Mn-Zn Ferrite Films Research Articles

A High-Performance Magnetic Shield with MnZn Ferrite and Mu-Metal Film Combination for Atomic Sensors.

This study proposes a high-performance magnetic shielding structure composed of MnZn ferrite and mu-metal film. The use of the mu-metal film with a high magnetic permeability restrains the decrease in the magnetic shielding coefficient caused by the magnetic leakage between the gap of magnetic annuli. The 0.1–0.5 mm thickness of mu-metal film prevents the increase of magnetic noise of composite structure. The finite element simulation results show that the magnetic shielding coefficient and magnetic noise are almost unchanged with the increase in the gap width. Compared with conventional ferrite magnetic shields with multiple annuli structures under the gap width of 0.5 mm, the radial shielding coefficient increases by 13.2%, and the magnetic noise decreases by 21%. The axial shielding coefficient increases by 22.3 times. Experiments verify the simulation results of the shielding coefficient of the combined magnetic shield. The shielding coefficient of the combined magnetic shield is 16.5%. It is 91.3% higher than the conventional ferrite magnetic shield. The main difference is observed between the actual and simulated relative permeability of mu-metal films. The combined magnetic shielding proposed in this study is of great significance to further promote the performance of atomic sensors sensitive to magnetic field.

Voltage Control of Two-Magnon Scattering in Multiferroic Layers for Tunable Magnetoelectric Devices

In this paper, multiferroic heterostructures have been prepared by growing MnZn ferrite films on ferroelectric single substrates using pulsed laser deposition technology. An enhanced magnetoelectric coupling has been achieved at the critical two-magnon scattering (TMS) angles, where the ferromagnetic resonance field shifts −653 and 211 Oe. The contribution of TMS effects is much larger than that of the conventional strain effect. This heterostructure provides an alternative route for novel integrated multiferroic materials and devices.

Effects of sol concentration on the structure and magnetic properties of sol-gel MnZn ferrites

ABSTRACTMnZn ferrite films were grown on Si substrate by sol-gel method with different sol concentrations varying from 0.1 to 0.4 M.The dependence of structural and magnetic properties of these films on sol concentrations was deeply investigated. The results show that high sol concentration is favorable for obtaining films with good crystalline quality. Morphology and surface roughness of the thin films depend on sol concentration. With the enhancement of sol concentration, the MnZn ferrite grains gradually increase and surface roughness is also gradually increased which is ascribed to the particle collision and electrostatic force between particles. Magnetic properties measurement indicate that the prepared MnZn ferrite films were typically soft ferrite materials. The Ms increased from 13.90 emu/cm3 to 89.13 emu/cm3 as sol concentration increased from 0.1 mol/L to 0.4 mol/L. The FMR linewidth decreased with the increasing of sol concentration, the film prepared by 0.4 mol/L sol has the FMR linewidth of 5.96 Oe. The mechanism of the improvement of magnetic properties is analyzed.

Spinel ferrite films by a novel solution process for high frequency applications

Highly crystalline spinel MnZn-ferrite films applicable in high frequency devices were prepared by a simple and novel wet-chemical process. A stable precursor solution was prepared using dextran as complexing agent. Thus prepared solution was sprayed onto substrates fixed on a rotating table. The reaction temperature of 90 °C and slightly alkaline pH of the precursor solution were suitable for the formation of MnZn-ferrite films. The as-prepared films were highly crystalline and hence post-annealing was not required to obtain spontaneous magnetization. The real and imaginary permeability ( μ′ and μ″), and the resonance frequency ( f r) could be tuned by varying the Zn concentration in the film. Since the film exhibits large magnetic loss, they can be used as electromagnetic compatible (EMC) materials, by which conducted noise in mobile computer and cellular phone can be suppressed effectively.

Elastic behaviour and internal friction studies on nanocrystalline Mn–Zn ferrite films prepared by the method of pulsed laser ablation

A laser ablation method was used for the preparation of nanocrystalline Mn–Zn ferrite thin films. Films were characterized using X-rays and TEM. The magnetic properties were measured using the vibrating sample magnetometer (VSM). The elastic behaviour and internal friction studies were carried out using composite piezoelectric oscillator method in the temperature range of 300–600 K. It was found that the value of Young's modulus decreases with an increase of temperature and shows anomalous behaviour in the vicinity of the Curie temperature. The internal friction for the present ferrites increases continuously with temperature up to the Curie point and a narrow peak was observed just below the Curie temperature. It was found that the anomalous behaviour observed in the temperature dependence of Young's modulus and internal friction disappears with the application of a magnetic field equal to the saturation field (900 mT) of the specimen under investigation. The observed anomalous behaviour in the vicinity of the Curie temperature was understood with the help of Landau's theory.

High resistive ferrite films by a solution process for electromagnetic compatible (EMC) devices

Mn–Zn ferrite films with high resistivity and good noise suppressing ability for use as ‘coupling-type noise suppressors’ have been prepared by the spin-spray ferrite plating. The as-prepared films were crystalline and exhibited single-phase spinel structure. The films had an ‘integrated nano-columnar’ morphology that resulted in a very high resistivity. Further, by varying the chemical composition, films with varying resistivity were prepared and then heat treated at 260 °C for 3 min, similar to that of the reflow soldering process. The reflection and transmission coefficients, S 11 and S 21 parameters, on coplanar micro-strip line (50 Ω) were measured for the as-prepared and heat-treated films in order to study the effect of heat treatment. When the resistivity was above 2×10 5 Ω/sq, S 11 and S 21 exhibited uniform profiles throughout the measurement frequency (50 MHz–10 GHz), which is ideal for the ‘coupling-type’ noise suppressor. These films retain a moderately high resistivity and hence do not show the downshift in the stopband frequency even after the heat treatment (reflow soldering process).

Coupling of MnZn-ferrite films onto electronic components by a novel solution process for high frequency applications

A novel approach for the preparation of “coupling-type noise suppressors” in which ferrite films are directly deposited onto the components of the printed circuit board is reported. Crystalline MnxZnyFe3−x−yO4 films were fabricated on IC chips and polyimide substrates by a soft-chemistry route at temperatures below 100 °C. A “reaction-solution” comprising MCl2 (M = Mn, Zn, Fe) and an “oxidizing-solution” (pH buffer + oxidizing agent) were sprayed simultaneously onto a substrate maintained at 90 °C on a rotating disk. The as-prepared films were highly crystalline and hence do not require any post annealing. The magnetic and electrical properties of the films were studied. The films exhibited a large magnetic loss (imaginary permeability µ″) in GHz range and also exhibited high resistivity in accordance to overcome the heat treatment during the reflow soldering process. Resistivity of 2 × 105 Ω sq−1 was found to be the lower limit for the coupling-type noise suppressors. Noise suppression of above 50% at 10 GHz was obtained for a 6.7 µm thick MnZn-ferrite film and was equivalent to that of commercialized composite sheet noise suppressors of 50 µm thickness.

The effect of substrates on magnetic properties and structure of MnZn ferrite films by alternate deposition

Mn1-xZnxFe2O4 films were prepared by alternative rf-sputtering from targets of MnFe2O4 and ZnFe2O4. The films were deposited on substrates such as single-crystal Si（100）, oxidized single-crystal Si（100）, single-crystal Si（100） with ZnFe2O4 underlayer and single-crystal MgO（100）. The deposited films are amorphous. After annealing in vacuum furnace at 550℃, the polycrystalline Mn-Zn ferrite crystallizes. The film with composition of Mn0.5 Zn0.5 FeO4 shows better magnetic properties: high magnetization Ms and lower coercivity Hc. The coercivity of the film deposited on MgO（100） substrate is the lowest. In this paper, the influences of substrate on film structure and the magnetic properties are investigated. It is believed that the magneto-elastic anisotropy resulting from stress in films dominates the coercivity of Mn-Zn ferrite films. The grain size may be refined to nanometer scale instrumentally by using suitable substrate; the stronger exchange coupling between grains would lead to a lower magneto-elastic anisotropy by averaging to the grains. Therefore, the soft magnetic properties of Mn-Zn ferrite films are improved.

The influence of substrate on the magnetic properties of MnZn ferrite thin film fabricated by alternate sputtering

Mn0.5Zn0.5Fe2O4 film which has the highest saturation magnetization among Mn1–x Znx Fe2O4 thin films was prepared by the alternate rf sputtering method from two targets with compositions of MnFe2O4 and ZnFe2O4, respectively. The films were deposited on single-crystal Si(100), MgO(100) and SiO2/Si(100) substrates. The as-deposited films were amorphous, and after annealing in a vacuum furnace at 550 °C, polycrystalline MnZn ferrite films with residual amorphous matrix were obtained. The coercivity of all films is low, and the film on the MgO(100) substrate shows a coercivity as low as 27 Oe. The grain size of all films is about 20 nm and is less than the ferromagnetic exchange length (160 nm), so magnetic anisotropies are averaged to lower effective values. Furthermore, the negative magnetostriction constant of crystalline MnZn ferrite and the positive magnetostriction constant of amorphous Fe-based matrix will cancel out and may lead to a low or vanishing saturation magnetostriction constant. (© 2008 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim)

Structure and 57Fe conversion electron Mössbauer spectroscopy study of Mn-Zn ferrite nanocrystal thin films by electroless plating in aqueous solution

Mn1−x Zn x Fe2O4 thin films with various Zn contents and of different thickness were synthesized on glass substrates directly by electroless plating in aqueous solution at 90°C without heat treatment. The Mn-Zn ferrite films have a single spinel phase structure and well-crystallized columnar grains growing perpendicularly to the substrates. The results of conversion electron 57Fe Mossbauer spectroscopy (CEMS) indicate that the cation distribution of Mn1−x Zn x Fe2O4 ferrite nanocrystal thin films fabricated by electroless plating is different from the bulk materials’ and a great quantity of Fe3+ ions are still present on A sites for x>0.5. When the Zn content of the films increases, Fe3+ ions in the films transfer from A sites to B sites and the hyperfine magnetic field reduces, suggesting that Zn2+ has strong chemical affinity towards the A sites. On the other side, with the increase of the thickness of the films, Fe3+ ions, at B sites in the spinel structure, increase and the array of magnetic moments no longer lies in the thin film plane completely. At x = 0.5, H c and M s of Mn1−x Zn x Fe2O4 thin films show a minimum of 3.7 kA/m and a maximum of 419.6 kA/m, respectively.

Pinning energy of domain walls in MnZn ferrite films

AbstractMn Zn ferrite films deposited on (100) MgO substrates by rf sputtering technique with different thicknesses ξ in the range of 30‐450 nm were studied. AFM images show grain size increase as film thickness increases. Grains with diameters between L ∼ 70 and 700 nm were observed. The mono and multidomain regime in MnZn ferrite films and their effect on the pinning energy of domain walls are observed via Magneto‐optical Kerr Effect, MOKE. At ξ ∼ 300 nm, the coercive field, Hc, reaches a maximum value of 80 Oe. This result indicates the existence of a multidomain regime associated to a critical grain size, Lc. We used the Jiles‐Atherton model (JAM) to discuss the experimental hysteresis loops. The k pinning parameter obtained from JAM shows a maximum value of k /μo = 67 Am2 for grains with Lc ∼ 529 nm. The total energy per unit area E was correlated with k and D. We found a simple phenomenological relationship given by E α kD; where D is the magnetic domain width. (© 2007 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)

The Structure and Magnetic Properties of Mn-Zn Ferrite Thin Films Fabricated by Electroless Plating in Aqueous Solution

Mn 1-x Zn x Fe 2 O 4 thin films with various Zn contents, 300 nm in thickness, were synthesized on glass substrates directly by electroless plating in aqueous solution at 90°C without a heat treatment. With XRD, SEM, VSM, the crystallographic structure, morphology of the films and the macroscopic magnetic properties were characterized. The Mn-Zn ferrite films have a single phase spinel structure and well-crystallized columnar grains grow perpendicularly to the substrate. The change of the coercivity is not consistent with that of the bulk materials. As the Zn content in the films increases, the value of He decreases firstly, and then increases. At x=0.5, the minimum value of He is 3.7 kA/m and the value of M s is 419.6 kA/m. The hyperfine magnetic fields, cation occupations and the distribution of the magnetic moments in film plane were studied by the conversion electron Mossbauer spectroscopy (CEMS).

A Flux Screening Technique for Growth of High-Quality Ferrite Films by Pulsed Laser Deposition

We present a new technique to improve growth of ferrite films by pulsed laser deposition (PLD). The technique utilizes a metal screen placed between target and substrate, effectively to impede formation of large particulates on the surface of ferrite films by changing the plume shape and plasma density in the PLD chamber. Structural, magnetic, electrical, and microwave properties were measured for the flux screened and conventionally grown films. We demonstrate that the flux screen deposited MnZn-ferrite film has a lower coercivity (39 versus 58 Oe) and ferromagnetic resonance linewidth (350 versus 430 Oe at 9.58 GHz). The improvement in magnetic properties is associated with a reduction in large particulate contamination. This simple approach has the potential to produce high-quality ferrite films for use in electronic and microwave devices.

Mn-Zn-Fe-O 금속타깃을 이용한 수직자기기록디스크의 하지연자성층용 Mn-Zn ferrite 박막제작

In order to attain high-rate deposition of Mn-Zn ferrite thin film for soft magnetic underlayer in perpendicular magnetic recording media, a reactive sputtering using powder-metal targets under the mixture gas of Ar and was performed. It was succeeded that Mn-Zn ferrite films with (111) crystal orientation were deposited on Pt(111) underlayer without any annealing process. The film revealed 3.4 kG of 4 , 70 Oe of coercivity. The deposition rate of the new method was 16 times as high as that of the conventional method using ferrite target.

The structure and magnetic properties of Mn–Zn ferrite thin films fabricated by alternately sputtering

Mn 1− x Zn x Fe 2O 4 thin films with various Zn content were deposited on Si (1 0 0) substrate by alternately sputtering from two targets with the composition of MnFe 2O 4 and ZnFe 2O 4, respectively. The as-deposited films are amorphous. After being annealed in the vacuum furnace with air pressure P Air = 2 × 10 −1 Pa at suitable temperature, crystalline Mn–Zn ferrite films are obtained. The optimum annealing temperature is 550 °C, at which a maximum of saturation magnetization and a minimum of coercivity are obtained. For Mn 1− x Zn x Fe 2O 4 thin films, the saturation magnetization increases firstly then decreases and coercivity decreases monotonously with increasing Zn content. The Mn–Zn ferrite thin films with ZnFe 2O 4 underlayer exhibit better magnetic properties than those deposited directly on Si substrates because ZnFe 2O 4 underlayer not only can impede the diffusion between the substrate and magnetic layer, but also can decrease the strain caused by mismatch between the lattice constants of the substrate and thin films.

Highly resistive Mn-Zn ferrite films prepared from aqueous solution for GHz conducted noise suppressors

We have prepared Mn-Zn ferrite films (MnxZnyFezO4.00−δ: 0.23<x<0.30, 0.0<y<0.38, 2.39<z<2.64) that are highly permeable in GHz range. The film resistivity ρ increased as the amount of Fe content z decreased and very high surface resistance R>108Ω∕sq was attained for the film having z<2.6. The deposited Mn-Zn ferrite films had a large saturation magnetization Ms=380–460emu∕cm3 and relatively low coercivity Hc=11–29Oe. The Mn-Zn ferrite films contacted to a microstrip line (50Ω) exhibited very large transmission loss ΔPloss per thickness t, ΔPloss∕t, of about 10 times larger than that of commercialized composite sheet. They exhibited sufficiently low reflection coefficient S11<−10dB. These films were applicable as noise current suppressors deposited on an interlayer of multilayer printed circuit boards.

Magnetostriction and stress measurements in plasma-sprayed MnZn ferrite films

The coercivity of the plasma-sprayed MnZn ferrite films decreases significantly after annealing in air at the temperature range of 500–800 °C. Magnetostriction and surface stress changes incurred in these ferrite films after the annealing process has been measured. It is found that the effects of the external stress on the magnetic properties of the plasma-sprayed MnZn ferrite films are minor. The coercivity mechanism arising from the magnetoelastic effects due to the nonzero magnetostriction has been analyzed to be small and is not dominant in controlling the magnetization process in these ferrite films.

Neutron diffraction and ferromagnetic resonance studies on plasma-sprayed MnZn ferrite films

The magnetic properties of MnZn ferrites are affected by the plasma spray process. It is found that improvements can be made by annealing the ferrite films at 500°C–800°C. The annealing induced magnetic property changes are studied by neutron diffraction and ferromagnetic resonance techniques. The increase of the saturation magnetization is attributed to the cation ordering within the spinel lattice, which increases the magnetic moment per ferrite formula. The refinements on the neutron diffraction data suggest that the redistribution of the cation during annealing neither starts from a fully disordered state nor ends to a fully ordered state. The decrease of the coercivity is analyzed with the domain wall pinning model. The measurements on the magnetostriction and residual stress indicate that coercive mechanisms arising from the magnetoelastic energy term are not dominant in these ferrite films. The decrease of the coercivity for annealed ferrite films is mainly attributed to the decrease of the effective anisotropic field, which may result from the homogenization of the film composition and the reduction of the microstructural discontinuity (e.g., cracks, voids, and splat boundaries).

Plasma-Sprayed MnZn Ferrites With Insulated Fine Grains and Increased Resistivity for High-Frequency Applications

Plasma-sprayed MnZn ferrite thick films are built up by splats, which consist of columnar grains with diameter /spl sim/200 nm and height /spl sim/1 /spl mu/m. The existence of the conductive wustite FeO in the as-sprayed films greatly reduces the dc resistivity. However, a useful structure can be developed in these ferrite films with fine equal-axis ferrite grains insulated by the high-resistivity hematite Fe/sub 2/O/sub 3/ because of the polygonization of the columnar grains and the oxidation of the wustite during an annealing process. The dc resistivity increases significantly after the annealing process, an effect ascribed to the growth of hematite Fe/sub 2/O/sub 3/ on the basis of impedance analysis. The magnetic properties of these ferrite films improve concurrently. The high-frequency response of the annealed plasma-sprayed MnZn ferrites shows a permeability of /spl sim/700 stabilized to above 10 MHz. The maximum Q factor at about 10 MHz increases from 5 to 20 as a result of the increase of the dc resistivity.

Mn–Zn spinel ferrite thin films prepared by high rate reactive facing targets sputtering

Mn–Zn ferrite thin films were deposited by sputtering a Mn0.6Zn0.4Fe2 alloy target, which was fabricated by powder metallurgy, in a mixture gas of Ar and O2. A 12 nm thick Pt underlayer was deposited at a substrate temperature of 300 °C. All specimen films were prepared in a reactive facing targets sputtering system. The degree of oxidization of the film is strongly related to the oxidation condition at the surface of the target. The surface condition of the target can be estimated by monitoring the discharge voltage. The discharge current–voltage characteristics clarify that there are three regions for the surface condition of the target, i.e. “oxidized,” “metallic,” and “transition.” Mn–Zn ferrite films with (111) crystallite orientation were deposited on Pt(111) underlayer under the transition region condition. The film prepared at O2 partial pressure ratio of 25% revealed 4.8 kG of saturation magnetization 4πMs. The deposition rate of the reactive sputtering method is 16 times as high as that of the conventional method.