Preparation and characterization of sodium silicate/epoxy resin composite bonded Nd-Fe-B magnets with high performance

As an organic binder for bonded Nd-Fe-B magnets, epoxy resin(EP) has poor heat resistance but good moisture resistance, while sodium silicate(SS) has poor moisture absorption but better heat resistance and corrosion resistance. In order to improve high temperature stability and decrease moisture absorption of bonded Nd-Fe-B magnets, EP/SS composites were applied as the binder to prepare bonded Nd-Fe-B magnets. The magnetic properties, moisture absorption, corrosion resistance, compressive strength and microstructure of composite bonded magnets were investigated. The results show that EP/SS bonded magnets can obtain excellent magnetic properties at room temperature, and even useable magnetic properties a thigh temperature environments at 200°C. EP/SS composite binder effectively improves heat resistance and corrosion resistance of bonded Nd-Fe-B magnets, and reduces the hygroscopic properties. The molecule of sodium silicateis rigid and keeps it original shape at high temperature environments. In addition, SS in composite binder improves the mobility of the magnetic powders during the pre-pressing process, which makes the magnetic powders attain a more regular structure. These two factors will increase the mechanical properties. Moreover, sodium silicate in the composite binder can also cover the surfaces protecting the magnetic powders from oxidation and corrosion. EP in composite binder can cover SS surface to reduce the water absorption of SS as epoxy is a hydrophobic material. The EDX analysis shows that the composite binder has accumulated in the gaps of the magnet powders, which not only improves heat resistance and corrosion resistance, but also increases the mechanical properties. Therefore, EP/SS composite binder endows bonded Nd-Fe-B magnets excellent comprehensive properties.     

Magnetic and magnetostrictive properties of amorphous TbFefFeAl multilayer thin film

Exchange coupling multilayer thin films, which combined giant magnetostriction and soft magnetic properties, were of growing interest for applications. The TbFe/FeAl multilayer thin films were prepared by dc magnetron sputtering onto glass substrates. The microstructure, magnetic, and magnetostrictive properties of TbFe/FeAl multilayer thin film was investigated at different annealing temperatures. The results indicated that the soft magnetic and magnetostrictive properties for TbFe/FeAlmultilayer thin film compared with TbFe single layer film were obviously improved./n comparison with the intrinsic coercivity JHo of 59.2 kA/m for TbFe single layer film, the intrinsic coercivity jHc for TbFe/FeAl multilayer thin films rapidly dropped to 29.6 kA/m. After optimal annealing （350 ℃×60 min）, magnetic properties of Hs=96 kA/m and jHc=16 kA/m were obtained, and magnetostrictive coefficient could reach to 574×10^-6 under an external magnetic field of 400 kA·m^-1 for the TbFe/FeA1 multilayer thin film.     

Relationship between crystal growth mode,preferred orientation and magnetostriction of （Tb0.3Dy0.7）Fe1.95 alloys

The relationship between crystal growth mode, preferred orientation and magnetostrictive properties of （Tb0.3Dy0.7）Fe1.95 alloys was investigated at different directional solidification rates. The results showed that preferred orientation had a strong influence on the characteristics of （Tb0.3Dy0.7）Fe1.95 alloys. At lower solidification rates, the sample with 〈110〉 preferred orientation showed larger low-field magnetostriction and apparent compressive stress effect. The excessive solidification rate resulted in failure of preferred orientation and a poor magnetostrictive performance. With an increase in solidification rates, the crystal growth modes changed gradually from cellular and primary dendrite morphology to developed dendritic morphology. In addition, domain configurations were observed using magnetic force microscopy, and the change of magnetostrictive properties was interpreted in terms of revealing the domain configurations.     

Preparation and Magnetic Properties of Melt-Spinning Nd2Fe14B/α-Fe Nanocomposite Magnets

Nd11Fe71Co8V1.5Cr1B7.5 magnet was prepared by melt-spinning and subsequently annealed. The effects of the wheel speed on the magnetic properties and microstructure were studied. The results reveal that fine nanocomposite microstructure consisting of Nd2Fe14B and α-Fe phases can be developed at an optimum wheel speed of about 21 m·s-1. After optimal annealing (640 ℃×4 min), magnetic properties of Br=0.64 T, jHc=903.5 kA·m-1 and (BH)max=71 kJ·m-3 were obtained for the bonded magnets. The addition of Cr element significantly reduces grain size, increasing the intrinsic coercivity and maximum magnetic energy product.     

High-performance α-Fe/Pr2Fe14B-type nanocomposite magnets fabricated by direct melt spinning

High-performance α-Fe/Pr2Fe14B-type nanocomposite magnets based on the compositions of Pr8Fe86B6 microalloyed with Co, Nb and C were fabricated by direct melt spinning. The coercivity was greatly improved from 5.5 kOe for the Pr8Fe86B6 ribbons to 7.4 kOe for the Pr8Fe85NbB5C ribbons. The balanced high coercivity and remanence were obtained in Pr8Fe75Co10NbB5C ribbons due to the Co substitution for Fe, which led to the significant improvement of magnetic properties in these ribbons. A remanence ratio of 0.82, a coercive field of 6.6 kOe and a maximum energy product of 26.2 MGOe in melt-spun Pr8Fe75Co10NbB5C ribbons were obtained at room temperature.     

Effect of praseodymium and cobalt substitution on magnetic properties and structures in La(Fe_(1–x)Si_x)_(13) compounds

Magnetic properties and structures in La1-zPrz(Fe0.895–xCoxSi0.105)13 (x=0.07, 0.08; z=0, 0.2, 0.4) compounds were investigated. When Pr and Co substituted for La and Fe, the Curie temperature of the compounds was adjusted to around room temperature. The magnetic phase transition was driven from first-order to second-order due to Co substitution. As a second-order phase transition material, the MCE of La0.6Pr0.4(Fe0.825Co0.07Si0.105)13, whose relative cooling power was 175 J/kg under a field change of 2 T, ...     

Effect of Gallium Addition on Magnetic Properties of Nd2Fe14B-Based/ α-Fe Nanocomposite Magnets

The influence of Ga addition on the crystallization behavior and the magnetic properties of nanocomposite Nd2Fe14B-based/α-Fe magnets was investigated. It was found that the addition of 0.2% did not change the crystallization temperature of amorphous alloy, but the magnetic properties were improved significantly because of the strong exchange coupling interaction between the hard and soft magnetic phases. The optimum magnetic properties with iHc = 600. 3 kA· m^-1, B r = 0.75 T, and （BH）max = 88.03 kJ· m^-3 were obtained in bonded Nd9.5（FeCoZr）83.8 Ga0.3 B6.5 magnet with 15 m·s^- 1 wheel speed and 670 ℃ annealing treatment. The apparent improvement of magnetic properties originates from the grain refinement calculated using the Scherrer formula from corresponding XRD patterns and the excellent rectangularity of the demagnetization curve.     

Influence of Zirconium Addition on Magnetic Properties and Temperature Coefficient for Nanocomposite Nd10Fe78.5-xCo5ZrxB6.5 Magnets

The influence of Zr addition on magnetic properties and temperature coefficient for nanocomposite Nd10Fe78.5-xCO5ZrxB6.5 (x=0~4) bonded magnets was investigated. It was found that the room-temperature magnetic properties were remarkably improved with Zr addition due to the grain refinement and increasing volume fraction of the hard magnetic phase. The optimal magnetic properties of Jr=0.689T, iHc=769.4kA·m-1 and (BH)max=84kJ·m-3 were obtained for 2.5% Zr addition. The temperature coefficient of remanence (α) increases slightly and the temperature coefficient of coercivity (β) decreases obviously with increasing Zr content for nanocomposite Nd10Fe78.5-xCo5ZrxB6.5 (x=0~4) bonded magnets.     

Influences of Niobium and Zirconium Additions on Crystallization Behaviors and Magnetic Properties of Melt-Spun （Nd, Pr）2Fe14B／α-Fe Alloys

Effects of Nb and Zr substitutions on the crystal]ization behaviors and magnetic properties of melt-spun (Nd,Pr)2Fe14B/α-Fe alloys were studied.The results show that for (Nd0.4Pr0.6)8.5Fe85.5B6 ribbons, the metastable (Nd,Pr)3Fe62B14 precipitates after the initial crystallization of α-Fe and decomposes into the final mixture of (Nd,Pr)2Fe14B and α-Fe. For(Nd0.4 Pr0.6)8.5 Fe84.5 Zr0.5 Nb0.5B6 ribbons, however,(Nd, Pr)2Fe14B and α-Fe phases precipitate simultaneously. This indicates that both Nb and Zr dopingcan avoid the formation of metastable phase and!     

Dependence of Magnetic Properties of Rapidly Quenching （Nd, Pr）x（FeCoZr）94-xB6 Bonded Magnets on Rare Earths Content

By using sub-everquenching and annealing method which has a wide processing window, (Nd, Pr)x(Fe-CoZr)94-xB6(x=12, 10.5, 10, 9) bonded magnets were prepared and the effect of rare earths content on magnetic properties was investigated. Being spun at sub-ove, quenching speed the as-spun ribbons consist of amorphous phases mixed with fine crystallites. After crystallization under optimum annealing conditions and bonded with 3.25%(mass fraction) epoxy, the magnets obtained the optimum magnetic properties. The rare earths content directly determines the magnetic properties. With the reduction of rare earths content, Br increases but Hci and (BH)max decrease, x=10 is the critical value for the magnetic properties change. Below this value, Br increases slowly meanwhile Hci and (BH)max decrease strongly because alloy contains extra fractions of soft magnetic phase which are not coupled with the hard magnetic phase. This experimental result is consistont with the calculated results using the model of volume fraction of soft magnetic phase coupled completely suggested.     

Synthesis of Iron-Based Laves Phase Containing Praseodymium Magnetostrictive Materials

The synthesis and magnetostriction of PrxTb1-x.Fe2, PrxTb1-x Fe2BO2 and PrxTb1-x（Fe0.6Co0.4）2 alloys were investigated in this study. The addition of boron or cobalt atom in PrxTb1-xFe2 could effectively prevent the formation of non-cubic phases, and Pr concentration limit was successfully increased from 0.2 to 0.4. X-ray step scanning for the PrxTb1-xFe2BO2 and PrxTb1-x（Fe0.6Co0.4）2 alloys showed that PrFe2 possessed a large spontaneous magnetostriction λ1111.     

Effect of niobium on glass-formation ability and soft magnetic properties of Gd-doping glassy alloys

The effect of niobium on glass-formation ability and soft magnetic properties were studied in Fe-Gd-B glassy alloys. The glassy alloys exhibited high glass-formation ability when the element of Nb was added. Bulk glassy rod （Fe0.87Co0.13）68.5Gd3.5Nb3B25 with a diameter up to 3 mm was produced by copper mold casting. The size of the atom might play an important role in increasing glass-formation ability. The coercive force of glassy （Fe0.87Co0.13）71.5.xGd3.sNbxB25 （x=1.2, 1.5, 2, 2.5, 3, 4） alloys decreased after the addition of niobium element and was in the range of 1.5-2.9 A/m. The permeability spectrum of （Fe0.87Co0.13）70.3Gd3.5Nb1.5B25 glassy ribbon showed that the relaxation frequency （f0） was 6.1 MHz.     

Investigation on the magnetomechanical behavior of trilayered GM actuator

In this article, it was suggested a TbFe/Co/Dy trilayered GM （Giant Magnetostrictive） film type actuator and investigated the magnetomechanical characteristics of the actuator for micro application. The trilayered films were fabricated at different thickness ratios to get an optimized structure. TbFe had positive GM properties, and cobalt, dysprosium layers made the magnetostriction property of composite film increase in low magnetic field. To fabricate the Si based microactuator with trilayered film, micromachining processes including RIE （Reactive Ion Etching） and selective DC magnetron sputtering techniques were combined. The deposited film thicknesses were measured by X-ray diffraction （XRD）. As a result, the magnetization of the film on the fabricated actuator was observed to characterize the magnetic properties of the TbFe/Co/Dy film using VSM （Vibrating Sample Magnetometer）. The magnetostriction of the actuator was determined by measuring the differences of curvature of the film coated silicon substrates using the optical cantilever method, and the deflections were also estimated under the external magnetic field lower than 0.5T for micro-system applications.     

Effect of Gallium Addition on Magnetic Properties of Nd2Fe14B-Based/α-Fe Nanocomposite Magnets

The influence of Ga addition on the crystallization behavior and the magnetic properties of nanocomposite Nd2Fe14B-based/α-Fe magnets was investigated. It was found that the addition of 0.2% did not change the crystallization temperature of amorphous alloy, but the magnetic properties were improved significantly because of the strong exchange coupling interaction between the hard and soft magnetic phases. The optimum magnetic properties with iHc=600.3 kA·m-1, Br＝0.75 T, and (BH)max=88.03 kJ·m-3 were obtained in bonded Nd9.5(FeCoZr)83.8Ga0.2B6.5 magnet with 15 m·s-1 wheel speed and 670 ℃ annealing treatment. The apparent improvement of magnetic properties originates from the grain refinement calculated using the Scherrer formula from corresponding XRD patterns and the excellent rectangularity of the demagnetization curve.     

Effect of Post Annealing on the Microstructure and Magnetic Properties of NdFeB/α-Fe/NdFeB Thin Films

A series of nanocomposite thin films, composed of Nd2Fe14B and α-Fe, has been prepared by DC-magnetron sputtering combined ion beam sputtering onto Si (100) substrates. The effects of post annealing on the microstructure and magnetic properties of [NdFeB/α-Fe/NdFeB]-type thin films have been investigated. The X-ray diffraction (XRD) study showed that annealing of the films for 30min at temperatures 550,600,650,700℃ resulted in the appearance of diffraction peaks, characteristic for Nd2Fe14B tetragonal structure, α-Fe and Nd2O3 phases. The investigation using the Vibrating Sample Magnetometer (VSM) with a maximum applied field of 2 T indicated that with the increase of the annealing temperature, the magnetic properties of the multilayer films were improved and reached peak value at 650℃ (Hci=41.72kA·m-1, Mr/Ms=0.4, (BH)max=30.35kJ·m-3), after which the magnetic properties were decreased greatly. Along with the increase of the thickness of α-Fe layer from Tα-Fe16nm, the coercivity Hci, saturation magnetization Ms, and remanence ratio Mr/Ms all declined. As the Atomic Force Microscope (AFM) indicated, after being annealed at 650℃ for 30min, the sample was showed fine surface morphology with grain size 60nm≤dα-Fe≤80nm and 100nm≤dNdFeB≤150nm.     

Effect of Post Annealing on the Microstructure and Magnetic Properties of NdFeB/α-Fe/NdFeB Thin Films

A series of nanocomposite thin films, composed of Nd2Fe14B and α-Fe, has been prepared by DC-magnetron sputtering combined ion beam sputtering onto Si (100) substrates. The effects of post annealing on the microstructure and magnetic properties of [NdFeB/α-Fe/NdFeB]-type thin films have been investigated. The X-ray diffraction (XRD) study showed that annealing of the films for 30min at temperatures 550,600,650,700℃ resulted in the appearance of diffraction peaks, characteristic for Nd2Fe14B tetragonal structure, α-Fe and Nd2O3 phases. The investigation using the Vibrating Sample Magnetometer (VSM) with a maximum applied field of 2 T indicated that with the increase of the annealing temperature, the magnetic properties of the multilayer films were improved and reached peak value at 650℃ (Hci=41.72kA·m-1, Mr/Ms=0.4, (BH)max=30.35kJ·m-3), after which the magnetic properties were decreased greatly. Along with the increase of the thickness of α-Fe layer from Tα-Fe16nm, the coercivity Hci, saturation magnetization Ms, and remanence ratio Mr/Ms all declined. As the Atomic Force Microscope (AFM) indicated, after being annealed at 650℃ for 30min, the sample was showed fine surface morphology with grain size 60nm≤dα-Fe≤80nm and 100nm≤dNdFeB≤150nm.     

Influence of melt spinning and annealing treatment on structures and hydrogen storage thermodynamic properties of La0.8Pr0.2MgNi3.6Co0.4 alloy

La0.8Pr0.2MgNi3.6Co0.4 alloys were prepared by induction melting,annealing and melt spinning techniques.The influences of annealing treatment and melt spinning on phase structure and hydrogen storage properties were systematically investigated.The results of X-ray diffraction determine that the as-cast and as-spun La0.8Pr0.2MgNi3.6Co0.4 alloys consist of LaMgNi4 and LaNi5 phases,while only LaMgNi4 phase is present in the as-annealed alloy.The scanning electron microscope images illustrate that the grain of the alloy is significantly refined by melt spin ning tech no logy.The gaseous hydrogen storage kinetic and thermodynamic properties were measured by using a Sievert's apparatus at different temperatures.The maximum hydrogen storage capacity of the as-cast,as?spun and as-annealed La0.8Pr0.2MgNi3.6Co0.4 alloy is 1.699,1.637 and 1.535 wt.% at 373 K and 3 MPa,respectively.The annealed alloy has flatter and wider pressure plateaus compared with the as-cast and as-spun alloys,which correspond to the hydrogen absorption and desorption process of LaMgNi4 and corresponding hydride.Furthermore,the enthalpy and entropy changes of LaMgNi4 during hydrogenation at different temperatures were calculated using Van't Hoff methods.     

Phase structure and magnetocaloric effect of （Tb1-xDyx）Co2 alloys

Phase structure and magnetocaloric effect of （Tb1-xDyx）Co2 alloys with x=0, 0.2, 0.4, 0.6, 0.8, and 1.0 were investigated using X-ray diffraction analysis, differential thermal analysis, and magnetization measurement. The samples were single phase with cubic MgCu2- type structure; with the increase of Dy content, Tc decreased from 240 K （TbCo2） to 130 K （DyCo2）, and the maximum magnetic entropy change ｜ △SM,max｜ increased from 3.133 to 8.176 J/kg-K under low magnetic field of 0-2 T. The Arrott plot and the change of ｜△SM,max｜ showed that magnetic phase transition from second order to first order occured with the increase of Dy content between x=-0.6 and 0.8.     

Sputtering-pressure dependence of magnetic properties in amorphous Tb_（40）（FeCoV）_（60） films

The Tb40(Fe49Co49V2)60 films were fabricated by magnetron cosputtering from a multiple target arrangement at different argon pressures.The samples were investigated using X-ray diffraction,magnetic force microscope and vibrating sample magnetometer.A strong perpendicular anisotropy was obtained for the sample prepared at 0.4 Pa.The easy direction of magnetization could be turned from perpendicular to in-plane direction either at high working pressures(P Ar >2.0 Pa) or by annealing at temperatures higher than 250 °C.An excellent magnetic softness with coercivity below 3 mT and saturating field of 20 mT in film-plane direction was obtained for the sample prepared at 0.7 Pa and then annealed at 350 °C.     

A Study of Two-Phase Nanocrystalline Nd8.5Fe75 Co5 Cul Zr3 NblB6.5 Permanent Magnet

Nanocrystalline Nd8.5Fe7.5Co5Cu1Zr3Nb1B6.5 ribbons were prepared by melt-spun(18m.s^-1) and subsequent heat treatment (670℃/4 min).Excellent magnetic properties of the bonded mangnet were achieved as follows:Br=0.68 T(6.8kGs).JHc=620.3kA.m^-1(7.8kO3).(BH)max=74kJ.m^-3(9.3MGOe)The results of TEM photomicrographs confirm that the appearance of α-Fe Phase is earlier than that of Nd2Fe14B phase during crystallization process.The addition of Cu and Zr elements shows to be advantageous to the improvement of an intrinsic coercivity and squareness of hysteresis loop.as well as energy product.