Saturation Magnetization 4πMs Research Articles

Epitaxial yttrium iron garnet film for fabrication of high frequency on-chip inductors

The application of epitaxial yttrium iron garnet (YIG) thin film on high frequency on-chip spiral inductors is investigated. The YIG thin film with the thickness of 3.6 μm was grown on GGG(111) substrate using the liquid phase method, which exhibits relatively high saturation magnetization 4πMs of 1615 Oe close to the bulk value of 1750 Oe and low initial coercivity Hc of 0.5 Oe that minimizes the hysteretic losses. Subsequently, the spiral inductors were directly fabricated on the YIG/GGG(111) substrate. The results show substantial improvement in the optimum operating frequency and self-resonance frequency of the on-chip spiral inductor with the YIG thin film with an increase of 50% up to ∼7.5 GHz and 14.2 GHz, respectively, implying that on-chip spiral inductors with the YIG thin film can be applied to much higher frequency RF circuits.

Synthesis of Fe16N2 compound Free-Standing Foils with 20 MGOe Magnetic Energy Product by Nitrogen Ion-Implantation.

Rare-earth-free magnets are highly demanded by clean and renewable energy industries because of the supply constraints and environmental issues. A promising permanent magnet should possess high remanent magnetic flux density (Br), large coercivity (Hc) and hence large maximum magnetic energy product ((BH)max). Fe16N2 has been emerging as one of promising candidates because of the redundancy of Fe and N on the earth, its large magnetocrystalline anisotropy (Ku > 1.0 × 107 erg/cc), and large saturation magnetization (4πMs > 2.4 T). However, there is no report on the formation of Fe16N2 magnet with high Br and large Hc in bulk format before. In this paper, we successfully synthesize free-standing Fe16N2 foils with a coercivity of up to 1910 Oe and a magnetic energy product of up to 20 MGOe at room temperature. Nitrogen ion implantation is used as an alternative nitriding approach with the benefit of tunable implantation energy and fluence. An integrated synthesis technique is developed, including a direct foil-substrate bonding step, an ion implantation step and a two-step post-annealing process. With the tunable capability of the ion implantation fluence and energy, a microstructure with grain size 25–30 nm is constructed on the FeN foil sample with the implantation fluence of 5 × 1017/cm2.

Effect of process temperature on structure, microstructure, residual stresses and soft magnetic properties of sputtered Fe70Co30 thin films

The effect of substrate and post-annealing temperatures on the structure, microstructure, residual stresses and soft magnetic properties of Fe70Co30 thin films was systematically investigated. Microstructural studies reveal that the films are continuous and undergo changes in shape of grain from plate like to spherical resulting in an increase in grain size with the increase in substrate temperature, whereas the post-annealed films show small pores and no significant grain growth till 500°C. Coercivity (Hc) was found decreasing with both the substrate and post-annealing temperatures; however, the best Hc value of 26Oe was obtained for the films deposited at substrate temperature of 500°C. The post-annealed films exhibited relatively higher Hc values. A good combination of high saturation magnetization 4πMs of ~23.2kG and low coercivity Hc of 26–65Oe was obtained for the films deposited at substrate temperature of 450–500°C. Residual stress analysis on films with different substrate temperatures shows the presence of tensile stress. The decrease in tensile stress is attributed to the relaxation of thermal stresses in the films.

Epitaxial Bi–Gd–Sc iron-garnet films for magnetophotonic applications

Novel magneto-optical epitaxial bismuth-substituted iron garnet films of composition (BiGd)3(FeSc)5O12 with large lattice parameter of 12.570 Å have been grown and investigated. Their composition was uniquely chosen to get necessary values of the magnetic and magneto-optical parameters crucial for magneto-optical applications. In particular, the fabricated films have the suppressed cubic magnetic anisotropy (down to 1.2 × 103 erg/cm3) and the large magnetic susceptibility (∼50), due to introducing Sc3+ ions; the diminished saturation magnetization (4πMS ∼ 750 Gs), caused by Gd3+ ions, and relatively large specific Faraday rotation (1.75°/μm, at 655 nm), due to Bi3+ ions. Therefore, the grown magnetic films have record values of the product of the magnetic susceptibility by the Faraday rotation that makes them extremely promising for applications, including magnetometers, magneto-optical visualizers, light modulators and nonreciprocal elements of the integrated optics.

Study on the microstructure, soft magnetic and high frequency properties of obliquely sputtered [Fe65Co35/ZnO]50 multilayer thin films

The effect of ZnO layer thickness t on the structure, static magnetic properties and high frequency properties is systemically studied for [Fe65Co35/ZnO(t)]50 multilayer films. The gradually increasing crystallinity of ZnO layer with increasing t is observed in the XRD patterns. The VSM measurements show good soft magnetic properties are obtained in these multilayer films, even though the ZnO layer is thick (up to 3.6nm). For the typical sample with t=3.6nm, an obvious in-plane anisotropy field and comparatively small coercivity are achieved, and high electric resistivity up to 12.6mΩcm is obtained. The measurement of permeability spectra indicates that the multilayers have an invariable ferromagnetic resonance frequency fr about 4.0GHz; however, the initial permeability μi can be adjusted from 48 to 136 by decreasing t from 3.6nm to 1.0nm. The phenomenon that fr is almost invariable is the result of the decreasing saturation magnetization 4πMs and the increasing dynamic anisotropy field Hk-dyn with increasing t. For our samples, the real part (μ‘2G) of complex permeability at f=2.0GHz remains a high value beyond 90, while the imaginary part (μ“2G) keeps a low value below 1.55, indicating that these multilayer films are promising for application in high frequency range.

Compositional dependence of magnetic and high frequency properties of nanogranular CoFe-Yttrium-doped Zirconia films

Soft magnetic nanogranular CoFe-Yttrium-doped Zirconia (CoFe-YSZ) thin films were prepared by co-sputtering YSZ with different compositions of CoFe. By simply adjusting the ingredients of films, full-width at half-maximum of the imaginary permeability spectra of CoFe-YSZ films changed greatly. Based on this phenomenon, nanogranular CoFe-YSZ films with various compositions were deposited. And the characteristics of the electromagnetic noise suppression have been evaluated using an integrated coplanar waveguide (CPW) transmission line. A saturation magnetization (4πMs) as high as 21 kGs, a ferromagnetic resonance (FMR) frequency above 3.5 GHz, a suitable value of 589 μΩ cm, and a low coercivity of 7.39 Oe were obtained simultaneously when the volume fraction of CoFe was 0.73. The CoFe-YSZ film with x = 0.73 shows a very wide resonance peak with the full-width at half-maximum of 1 GHz. The absorption attenuation amplitude reaches to −8.1 dB at the resonance frequency fr = 3.5 GHz. In addition, the transmission signal attenuation decreases sharply at the resonance frequency and almost keeps constant when the frequency is lower than 1.2 GHz. It means the input transmission signal will pass through the signal line with tiny signal attenuation below its resonance frequency.

Magnetic hardening of Ce1+xFe11−yCoyTi with ThMn12 structure by melt spinning

A recent study on the intrinsic magnetic properties of CeFe11−yCoyTi has revealed that substituting one Co for Fe retains the favorable magnetocrystalline anisotropy Ha found in the ternary Fe end member, while enhancing the Curie temperature Tc and saturation magnetization 4πMs. These findings warrant further optimization around Co substitution y = 1 to try to exploit the hard magnetic properties of these Ce-based magnets. Both Ce and Co concentrations in Ce1+xFe11−yCoyTi have been optimized in the range of x = 0 − 0.2 and y = 0 − 1.5. It was found that Co substitution effectively enhances all hard magnetic properties, although the values are still lower than those predicted from the intrinsic magnetic properties. Specifically, Tc increases from 210 °C to 285–350 °C; 4πM19 (magnetization at 19 kOe) from 8.9 kG to 10.5–11.5 kG, remanence Br from 3.1 kG to 4.1–4.5 kG, and most importantly, Hci from 1.1 kOe to 1.5 kOe. As a result, the room temperature energy product (BH)max has been increased by over 100% from 0.7 MGOe in Ce1.1Fe11Ti to 1.5 MGOe in Ce1.05Fe9.75Co1.25Ti. Microscopy analysis indicates that the addition of Co refines the grain size and promotes chemical homogeneity at the microscopic scale. The beneficial effect of Co on the microstructure contributes to the improved hard magnetic properties.

Intrinsic magnetic properties of L1 FeNi obtained from meteorite NWA 6259

FeNi having the tetragonal L10 crystal structure is a promising new rare-earth-free permanent magnet material. Laboratory synthesis is challenging, however, tetragonal L10 FeNi—the mineral “tetrataenite”—has been characterized using specimens found in nickel-iron meteorites. Most notably, the meteorite NWA 6259 recovered from Northwest Africa is 95 vol. % tetrataenite with a composition of 43 at. % Ni. Hysteresis loops were measured as a function of sample orientation on a specimen cut from NWA 6259 in order to rigorously deduce the intrinsic hard magnetic properties of its L10 phase. Electron backscatter diffraction showed that NWA 6259 is strongly textured, containing L10 grains oriented along any one of the three equivalent cubic directions of the parent fcc structure. The magnetic structure was modeled as a superposition of the three orthonormal uniaxial variants. By simultaneously fitting first-quadrant magnetization data for 13 different orientations of the sample with respect to the applied field direction, the intrinsic magnetic properties were estimated to be saturation magnetization 4πMs = 14.7 kG and anisotropy field Ha = 14.4 kOe. The anisotropy constant K = 0.84 MJ/m3 is somewhat smaller than the value K = 1.3 MJ/m3 obtained by earlier researchers from nominally equiatomic FeNi prepared by neutron irradiation accompanied by annealing in a magnetic field, suggesting that higher Ni content (fewer Fe antisite defects) may improve the anisotropy. The fit also indicated that NWA 6259 contains one dominant variant (62% by volume), the remainder of the sample being a second variant, and the third variant being absent altogether.

Performance improvement of S-band phase shifter using Al, Mn and Gd doped Y3Fe5O12 and sintering optimization

The searching for Y3Fe5O12 (YIG) ferrite base material is a difficult challenge for microwave phase shifter. Although YIG ferrite is promising for its good microwave characteristics, the adjustment of its corresponding magnetic properties for applied frequency is always a tough challenge. In this work, a study was made to evaluate the impacts of stoichiometry and sintering temperature on hysteresis properties of Mn, Al and Gd substituted YIG ferrites. The Mn, Al substituted YIG ferrite, (Y3)(MnxAl0.83−xFe4.17)O12 showed its best properties for application in 2–4GHz frequency range (i.e. S-band) latching phase shifter at x=0.13. Magnetic properties were further improved by sintering optimization. The increasing sintering temperature increases saturation magnetization (4πMs), remanence (Br) and squareness ratio (SQR), while decreasing the coercivity (Hc). To further investigate the impact to sintering process, Gd substituted YIG ferrites are also discussed. (Y3−yGdy)(Mn0.13Al0.7−0.5yFe4.17)O12 with y=0.6 demonstrated its best magnetic properties at 1450°C sintering. Although the 4πMs, Br and SQR are comparable to that of previous results, its Hc cannot meet the requirement. (Y3)(MnxAl0.83−xFe4.17)O12 ferrites with x=0.13 sintered at 1430°C shows the optimum magnetic properties: 4πMs=675G, Br=575G, Hc=0.45Oe, SQR=0.86. Good ferromagnetic resonance (FMR) linewidth (i.e. ΔH) were also realized as 38.6Oe at 3.2GHz. Base on above results, we reveal Mn, Al substituted YIG ferrite is a good candidate for practical latch phase shifter applications at S-band.

Impact of Stoichiometry and Sintering Temperature on Magnetic Properties of Y3MnxAl0.83−xFe4.17O12 Ferrites

A study was made to evaluate the impacts of stoichiometry and sintering temperature on hysteresis properties of an Mn, Al substituted Y 3 Fe 5 O 12 (YIG) ferrite. The Mn, Al substituted YIG ferrite, (Y 3 )(Mn x Al 0.83-x Fe 4.17 )O 12 showed the best properties for application in 2-4 GHz frequency range (i.e., S-band) latching phase shifter at x =0.13 . Magnetic characteristics were further improved by sintering process. The increasing sintering temperature increases saturation magnetization (4π M s ), remanence (B r ), and squareness ratio, while decreasing the coercivity (H c ). In addition, good ferromagnetic resonance linewidth (i.e., ΔH) properties were also realized as 38.6 Oe at 3.2 GHz. Based on above magnetic characteristics, (Y 3 )(Mn x Al 0.83-x Fe 4.17 )O 12 is a good candidate for practical latch phase shifter applications at S-band.

Effect of thickness on structure, microstructure, residual stress and soft magnetic properties of DC sputtered Fe65Co35 soft magnetic thin films

The effect of film thickness on structure, microstructure, residual stress and soft magnetic properties of Fe65Co35 thin films deposited on Si(001) and MgO(001) substrates was investigated by varying film thickness from 30 to 600nm. X-ray diffraction studies showed that the FeCo films are polycrystalline in the as-deposited condition irrespective of deposition on Si or MgO substrate. The microstructure of films consisted of spherical grains for 30nm film thickness and columnar grains for all other film thicknesses. The grain size for the films was found to increase from 15 to 50nm with increasing film thickness. The sputtered films also exhibited tensile residual stresses with the magnitude of stress decreasing with increasing film thickness. The Fe65Co35 films deposited on both substrates also exhibited very good in-plane soft magnetic properties with a saturation magnetization 4πMs of ~23.6–23.8kG and coercivity of ~27–30Oe without any under-layer only for films with thickness of 30nm. For all other thicknesses, these films exhibited a significantly higher coercivity. The observed variations in soft magnetic properties with film thickness were explained in terms of residual stress and microstructure of the films.

Magnetic and high frequency properties of nanogranular CoFe-yttrium-doped zirconia films

Soft magnetic nanogranular FeCo-Yttrium-doped Zirconia thin films were fabricated using RF magnetron sputtering at different sputtering power. It was found that film electrical resistivity (ρ) decreased steeply with the increase of sputtering power, while both saturation magnetization (4πMs) and natural ferromagnetic resonant frequency (ƒr) increased with the sputtering power ascending from 100 W to 200 W, but decreased when sputtering power exceeded 200 W. X-ray diffraction analysis and transmission electron microscopy confirmed that the films were nanocrystalline/amorphous composites. A saturation magnetization as high as 15.4 kGs and a ferromagnetic resonance frequency above 3 GHz were obtained.

Optimization of high frequency characteristics in Co-Ta thin films

Magnetic properties and high frequency characteristics of binary Co100−xTax (x = 0–24) thin films, prepared by using the oblique sputtering method under an external magnetic field of 1200 Oe have been studied. All the Co100−xTax films are easy to form amorphous phase, and thus exhibit strong in-plane uniaxial magnetic anisotropy, high resistivity, and low coercivity. With increasing x, the saturation magnetization (4πMs) and coercivity along the easy and hard axes (Hce and Hch) are decreased, while the magnetic anisotropy field (Hk) reaches the maximum value of 578 Oe for the films with the composition to become fully amorphous phase. Due to large Hk, high ferromagnetic-resonance frequency (fFMR) of 4.7–6.6 GHz is obtained for Co100−xTax (x = 11–24) films. The optimal magnetic properties of 4πMs = 10.9 kG, Hce = 6.2 Oe, Hch = 6.0 Oe, Hk = 507 Oe, and high resonance characteristics of fFMR = 6.4 GHz, respectively, are reached for Co84Ta16 films. Finally, high fFMR of 5.4–7.2 GHz and Hk of 434–617 Oe can be tuned by the modification of the sputtering parameters. This result reflects the benefit of Co100−xTax (x = 11–22) films for above 5 GHz applications.

Magnetic properties of CeFe11−xCoxTi with ThMn12 structure

A series of novel alloys CeFe11−xCoxTi (0 ≤ x ≤ 11) with ThMn12 structure has been successfully prepared by melt-spinning. The Curie temperature Tc increases with Co content x, reaching a maximum of 689 °C at x = 9 and declining to 664 °C at complete Co filling (x = 11). The room temperature saturation magnetization 4πMs and magnetocrystalline anisotropy Ha have been estimated by fitting the first quadrant demagnetization curve with the Stoner-Wohlfarth model. 4πMs first increases with increasing Co up to x = 3, then decrease. Ha has a complex dependence on Co content, which is indicative of a change in the easy magnetization direction from axis to plane and back as the Co content increases.

Magnetic and microwave properties of U-type hexaferrite films with high remanence and low ferromagnetic resonance linewidth

U-type barium hexaferrite films (Ba4Ni1.4Co0.6Fe36O60) were deposited on (0001) sapphire substrates by pulsed laser deposition. Microstructure and magnetic properties of the films were characterized by X-ray diffraction, scanning electron microscopy and vibrating sample magnetometry. Ferromagnetic resonance (FMR) measurements were performed at X-band. The results indicate an anisotropy field of ∼8 kOe, and the saturation magnetization (4πMs) of ∼3.6 kG. An optimal post-deposition annealing of films results in a strong (0 0 n) crystallographic texture and a high hysteresis loop squareness (Mr/Ms = 92%) leading to self biased properties. Furthermore, the highly self-biased ferrite films exhibited an FMR linewidth of ∼200 Oe. The U-type hexaferrite films having low microwave loss, low magnetic anisotropy field, and high squareness are a suitable alternative to Sc or In doped BaM ferrites that have been the choice material for self-biased microwave devices at X-band frequencies.

Improving soft magnetic properties of nanometer CoNbZr films in gigahertz frequency range by electrical pulse annealing

A new method using electrical pulse annealing to improve soft magnetic properties of nanometer CoNbZr thin films was presented in this investigation. The effects of various parameters on the properties of the synthesized nanometer crystal films, such as grain size, structure, and ferromagnetic resonance with different electrical pulse annealing have been analyzed. The results showed that (1) the saturation magnetization (4πMs) of the thin films increased from 7.89 kGs to 12.67 kGs, (2) the ferromagnetic resonance field decreased from 870.36 Oe to 764.57 Oe at the frequency of 10 GHz, and (3) the cutoff frequency (fr) increased up to 2.3 GHz when the power of the electrical pulse was increased from 0.16 W to 0.81 W. It has been found that the optimal point of electrical pulse power is ∼0.54 W. Under this annealing condition, the soft magnetic property of a CoNbZr film, such as a 4πMs, anisotropy field (Hk) has been improved rapidly. Additionally, the grain size of the film has been decreased as well. On the other hand, the variation of the damping coefficient was found to be the minimum when the power of the annealing electrical pulse was 0.54 W.

Structural, magnetic and Mössbauer spectral studies of aluminum substituted Mg–Mn–Ni ferrites (Mg0.2Mn0.5Ni0.3AlyFe2−yO4)

Nanocrystalline Al3+ ions doped Mg0.2Mn0.5Ni0.3AlyFe2−yO4 compositions, where y=0.0, 0.05 and 0.10 have been synthesized by citrate precursor method. Crystal structure and magnetic properties have been investigated at 300K by means of X-ray diffraction, transmission electron microscope (TEM), vibrating sample magnetometer (VSM) and Mössbauer spectra measurements. XRD study reveals that particle size decreases from 102.25nm to 41.65nm. A decrease in lattice constant and saturation magnetization was attributed to smaller ionic radius of Al3+ ions and weakening of super exchange interaction. Experimental and X-ray density decrease with increasing aluminum concentration. Though Mössbauer spectra of y=0.0 exhibit normal Zeeman split sextets, spectra of samples for y=0.05 and 0.10 are characterized by simultaneous presence of a central paramagnetic doublet. Dependence of Mössbauer parameters such as isomer shift, quadrupole splitting, linewidth and hyperfine magnetic field on Al3+ ions concentration have been discussed. Initial permeability ‘μi’, saturation magnetization (4πMS), retentivity (MR), Bohr magneton number (nBN), magneto crystalline anisotropy constant (K1) and magnetic loss decreases while coercivity (HC) increases with increasing substitution of Al3+ ions. Magnetic loss has very low value in the range of 10−3 which is two orders of magnitude less than samples prepared by conventional method.

Effect of Bi-substitution on the microstructure and electromagnetic properties of YCaZrVIG with low sintering temperature

Bi substituted YCaZrVIG ferrites, Y2.3−xBixCa0.7Zr0.3V0.2Fe4.42O12 (x=0.1, 0.25, 0.4, 0.5, 0.75) ferrites were prepared by conventional oxide method. The addition of Bi2O3 promoted the sintering performance and lowered the sintering temperature from 1420–1230°C. However, it also resulted in the formation of minor second phases and the decrease of grain size. With the increase of Bi concentration, the dielectric constant increases linearly and then remains unchanged. The dielectric loss decreased firstly and then increased. The saturation magnetization (4πMs) almost retained unchanged as the Bi concentration increased except for the sample with 0.75. The coercivity (Hc) decreased firstly and reached the minimum of 1.32Oe at 0.25, and then rose when x>0.25, which was related to the facility of magnetic domain wall motion and magnetic moment reverse. Moderate addition of Bi also can increase the remanence (Br) by improving sintering process. Additionally, we got the optimum electromagnetic properties in the samples with x=0.25 at 1230°C: RD>97%, εr=15.7, tanδe=2.48×10−4, Hc=1.32Oe, 4πMS=1663Gs, Br=583.91Gs.

Magnetic properties and high-frequency characteristics of FeCoAlO gradient composition thin films

5 × 25 mm FeCoAlO gradient composition thin film was prepared with composite target by using RF magnetron sputtering. The Al-O composition gradient along the length direction of the film was introduced by Al2O3 chips asymmetrically arrayed on a Fe70Co30 target disk. The film was divided into five equal segments. All samples showed a low coercive force Hc of 4 – 8 Oe. The saturation magnetization 4πMs increased continuously from 17.3 kGs for sample 1 (has more Al-O content) to 19.7 kGs for sample 5 and it was consistent with the increasing of Fe-Co composition. Meanwhile, these samples showed different anisotropy behaviors relating with Al-O composition. The sample 1 exhibited the same magnetization curve along the directions of G‖ and G⊥ (G‖ and G⊥ are parallel and perpendicular to the direction of the Al-O composition gradient, respectively). In both of G‖ & G⊥ directions, the sample 1 showed a resonance frequency (fr) of around 2.6 – 3.0 GHz, while, in G‖ direction, it showed a high value of real permeability μ′. The sample 5 exhibited a distinct in-plane uniaxial anisotropy and a good high-frequency response of 3.0 GHz resonance frequency. So these films having gradient composition exhibit are suggested for the use in integrated magnetic devices working in the GHz frequency range.

GROWTH AND DEPTH-DEPENDENCE OF SATURATION MAGNETIZATION OF IRON NITRIDE THIN FILMS ON MgO SUBSTRATE

We used polarized neutron reflectometry (PNR) to investigate the depth-dependent saturation magnetization (4πMs) of bi-layer structured Fe–N/Fe grown on MgO substrates, which were prepared by a facing target sputtering method followed by a subsequent annealing process to purposely study the N inter-diffusive effect. It is observed that by tuning the Fe layer thickness from 2 nm to 5 nm, the magnetic properties of the resulting product varies substantially. According to X-ray diffraction, an additional peak, indexed to Fe16N2(004) , was developed in the sample with thinner (2 nm) underlayer. Its corresponding PNR study shows a 4πMs of up to 2.82 T towards the substrate interface, which is 14% higher than the known limit ( Fe 65 Co 35 ~ 4πMs = 2.45 T ). We attribute this giant magnetization to the presence of chemically ordered Fe1N2 . We have seen evidence that the high Ms is favorably stabilized due to the lattice misfit. The thickness range is consistent with the strained region of the films. This depth-dependent saturation magnetization analysis can shed a light to help understand the previous magnetization reports by classical magnetometry methods for the samples prepared using the same underlayer.