Excellent Hard Magnetic Properties Research Articles

Significant enhancement in the magnetic properties of Cr2Te3 nanosheets by atom substitution doping.

Ferromagnetic Cr2Te3 nanocrystals, with their high spin-orbit coupling and low symmetry, have attracted considerable attention as rare-earth-free magnetic nanomaterials due to their potential to achieve high magnetic anisotropy. However, their relatively low values of remanence (Mr) and saturation (MS) magnetisation limit their energy product, making them unsuitable for practical applications. Herein, we report a straightforward one-pot heat-injection technique for the synthesis of high-remanence hexagonal Cr2Te3 nanosheets by heterogeneous doping with atoms of M (M = V, Mn and Se). The doped materials provide enhanced Mr and MS at an unchanged Curie temperature (TC), resulting in excellent hard magnetic properties. With Mn doping, the Mr of the matrix increases significantly, reaching 18.38 emu g-1 at 5 K, far exceeding the original undoped Cr2Te3 nanosheets. The nearly square hysteresis loop makes it valuable for many low temperature applications. These results provide a valuable case for tuning the magnetism of ferromagnetic Cr2Te3 by substitutional doping.

Preparation of hard magnetic Co2C nanospheres as electrocatalysts for hydrogen evolution reaction

Cobalt carbide as a new type of transition metal carbides (TMACs) has received extensive attention in the field of magnetism and electrocatalysis. As one of the cobalt carbide materials, Co2C shows good hard magnetism. In this paper, we have designed a simple and efficient method to successfully prepare single-phase Co2C nanospheres. Co2C is synthesized by using Co3O4 as precursor and small molecule amino ethylenediamine as carbon source. The material exhibits excellent hard magnetic properties, with saturation magnetization up (Ms) to 32.19 emu/g and coercivity up to 1111 Oe at room temperature. Co2C also demonstrats excellent hydrogen evolution reaction performance in 1 M KOH solution. Using nickel foam as the working electrode, the overpotential of only 92 mV can reach the current density of 10 mA cm−2, and the Tafel slope is 104 mV dec−1. This provides a new idea for the further development of synthetic cobalt carbide and its composite materials.

Microstructure and magnetic properties of Sm-Co-based amorphous nanocrystals controlled by B addition

The crystalline Sm-Co alloys show excellent hard magnetic properties, while the amorphous Sm-Co alloys have a poor performance. In this paper, Sm12Co76-xFe4Zr7Cu1Bx (x = 0, 2, 4, 5, 5.2) ribbons were melt-spun at 40 m/s, and the effects of B content on the phase composition, microstructure, and magnetic properties of the ribbons were studied. The results show that the main phase of all ribbons with different B content is Sm(Co, M)7. With an increase in B content, the content of amorphous and fine soft magnetic phases increases. Besides, nano-scale crystalline clusters are embedded in the amorphous matrix, forming different forms of exchange coupling microstructures between the soft and hard magnetic phases. The x = 5 ribbons have the finest grains, the most uniform grain distribution, and the strongest exchange coupling effect. Without heat treatment, their coercivity reaches 19.5 ± 0.9 kOe, and the other magnetic properties are also excellent, Mr = 24.8 ± 1.7 emu/g, M2T = 29.0 ± 1.7 emu/g, and Mr/M2T = 0.858 ± 0.015.

Calcium vapor synthesis of extremely coercive SmCo5.

Exceptionally coercive SmCo5 particles are produced through calcium vapor reduction of SmCo5O9 powders synthesized by flame spray pyrolysis. The resulting powders are composed of oblate hexagonal particles approximately 2 microns across with smooth surfaces. This microstructure yields record-breaking room temperature coercivity Hc,i >80 kOe, or >60 kOe when combined with advanced manufacturing approaches such as electrophoretic deposition or molding with tetraglyme inks. These techniques enable straightforward low-loss fabrication of bulk parts. The high coercivity is extremely robust at elevated temperatures, exceeding 10 kOe even at 600 °C. The oxide precursor approach removes the need for strict environmental control during synthesis that is common to other nanoparticle-based routes and can readily be scaled to kilogram quantities of feedstock production. Magnet powders produced by calcium vapor reduction can thus function as the building blocks for traditional or advanced manufacturing techniques, while the high coercivity enables consistent performance across a wide range of temperatures.

Intrinsic Magnetic Properties of a Highly Anisotropic Rare‐Earth‐Free Fe2P‐Based Magnet

AbstractPermanent magnets are applied in many large‐scale and emerging applications and are crucial components in numerous established and newly evolving technologies. Rare‐earth magnets exhibit excellent hard magnetic properties; however, their applications are limited by the price and supply risk of the strategic rare‐earth elements. Therefore, there is an increasing demand for inexpensive magnets without strategic elements. Here, the authors report the intrinsic highly‐anisotropic magnetic properties of Co and Si co‐doped single crystals (Fe1−yCoy)2P1−xSix (y ≈ 0.09). Co increases Curie temperature TC; Si doping decreases magnetocrystalline anisotropy K1 and also increases TC significantly because of the enhanced interlayer interaction. The maximum room temperature magnetocrystalline anisotropy K1 = 1.09 MJ m−3 is achieved for x = 0.22, with saturation magnetization µ0Ms = 0.96 T and TC = 506 K. The theoretical maximum energy product is one of the largest for any magnet without a rare earth or Pt. Besides its promising intrinsic magnetic properties and absence of any strategic elements, other advantages are phase stability at high temperatures and excellent corrosion resistance, which make this material most promising for permanent magnetic development that will have a positive influence in industry and daily life.

Development of a High-Performance-Ferrite Magnet Fabrication Process without Sintering Additives

Sintered M-type hexaferrites with the chemical formula of Sr0.3Ca0.4La0.3Fe9.8Co0.2-xMnxSi0.135O19-d (<i>x</i> = 0, 0.05, 0.1, 0.2) and Sr0.3Ca0.4La0.3Fe9.8-yCo0.2MnySi0.135O19-d (<i>y</i> = 0.05, 0.1, 0.2) were prepared by conventional solid station reaction routes. A high sintering density of more than 95% of the theoretical density was achieved in all hexaferrite samples when calcination was carried out at 1100 oC for 4 h, followed by sintering at 1230-1250 oC for 2 h without the use of sintering additives. High saturation magnetization and coercivity were achieved simultaneously at the <i>x</i> = 0.05 composition, where Mn replaces part of the Co. The secondary phase Fe2O3 generated by the initial addition of SiO2 was gradually reduced when the Fe contented was decreased in the Sr0.3Ca0.4La0.3Fe9.8-zCo0.15Mn0.05Si0.135O19-d samples, and a single M-type hexaferrite phase was confirmed in the Sr0.3Ca0.4La0.3Fe8.3Co0.15Mn0.05Si0.135O19-d (<i>z</i> = 1.5) sample, which also exhibited optimized hard magnetic properties, with a saturation magnetization of 4581 G and coercivity of 4771 Oe. Anisotropic sintered magnets were fabricated using the optimized composition, and showed excellent hard magnetic properties, with a remanent magnetic flux density of 4400 G and intrinsic coercivity of 4118 Oe, and a maximum energy product of 4.72 M·G·Oe. This result is very promising because high magnet performance can be achieved with a single batch process without the need for sintering additives during the process.

Achievement of high coercivity in Sm(Fe0.8Co0.2)12 anisotropic magnetic thin film by boron doping

SmFe12-based compounds have been considered as promising candidates for next generation permanent magnet materials because of their excellent intrinsic hard magnetic properties with a minimum usage of rare earth elements. However, realizing high coercivity in anisotropic microstructure is a big challenge, which hinders their practical applications. In this work, a novel anisotropic granular microstructure of Sm(Fe0.8Co0.2)12 with a sufficiently large coercivity (µ0Hc) of 1.2 T and with a high remanent magnetization of 1.50 T is demonstrated in thin films prepared by co-sputtering Sm(Fe,Co)12 with boron. Detailed microstructure characterization using high resolution scanning transmission electron microscopy (STEM) and atom probe tomography (APT) indicate that the addition of B leads to the development of columnar-shaped Sm(Fe0.8Co0.2)12 grains with a size of ∼40 nm, which are surrounded by ∼3 nm-thick B-enriched amorphous intergranular phase. Domain wall pinning at the amorphous grain boundary phase is attributed to the high coercivity. This work provides a guiding principle for realizing high-coercivity anisotropic SmFe12-based permanent magnets, which can outperform Nd-Fe-B magnets and could be used as the next-generation high-performance permanent magnets in various applications.

Magnetic Properties of NdFeB Alloys Obtained by Gas Atomization Technique

Since Sagawa reported in [1]on the excellent hard magnetic properties of NdFeB permanent magnets, the utilization of anisotropic sintered NdFeB magnets in large motor and generator applications has grown spectacularly. Such hard magnetic material consists of a major tetragonal intermetallic compound (Nd 2 Fe 14 B), with excellent intrinsic hard magnetic properties, and a minor Nd-rich phase. Obviously, the magnetic behavior depends strongly on the microstructure of the magnet material, which in turn is determined by the production process. Microstructural factors affecting the hard magnetic character include the mean and the standard deviation of the grain size distribution, the orientation degree of the grains, the distribution of the Nd-rich phase, and the presence of a residual amount of other secondary phases (e.g. α-Fe, NdFe 4 B 4 , and other borides). All kind of defects in the microstructure, especially soft magnetic phases, can easily deteriorate the hard magnetic properties. It has been reported a slope change in the curve of magnetization as a function of temperature at around 150 K due to a spin reorientation transition (SRT) [2]. Such effect has been carefully analyzed for sintered magnets, since it is essential for the design of sensors, magnetic apparatus or magnetomechanical devices for cryogenic applications [3]. Alternative production routes of NdFeB magnets result in new microstructures whose impact on magnetic properties has to be carefully studied. Inert gas atomization is one of the novel processes under evaluation to produce NdFeB powders [4]. This technique consists on breaking a liquid metal stream into droplets by means of a high velocity inert gas flow. These droplets become spherical particles after solidification. The small size of the droplets, typically in the microns range, and the high velocity of the gas enable a fast heat transfer between both, resulting in high cooling rates and fine microstructures. Using this technique, we have produced several NdFeB alloys. After splitting the as-atomized powders in different size fractions by sieving, their microstructure and magnetic properties have been studied. In this work, we report the magnetic properties as a function of temperature, between 1.8 and 400 K, and of particle size. Fig. 1shows the characteristic microstructure of a single gas atomized NdFeB particle, whose main constituents are Nd 2 Fe 14 Bgrains of a few microns in size. The Inverse Pole Figure (IPF) demonstrates the random crystallographic texture of the material. The cooling rate of gas atomized particles increases when the particle size is reduced. As a result, larger particles exhibit higher microsegregation and, hence, the precipitation of soft magnetic α-Fe phase. On the other hand, smaller particles display finer microstructures. As for the coercive field, it was observed that it increases significantly when the particle size is reduced, reflecting a higher difficulty for reverse domain nucleation (less surface defects, finer grain size, lower volume fraction of secondary soft magnetic phases, etc.). Fig. 2shows the temperature dependency of the saturation magnetization, M s (T). The anomaly, i.e. a slope change of the M s (T) curve, observed around 150 K could be ascribed to the spin-reorentation transition (SRT) mentioned before, which has been reported to occur in the same temperature range when the magnetic field is applied parallel and perpendicularly to the sample direction [2]. In contrast with the measurements performed in single crystals and anisotropic sintered magnets, isotropic gas atomized powders exhibit an increment of saturation magnetization below the split tilt temperature of the SRT. This work has received funding from the European Union’s Horizon 2020 research and innovation programme under grant agreement No 720838 (NEOHIRE project).

Synthesis of Samarium-Cobalt Sub-micron Fibers and Their Excellent Hard Magnetic Properties.

High-throughput synthesis of Samarium-Cobalt sub-micron fibers with controlled composition and dimension was demonstrated by combining electrospinning and reduction-diffusion processes. The composition of fibers was readily varied (8 < Sm < 20 at.%) by adjusting precursor composition whereas the diameter of fibers was precisely controlled by varying electrospinning parameters (e.g., applied voltage, solution feed rate, temperature, and humidity) to reach single-domain size. X-ray diffraction patterns confirmed that single phase Sm2Co17 fibers were synthesized when the metal precursor ratio (Sm3+/(Sm3++Co2+)) was precisely controlled at 10.6%, whereas mixed phases (i.e., Co-Sm2Co17 or Sm2Co17-Sm2Co7) were observed when the ratio is deviated from the stoichiometric. Magnetic saturation (Ms) of the synthesized fibers monotonically decreased with an increased in Sm content. In contrast, coercivity (Hci) monotonically increased with an increase in Sm content.

Intrinsic hard magnetic properties of Sm(Fe1 − xCox)12 compound with the ThMn12 structure

We have grown Sm(Fe1−xCox)12 (x=0, 0.1 and 0.2) films epitaxially on V(001) buffered MgO(001) single crystalline substrates in order to investigate the intrinsic hard magnetic properties of the Co substituted SmFe12 phase with the ThMn12 structure. We found Sm(Fe0.8Co0.2)12 has excellent intrinsic hard magnetic properties with spontaneous magnetization of 1.78T, anisotropy field of 12T and Curie temperature of 859K, all of which are superior to those for Nd2Fe14B. Hence, the Sm(Fe0.8Co0.2)12 compound is promising as permanent magnet material, if it can be stabilized in a bulk form.

Electrodeposition as an Alternative Route to Prepare Nanostructured Lead-Free Solder Alloy: A Short Review

With world-wide strict legislation for reduction or removal of lead from industrial waste, development of a large number of lead-free alternative solder materials had been intensively examined. The drive for lead-free solders development was towards systems that can imitate conventional lead containing solder alloys in terms of melting temperatures and improvement of mechanical properties. Nanostructured solder alloy, with a grain size of typically &lt; 100 nm, was a new class of materials with properties distinct from and frequently distinguished to those of the conventional alloy. In comparison, nanostructured solder alloys exhibit higher strength and hardness, enhanced diffusivity, and excellent soft and hard magnetic properties. Numerous different techniques were performed to synthesize these nanostructured solder alloys. Electrodeposition method has generated huge interest in nanostructured solder preparation, mainly due to its ability to deposit solders selectively and uniformly at nanoscale. These factors bring significant influences on the behaviors of products, such as magnetization, density, ductility, wear resistance, corrosion resistance, porosity, molecular structure, and crystal properties which plays a vital part in the field of electronic manufacturing. In this paper, a short review on the electrodeposition, a useful technique to deposit different metals and alloys, as a method for nanostructured lead-free solder alloys preparation is presented.

Plate-like SrFe12O19 particles prepared by modified sol–gel method

M-type strontium hexaferrite powders were synthesized by the modified sol–gel method with calcination in NaCl matrix in a temperature range 790–850°C for 1h. X-ray diffraction analysis shows the formation of pure M-type strontium hexaferrite phase. The SrFe12O19 particles have a plate-like shape with a mean diameter 130–185nm and a thickness 45–55nm. The prepared powders show a saturation magnetization 70–72emu/g and a coercive force 6.0–6.4kOe. The suggested synthesis method combines simplicity, using of low calcination temperatures and allows to synthesize pure strontium hexaferrite powders with excellent hard magnetic properties.

NdFe12Nx hard-magnetic compound with high magnetization and anisotropy field

The NdFe12Nx compound with a ThMn12 structure (space group I4/mmm) was successfully synthesized by nitriding an NdFe12 layer grown on a W underlayer on a single-crystalline MgO(001) substrate. The c-axis expanded from 0.480 to 0.492 nm while the a-axis showed a slight contraction from 0.852 to 0.849 nm after the nitriding. Excellent intrinsic hard magnetic properties of μ0Ms ≈ 1.66 ± 0.08 T, μ0Ha ≈ 8 T, and Tc ≈ 550 °C, which are superior to those of Nd2Fe14B, were obtained.

The structure, anisotropy and coercivity of rapidly quenched TbCu7-type SmCo7−xZrx alloys and the effects of post-treatments

The effects of wheel speed, Zr content, post-ball milling process and heat treatment on the structure, anisotropy, magnetic properties and phase transition of the melt-spun SmCo7−xZrx alloys were investigated. The crystallographic c-axis is parallel to the ribbon plane for the ribbons prepared at low speeds of 5 and 15m/s, and this orientation is reduced at higher speeds. The out-of-plane coercivity of SmCo6.8Zr0.2 ribbon increases from 123kA/m for 5m/s to 1076kA/m for 60m/s. Zr doping improves the hard magnetic properties and the in-plane coercivity of SmCo7−xZrx alloys increases with the Zr content from 592kA/m for x=0.1 to 1376kA/m for x=0.4. The Rietveld refinements and theoretical analysis reveal that Zr atoms occupy the 2e site. The coercivity mechanisms are different for the alloys with various Zr contents. The ball milling process could enhance the coercivity and remanence of the ribbons due to the grain refinement and the precipitation of Co phase. Heat treatment can further modify the magnetic properties of the alloys. SmCo6.7Zr0.3 alloy heat treated at 400°C has the high maximum energy product (BH)max of 64.5kJ/m3, where the coercivity was enhanced to 1560kA/m by 650°C heat treatment. In addition, the SmCo7−xZrx alloys exhibit excellent hard magnetic properties at elevated temperatures.

Formation of Disordered ${\rm Th}_{2}{\rm Zn}_{17}$-Type ${\rm Sm}_{2}{\rm Fe}_{17}$ With Ti and B Additions and Hard Magnetic Properties of Their Nitrides

Compounds with nominal compositions Sm <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">10</sub> Fe <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">90</sub> and Sm <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">10</sub> Fe <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">90</sub> Ti <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sub> B were prepared by strip casting method. Disordered Th <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sub> Zn <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">17</sub> -type phase of Sm <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">10</sub> Fe <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">90</sub> Ti <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sub> B was achieved. This disordered Th <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sub> Zn <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">17</sub> (space group R-3m) phase was formed by randomly replacing Sm(3a) with Fe(6c)-dumbbell ((3a) and (6c) are Wyckoff symbols)). Scanning electron microscopy image revealed that the disordered Sm <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">10</sub> Fe <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">90</sub> Ti <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sub> B crystallized in micron-scaled grains, which is useful for the improvement of its hard magnetic properties. By annealing this disordered phase, it transformed into ordered rhombohedral Th <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sub> Zn <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">17</sub> structure. This derivative 2:17 type compound was further nitrided and then finely pulverized using surfactant-assisted grinding method. The final anisotropy powders showed excellent hard magnetic properties with coercivity of 12.4 kOe and (BH) <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">max</sub> ~ 37 MGOe.

High coercivity (Nd8Y3)–(Fe62Nb3Cr1)–B23 magnets produced by injection casting

High coercivity (Nd8Y3)–(Fe62Nb3Cr1)–B23 magnets in rods have been produced by copper mold injection casting. Magnetic properties, microstructure, and phase evolution in the as-cast and annealed states have been presented and discussed. The (Nd8Y3)–(Fe62Nb3Cr1)–B23 alloys show hard magnetic properties in the as-cast state. Annealing induces ideal microstructure containing magnetically hard and soft phases with hard/soft volume ratio of 73/27. Exchange coupling between magnetically hard (Nd,Y)2Fe14B phase and soft α-Fe (Fe3B) phase leads to excellent hard magnetic properties. Highest coercivity of 1230 kA/m in (Nd8Y3)–(Fe62Nb3Cr1)–B23 magnet originates from the large amount of hard phase with high magnetocrystalline anisotropy, formation of thin grain boundary phase and refinement of magnetic grains. Nb and Cr doping modify the magnetic phases. Annealed magnetic rods with a diameter of 2 mm and 36 mm in length demonstrated the maximum magnetic properties i.e., iHc of 1230 kA/m, Br of 0.49 T, and (BH)max of 45.6 kJ/m3.

Crystal structure and its correlation to intrinsic and extrinsic magnetic properties of epitaxial hard magnetic Pr-Co films

Pulsed laser deposited epitaxial ${\mathrm{Pr}}_{x}{\mathrm{Co}}_{100\ensuremath{-}x}$ $(x=8.7\char21{}27.6\phantom{\rule{0.3em}{0ex}}\mathrm{at.}\phantom{\rule{0.2em}{0ex}}%)$ thin films were systematically studied as a function of Pr content. Structural and magnetic measurements reveal different phases for specific composition ranges. In some cases, the phases observed are in contrast to their bulk counterparts. Uniaxial anisotropy at room temperature is observed in all the films enabling excellent hard magnetic properties. Polarization decreases monotonically with the increase of Pr content, whereas coercivity exhibits a broad maximum near the highly anisotropic $\mathrm{Pr}{\mathrm{Co}}_{5}$ composition. For the optimum combination of coercivity and polarization, the measured ${(BH)}_{\mathrm{max}}$ reaches values of $310\phantom{\rule{0.3em}{0ex}}\mathrm{kJ}∕{\mathrm{m}}^{3}$, which exceeds the highest-energy product value reported for RE-Co $(\mathrm{RE}=\text{rare}\text{\ensuremath{-}}\text{earth})$ systems. Temperature-dependent ac susceptibility measurements reveal that films with $x=8.7\char21{}20.4$ undergo a spin reorientation from easy axis to easy cone, but films with $x=22.9\char21{}27.6$ maintain their uniaxial anisotropy throughout the temperature range of investigation. From the comparison of the structural investigations and the spin reorientation temperature measurements, it is concluded that the spin reorientation temperature is insensitive to the change in the lattice parameter of the $\mathrm{Pr}{\mathrm{Co}}_{5\ifmmode\pm\else\textpm\fi{}\ensuremath{\delta}}$ phase.

Fabrication of RE–Fe–B films with highly c-axis texture and excellent hard magnetic properties

RE–Fe–B films were prepared on a Ta buffer layer on thermally oxidized Si substrates by dc magnetron sputtering. The structure, magnetic structure, and magnetic properties of RE–Fe–B films were studied. The results show the preparation procedure of deposition at 470°C to obtain a strong c-axis RE2Fe14B texture coexisting with an amorphous phase and following annealing at 590°C can effectively fabricate RE–Fe–B thin films with highly texture. The result shows that the film, which was deposited at 470°C and following annealing at 590°C, has a high perpendicular coercivity μ0Hci=1.8T and large magnetic energy product (BH)max=238kJ∕m3.

An effective route for the fabrication of rare earth-iron-boron thin films having strong c-axis texture and excellent hard magnetic properties

Rare-earth iron-boron (RE-Fe–B) thin films with a c-axis texture were prepared on a Ta (110) buffer layer on thermally oxidized Si substrates by dc magnetron sputtering. The microstructure, magnetic structure, and magnetic properties of these films were studied as a function of the deposition temperature. The results show that c-axis texture can be obtained over a wide range of deposition temperatures and that the degree of c-axis orientation improves with deposition temperature. It was established that deposition of a RE-Fe–B thin film to obtain grains with a strong c-axis RE2Fe14B texture, coexisting with an amorphous phase, followed by annealing at higher temperature, is an effective route for obtaining excellent hard magnetic properties. Initial results show that a film, which was deposited at 470°C and annealed at 590°C, had a high perpendicular coercivity of 1.8T, in combination with a large maximum energy product of 238kJ∕m3.

Electrodeposition of hard magnetic films and microstructures

Electrochemical deposition of materials with hard magnetic properties in the as-deposited state is essential for the efficient integration of micro-magnetic components into MEMS devices. Here we discuss the growth process and the microstructure-magnetic properties correlation for two Co-rich alloys, Co–Ni–P and Co–Pt. Under suitable synthesis conditions, these materials exhibit perpendicular anisotropy and hard magnetic properties in the as-deposited state; in addition, such properties are maintained up to several micrometer film thickness through close control of the film microstructure. In the case of Co–Ni–P films we achieved a saturation magnetization of 1.21 T (963 emu/cm 3), perpendicular coercivity up to 188 kA/m (2.36 kOe) at a thickness of 10 μm, and energy products up to 4.2 kJ/m 3. Co-rich Co–Pt films were grown on several substrates – Cr, Cu(0 0 1), Cu(1 1 1), and Ru(0 0 0 1) – in order to control magnetic anisotropy and achieve optimum hard magnetic properties. Cu(1 1 1) contributes to stabilize the hexagonal hcp phase at high current density yielding excellent hard magnetic properties, although only in films thicker than 100 nm; saturation magnetization in these films was about 1.04 T (828 emu/cm 3). Perpendicular coercivities up to 485.6 kA/m (6.1 kOe) were obtained in 1 μm thick film deposited at 50 mA/cm 2. Ru(0 0 0 1) seed layers provide an appropriate interface structure to further facilitate the epitaxial growth of hcp films, yielding hard magnetic properties and perpendicular coercivity with a squareness ∼1 in films as thin as 10 nm. The hard magnetic properties were only marginally compromised at large film thickness. Deposition at higher current density (50 mA/cm 2) favored markedly improved hard magnetic properties. The Co–Pt films on Ru exhibited perpendicular anisotropy with anisotropy constant up to 1.2 MJ/m 3. The electrodeposition process was further extended to fill lithographically patterned hole arrays (850 nm diameter, center-to-center distance 2550 nm and about 700 nm thick resist), yielding arrays of micron-sized hard magnetic cylinders with perpendicular coercivity of 361 kA/m (4.54 kOe) and high squareness.