Ferromagnetic Resonance Linewidth Research Articles

Magnetic NiFe thin films composing MoS2 nanostructures for spintronic application

We demonstrate a nanostructure layer made of Ni80Fe20 (permalloy:Py) thin film conjugated MoS2 nano-flakes. Layers are made based on a single-step co-deposition of Py and MoS2 from a single solution where ionic Ni and Fe and MoS2 flakes co-exist. Synthesized thin films with MoS2 flakes show increasing coercivity and enhancement in magneto-optical Kerr effect. Ferromagnetic resonance linewidth as well as the damping parameter increaseed significantly compared to that of the Py layer due to the presence of MoS2. Raman spectroscopy and elemental mapping is used to show the quality of MoS2 within the Py thin film. Our synthesis method promises new opportunities for electrochemical production of functional spintronic-based devices.

Effect of site disorder on the resonant microwave absorption in Co2Fe0.5Ti0.5Si Heusler alloy thin films

100 nm Co2Fe0.5Ti0.5Si (CFTS) thin films were grown on Si (100) substrate at different substrate temperatures TS to study the effect of site disorder on the magnetization relaxation processes and magnetic anisotropy in them. To this end, two different ferromagnetic resonance (FMR) techniques have been employed: broad-band (3 – 17 GHz) FMR at a fixed static magnetic field angle in the ‘in-plane’ (IP) sample geometry, and X-band (9.45 GHz) FMR at different polar field-angles, θH, in the ‘out-of-plane’ (OP) sample configuration. Increase in TS reduces the degree of disorder and improves crystalline order. Improvement in crystallinity, in turn, results in the decrease in the strength of magnetocrystalline anisotropy. Irrespective of the degree of disorder present, the OP anisotropy field, Hk⊥, is an order of magnitude higher than the IP counterpart, Hk‖. Out of the CFTS thin films studied, the film (TS500), deposited at TS = 500 °C, has the maximum L21 crystalline order, maximum saturation magnetization (MS = 779 G), and the least values for Hk‖ (5.3 Oe), Hk⊥ (17 Oe), Landé splitting factor, g = 2.02, and the Gilbert damping constant, α=5.5×10-3. These optimum values of MS, g and α, at room temperature, are conducive for spintronics applications. In the OP configuration, the FMR linewidth, ΔH⊥, mainly arises from the intrinsic Landau-Lifshitz-Gilbert damping and extrinsic angular spread of crystallite misorientation. However, the extrinsic two-magnon scattering contribution to ΔH⊥, is appreciable only in the angular range 70° ≤ θH ≤ 110° .

Annealing enhanced ferromagnetic resonance of thickness-dependent FeGa films

We report the influence of different annealing temperatures on the magnetic property of FeGa thin films. The measurement was done for the film thickness from 42 to 420 nm. Our results show that the annealing temperature affects not only the microstructure but also the ferromagnetic resonance signal of the film. Annealing of a FeGa film improves the in-plane remanence ratio and reduces the in-plane ferromagnetic resonance linewidth by a factor of five. This annealing treatment promotes film texture and releases compressive stresses in the film. Our results demonstrate that the structural control via annealing is viable. The necessary magnetic softness of the FeGa film for microwave applications can be achieved.

Room-temperature intrinsic and extrinsic damping in polycrystalline Fe thin films

We examine room-temperature magnetic relaxation in polycrystalline Fe films. Out-of-plane ferromagnetic resonance (FMR) measurements reveal Gilbert damping parameters of $\approx$ 0.0024 for Fe films with thicknesses of 4-25 nm, regardless of their microstructural properties. The remarkable invariance with film microstructure strongly suggests that intrinsic Gilbert damping in polycrystalline metals at room temperature is a local property of nanoscale crystal grains, with limited impact from grain boundaries and film roughness. By contrast, the in-plane FMR linewidths of the Fe films exhibit distinct nonlinear frequency dependences, indicating the presence of strong extrinsic damping. To fit our in-plane FMR data, we have used a grain-to-grain two-magnon scattering model with two types of correlation functions aimed at describing the spatial distribution of inhomogeneities in the film. However, neither of the two correlation functions is able to reproduce the experimental data quantitatively with physically reasonable parameters. Our findings advance the fundamental understanding of intrinsic Gilbert damping in structurally disordered films, while demonstrating the need for a deeper examination of how microstructural disorder governs extrinsic damping.

Submicron pre-sintering grain size effects on the microstructure and magnetic properties of hot-press sintered barium hexaferrite thick films

Grain size plays an important role in affecting the physical properties of ceramics. In this work, the effects of pre-sintering grain size G0 of BaFe12O19(BaM) on the microstructure and magnetic properties of hot-press sintered BaM thick films were studied. Results show that reducing G0 in submicron scale leads to notable decreases in grain growth activation energy and final sintered grain size. Smaller G0 makes BaM grains easier to be aligned by magnetic field before sintering and less magnetic domain walls in the sintered film. This increases the c-axis orientation, out-of-plane remanence ratio SQ (>0.9) and coercivity of sintered film. Moreover, the zero-field ferromagnetic resonance linewidth ΔH decreases 54% as G0 reduces from 1 μm to 0.3 μm. This is attributed to the increased film uniformity with larger SQ and film density Drel at smaller G0. The above findings enable better understanding on the role of G0 in improving the magnetic properties of hot-press sintered BaM and other hexaferrite thick films for self-biased microwave devices.

Suppressing Magnetic Damping Related to Two-Magnon Scattering in Ultrathin NiFe Films by Interface Engineering

Designing the ferromagnetic/nonmagnetic (FM/NM) heterostructure with desirable low magnetic damping is important for spintronic devices to reduce the critical current density of magnetization switching. For ultrathin FM/NM films, magnetic damping from the two-magnon scattering (TMS) effect is a critical component, and suppressing TMS damping becomes one of the crucial ways to achieve low damping. In this paper, we have demonstrated the depressed linewidth in Ta (1 nm)/NiFe (3 nm)/NM (4 nm)/Ta (1.5 nm) heterostructure with Cu instead of Pt as the NM layer, where the maximal linewidth of ferromagnetic resonance (FMR) decreases from 440 to 190 Oe. And the decrease of TMS damping from 55 to 0 Oe is one of the main reasons for the lower FMR linewidth. The nonzero surface magnetic anisotropy implies that the suppression of interfacial defect scattering causes reduced TMS damping. Meanwhile, a noticeable enhancement of TMS damping from the lack of seed layer may be due to the lattice structure change. Thereby, our findings provide a way toward the design of low-damping spintronic devices.

A sintering strategy for lithium zinc ferrite with a high saturation magnetization and low ferromagnetic resonance line-width

Based on the activation energy and diffusion kinetics theory of grain growth, Li0.42Zn0.28Ti0.1Fe2.2O4 ceramics with a low ferromagnetic resonance line-width (ΔH) and high saturation magnetization (Ms) were synthesized by adopting LTCC (low-temperature cofired ceramics) technology. The critical sintering temperature of ferrite synthesis was reduced to 925 °C due to activation energy reduction and the liquid phase sintering mechanism of Bi2O3. The sintering agent B2O3 further improved the grain size, homogeneity, density and properties. EDS and XRD refinement showed that Bi3+ and B3+ ions did not enter lattices, but Ti4+ ions entered lattices and replaced part of the Fe3+ ions, leading to the lattice expansion. Finally, homogeneous and compact Li0.42Zn0.28Ti0.1Fe2.2O4 ferrite with Ms up to 354.6 kA/m and ΔH as low as 184.2 Oe was synthesized at temperatures as low as 925 °C by adding an appropriate content of Bi2O3 and B2O3. In the present study, the exploration and practice of reducing the sintering temperature and improving the material properties based on sintering agents is a beneficial supplement and improvement to the wider application of the LTCC technique.

Emerging magnetodielectric materials for 5G communications: 18H hexaferrites

With the rapid development of 5G technologies, it is crucial to seek magnetodielectric materials with high permeability and permittivity, low magnetic and dielectric losses, and high cutoff frequency over the sub-6 GHz frequency bands. Due to limited resonant frequency and large natural resonance linewidth, conventional microwave ferrites and their composites do not meet these requirements. Here, the microwave properties and their temperature dependence of a unique type of hexaferrites, Mg-Zn 18H hexaferrite (Ba5Mg2−xZnxTi3Fe12O31), are reported. Polycrystalline Mg-Zn 18H hexaferrite exhibited an extremely low damping coefficients (α = 0.1-0.2), remarkably low magnetic loss (tan δm = 0.06), excellent thermal stability of the damping coefficient (Δα/ΔT = 0.0004 K−1), and a narrow ferromagnetic resonance (FMR) linewidth (ΔH = 486–660 Oe). Moreover, Mg-Zn 18H hexaferrite possessed significant enhancement in the figure of merit (FOM = μ'Qf) compared to conventional microwave ferrites and their composites. When employed as the substrate of a 3.6-GHz patch antenna, Mg-Zn 18H hexaferrite demonstrated significant advantages for miniaturization (∼5 ×) and bandwidth improvement (∼50–110%) over conventional dielectric substrates. These results represent the best magnetic performance among the microwave ferrites reported at the S band and reveal the great technological value and commercial potential for 5G communications.

Improved coercivity of W- and M-type composite hexaferrites using two different synthesis routes

Two series of W- and M-type composite hexaferrites were synthetized using the conventional ceramic method in two different synthesis routes. In the first synthesis route, W- and M-type composite hexaferrites were formed by reaction in the pre-sintering stage. In the second synthesis route, W- and M-type composite hexaferrites were obtained by physically mixing W- and M-type hexaferrites in the second ball milling stage. The influence of M-type phase on the structure and magnetic properties of W-type hexaferrites synthesized in both synthesis routes are investigated in detail. For both synthesis routes, X-ray diffraction (XRD) patterns of all samples indicated crystallization of W- and M-type hexaferrites phase and scanning electron microscopy (SEM) measurements revealed hexagonal platelet-like grains. In the pre-sintering stage, the saturation magnetization (4πMs) of all samples ranged between 3.30 kG and 4.25 kG. The remanence ratio (Mr/Ms) changed from 0.77 to 0.88 with the increase of pre-sintering temperature. The coercivity (Hc) of all samples ranged between 456 Oe and 1846 Oe. The ferromagnetic resonance (FMR) linewidth (ΔH) ranged between 466 Oe and 748 Oe. In the second ball milling stage, 4πMs and Mr/Ms maintained a relatively stable value of ~4.5 kG and ~0.89, respectively. Hc increased from 519 Oe to 620 Oe with the increase of M-type hexaferrites. ΔH ranged between 317 Oe and 573 Oe. We note that in both synthesis routes only the composite hexaferrites synthesized in the pre-sintering stage have a significantly improved coercivity from 456 Oe to 1846 Oe. This enhancement in coercivity is attributed mainly to the effect of exchange coupling among ferrite grains. In addition, the ΔH decreases with the addition of M-type hexaferrites.

Thickness-dependent magnetic properties in Pt/[Co/Ni] n multilayers with perpendicular magnetic anisotropy

We systematically investigated the Ni and Co thickness-dependent perpendicular magnetic anisotropy (PMA) coefficient, magnetic domain structures, and magnetization dynamics of Pt(5 nm)/[Co(t Co)/Ni(t Ni)]5/Pt(1 nm) multilayers by combining the four standard magnetic characterization techniques. The magnetic-related hysteresis loops obtained from the field-dependent magnetization M and anomalous Hall resistivity (AHR) ρxy showed that the two serial multilayers with t Co = 0.2 nm and 0.3 nm have the optimum PMA coefficient K U as well as the highest coercivity H C at the Ni thickness t Ni = 0.6 nm. Additionally, the magnetic domain structures obtained by magneto-optic Kerr effect (MOKE) microscopy also significantly depend on the thickness and K U of the films. Furthermore, the thickness-dependent linewidth of ferromagnetic resonance is inversely proportional to K U and H C, indicating that inhomogeneous magnetic properties dominate the linewidth. However, the intrinsic Gilbert damping constant determined by a linear fitting of the frequency-dependent linewidth does not depend on the Ni thickness and K U. Our results could help promote the PMA [Co/Ni] multilayer applications in various spintronic and spin-orbitronic devices.

Effect of Bi2O3 contents on magnetic and electromagnetic properties of LiZnMn ferrite ceramics

Soft LiZnMn ferrites with low coercive force values and small grain sizes were developed by the solution combustion synthesis and low temperature sintering technique for microwave applications at a high frequencies. Bismuth oxide was used as an additive to lower the sintering temperature. The examination covered the influence of Bi2O3 on the crystal structure, microstructure, primary magnetic and dielectric characteristics of lithium-zinc-manganese ferrites. The most promising sample designed for using in microwave devices was produced by sintering at 1075 ℃ temperature for 8 h with added 1.5 wt% Bi2O3. These production conditions have yielded 2.98 µm average grain size in a ceramic product, the density is 4.84 cu cm/g, and the coercive force, residual induction, and saturation induction are 58 A/m, 2078.4 G, and 3439.1 G, respectively. In addition, this sample demonstrates a high initial magnetic permeability (μi = 168), Curie temperature (Tc = 437.5 ℃), high values of the dielectric loss tangent (tan δɛ = 6.32⸱10−3), ferromagnetic resonance line width (ΔH = 280 Oe) and the resonance line of spin waves (ΔHk = 1.87 Oe). Further increase in the bismuth oxide content allows observing a change in the ceramics microstructure, accompanied by a deterioration in the magnetic and electromagnetic characteristics. Here, the discussion covers the mechanism of change in the functional properties of lithium-zinc-manganese ferrites produced in the conditions of solution combustion with added bismuth oxide. Thus, synthesizing of initial pre-ceramic powder by glycine-nitrate combustion and subsequent low-temperature sintering with added bismuth oxide is a novel efficient technique of producing advanced soft high-frequency LiZnMn ferrites.

Temperature dependence of the Gilbert damping of La0.7Sr0.3MnO3 thin films

Due to its half metallic nature, ${\mathrm{La}}_{0.7}{\mathrm{Sr}}_{0.3}{\mathrm{MnO}}_{3}$ is an attractive highly correlated electronic system to obtain ultralow magnetic damping. In this paper we analyze the temperature and thickness dependence of the damping of the magnetization dynamic of epitaxial thin ${\mathrm{La}}_{0.7}{\mathrm{Sr}}_{0.3}{\mathrm{MnO}}_{3}$ films. Our analysis reveals that the damping encompasses resistivelike and conductivelike contributions, as in transition metal ferromagnets. The data also show a large increase of the ferromagnetic resonance linewidth at low temperature, a feature that we ascribe to the presence of a dead layer, insulating and magnetically active, that behaves like a spin sink. The associated spin-pumping term shows a strong temperature dependence, linked to that of the spin mixing conductance. By clarifying some unexplored aspects of spin dynamics in half-metallic manganites, our results contribute to the progress in the burgeoning field of oxide spin orbitronics.

Role of the surface effects and interparticle magnetic interactions in the temperature evolution of magnetic resonance spectra of ferrihydrite nanoparticle ensembles

Ferrihydrite is characterized by the antiferromagnetic ordering and, in ferrihydrite nanoparticles, as in nanoparticles of any antiferromagnetic material, an uncompensated magnetic moment is formed. We report on the investigations of ferrihydrite powder systems with an average particle size of ∼ 2.5 nm obtained (i) as a product of the vital activity of bacteria (sample FH-bact) and (ii) by a chemical method (sample FH-chem). In the first approximation, these samples can be considered to be identical. However, in sample FH-chem, particles contact directly, while in sample FH-bact, they have organic shells; therefore, the interparticle magnetic interactions in these samples have different degrees. The main goal of this work has been to establish the effects of the interparticle magnetic interactions and individual characteristics of ferrihydrite nanoparticles on ferromagnetic resonance (FMR) spectra. The FMR spectra have been measured at different (9.4–75 GHz) frequencies in a wide temperature range. It has been found that, at low temperatures, the field-frequency dependence ν(HR) of the investigated systems has a gap ν/γ = HR + HA, where HR is the resonance field and HA is the induced anisotropy, which decreases with increasing temperature. To estimate a degree of the effect of interparticle interactions on the results obtained and to correctly determine the temperature range of the superparamagnetic (or blocked) state, the static magnetic measurement and Mössbauer spectroscopy data have been obtained and analyzed. It has been shown that the most striking feature of the FMR spectra - a gap in the field-frequency dependences - is a manifestation of individual characteristics of ferrihydrite nanoparticles. The induced anisotropy is caused by freezing of a subsystem of surface spins and its coupling with the particle core, which is observed in both samples at a temperature of ∼80 K. The temperature range (below 80 K) in which the gap exists corresponds to the blocked state in the FMR technique. In sample FH-bact, the ratio between the FMR parameters HA and linewidth ΔH obeys the standard expression HA ∼ (ΔH)3. In sample FH-chem, however, the interparticle magnetic interactions dramatically affect the behavior of parameters of the FMR spectra, which change nonmonotonically upon temperature variation. This fact is attributed to the collective freezing of the magnetic moments of particles under the conditions of sufficiently strong interactions, which follows from the temperature dependence of the particle magnetic moment relaxation time determined from the Mössbauer spectroscopy and static magnetometry data obtained in weak magnetic fields.

Influence of ferromagnetic layer thickness on the Gilbert damping and magnetocrystalline anisotropy in PLD grown epitaxial Co2FeSi Heusler alloy thin films

In the present work, full Heusler alloy (FHA) Co2FeSi (CFS) epitaxial thin films with thickness (tCFS) ranging from 5–25 nm were grown by Pulse laser deposition (PLD) on MgO (001) substrates at an optimized deposition temperature of 600°C. Dynamic magnetization response of PLD-grown CFS thin films was systematically investigated as a function of tCFS. Thickness-dependent structural and magnetic correlation exhibit a non-monotonic variation in Gilbert damping parameter, α. The ferromagnetic resonance (FMR) investigation revealed that the presence of lattice strain and a lower degree of atomic ordering in the thinner FHA CFS films, results in additional enhancement of α. The lowest α value of 4×10−3 is obtained from the theoretical fit of experimental data in a 20 nm thick film. This low value of α is suitable in magnonic devices, such as spin-transfer torque magnetic random-access memories (STT-MRAMs) where an efficient spin injecting source from a FHA ferromagnet to a non-magnetic interface is required. Further, in-plane angle-dependent (φ-variation) FMR measurements of the sample yield an intrinsic four-fold magnetocrystalline anisotropy (MCA) along with the presence of uniaxial anisotropy that has non-monotonicity with tCFS. A significant value of cubic anisotropy constant of 5.16×105erg/cm3 has been obtained in the film with a thickness of around 15nm. Further investigation suggests that uniaxial anisotropy in the CFS/MgO film is a combination of strain-induced magneto-elastic and interface-related contribution that is intrinsic in nature. The experimental observations have been verified by using micromagnetic simulations run on the epitaxial crystal structure. FMR mode position and linewidth of varied thickness CFS films are generated by micromagnetic simulations utilizing the Landau–Lifshitz–Gilbert formalism.

Nb5+ ion substitution assisted the magnetic and gyromagnetic properties of NiCuZn ferrite for high frequency LTCC devices

Nowadays, developing nickle zinc ferrites with excellent magnetic and gyromagnetic properties are of great importance for solving the matching problem of 5G communication system. However, much is discussed about soft magnetic properties, but little is reported gyromagnetic properties that is critical for microwave device applications. Herein, Nb5+ ions substituted Ni0.29Cu0.18Zn0.53NbxFe2-xO4 (x = 0.00-0.05), possessing high saturation magnetization, approriate initial permeability, high cut-off frequency and low ferromagnetic resonance linewidth (@9.55 GHz), were synthesized by low-temperature firing (900 °C). The phase structure and morphology evolutions were studied in detail. The results of morphology observations revealed that Nb5+ substitution has significant role in determining produce compact and uniform microstructures of NiCuZn ferrites via suppress the grain growth, which further corresponding enhance the magnetic and gyromagnetic properties. As a result, a uniform and compact grain size can be obtained, corresponding to the change of magnetic and gyromagenetic properties have different trends. Enhanced magnetic and gyromagnetic performance including high initial permeability (μ' = 203 @1 MHz), saturation magnetization (4πMs = 3966 Gauss) and low ferromagnetic resonance linewidth (ΔH = 203 Oe) of the NiCuZn ferrites is achieved though adjusting Nb5+ ions substitution. More importantly, this work not only for low temperature co-fired ceramic (LTCC) technology but also for high frequency and microwave frequency devices including phase shifter and radars.

Twofold and fourfold anisotropies in zinc ferrite thin films investigated by ferromagnetic resonance

By means of the ferromagnetic resonance (FMR) technique (at the $X$ band) we investigated the magnetic properties of ${\mathrm{ZnFe}}_{2}{\mathrm{O}}_{4}$ (ZFO) films grown on different substrates. Angular dependence of the FMR field showed the existence of twofold and fourfold anisotropies for the same material, grown on Si(111), MgO(100), and STO(100), respectively. By using a model that takes into consideration the relevant contributions to the energy, we were able to extract the following parameters: effective magnetization ${M}_{\mathrm{eff}}$, cubic magnetocrystalline anisotropy field, in-plane and out of plane uniaxial anisotropy fields, and the $g$ factor. The samples deposited on Si showed a twofold in-plane anisotropy while a fourfold magnetic anisotropy was observed for the ZFO/MgO and ZFO/${\mathrm{SrTiO}}_{3}$ samples. All samples showed a strong perpendicular uniaxial anisotropy above 1 kOe and low in-plane uniaxial and cubic anisotropy field, on the order of tens of oersteds. The FMR linewidth ($\mathrm{\ensuremath{\Delta}}H$) fitted from FMR data shows $\mathrm{\ensuremath{\Delta}}H$ values above 190 Oe for all samples, indicating high damping of this material to be $\ensuremath{\sim}{10}^{\ensuremath{-}2}$ for the ZFO/MgO. The present analysis compared the FMR data obtained for the in-plane and out of plane measurements. Likewise, the effective magnetization and perpendicular uniaxial anisotropy field by FMR were compared with the magnetic response obtained by a vibrating sample magnetometer.

Effects of V<sub>2</sub>O<sub>5</sub>-Al<sub>2</sub>O<sub>3</sub> sintering aid on properties of low temperature sintered Li-Zn microwave ferrites

With the progress of modern wireless communication technology, microwave communication devices are developing toward miniaturization and integration, and low temperature co-firing ceramic/ferrite technology is the key to meet the above demands. In this paper, V<sub>2</sub>O<sub>5</sub>-Al<sub>2</sub>O<sub>3</sub> (VA) sintering aid is used to realize low temperature sintering (below melting point of silver that is 950 ℃) of Li-Zn microwave ferrite, which is suitable for radar phase shifter. In this paper, firstly, Li-Zn ferrite pre-firing material is prepared by mechanochemical ball milling method, and then VA composite is selected as sintering aid to prepare Li<sub>0.42</sub>Zn<sub>0.27</sub>Ti<sub>0.11</sub>Mn<sub>0.1</sub>Fe<sub>2.1</sub>O<sub>4</sub> ferrite at low temperatures. The effects of adding amount of VA sintering aid and sintering temperature on crystal structure, microstructure and magnetic properties (saturation induction, coercivity, linewidth of ferromagnetic resonance, et al.) of the materials are also studied. The VA sintering aid can reduce the sintering temperature and maintain the spinel crystal structure of Li-Zn microwave ferrite, the diffraction peaks of V<sub>2</sub>O<sub>5</sub> and Al<sub>2</sub>O<sub>3</sub> involved in the sintering process are not observed for all the samples sintered at different temperatures, because the mass ratio of V<sub>2</sub>O<sub>5</sub> and Al<sub>2</sub>O<sub>3</sub> in VA sintering aid is very low compared with Li-Zn ferrite, so there are no corresponding impurity peaks. The introduction of VA sintering aid can promote the grain growth, with the average grain size increasing from 0.92 mm to 9.74 mm. In the sintering process of Li-Zn ferrite, V<sub>2</sub>O<sub>5</sub> in VA sintering aid will melt first to form liquid phase due to its low melting point, which promotes the growth of grains. At the same time, Al<sub>2</sub>O<sub>3</sub> with higher melting point can inhibit the grain growth and make the grain uniform. It is worth noting that when excessive VA sintering aid is added, the grain size of ferrite will decrease instead, because too much VA sintering aid will form a large number of liquid phases around the grains, thus splitting the grains and hindering the further growth of the Li-Zn grains. Under the condition of optimal VA sintering aid addition (0.18 <em>wt. </em>%), the saturation induction of the sample increased from 144 mT to 281 mT; The rectangular ratio increased from 0.57 to 0.78; The coercivity decreased from 705 A/m to 208 A/m; The linewidth of ferromagnetic resonance decreased from 648 Oe to 247 Oe. In summary, VA sintering aid can effectively improve the properties of Li-Zn microwave ferrite, which has a positive significance for the development of low temperature co-firing ceramic/ferrite technology.

Monocrystalline ferrogarnet films with low magnetizations and small magnetic losses

Monocrystalline ferro-garnet films of Y3Fe5-xGaxO12 (0,1 ≤ x ≤ 0,6) and Y3-yLayFe5-xGaxO12 (0,17 ≤ x ≤ 0,94; 0,033 ≤ y ≤ 0,161) were grown on gadolinium-gallium garnet (GGG) Gd3Ga5O12 substrates by the method of liquid phase epitaxy. The mixture of Fe2O3, Y2O3, Ga2O3, La2O3 oxides and PbO-B2O3 solvent to prepare the melt solution were used. The (111) orientation substrates of GGG single crystal were round with a diameter of 50,8 mm and a thickness of 0,5 mm. The mismatch between film and substrate crystal lattice parameters increases with increase of substitution degree × in Y3Fe5-xGaxO12 films which leads to mechanical stresses in film. Through the introduction of the large in size La3+ ions into the composition of Y3Fe5- xGaxO12 ferro-garnet films this shortcoming has been corrected. The thicknesses of Y3Fe5- xGaxO12 films did not exceed 5…8 μm and of Y3-yLayFe5-xGaxO12 films they were 20…70 μm. Concentration dependencies of saturation magnetization (4πMs), anisotropy field (Ha) and ferromagnetic resonance (FMR) line width (ΔH) for both film systems were studied. It was found that Y3-yLayFe5-xGaxO12 films in a wide range of × and y substitutions are characterized by low values of saturation magnetization (400 Gs ≤ 4πMs ≤ 1700 Gs), compared to Y3Fe5O12, and narrow FMR lines width (ΔH = 0,4…0,5 Oe).

Spin transport properties of Bi<sub><i>x</i></sub>Y<sub>3–<i>x</i></sub>Fe<sub>5</sub>O<sub>12 </sub>thin films prepared by spin coating

Yttrium iron garnet (YIG), as a room temperature ferrimagnetic insulator with low damping and narrow ferromagnetic resonance linewidth, has been the research hotspot in spintronics because of its spin transport properties. Bi is one of the most common doping elements used in YIG, and some researches have proved that it can tune the magnetic properties of YIG. Previous studies of Bi<sub><i>x</i></sub>Y<sub>3–<i>x</i></sub>Fe<sub>5</sub>O<sub>12</sub> thin films focused on the evolutions of their structures, morphologies, and magnetic characteristics. Yet, the effects of Bi<sup>3+</sup> substitution of Y<sup>3+</sup> on spin transport in YIG thin films have not been systematically studied. The regulation of YIG spin transport by doping is expected to provide a new idea for the spintronics exploration of Pt/YIG system. In this work, we prepare a series of Bi<sub><i>x</i></sub>Y<sub>3–<i>x</i></sub>Fe<sub>5</sub>O<sub>12</sub> films with different doping ratios by spin coating. And we investigate the effects of Bi<sup>3+</sup> on morphology, structure and spin transport properties of YIG films. The results show that Bi doping does not change the crystal structure of YIG. The absorption of the film increases and the bandgap decreases with the increase of doping ratio. The X-ray photoelectron spectroscopy (XPS) indicates the co-existence of Bi<sup>3+</sup> and Bi<sup>2+</sup>. The regulation of Bi doping on spin transport is reflected in the fact that the magnon diffusion length of Bi<i><sub>x</sub></i>Y<sub>3–<i>x</i></sub>Fe<sub>5</sub>O<sub>12</sub> films is significantly smaller than that of pure YIG films. Meanwhile, we find that the obvious spin Hall magnetoresistance can still be detected in the Pt/Bi<sub><i>x</i></sub>Y<sub>3–<i>x</i></sub>Fe<sub>5</sub>O<sub>12</sub> heterostructure, and the amplitude is the largest when <i>x</i> = 0.3.

Stress-induced controllable magnetic properties in flexible epitaxial Mn0.5Zn0.5Fe2O4 ferrite films

Flexible ferrite film has high potential applications in electronic skins and wearable devices. However, it is an enormous challenge to fabricate flexible ferrite film because of its high fragility. This work uses a novel etching sacrificial Sr3Al2O6 (SAO) layer to synthesize flexible Mn0.5Zn0.5Fe2O4 (MZFO) ferrite film. The MZFO film remains its single crystal structure after being transferred onto a flexible substrate. Owing to the great lattice mismatch between SAO and MZFO, the as-grown and transferred MZFO films exhibit the difference in magnetic properties, which is more sensitive along out-of-plane direction. The controllable magnetic properties of the film under the bending test are characterized by ferromagnetic resonance (FMR). A huge FMR field (Hr) shift of 704 Oe is achieved along out-of-plane direction when the bending radii are 5 mm. Meanwhile, the FMR linewidth (δH) of bent MZFO film (1267 Oe) is about 4 times higher than that of the unbent film (310 Oe). These controllable changes mainly come from the contribution of the two magnon scattering (TMS) effect. Finally, the Hr and δH almost return to their initial states when the stress is released, indicating a great recoverability.