High Ferromagnetic Resonance Frequency Research Articles

Effect of annealing temperature on crystallographic texture, magnetic and microwave properties of barium ferrite thin films

Due to it has large saturation magnetization (Ms), high magnetocrystalline anisotropy field and high ferromagnetic resonance (FMR) frequency, barium ferrite (BaM) has attracted more and more attentions in the fields of magnetic recording media, permanent magnets and microwave devices. Here, BaM thin films were deposited on Pt/TiO2/SiO2/Si substrates, and the effect of annealing temperature on the microstructure, magnetic and microwave properties of barium ferrite thin films was investigated in detail. It is found that when the BaM thin film was annealed at 1035 °C, it has good properties. The XRD data provide clear evidence that the BaM thin films have high c-axis orientation, and the Lotgering factor is as high as 0.96. The AFM morphology show that BaM grains are out of the film plane, and they are hexagonal. The magnetic hysteresis curves indicated that both saturated magnetization (4πMs), remanence ratio and coercive (Hc) for out of plane increase with increasing Ta first, then decreased, and get the maximum value at 1035 °C. The ferromagnetic resonance (FMR) measurement show that the FMR linewidth is 143 Oe@50 GHz, it means that this this sample has low microwave loss in millimeter wave loss, and the FMR absorption can be tuned by applied magnetic field. These results make sure that this BaM thin film is possible use in millimeter wave devices such as filers, circulators and isolators.

Extremely High Ferromagnetic Resonance Frequency Induced by Triclinic Lattice Distortion in Epitaxial FeCo/MgAl2O4 (001) Films

Theoretically, tetragonal lattice distortion of FeCo epitaxial films can result in a very large in‐plane magnetic anisotropy field, leading to an extremely high ferromagnetic resonance (FMR) frequency. Herein, thin films are epitaxially grown on (001) MgAl2O4 single‐crystal substrates. A triclinic lattice distortion with , instead of a tetragonal one, is found in the FeCo films. The cubic symmetry breaking leads to a deviation of easy axes from the directions, forming a distribution of magnetic moments with a strong perpendicular magnetic anisotropy (PMA) along the out‐of‐plane [001] directions and a deviation of the in‐plane components from the ([10 100]) directions. The effective field of the former is as high as 1.5–2.5 T, enough to overcome the thin film shape anisotropy, while that of the latter stays at a low value of around 0.05 T. The strain‐induced PMA gradually relaxes to in‐plane for thicker films with a strained sublayer remaining. As a result, an extremely high out‐of‐plane FMR frequency over 40 GHz is achieved, accompanied by a lower in‐plane FMR frequency around 8 GHz. This study provides a possible approach to prepare self‐biased soft magnetic films with extremely high‐resonance frequency for applications in microwave‐integrated circuits.

Development of high-efficient tri-layer microwave absorbers based on fabricated SrFe12O19 with polygonal, rod, and porous ball-like morphologies

Recently, widespread microwave applications have generated plenty of unwanted electromagnetic radiation, which has become a global environmental pollution problem. Therefore, finding an efficient microwave absorbing material (MAM) is a trendy topic, and strontium hexaferrite (SrFe12O19, SrM) is a promising candidate. However, its high ferromagnetic resonance frequency (fFMR) prevents SrM from becoming an excellent MAM for wide-frequency range applications. Herein, as-prepared SrM samples with the morphologies of polygonal shape (Sr-P), rod (Sr-R), and porous ball-like (Sr-PH) were successfully prepared. Differences in morphology were effective to the static magnetic and optical properties. Furthermore, the fFMR of SrM was modified to the X-band frequency range. In particular, Sr-PH samples could reach reflection loss (RL) values of –10 dB for 2.5 and 3 mm thicknesses. The microwave absorption of SrM as-prepared samples could be enhanced by making the tri-layer microwave absorbers from as-prepared samples. The simulated RL curves of the 2mm tri-layer-absorber with Sr-PH as the top layer, Sr-R as the middle layer, and Sr-P as the bottom layer (Sr-PH/Sr-R/Sr-P) could achieve a minimum RL of –12 dB and an effective absorption bandwidth (EAB) value of 2.95 GHz. The microwave absorption performance was significantly increased with an increase of 0.5 mm in the total thickness of the tri-layer absorbers. In detail, the Sr-PH-0.5/Sr-R-1.5/Sr-P-0.5 absorber achieved the best values of RL and EAB at –20 dB (illustrating 99% of the microwave incident wave being absorbed) and 4 GHz (covering 95% of the width of the X band frequency), respectively. The results indicated that the microwave absorption performance of SrM could improve by mixing up its different morphologies types.

Enhancement of high-frequency performances by Al2O3 interlayer in FeCoHf/Al2O3/FeCoHf trilayers

In this study, Hf-doped FeCo alloy films with a high ferromagnetic resonance (FMR) frequency at zero external fields were prepared by a composition gradient sputtering method. In order to further enhance the high-frequency performances, Al2O3 spacers of various thicknesses were inserted in the middle of the FeCoHf film. It is revealed that the Al2O3 interlayer improves the magnetic anisotropy of trilayers, enhances the resistivity, and refines the grain size. As a result, the FMR frequency of the trilayer was enhanced to over 3 GHz, and the permeability was also evidently improved from 41 (single layer) to 86 (trilayer with Al2O3 thickness of 40 Å).

Microstructure and magnetic properties of FeCoHfN thin films deposited by DC reactive sputtering

The microstructure and electro-magnetic properties of FeCoHfN thin films deposited by reactive sputtering under an in-situ magnetic field have been studied as a function of nitrogen partial pressure (R(N2)). As the (R(N2)) increases, the grain size of α-FeCo phase can be effectively reduced, and the structure of the films changes from an amorphous/nanocrystalline dual-phase structure with ultrafine α-FeCo magnetic nanoparticles isolated by a nonmagnetic insulating layer to a single amorphous structure. The structural transformation and the enrichment of HfN layer improve the resistivity and static and dynamic soft magnetic properties of the films. Higher resistivity is expected to reduce eddy current losses at high frequencies. The critical (R(N2)) when the film shows indications of excellent high-frequency magnetic properties is 8%. The deposited FeCoHfN thin films have high saturation magnetization of 14.9–16.2 kGs, great permeability of 222–322 at GHz, and high ferromagnetic resonance frequency up to 3.5 GHz, showing the promise of high-frequency applications.

Orientation control of optical mode ferromagnetic resonance: From uniaxial to omni-directional

Both high ferromagnetic resonance frequency (fr) and homogeneous angular performance are important for soft magnetic films to be used in high-frequency integrated circuit devices. However, high fr are obtainable only along the easy axis direction of the magnetic anisotropic materials. In uniaxially anisotropic FeCoB/Ru/FeCoB films, we could obtain an ultrahigh optical mode ferromagnetic resonance frequency (frO) up to 19.16 GHz along the easy axis under a self-bias field due to the enhancement from strong interlayer exchange coupling. However, the uniaxial intensity distribution of optical mode resonance seriously hinders the practical application in microwave components. In order to obtain the desired homogeneous angular performance, soft magnetic films with widely distributed magnetic anisotropy directions in the films were prepared and a nearly omni-directional frO with uniform values around 13.5 GHz was achieved. This study demonstrates that controlling the magnetic anisotropy's angular distribution is an effective way to obtain isotropic, self-bias magnetic films with ultrahigh fr.

Low Weight Hollow Microspheres of Iron with Thin Dielectric Coating: Synthesis and Microwave Permeability

Spray pyrolysis of an aqueous solution of iron nitrate, proceeded with reduction of the product in hydrogen, gave iron powder with micron-sized hollow particles. Coating these iron particles with SiO2 through tetraethyl orthosilicate hydrolysis prevented interparticle electrical contacts and suppressed DC percolation. This material shows a high ferromagnetic resonance frequency of 18 GHz, low permittivity, and weighs 20% less than common carbonyl iron. Potential microwave applications are for inductors and electromagnetic interference shielding designs.

Soft magnetic nanocomposite CoZrTaB–SiO2 thin films for high-frequency applications

With increasing switching frequencies for passive components in power supplies, there lies a demand for materials that exhibit excellent soft magnetic properties at high frequencies. Electrical resistivity is of particular importance, as a high value is of significant importance in suppressing eddy current loss. The present work is focused on improving material with ultra-soft magnetic properties at high working frequencies by making nanocomposite CoZrTaB–SiO2 thin films using co-sputtering. The films show an increasing trend of resistivity with SiO2 incorporation, attributed to the high degree of electron scattering based on a metal–insulator–metal network. The ultra-low coercivity (Hc ∼ 0.1 Oe) and enhanced anisotropic field (Hk ∼ 42 Oe) of films were correlated to the ferromagnetic exchange coupling, which were significantly affected by a small concentration of SiO2. Relatively high permeability, ultra-low loss response, and high ferromagnetic resonance frequency make this material a promising candidate for replacing conventional magnetic cores in passives, in addition to noise suppression applications.

Improvement of high-frequency properties of Co2FeSi Heusler films by ultrathin Ru underlayer**Project supported by the National Natural Science Foundation of China (Grant Nos. 11674187 and 51871127) and the Fund from the Technology on Electronic Test & Measurement Laboratory (Grant No. 6142001180103).

Heusler Co2FeSi films with a uniaxial magnetic anisotropy and high ferromagnetic resonance frequency fr were deposited by an oblique sputtering technique on Ru underlayers with various thicknesses tRu from 0 nm to 5 nm. It is revealed that the Ru underlayers reduce the grain size of Co2FeSi, dramatically enhance the magnetic anisotropy field HK induced by the internal stress from 242 Oe (1 Oe = 79.5775 A⋅m−1) to 582 Oe with an increment ratio of 2.4, while a low damping coefficient remains. The result of damping implies that the continuous interface between Ru and Co2FeSi induces a large in-plane anisotropic field without introducing additional external damping. As a result, excellent high-frequency soft magnetic properties with fr up to 6.69 GHz are achieved.

Higher ferromagnetic resonance frequency in NiFe/FeMn film obtained by flash annealing in reversing field

The unsaturated magnetization reversal by pulsed current annealing was investigated in exchange biased NiFe(15 nm)/FeMn(10 nm) bilayer. The magnetization reversal was conducted by energizing and thus heating the film under an external applied magnetic field ( $$H_{\text{a}}$$ ) with the direction opposite to the deposition field ( $$H_{\text{d}}$$ ). The static and dynamic magnetic properties of the films before and after rapid annealing were characterized using vibrating sample magnetometer, anisotropic magnetoresistance (AMR) and vector network analyzer measurements. When the samples were annealed at 40 and 45 V condenser voltages, greater values of rotational anisotropy $$(H_{\text{rot}} )$$ , ferromagnetic resonance frequency ( $$f_{\text{r}}$$ ) and smaller values of exchange bias field $$(H_{\text{e}} )$$ , exchange bias field in AMR measurement ( $$H_{\text{e}}^{\text{MR}}$$ ), and magnetoresistance in the samples were obtained, which is attributed to the unsaturated reversed magnetization in reversing magnetic field. A suggested model for which the scattered magnetization of magnetic moment results in additional unstable antiferromagnetic spins in the film was proposed to explain this interesting phenomenon.

Fabrication and magnetic properties of strip-patterned FeCoB-SiO2 nanoparticle films for GHz application

A series of high stacking density FeCoB-SiO2 nanoparticle films with strip structures were prepared by electric field-assisted deposition technique attached by thermal oxidization processing. We obtained the expected soft magnetic properties for strip-patterned FeCoB-SiO2 nanoparticle films. In this situation, relatively large permeability and high ferromagnetic resonance frequency are easily achieved in a wide gigahertz range. More importantly, the great GHz electromagnetic performance can be maintained in a wide SiO2 volume fraction range by carefully controlling the width of SiO2 strips. These results show that this kind of film materials have great potential for application in integrated devices operated in the gigahertz frequency range. Meanwhile, these single layer soft magnetic film materials with high permeability in the GHz range and high resistivity are easily merged into the micro manufacturing technology, such as CMOS and MEMS technique.

Optimized microwave magnetic characteristics for patterned FeNi nanoparticle films manufactured by electric field-assisted deposition

The high-density FeNi nanoparticle films with strip structures were prepared by electric field-assisted deposition technique. The electric field of 10–40kV was applied on the sputtering platform during thin film deposition in order to obtain superior in-plane soft magnetic properties. The dependence of magnetic properties and microwave behavior on electric field was investigated. It is found that these high-density films have magnetically easy-modulated characteristics, especially for the strip-patterned ones. Application of electric field is very effective to obtain stronger in-plane magnetic anisotropy field and higher saturation magnetization simultaneously for our samples. In this case, large permeability and high ferromagnetic resonance frequency are easily achieved when the strip-patterned films are used in a wide gigahertz range. The experimental results indicate that electric field-assisted deposition technique is one of the important and promising manufacture methods to prepare thin film materials with enhanced gigahertz electromagnetic wave properties.

Magnetic Nanoferrites for RF CMOS: Enabling 5G and Beyond

The upcoming 5th generation (5G) telecommunication technology will enable realization of the full potential of the Internet-of-things (IoT) by utilizing various frequency bands, ranging from <4 GHz to 100 GHz. A brief review of the technical requirements of RF CMOS at the unveiling of the 5G system is provided. Key challenges associated with 5G are illustrated, with a focus on the need for, and state of the art of, magnetic materials, especially ferrites, in enhancing the performance of RF integrated circuits. The suitability of a low-temperature, CMOS-compatible, on-chip ferrite thin film deposition technique, which was elusive until recently, is compared with traditional deposition processes for thin ferrite films. The uniqueness of this microwave-irradiation-assisted, far-from-equilibrium, solution-based deposition technique in achieving an unusually high ferromagnetic resonance frequency is discussed. The effect of magnetic ferrite films in niche applications such as in X-band (8~12 GHz) inductors and K-band (18~40 GHz) electromagnetic noise suppressors is discussed and demonstrated.

X-Ray Absorption Spectra and Self-Bias Ferromagnetic Resonance of FeCoB Films Prepared by Composition Gradient Sputtering

Microwave soft magnetic films (SMFs) are key materials, which can effectively miniaturize and multifunctionalize the electromagnetic components and devices, such as filters, phase shifters, thin film wireless inductors, magnetic recording write heads, antennas, etc.1, and reduce their occupation area in microwave monolithic integrated circuit (MMIC) boards. Modern electronic products are heading towards high density, high-frequency, frequency tunability, lightweight and low energy consumption, etc., which give rise to increasing demands for microwave SMFs. Microwave SMFs should have higher ferromagnetic resonance frequency (f FMR ), high permeability, and are to be fabricated in an IC compatible process. Metallic soft magnetic films exhibit special advantages in MMIC devices since they have higher 4πM S and permeability, and good compatibility with the IC fabrication process. Therefore, self-biased metallic SMFs prepared at IC compatible process have drawn an increasing attention2.

Self-Bias Ferromagnetic Resonance and Quasi-Magnetic Isotropy of (FeCoB/MgO)&lt;sub&gt;6&lt;/sub&gt; Multilayers Prepared by Composition Gradient Sputtering

Soft magnetic films (SMFs) are key materials for miniaturization and multifunctionality of radio frequency and microwave components and integrated circuits (ICs) due to the good high-frequency soft magnetic performances and the compatibility to IC processing technologies. Magnetic micro-inductors are one of widely used microwave IC components. The SMFs in magnetic micro-inductors should have a well-defined in-plane uniaxial magnetic anisotropy in order to reach a high ferromagnetic resonance frequency f FMR . On the other hand, a high permeability is only available when excitation magnetic field being along the magnetic hard-axis (HA) direction, i.e. HA excitation. However, the typical planar micro-inductors are round or square, the magnetic anisotorpy characterisitics of the SMFs above indicates that the efficiency of SMFs can only reach 50% in inductors. Although many attempts have been made to enhance the efficiency of SMFs in inductors,1 100% HA excitation is still difficult to be reached.

Adjustable ferromagnetic resonance frequency in CoO/CoFeB system

Static and dynamic properties of (CoO/CoFeB)n multilayers have been investigated. An anisotropy field enhancement was evidenced when the CoO layer was deposited under the CoFeB layer. Tuning the relative CoFeB and CoO layers thicknesses, high ferromagnetic resonance frequencies up to 4 GHz were achieved. The coupling effect between the CoO and CoFeB layers was induced by a dipolar coupling due to the anisotropic roughness topology of the CoO layer. This anisotropic roughness was induced by the deposition geometry and evidenced by atomic force microscopy. The strength of the dipolar interfacial coupling was calculated thanks to Schlömann's model. Multilayer stacks were fabricated and the magnetic properties observed for the trilayers could be maintained.

Driving ferromagnetic resonance frequency of FeCoB/PZN-PT multiferroic heterostructures to Ku-band via two-step climbing: composition gradient sputtering and magnetoelectric coupling.

RF/microwave soft magnetic films (SMFs) are key materials for miniaturization and multifunctionalization of monolithic microwave integrated circuits (MMICs) and their components, which demand that the SMFs should have higher self-bias ferromagnetic resonance frequency fFMR, and can be fabricated in an IC compatible process. However, self-biased metallic SMFs working at X-band or higher frequency were rarely reported, even though there are urgent demands. In this paper, we report an IC compatible process with two-step superposition to prepare SMFs, where the FeCoB SMFs were deposited on (011) lead zinc niobate–lead titanate substrates using a composition gradient sputtering method. As a result, a giant magnetic anisotropy field of 1498 Oe, 1–2 orders of magnitude larger than that by conventional magnetic annealing method, and an ultrahigh fFMR of up to 12.96 GHz reaching Ku-band, were obtained at zero magnetic bias field in the as-deposited films. These ultrahigh microwave performances can be attributed to the superposition of two effects: uniaxial stress induced by composition gradient and magnetoelectric coupling. This two-step superposition method paves a way for SMFs to surpass X-band by two-step or multi-step, where a variety of magnetic anisotropy field enhancing methods can be cumulated together to get higher ferromagnetic resonance frequency.

Dual band microwave ferromagnetic resonance absorption in annealed cobalt nanowire arrays

In this letter, we present a dual band microwave absorption phenomenon in 60 nm diameter Co ferromagnetic nanowire arrays annealed at 500 °C in nitrogen atmosphere. The frequency dependent microwave response of the wires is obtained for applied field parallel to the nanowire axis, below 4 kOe and above saturation magnetization up to 8 kOe, in steps of 1 kOe. For applied magnetic fields above saturation magnetization, two sets of absorption peaks are observed, while below saturation, only one single peak is obtained. Combining structural characterization and ferromagnetic resonance measurements, it is proven that the two ferromagnetic resonance peaks are associated with a coexistence of two kinds of nanopillars with different crystal structure in annealed nanowires, one for nanopillars with hexagonal close packed structure at higher ferromagnetic resonance frequency, and the other with face center cubic structure.

Synthesis of self-forming core/shell nanoparticles of magnetic metal/nonmagnetic oxide

Various kinds of self-forming core/shell nanoparticles with a core consisting of magnetic metal and a protective shell consisting of nonmagnetic metal oxide (magnetic metal: Co or FeCo; nonmagnetic metal: Al or Si) were synthesized. The synthesis conditions and compositions of the materials were controlled in order to obtain homogeneous core/shell nanoparticles with high dispersivity. The process of applying carbon coating to the nanoparticles using thermal plasma and subsequently removing the carbon shell by heating in hydrogen was effective for obtaining relatively homogeneous core/shell nanoparticles with crystalline grain sizes of approximately 20nm. Partial oxidation after the carbon-coating process suppressed aggregation of the core/shell nanoparticles and promoted phase segregation of the oxide shells from metallic cores. Similar effects were also achieved by either increasing the amount of nonmagnetic metal or adding a small amount of another nonmagnetic metal to the metal. The bulk nanocomposite of the self-forming core/shell nanoparticles with high dispersivity that were obtained by phase segregation of oxide shells from metallic cores exhibited low magnetic losses with a high ferromagnetic resonance frequency in the gigahertz band.

Microwave ferromagnetic properties of as-deposited Co2FeSi Heusler alloy films prepared by oblique sputtering

The Co2FeSi films are deposited on Si (100) substrates by an oblique sputtering method at ambient temperature. It is revealed that the microwave ferromagnetic properties of Co2FeSi films are sensitive to sample position and sputtering power. It is exciting that the as-deposited films without any magnetic annealing exhibit high in-plane uniaxial anisotropy fields in a range of 200 Oe–330 Oe (1 Oe = 79.5775 Am−1), and low coercivities in a range of 5 Oe–28 Oe. As a result, high self-biased ferromagnetic resonance frequency up to 4.75 GHz is achieved in as-deposited oblique sputtered films. These results indicate that Co2FeSi Heusler alloy films are promising in practical applications of RF/microwave devices.