Large Anisotropy Field Research Articles

Magnetic properties and frequency characteristics of (CoFeB)x-(Si01.9)i-x and CoFeB films for RF application

(CoFeB)-(Si01.9) and CoFeB films were fabricated by synchronous triple RF magnetron sputtering with rotating a cylindrical electrode. Three types films for RF application in the range over 1 GHz were obtained, and these permeability characteristics and micro-structures were investigated.The as-deposited films exhibited large anisotropy field Hκ in the range from 40 to 550 Oe, and exhibited highferromagnetic resonance (FMR) frequencies of 1.6-6.0 GHz in permeability characterisrtics. The films exhibited amorphous like or hetero-amorphous structures, which led to good soft magnetic properties with electrical resistivity ρ of 100-100, 000 μΩcm and saturation magnetization 4πMs, of 6.5-20kG.It was found that the obtained larger Hκ was effective to attain the higher frequency characteristics with the lower losses for RF inductor cores.

Ultrahigh frequency properties of amorphous Co-Fe-Zr-B thin films

We have investigated ultrahigh frequency magnetic properties of amorphous Co-Fe-Zr-B alloy films deposited on glass substrates by dc magnetron sputtering. Microstructural characterization carried out on these films shows the amorphous nature of the films. The Co-Fe-Zr-B film with a thickness of /spl sim/2300 A exhibits excellent soft magnetic properties in the as-deposited condition, e.g., easy axis coercivity (H/sub c/) of /spl sim/1.5 Oe and 4 /spl pi/Ms of /spl sim/8.4 kG. The in-plane uniaxial anisotropy field (H/sub k/) is as high as /spl sim/28 Oe. This large anisotropy field significantly enhances the ferromagnetic resonance frequency (f/sub res/) to /spl sim/1.86 GHz. The relative permeability /spl mu/' of this film is shown to be /spl sim/200 and to stay nearly constant in the frequency range of 0.1 GHz-0.75 GHz. The full width at half maximum (/spl Delta/f) for the peak in the imaginary part of the permeability at resonance is /spl sim/0.35 GHz. It Is also found that the soft magnetic properties as well as the ultrahigh frequency properties of amorphous films have a strong dependence on film thickness. This is attributed to the change in the microstructure of films, which is closely related to the film growth conditions.

Thermal stability of Ta-pinned spin valves

It has recently been found that large uniaxial anisotropy fields in excess of 120 kA/m (1500 Oe) can be created in thin (3–5 nm) films of Co by obliquely sputtered Ta underlayers. This anisotropy can be used to pin the bottom film of a spin valve while having only a modest effect on the top “free” film, separated by a 2.5 nm Cu spacer layer. This article describes measurements of thermal stability in these Ta-pinned spin valves. Using room temperature giant magnetoresistance (GMR) as a measure, we find that the structure is stable under cumulative 20 min anneals at 25 °C intervals up to 300 °C; GMR decreases to zero upon further anneals up to 450 °C. Measurements taken at elevated temperatures reveal that GMR decreases linearly with temperature, extrapolating to zero at approximately 425 °C, while the anisotropy field is much less temperature dependent, remaining nearly constant up to 150 °C and gradually decreasing to 50% of its room temperature value at 325 °C.

Magnetic characteristics of Fe–N films prepared by reactive ion beam sputtering with a nitrogen bombardment process

Fe–N films were prepared by reactive ion beam sputtering with a nitrogen bombardment at the ratio in arrival rate of nitrogen ions to sputtered iron atoms of 0.1, of which the value was nearly equal to the Fe16N2 composition. The voltage for nitrogen bombardment VA was varied in the range between 80 and 2000 V. The nitrogen content of the Fe–N films was in the range of 8–13 at. %. The phase of the films changed from α′ to α+γ′ at VA higher than 400 V. The saturation magnetization 4πMS of the films took the large value in the range of 22–23.5 kG at VA lower than 200 V. 4πMS with the α+γ′ phase was smaller than pure Fe ones. The films exhibited a large perpendicular magnetic anisotropy field to 3.4 kOe with an increase of VA. After the films of α′ phase prepared at VA of 100 V were postannealed, the films appeared at the γ′ phase from the annealing temperature TA of 400 °C. 4πMS of the films decreased gradually with an increase of TA in the range higher than 300 °C and was smaller than that of pure Fe at TA of 400 °C. These results indicate that the energy of the nitrogen bombardment should impact significantly the phase of the films by the thermal effects of the bombardment energy and the energy below 200 eV may be suitable for preparing the Fe–N films with large 4πMS.

Ultrahigh frequency permeability of sputtered Fe–Co–B thin films

Amorphous FeCoB alloys can have high resistivity and relatively high saturation magnetization which are desired for ultrahigh frequency devices such as future write heads and wireless inductors. In this study, FeCoB films are observed to have a low easy axis coercivity (1–2 Oe), a field deposited induced anisotropy of ∼35 Oe and 4πMs∼17 500 G when sputtered in a typical configuration. However, samples sputtered in an off axis arrangement are found to have an additional uniaxial anisotropy as a result of the oblique incidence of the atomic flux onto the substrate. This extra anisotropy increases with increasing oblique angle. For these same samples, there is little change in the easy axis coercivity, saturation magnetization, and the Hoffmann structure factor (S∼0.05 ergs/cm2). The obtained large anisotropy fields (>35 Oe) are found to push the ferromagnetic resonance frequency to at least above 1 GHz at the expense of the initial permeability.

Effect of post-annealing on ultra-high frequency properties of amorphous Fe-Co-B thin films

In this paper, FeCoB amorphous thin films were deposited on glass substrates using a triode sputtering source under a uniform applied magnetic field. The as-deposited films exhibit a low coercivity of /spl sim/1.7 Oe, a high anisotropy field of /spl sim/37 Oe and 4/spl pi/M/sub s//spl sim/17.5 kG, when sputtered with a bias voltage of 180 V. The large anisotropy fields and saturations in these films result in a ferromagnetic resonance frequency as high as /spl sim/2.63 GHz, a relative permeability /spl mu/' of /spl sim/400-500 and a low dissipation /spl mu/" of 10-30 in the frequency range of 0.1-1 GHz. Upon subsequent annealing at 200-400/spl deg/C for 2 hrs, the magnetic properties of the films are found to be affected significantly. The magnetic properties of the as-deposited and the annealed films have been compared with a considering of the microstructure modification during annealing.

Structure and Magnetic Properties of Y1.8-zCa1.2+zFe4-zV0.6In0.4SizO12

Polycrystalline Y1.8-zCa1.2+zFe4-zV0.6In0.4SizO12 (0 ≤ z ≤ 1.2) were prepared by the conventional ceramic method. The structure, magnetic and microwave properties were characterized by using scanning electron microscopy, X-ray diffraction (XRD), magnetization and ferromagnetic resonance experiments. The Ca-V-In-Si substituted polycrystalline specimens consist of a single cubic garnet phase. The lattice constant of the specimens decreased linerly from 12.457 Å to 12.348 Å and also the Curie temperature of the specimens decreased from 477 K to 329 K with increasing z from 0 to 1.2. Spontaneous magnetic moment per formula unit of Y1.8-zCa1.2+zFe4-zV0.6In0.4SizO12 samples, measured at 5 K decreased with increasing z. The ferromagnetic resonance linewidth of the samples showed a maximum at z=0.8, which may be explained by the relatively large anisotropy field contribution to ferromagnetic resonance linewidth.

Magnetic Properties of Sputtered Co Films

Magnetic properties of sputtered Co films with thicknesses of 20 to 280 nm which were deposited at Ar gas pressures P Ar of 0.4 to 6.6 Pa were studied. The crystal phase was a mixture of fcc and hcp, and there was no preferred orientation. The relative volume fraction of hcp phase tends to increase with P Ar . The in-plane coercive force H c ranges from 2.4 to 12.1 kA/m. The remanence ratio J r /J s was 0.55 to 0.95. Large intrinsic perpendicular anisotropy fields 2K u /J s of 0.54 MA/m due to the columnar structure were observed for films prepared at high P Ar . Both H c and J r /J s are found to be determined by internal stress, crystallite size and perpendicular anisotropy. The saturation polarization J s was 73 to 94% of that of bulk hcp Co.

Magnetic Properties of Sputtered Co Films

Magnetic properties of sputtered Co films with thicknesses of 20 to 280 nm which were deposited at Ar gas pressures PAr of 0.4 to 6.6 Pa were studied. The crystal phase was a mixture of fcc and hcp, and there was no preferred orientation. The relative volume fraction of hcp phase tends to increase with PAr. The in-plane coercive force Hc ranges from 2.4 to 12.1 kA/m. The remanence ratio Jr/Js was 0.55 to 0.95. Large intrinsic perpendicular anisotropy fields 2Ku/Js of 0.54 MA/m due to the columnar structure were observed for films prepared at high PAr. Both Hc and Jr/Js are found to be determined by internal stress, crystallite size and perpendicular anisotropy. The saturation polarization Js was 73 to 94% of that of bulk hcp Co.

Analytical micromagnetics of near single domain particles

A formalism based on the perturbation theory is described which allows for an analytical approximation to the solution of the micromagnetic equations. The approximation is valid in the limit of small deviations of the magnetization from the uniformly magnetized state. These small deviations can lead to large effective anisotropy fields in magnetic elements, which can be large enough to dominate the spin reversal behavior. We demonstrate the formalism by calculating the energy of the single domain state in nanometer scale square magnetic prisms. Good agreement is found with values calculated by conventional finite element numerical methods.

Composite perpendicular recording medium consisting of CoCrPt with large H/sub k⊥/ and CoCr with positive inter-particle interaction

The demagnetizing field near the top surface of a medium for perpendicular recording is compared with that of a medium for longitudinal recording. On the basis of both the result of this comparison and the output dependence on the medium thickness, a perpendicular medium with a large anisotropy field, H/sub k/spl perp// or (H/sub k/spl perp//-4/spl pi/M/sub s/), of over 10 or 5 kOe, respectively, is needed to obtain large output and high resolution. Exploiting this large anisotropy field, a composite perpendicular medium with a (Co/sub 72/Cr/sub 28/)/sub 78/Pt/sub 22/ layer over a Cr-rich Co/sub 72/Cr/sub 28/ layer was fabricated. By taking advantage of both the large anisotropy in the upper layer and the strong particle interaction in the lower layer, the composite medium with a merged MR head obtained an S/N of 24.0 dB at 200 kFCI and a D/sub 50/ of 205 kFCI, with a 50-nm magnetic spacing.

Ferrimagnetism in dicarboxylate‐bridged cobalt hydroxide layers

The synthesis, characterisation (XRD, DTA, IR, UV-Vis) and magnetic properties of the layered compound Co 5 (OH) 8 (O 2 CC 4 H 8 CO 2 )·5H 2 O are reported. It is characterised by a triangular magnetic lattice with a metal–metal distance of 3.1 A and an interlayer distance of 14.3 A. The layers are bridged through the carboxylate groups of the adipate anions. Long range ferrimagnetic (three octahedrally coordinated cobalt centres with spin α and two tetrahedrally coordinated cobalt centres with spin β) ordering is characterised by spontaneous magnetization, an out-of-phase component in the AC susceptibility and a hysteresis loop. The Curie temperature is 52 K and the coercive field is 11 200 Oe at 2 K. Complete reversal of moment to the expected saturation of 3 µ B was not observed due to the large anisotropy field. The long range ordering does not depend on whether the layers are covalently linked, confirming therefore the importance of dipolar interaction between layers having large effective moments as a consequence of short range intralayer interactions. The large coercive field is due to perpendicular alignment of the moment with respect to the layers and the synergy of crystalline shape and single ion anisotropies.

Praseodymium and Neodymium-Based Nanocrystalline Hard Magnetic Alloys

ABSTRACTThe magnetic properties of nanophase exchange enhanced RE-Fe-B based alloys ribbons prepared by melt spinning are presented and discussed. The alloy systems investigated include NdyFe94−yB6 and PryFe94−yB6, for y within the range 6-20 at%, and the data are compared in the context of the larger anisotropy field for the Pr2Fe14B phase in comparison with Nd2Fe14B. Experimental studies are also reported for nanophase (Nd-Pr)- Fe-B alloys with various proportions of Nd:Pr, to investigate the increase in coercivity of NdFeB by partial substitution of Nd by Pr, and for (Nd, Pr)-(Fe-Co)-B-based systems, to study the degree to which the remanence enhancement can be maintained for alloys in which Co substitutes for Fe to increase the thermal stability.

Confrontation of mantle seismic anisotropy with two extreme models of strain, in central Asia

Although most authors agree that convergence is accommodated by a large shortening in Asia, two radically different modes of shortening have been put forward. In one approach, the mechanism of shortening is considered to be homogeneous, producing diffuse deformation in the crust and the mantle. In the second one, motions are localized along faults which are supposed to extend into deep lithospheric shear zones, inducing a heterogeneous deformation pattern. Seismic anisotropy is one observable manifestation of large scale deformation. Large scale seismic anisotropy field are inferred from the two extreme competing models. 3D‐mapping of anisotropy, inferred from surface waves, reveals a better coherence on average with filtered heterogeneous strain models between 100 and 200 km depths. It suggests a strong coupling between surface and deep motions down to at least 200 km. At larger depths, the coherence with homogeneous strain models suggests that mantle flow becomes more homogeneous.

High Frequency Characteristics of Nanocrystalline Co-Fe-Hf-O Soft Magnetic Films

The microstructure, electrical resistivity, and high frequency soft magnetic properties of nanocrystalline Co-Fe-Hf-O films were investigated. The films were prepared by rf reactive sputtering technique in Ar + O 2 mixed atmosphere under a static magnetic field or no field. In an as-deposited state, a Co 44.3 Fe 19.1 Hf 14.5 O 22.1 film deposited in a static field consists of mixed structure of amorphous phase and bcc nanocrystals with 3 - 4 nm in diameter. The real part (μ') of complex permeability of 160 is almost constant up to 1GHz, and extremely high μ'/μ of 61 at 100 MHz is obtained. These high frequency characteristics are caused by the high electrical resistivity (Ρ) of 13 μ ω and large anisotropy field (H k ) of 4.8 kA/m.

Novel composite perpendicular recording medium with Co/sub 78/Cr/sub 22/ over Cr-rich Co/sub 72/Cr/sub 28/ for merged MR heads

We propose a new type of composite perpendicular medium consisting of a 50-nm-thick Co/sub 78/Cr/sub 22/ upper layer and a 50-nm-thick Cr-rich Co/sub 72/Cr/sub 28/ lower layer for magnetic recording systems using MR heads. The lower Cr-rich layer, with strong magnetic interaction in the perpendicular direction and good crystalline orientation, contributes to the high resolution and high signal-to-noise ratio (S/N). The upper layer, with large saturation magnetization (M/sub s/) and large anisotropy field (H/sub kl/), plays a major role in increasing the signal amplitude. Magnetic recording characterization using this medium and a merged MR head yielded a D/sub 50/ of 140 kFCI, an S/N of 33.4 dB, and a signal amplitude of 411 /spl mu/V/sub pp/ at 100 kFCI with a 62-nm magnetic spacing.

Structure and properties of sputtered FeMn/NiFe bilayer thin films

The exchange anisotropy and magnetic properties of FeMn/NiFe exchange coupled bilayer thin films with various NiFe [111] crystal axis distributions have been investigated. The exchange anisotropy and magnetic properties of the exchange coupled films have been found to be very sensitive to the dispersion of the NiFe [111] crystal axis, i.e. /spl Delta//spl theta//sub 50/. Higher exchange anisotropy field (H/sub e/) is obtained for the FeMn deposited on the highly oriented NiFe film (/spl Delta//spl theta//sub 50/ of 2.8/spl deg/). While lower exchange anisotropy field is obtained for the FeMn film deposited on NiFe film having more random [111] crystal axis distribution (/spl Delta//spl theta//sub 50/ of 11.8/spl deg/). Also, the magnetic characteristics of the exchange coupled films were found to be dependent upon the [111] orientation distributions of the NiFe films. Very low coercivity H/sub c/spl par// (measured along the easy direction) and large anisotropy field increase (/spl Delta/H/sub k/) were found for the sample film of FeMn deposited on highly oriented NiFe film.

Nitrided and carbided magnets

In this article, we review our recent studies on new rare-earth intermetallic compounds including the Ga, Si substituted 2:17-type compounds, their nitrides, carbides, and the Sm3 (Fe,Ti)29N5 compounds. Much of our recent work is focused on the Sm2(Fe,Ga)17Cx alloys where we used melt spinning and subsequent annealing to obtain high coercivity. The highest coercivity obtained so far was in Sm2Fe14Ga3C2.5 with a value of 12.8 kOe at room temperature. The off-stoichiometric Sm2Fe14-xCoxSi2Ny nitrides maintain the Th2Zn17-type structure but with a unit-cell expansion ΔVV up to 5 % compared to the host materials. The Sm2Fe14-xCoxSi2Cz carbides maintain the Tr2Zn17-type structure when z = 1 and transform to the BaCd11-type structure when z = 2. A very large anisotropy field with an applied magnetic field (Ha) value of 227 kOe for Sm2Fe14Si2N2.6 and 276 kOe for Sm2Fe10Co4Si2N2.3 is observed at low temperature (1.5 K). The Sm3(Fe,Ti)29N5 compound and its nitrides show very interesting magnetic properties. Both of these compounds exhibit ferromagnetic ordering with Curie temperature (Tc) of 486 and 750 K, respectively. The room temperature saturation magnetization is 119 emu/g for the parent compounds and 145 emu/g for the nitrides. The easy magnetization direction changes from planar to uniaxial upon nitrogenation. The anisotropy field for the nitrides is 12 T at room temperature and 25 T at 4.2 K.

Recent developments in rare-earth nitrides and carbides

In this article, we review our recent studies on new rare-earth intermetallic compounds including the Ga, Si substituted 2:17-type compounds, their nitrides and carbides, and the Sm 3(Fe,Ti) 29N 5 compounds. Much of our recent work has been focused predominantly in the Sm 2(Fe,Ga) 17C x alloys, where we used melt-spinning and subsequent annealing to obtain a high coercivity. The highest coercivity obtained so far was in Sm 2Fe 14Ga 3C 2.5, with a value of 12.8 kOe at room temperature. The off-stoichiometric Sm 2Fe 14− x Co x Si 2N y nitrides maintain the Th 2Zn 17-type structure but with a unit-cell expansion ΔV V up to 5% compared to the host materials. The Sm 2Fe 14− x Co x Si 2C z carbides maintain the Th 2Zn 17-type structure when z = 1 and transform to BaCd 11-type structure when z = 2. A very large anisotropy field with H a value of 227 kOe for Sm 2Fe 14Si 2N 2.6 and 276 kOe for Sm 2Fe 10Co 4Si 2N 2.3 is observed at low temperature (1.5 K). The Sm 3(Fe,Ti) 29N 5 compound and its nitrides show very interesting magnetic properties. Both of these compounds exhibit ferromagnetic ordering with T c of 486 and 750 K, respectively. The room-temperature saturation magnetization is 119 e.m.u. g −1 for the parent compounds and 145 e.m.u. g −1 for the nitrides. The easy-magnetization direction changes from planar to uniaxial upon nitrogenation. The anisotropy field for the nitrides is 12 T at room temperature and 25 T at 4.2 K.

Control of orientation and crystallite size of barium ferrite thin films in sputter deposition

Hexagonal barium ferrite thin films were deposited in a facing target sputtering system. Films with random orientation, and c-axis orientation were obtained by depositing the films on a thermally oxidized silicon wafer and on a c-axis oriented ZnO underlayer, respectively. The film deposited on the thermally oxidized silicon wafer had crystallite sizes as large as 1500 /spl Aring/, which was increased to about 2000 /spl Aring/ by depositing the film on the substrate with ZnO underlayer. The randomly oriented film had a large coercive force of about 4000 Oe and exhibited almost isotropic properties. In contrast, the c-axis oriented film deposited on ZnO underlayer had a large perpendicular magnetic anisotropy field above 10 kOe and exhibited an angular dependence of coercivity consistent with a fanning model, although the film had a smaller coercive force and smaller saturation magnetization. A strong negative magnetic interaction operated between the particles in the perpendicular direction of the film. These BaM films had a large dispersion in coercivity even in the film with excellent c-axis orientation (/spl Delta//spl theta//sub 50/=1.6/spl deg/).