency of thin W interlayer on modification of magnetic parameters in Pt/Co/Pt trilayer.

Thickness dependence of magnetic properties of Ir/FeV-based systems

Ir-buffered ${\mathrm{Fe}}_{0.7}{\mathrm{V}}_{0.3}$ (FeV) thin films of variable thickness ($1.4\phantom{\rule{0.28em}{0ex}}\mathrm{nm}\ensuremath{\le}{t}_{\mathrm{FeV}}\ensuremath{\le}10\phantom{\rule{0.28em}{0ex}}\mathrm{nm}$) were sputtered on thermally oxidized Si substrate and capped with Cu or MgO films. Vibrating sample magnetometery measurements allowed deducing their magnetization at saturation and the magnetic dead layer thickness, found to be capping layer independent. Microstrip line ferromagnetic resonance measurements under in-plane and perpendicular to the film plane applied magnetic fields are employed to investigate the perpendicular magnetic anisotropy (PMA) and damping. PMA is found to result from a uniaxial interfacial contribution which is slightly capping layer dependent. In contrast, the second-order PMA constant, which could result from the inhomogeneous distribution and the spatial fluctuations at the nanoscale of the uniaxial PMA at interface, is significantly stronger for Ir/FeV/Cu films. The damping dependence on the inverse of FeV effective thickness revealed a low Gilbert damping constant for FeV $({\ensuremath{\alpha}}_{\mathrm{FeV}}=1.7\ifmmode\times\else\texttimes\fi{}{10}^{\ensuremath{-}3})$ and allowed concluding that damping enhancement is mainly induced by Ir/FeV. The zero frequency linewidth for in-plane configuration is attributed to two magnon scattering contribution, found to be higher for Cu capped FeV. The investigation of the FeV thickness dependence of interfacial Dzyaloshinskii-Moriya interaction (iDMI) of both systems via Brillouin light scattering allowed to conclude to the zero iDMI constant of FeV/Cu. It also led to deduce iDMI constants of Ir/FeV and FeV/MgO, estimated to be ${D}_{\mathrm{s}}^{\mathrm{Ir}/\mathrm{FeV}}=(0.13\ifmmode\pm\else\textpm\fi{}0.02)\phantom{\rule{0.28em}{0ex}}\mathrm{pJ}/\mathrm{m}$ et ${D}_{s}^{\mathrm{FeV}/\mathrm{MgO}}=(\ensuremath{-}0.07\ifmmode\pm\else\textpm\fi{}0.02)\phantom{\rule{0.28em}{0ex}}\mathrm{pJ}/\mathrm{m}$, respectively.

Design and fabrication of Co2FeSi/Pt multilayers with perpendicular magnetic anisotropy

A series of multilayers consisting of Co2FeSi (CFS) and Pt are sputtered. Perpendicular magnetic anisotropy (PMA) is demonstrated in the CFS/Pt multilayers with CFS thickness in the range of 0.4 ∼ 1.0 nm. The individual thicknesses of Pt spacer and Co2FeSi layer as well as interface numbers are shown to strongly affect PMA. Two-step switching is observed in the multilayers with 8 nm Pt spacer, showing typically decoupled feature. The effective perpendicular anisotropy energy is determined to be in the order of 106 erg/cm3. The interfacial perpendicular anisotropy energy density is estimated to be 0.32 erg/cm2. The magnetic reversal with multi-domain feature is observed with increasing interface number. Sufficiently large saturation magnetization is derived from the multilayers with various repetitions. The thickness of magnetic dead layer is found to increase with the number of interface, which may be ascribed to more interdiffusion occurring at the multi-interfaces. Our results provide some useful information for the design and development of spintronic devices based on CFS/Pt multilayers.

Annealing Temperature and Thickness Dependencies of Perpendicular Magnetic Anisotropy and Dzyaloshinskii– Moriya Interaction of Pt/Co/MgO Thin Films

Effects of the ferromagnetic layer thickness and annealing temperature were studied in Pt-/Co-/MgO-based systems grown on thermally oxidized Si substrates using magnetron sputtering system. The Co thicknesses were varied in the range of 1–6 nm and the samples were annealed <italic xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">ex situ</i> at 200 °C, 300 °C, and 400 °C. Vibrating sample magnetometry was used to determine the magnetization at saturation and the magnetic dead layer thickness that were found to be insignificantly affected by the annealing. Brillouin light scattering, in Damon–Eshbach configuration, was used to measure the thermally excited spin wave (SW) frequencies versus the in-plane applied magnetic field and the SW vector which were used to investigate the perpendicular magnetic anisotropy (PMA) and interfacial Dzyaloshinskii–Moriya interaction (iDMI), respectively. The Co effective thickness dependence of the effective magnetization ( <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$M_{\mathrm {eff}}$ </tex-math></inline-formula> ), which provides information on the PMA constants, shows the existence of two linear regimes with different slopes due to misfit strain-induced magnetoelastic anisotropy contributions to volume and surface terms. The volume magnetocrystalline anisotropy constant increases monotonously with annealing temperature, whereas the pure surface (Néel type) constant increases with annealing up to 300 °C and degrades at 400 °C. The surface iDMI constant decreases with increasing annealing temperature and no obvious correlation with interface PMA constant has been found, suggesting different interfaces contribution to PMA and iDMI.

Size Effect of Fe3O4 Nanoparticles on Magnetism and Dispersion Stability of Magnetic Nanofluid

It is well known that magnetic nanofluids are widely applied in various fields ranging from heat transfer to miniature cooling, and from damping to sealing, due to the mobility and magnetism under magnetic field. Herein, the PFPE-oil based magnetic nanofluids with superior magnetization and dispersion stability were obtained via regulating reaction temperature. The structures of particles were characterized by X-ray diffraction (XRD) and transmission electron microscopy (TEM). The size effects of particles on the magnetism and coating effect of particles, and on the stability and saturation magnetization of the fluids were characterized by Fourier transform infrared spectroscopy (FTIR), thermogravimetric analysis (TGA), vibrating sample magnetometer (VSM) and density instrument, respectively. The results indicate that the impurity phase FeOOH only appear in the sample prepared at 18°C and the average size of Fe3O4 nanoparticles reduces from 120 to 20 nm with raising reaction temperature. The saturation magnetization of Fe3O4 particles increases firstly and then reduces with increasing particle size, which is affected by the thickness of magnetic dead layer and impurity phase FeOOH. The Fe3O4 particles could be chemically coated by PFPE-acids, and the coated mass is a little affected by particle size. The stability of the nanofluids lowers while the saturation magnetization increases firstly and then decrease with increasing particle size. At reaction temperature of 60°C, Fe3O4 particles of 25 nm and the nanofluids with superior stability and saturation magnetization were obtained. Our results indicate that the control of nanoparticles size by regulating reaction temperature can be a useful strategy for preparing magnetic nanofluids with desirable properties for various potential applications.

Hf thickness dependence of perpendicular magnetic anisotropy, damping and interfacial Dzyaloshinskii-Moriya interaction in Pt/CoFe/Hf/HfO2

Vibrating sample magnetometery (VSM) combined with Brillouin light scattering (BLS) were used to investigate the Dzyaloshinskii-Moriya interaction (iDMI), the perpendicular magnetic anisotropy (PMA) and the damping in ${\mathrm{Co}}_{0.5}{\mathrm{Fe}}_{0.5}$-based systems grown by sputtering on $\mathrm{Si}/{\mathrm{SiO}}_{2}$ substrates, using Pt or Cu buffer layers and Hf capping layer of variable thickness $(0\ensuremath{\le}{t}_{\mathrm{Hf}}\ensuremath{\le}2\phantom{\rule{0.28em}{0ex}}\mathrm{nm})$. VSM measurements revealed a significant decrease of the areal magnetic moment at saturation as ${t}_{\mathrm{Hf}}$ increases, most likely due to the increase of the magnetic dead layer thickness at CoFe/Hf interface up to $0.73\ifmmode\pm\else\textpm\fi{}0.06\phantom{\rule{0.28em}{0ex}}\mathrm{nm}$ for ${t}_{\mathrm{Hf}}=2\phantom{\rule{0.28em}{0ex}}\mathrm{nm}$. Damping measurements allowed concluding to the weaker spin pumping contribution by the CoFe/Hf interface compared to Pt/CoFe. The analysis of the ${t}_{\mathrm{Hf}}$ dependence of damping within a model considering the contribution of each interface allowed us to determine the spin diffusion length of Hf, found to be 1.7 nm. The Hf thickness dependence of iDMI and PMA constants revealed significant (weak) contribution of the CoFe/Hf interface to PMA (iDMI). The surface iDMI constant of CoFe/Hf interface was estimated to be $(\ensuremath{-}0.37\ifmmode\pm\else\textpm\fi{}0.12)\ifmmode\times\else\texttimes\fi{}{10}^{--7}\phantom{\rule{0.28em}{0ex}}\mathrm{erg}/\mathrm{cm}$. This suggests that the iDMI sign of Hf and Pt are opposite, and an additive behavior can be obtained when they are placed in opposite sides of the CoFe layer, allowing thus to strengthen the iDMI, needed for some applications. Quadratic correlations between PMA and iDMI constants and linear dependence of damping versus PMA constant were obtained confirming their relationship with the spin-orbit coupling.

Determination of ferrimagnetic and superparamagnetic components of magnetization and the effect of particle size on structural, magnetic and hyperfine properties of Mg0.5Zn0.5Fe2O4 nanoparticles

The fine-tuning of magnetic parameters and the identification of different magnetic phases are essential for the effective utilization of magnetic nanoparticles. In this work, we aim at controlling the magnetic parameters of Mg0.5Zn0.5Fe2O4 nanoparticles by varying the particle size and to determine magnetic phases using three analytical techniques having different operating time scales: VSM, ESR, and Mössbauer spectroscopy. Single-phase cubic spinel structured Mg0.5Zn0.5Fe2O4 nanoparticles were prepared by the sol-gel auto-combustion route and calcinated at 200, 300, 500, 700, and 900 °C. The cation distribution and structural parameters obtained from the Rietveld analysis had an insignificant variation with the calcination temperature. From the TEM analysis, an increase of the average particle size from 5 to 38 nm and widening of the particle size distribution with the calcination temperature were found. The saturation magnetization increased from 25.6 to 43.7 emu/g with the particle size due to the reduction in the magnetic dead layer thickness. The coercivity decreased from 128 to 31 Oe and the blocking temperature from 76 to 38 K with the particle size and these variations are explained in terms of surface anisotropy and dipolar interactions. Ferrimagnetic, superparamagnetic, and paramagnetic components of magnetization were deconvoluted by the curve fitting of room temperature VSM data. The ferrimagnetic component increased from 56% to 74% and the superparamagnetic component decreased from 37% to 20% respectively with the particle size. The ESR and Mössbauer spectroscopy also identified the ferrimagnetic and superparamagnetic components in the samples and their variations with the particle size were found to be in agreement with that of VSM. Thus, the variation of magnetic parameters in correlation with the particle size offers the possibility of fine-tuning the magnetic parameters of nanoparticles by adjusting the particle size. The deconvolution of magnetic phases using the three analytic methods revealed the coexistence of ferrimagnetic and superparamagnetic components of magnetization in Mg0.5Zn0.5Fe2O4 nanoparticles. Also, this deconvolution unveiled the particle size dependence on the emergence of inhomogeneity in magnetic phases of the samples.

Tailoring the magnetic properties of sputtered amorphous CoZrTa/metal-oxide (MO) by interfacial oxygen migration

Modulating the soft magnetic properties of amorphous magnetic thin films is important for constructing energy-efficient and high performance thin film inductors. Here, a metal (Pt) and an oxide (Al2O3) are selected as the covering layer to investigate the effect of the interfacial microstructure on the magnetic properties of CoZrTa thin films. The results show that the magnetic dead layer thickness (tDL) and coercivity (Hc) decrease and saturation magnetization (Ms) increases with the annealing temperature for the CoZrTa/Al2O3 sample. However, tDL, Hc, and Ms of the CoZrTa/Pt sample show an opposite variation tendency with the annealing temperature. Interfacial structural results indicate that different magnetisms can be ascribed to different interfacial oxygen migration and interfacial diffusion processes. The effective interfacial oxygen migration in CoZrTa/Al2O3 reconstructs oxygen atom distribution at the interface and provides an effective way to enhance the magnetic properties of CoZrTa, whereas the intensified interfacial diffusion between CoZrTa and Pt after annealing in the CoZrTa/Pt sample caused the deterioration of the magnetism. This study will be helpful in advancing the development of magnetic thin film inductor devices.

Perpendicular magnetic anisotropy and interfacial Dzyaloshinskii–Moriya interaction in as grown and annealed X/Co/Y ultrathin systems

The perpendicular magnetic anisotropy (PMA) and the interfacial Dzyaloshinskii–Moriya interaction (iDMI) are investigated in as grown and 300 °C annealed Co-based ultrathin systems. For this, Co films of various thicknesses (0.8 nm ⩽ tCo ⩽ 5.7 nm) were deposited by magnetron sputtering on thermally oxidized Si substrates using Pt, W, Ir, Ti, Ru and MgO buffer or/and capping layers. X-ray diffraction was used to investigate their structural properties and vibrating sample magnetometry (VSM) was used to determine the magnetic dead layer thickness and the magnetization at saturation (Ms). VSM revealed that the Ms for the Pt and the Ir buffered and capped films is the largest. Microstrip line ferromagnetic resonance (MS-FMR), used to extract the gyromagnetic ratio of the thicker Co films, revealed the existence of a second order PMA term, which is thickness dependent. Brillouin light scattering (BLS) in the Damon–Eshbach configuration was used to investigate the thickness dependence of the iDMI effective constant from the spin wave vector dependence of the frequency difference between Stokes and anti-Stokes lines. BLS and MS-FMR techniques were combined to measure the spin wave frequency variation as a function of the in-plane applied magnetic field (where the second order PMA contribution vanishes). The thickness dependence of the effective magnetization was then deduced and used to investigate PMA. For all the systems, PMA results from interface and volume contributions that we determined. The largest interface PMA constants were obtained for Pt- and Ir-based systems due to the electron hybridization of Co with these heavy metals having high spin orbit coupling. Annealing at 300 °C increases both the interface PMA and iDMI for the Pt/Co/MgO most probably due to de-mixing of interpenetrating oxygen atoms from the Co layer and the formation of a sharp Co/O interface.

Spin Pumping and Magnetic Anisotropy in La2/3Sr1/3MnO3/Pt Systems

La2/3Sr1/3MnO3 (LSMO) thin films of various thicknesses (6, 8, 10, 20, and 30 nm), capped by 7 nm‐thick Pt layer, are grown by pulsed laser deposition on SrTiO3 (001) substrates. X‐ray diffraction revealed that LSMO films are (001) oriented. Vibrating sample magnetometer is used to determine the magnetization at saturation and the magnetic dead layer thickness. This latter is around 3.4 nm, significantly thicker compared with the one induced at interfaces of Pt with ferromagnetic transition metals. Microstrip line ferromagnetic resonance (MS‐FMR) is used to extract the gyromagnetic ratio, which is found to increase with LSMO thickness. MS‐FMR revealed that the in‐plane magnetic anisotropy is dominated by a uniaxial contribution for the Pt capped film, whereas the noncapped 10 nm‐thick LSMO layer shows a fourfold anisotropy. Furthermore, the thickness dependence of the effective magnetization reveals the existence of a second‐order perpendicular anisotropy term, which is thickness‐dependent, and of a weak uniaxial interface anisotropy. The Gilbert damping coefficient is found to vary linearly with the inverse of the effective LSMO thickness due to spin pumping leading to relatively low spin mixing conductance of LSMO/Pt interface.

Composition dependence of the second-order interfacial magnetic anisotropy for MgO/CoFeB/Ta films

The CoFeB thickness, t dependence of the effective first- and second-order magnetic anisotropy, K1eff and K2, for MgO/(Co1-xFex)80B20/Ta films (x=0.3-1.0) is investigated. As Co40Fe40B20 thickness decreases, K1eff increases and shows a perpendicular magnetic anisotropy for t=1.2 nm. On the other hand, in-plane magnetic anisotropy is observed for t≥1.4 nm. Also, a 1.3-nm-thick CoFeB sample demonstrates an easy-cone behavior, which suggests that the magnitude of K1eff and K2 becomes comparable. By plotting the product of K2 and t-td as a function of t-td, where td is a magnetic dead layer thickness, linear dependences with negative y-axis intercepts are displayed for all ranges of x. The extracted interfacial K2, Ki(2) are varied depending on the compositions in the range of-0.024 to −0.042 erg/cm2 for x=100% and 30, 50%, respectively. A magnetic phase diagram summarizing the results of K1-2πMs2 and K2 suggests that the ratio of K2 against K1-2πMs2 is varied depending on the compositions. These results give us a guideline to achieve the desired magnetic properties of CoFeB for spintronic applications.

Magnetic Anisotropy and Damping Constant in CoFeB/Ir and CoFeB/Ru Systems

Co20Fe60B20 thin films of various thicknesses (3 nm $\le t_{\text {CFB}} \le 14$ nm) have been sputtered on thermally oxidized Si substrates and capped with 8 nm-thick Ir or Ru layers and then annealed at 400 °C. A vibrating sample magnetometer has been used to measure the CoFeB thickness dependence of the saturation magnetic moment per unit area in order to straightforwardly determine the magnetization at saturation and the magnetic dead layer thickness, found to be 1115 ± 50 emu/cm3 (930 ± 50 emu/cm3) and 1.53 nm (0.76 nm) for the as-deposited CoFeB/Ir (CoFeB/Ru) sytems, respectively. These values change to 1185 ± 50 emu/cm3 (1110±50 emu/cm3) and 2.93 nm (1.62 nm) for CoFeB/Ir (CoFeB/Ru) films annealed at 400 °C. Microstrip ferromagnetic resonance (MS-FMR) was used to investigate the Gilbert damping parameter and the magnetic anisotropy as a function of the CoFeB thickness. While the in-plane anisotropy field for the as-deposited films does not show a regular behavior versus the CoFeB thickness, a clear linear behavior of this field versus the reciprocal CoFeB effective thickness can be observed for the annealed samples. Moreover, the effective magnetization varies linearly with the inverse effective thickness of CoFeB due to the perpendicular interface anisotropy. This surface anisotropy constant, which was estimated to be 0.84 and 0.89 erg/cm2 for the as-deposited CoFeB films capped with Ir or Ru, respectively, reinforces the perpendicular easy axis. The corresponding anisotropy constants for the annealed Ir and Ru capped films are found to be 1.07 and 0.57 erg/cm2, respectively. Moreover, MS-FMR results revealed that the damping constant increases linearly with the reciprocal effective thickness of CoFeB, most probably due to spin pumping. The effective spin mixing conductance of the as-deposited (annealed) CoFeB/Ru and CoFeB/Ir has been estimated to be 12.93 nm−2 (22.4 nm−2) and 29.3 nm−2 (43.85 nm−2), respectively.

Influence of nano-dimensionality on magnetotransport, magnetic and electrical properties of Nd1-xSrxMnO3-δ (0.3 ≤ x ≤ 0.7)

Magneto-electric and electronic properties of Nd1-xSrxMnO3-δ (0.3 ≤ x ≤ 0.7) (NSMO) nanoparticles are investigated. NSMO nanoparticles are synthesized by glycine assisted auto combustion method. The structural and morphological properties are probed using X-ray Diffraction (XRD) and Field Emission Scanning Electron Microscopy (FESEM). NSMO crystallizes in orthorhombic structure and nearly spherical agglomerated morphology is observed. Resistivity of the order of few MOhm-cm is recorded for all the compositions and the transport mechanism is interpreted by using Mott variable range hopping (VRH) model. In absence of magnetic field all samples show insulating nature over the studied temperature region (300- 5 K), while Metal to Insulator transition is observed in the presence of magnetic field (8T). Large Colossal Magnetoresistance (CMR) is noticed below 50 K for NSMO.Observed Curie temperature is in the range of 102–115 K and it is found to be independent of Strontium doping concentration. Bifurcation in FC-ZFC, for all the samples, is at higher temperature than blocking temperature (∼72 K) indicates glassy state. We have calculated thickness of magnetic dead layer by two different ways and it lies between 1.6 and 2.9 nm. Concentration of divalent element and oxygen non-stoichiometry affects the relative fraction of Mn3+/Mn4+ ions. Mn3+/Mn4+ in our samples is determined from areas under the deconvoluted X-Ray Photoelectron Spectra (XPS) of Mn core level. The Mn3+/Mn4+ ratio is higher than the value expected from nominal composition, which indicates oxygen non-stoichiometry. Oxygen non-stoichiometry is also confirmed by chemical titration method.

Annealing temperature dependence of magnetic properties of CoFeB/MgO stacks on different buffer layers

We investigate the annealing temperature dependence of the magnetic properties of CoFeB/MgO stacks with different buffer materials (Mo, Ta, and W). For Mo and W, bcc-crystalline and amorphous-like films are prepared by changing the deposition conditions. A relatively small saturation magnetization is maintained after annealing up to 400 °C for the samples with bcc-W, bcc-Mo, and amorphous-like Mo buffers. A small variation in magnetic dead layer thickness with annealing is observed for the samples with bcc-crystalline buffer layers. The interfacial anisotropy is found to mainly depend on the element of the buffer layer used regardless of its crystalline structure, and is larger for the samples with W and Mo buffers than those with Ta buffer. The sample with bcc-Mo buffer shows the highest robustness against annealing among the studied systems. We give a systematic picture based on the thermochemistry that can reasonably explain the observed buffer layer dependence of the variations in magnetic properties with annealing.

Influence of the magnetic dead layer thickness of Mg-Zn ferrites nanoparticle on their magnetic properties

Nanoparticle ferrite with chemical formula Mg(1−x)ZnxFe2O4 (where x=0.0, 0.2, 0.4, 0.6, 0.8 and 1) were prepared by sol-gel technique. Single phase structure of these ferrites was confirmed using X-ray diffraction (XRD). Transmission Electron Microscope (TEM) showed that the particle size of the samples in the range of (5.7–10.6nm). The hysteresis studies showed superparamagnetic behaviour at room temperature. The magnetization behaviour with Zn-content is expressed in the light of Yafet-Kittel angles. The dead layer thickness (t) was calculated and its effect on the magnetization and magnetic losses was debated. The Specific Absorption Rate (SAR) in an alternating magnetic field with frequency 198kHz for these ferrites has been studied. It is found that, the thickness of magnetic dead layer of the surface of the materials has greatly affected the SAR value of the samples.

Buffer influence on magnetic dead layer, critical current, and thermal stability in magnetic tunnel junctions with perpendicular magnetic anisotropy

We present a detailed study of Ta/Ru-based buffers and their influence on features crucial from the point of view of applications of Magnetic Tunnel Junctions (MTJs) such as critical switching current and thermal stability. We study buffer/FeCoB/MgO/Ta/Ru and buffer/MgO/FeCoB/Ta/Ru layers, investigating the crystallographic texture, the roughness of the buffers, the magnetic domain pattern, the magnetic dead layer thickness, and the perpendicular magnetic anisotropy fields for each sample. Additionally, we examine the effect of the current induced magnetization switching for complete nanopillar MTJs with lateral dimensions of 270 × 180 nm. Buffer Ta 5/Ru 10/Ta 3 (thicknesses in nm), which has the thickest dead layer, exhibits a much larger thermal stability factor (63 compared to 32.5) while featuring a slightly lower critical current density value (1.25 MA/cm2 compared to 1.5 MA/cm2) than the buffer with the thinnest dead layer Ta 5/Ru 20/Ta 5. We can account for these results by considering the difference in damping which compensates for the difference in the switching barrier heights.

Large enhancement of magnetoresistance in NiFe film with MgO layers sandwiched after annealing

A large enhancement of magnetoresistance (MR) up to 6.0% has been observed in NiFe sandwiched by MgO layers, which is 50% larger than the highest MR (4%) in bulk materials. The great improvement of MR derives from the slight increase in corresponding resistivity change Δρ and the great decrease in resistivity ρ. The enhancement of Δρ is attributed to the strengthened spin-dependent scattering of the interfacial conductive electrons but the contribution will be slight with the increase in NiFe thickness. The main contribution is from the significant decrease in ρ, originating from confinement effect on electrons from well-formed oxide/metal interfaces after annealing. Surprisingly, this effect still exists when the NiFe thickness reaches 100nm. Meanwhile, the oxide (MgO) layers inserted prevents the atomic interdiffusion of Ta and NiFe at the interfaces, which decreases the thickness of magnetic dead layer.

Magnetic properties of ultrathin Ni81Fe19 films with Ta and Ru capping layers

Magnetic properties of Ni81Fe19 (permalloy) ultrathin films with Ru and Ta capping layers (CLs) were investigated for applications to magnetic random access memory units (MRAM). The sample structure, which simulated an MRAM free layer, is Si- sub./SiO2/Ni81Fe19/Ru(Ta). The Ni81Fe19 thin films less than 3 nm thick with Ru CL show low coercive fields compared with the Ta capping layer. Both systems showed loss of momentum equivalent to magnetically dead layers of thickness (δ) ∼0.6 nm for Ru cap layer and ∼1.4 nm for Ta cap layer, respectively. Moreover, after annealing the thicknesses are slightly increased to an equivalent magnetic dead layer thickness of δ ∼ 0.84 nm and ∼1.80 nm for Ru and Ta CL, respectively. Our calculations showed that the presence of only 11% Ta concentration at the interface reduced the Ni momentum to zero, with the Ni–Ta coupling being anti-ferromagnetic; while 50% Ru intermixing at the interface reduced the Ni momentum to zero with the coupling between Ru and Ni being ferromagnetic. To find out more about the intermixing at the interface, the composition and chemical states were characterized by the x-ray photoelectron spectroscopy and peak decomposition technique. The result showed that the peak positions were different from the pure metallic case at the interface region, mainly because of the intermixing between two layers. In conclusion, the Ru capping layer might be important for MRAM use in terms of low coercive field and small δ layer thickness if compared with the Ta capping layer.

Thickness Effect on Spin Moment in Amorphous Co&lt;sub&gt;0.9&lt;/sub&gt;Fe&lt;sub&gt;0.1&lt;/sub&gt; Films

Utilizing X-ray magnetic circular dichroism spectra the thickness effect on spin moment is examined in amorphous Co0.9Fe0.1films fabricated by RF magnetron sputtering. As film thickness increases from 5nm to 50nm, the variations of spin moments for Fe is a gradual decrease from 1.87μB to 1.70μB, while for Co it increases from 1.41μB to 1.69μB monotonously. Based on magnetic dead layer (MDL) model, the above changes are well explained, and the thickness of MDL, 0.83 nm, is estimated as well. That is not changed with increasing CoFe layer thickness.