Magnetic Properties Of Nd Research Articles

Effect of Nd on structure and magnetic properties of CoPt alloys

The effects of Nd on the microstructure and magnetic properties of Nd x Co 50− x Pt 50 alloys ( x = 0, 0.5, 1.0, 1.5) were investigated. The XRD results indicated that all the alloys that were homogenized at 1000 °C mainly contain the A1 (fcc) phase, while the alloys that were annealed at 675–750 °C consist of the hard magnetic face-centered-tetragonal (fct) phase and magnetically soft fcc phase. In any case, a few amount of NdPt 5 phase exists in alloys when x > 1.0. The (1 1 1) reflection belonging to fct phase shifts to a higher angle and the c/a ratio increases as the Nd content increases, which leads to the decrease in degree of ordering S. As a function of annealing time, both maximum values of the coercivity H c and remanence ratio m r were reached in Nd 0.5Co 49.5Pt 50 alloys annealed at 675 °C for 40 and 60 min, respectively. For the series of Nd x Co 50− x Pt 50 alloys annealed at 675 °C for 60 min, the H c decreases monotonically with the increase in Nd concentration but the value of m r is enhanced at first and then weakened, showing the highest value of 0.84 at x = 0.5.

Effect of film morphology on the magnetic properties for Nd–Fe–B thin films

The microstructure and magnetic properties of Nd–Fe–B thin films with a particulate structure were investigated. The nominal thickness of the Nd–Fe–B layer ( t N) was varied from 2 to 50 nm on a (0 0 1) Mo buffer layer. The films were grown with their c-axis perpendicular to the plane, and the morphology of the film with t N=2 nm was shown to be particulate from an atomic force microscope image. The slope of the initial magnetization curve became steeper by increasing the t N value in the initial magnetization curve, indicating that the film morphology composed of single domain particles changed to that of multi-domain particles with growth. The film with t N=8 nm, which had a structure consisting of a mixture of single and multiple domain particles, showed the maximum value of the coercivity measured in the direction perpendicular to the film plane ( H c) as 19.5 kOe.

Structural and Magnetic Properties of Nd(Fe,Mo)12Nx, Compounds Produced by Strip-Casting Method

The strip casting (SC) technique is employed to fabricate Nd(Fe,Mo)12Nx magnets. The crystallographic structure, intrinsic and permanent magnetic properties, as well as the microstructures of the compound are investigated. There are prominent advantages for the SC Nd-Fe-Mo alloys and their nitrides when compared with the samples prepared by the conventional casting (CC) method: (1) SC technique rebounds to the formation of the compounds crystallizing in a ThMn12-type structure. A single-phased host alloy Nd(Fe,Mo)12 can be directly prepared by strip casting without any isothermal annealing. Accordingly, lower energy cost and less rare earth demand notablely benefit the manufacture processing from a point of economizing. (2) The intrinsic magnetic properties, such as Curie temperature Tc, saturation magnetization Ms and anisotropy field Ha of the SC sample exceed the CC sample due to a phase forming condition with less-Mo-depended. (3) The microstructure studies also demonstrate that the SC compound contains finer grains, better-proportioned phase distribution than the CC compound. Optimized final particles are observed aligned in their easy axis and the energy product of powder sample is up to (BH)max ∼ 22 MGOe (176kJ/m3).

Electrical resistivity and magnetic properties of Nd–Fe–B alloys produced by melt-spinning technique

The electrical resistivity and magnetic properties of Nd–Fe–B alloys produced by the melt-spinning technique were examined. The wheel speed, which is closely associated with the cooling rate, was varied in the production of the melt-spun ribbons. The resultant melt-spun ribbons had various microstructures ranging from dendrite to equiaxed grains, and finally to an amorphous structure, depending on the wheel speed. It was found that both the resistivity and coercivity of the melt-spun ribbons were strongly dependent on the wheel speed. The maximum resistivity of 3.15 μΩ m was achieved in a melt-spun ribbon primarily consisting of the amorphous phase with a small amount of the Nd 2Fe 14B phase, while the highest coercivity of 1.97 MA/m was achieved in a melt-spun ribbon primarily consisting of the Nd 2Fe 14B phase with a small amount of the amorphous phase. The relationships among the cooling rate, microstructure, resistivity, and coercivity of the Nd–Fe–B alloys were determined.

Effects of Ti and C additions on the nanostructure and magnetic properties of (Nd, Pr)– (Fe, Co, Ga)–B melt-spun nanocomposite ribbons

In this work the effects of Ti and C additions on the structure and magnetic properties of Nd–Fe–B nanocomposite permanent magnetic alloys with nominal composition of Nd 9.4Pr 0.6Fe bal.Co 6B 6Ga 0.5Ti x C x ( x=0, 1.5, 4.5) have been investigated. As-spun ribbons were examined by using X-ray diffractometer (XRD) and differential scanning calorimetry (DSC). The results show that Ti and C additions enhance the glass forming ability and increase crystallization temperature. XRD results of annealed ribbons indicate that Ti and C compose TiC. TEM observation reveals that the formation of TiC refines the microstructure of annealed ribbons consisting of 1.5 at% Ti and 1.5 at% C additions, which leads to enhancement of magnetic properties.

Effect of super heat treatment on crystallization behavior and magnetic properties of Nd 4.5Fe 77B 18.5 nanocomposites

Melt-spun Nd 4.5Fe 77B 18.5 ribbons were prepared under various superheat temperatures. The microstructure characteristics, crystallization behavior, and subsequent magnetic properties of Fe 3B/Nd 2Fe 14B nanocomposite magnets were investigated using X-ray diffraction, differential thermal analysis, and vibrating sample magnetometry. It was shown that melt spinning at different quenching temperatures caused the as-quenched ribbons to have distinctive crystallization behavior. Depending on superheat temperature, phase transformation of the ribbons during annealing may take place in one of the following sequences: (1) amorphous phase (Am)→Am'+Fe 3B→Fe 3B+ Nd 2Fe 23B 3→ Fe 3B+Nd 2Fe 14B, or (2) amorphous phase(Am)→Am'+Fe 3B→Fe 3B+Nd 2Fe 14B. For the latter, the ribbon after optimal annealing exhibited single-phase magnetic behavior. In the first case, magnetic properties of the optimally heat treated ribbons deteriorated and an apparent kink could be seen along the demagnetization curves near the zero field.

Effects of compositions on characteristics and microstructures for melt-spun ribbons and die-upset magnets of Nd 12.8+ xFe 81.2− x− y− zCo yGa zB 6

The effects of varying Nd-contents on the magnetic properties of Nd 12.8+ x Fe 81.2− x− y− z Co y Ga z B 6 ribbons and the resulting die-upset magnets have been investigated. It was found that the Nd content has a significant effect on both magnetic properties and texture of the die-upset magnets. An optimum Nd content exhibits good texture, while both Nd-lean and excessively Nd-rich Nd–Fe–B alloys lead to unsatisfactory textures. The magnetic properties and texture of the die-upset magnets strongly deteriorated with a further increase in the Nd-content. The thermo-mechanical characteristics and the formation mechanism of two kinds of cracks in backward-extruded ring magnets have also been investigated.

Effect of annealing on microstructural changes of Nd-rich phases and magnetic properties of Nd–Fe–B sintered magnet

The microstructural changes of Nd-rich interface phases during postsintering annealing were investigated. A mixture of very fine (about 2–3 nm) crystallites of hexagonal h-Nd2O3, cubic Ia3¯-Nd2O3 (C-Nd2O3), and amorphous phases were observed at the interface phase in the as-sintered magnet and after the first postsintering annealing process. The transformation from h-Nd2O3 to C-Nd2O3 occurred during the second postsintering annealing process, and the resulting C-Nd2O3 has the proper crystallographic relation with the main phase. The reduced lattice mismatch between the (110) plane of C-Nd2O3 interface phase and the (001) or (100) plane of Nd–Fe–B main phase after the second postsintering annealing process is the primary reason for the enhancement in the magnetic properties.

Magnetic properties of Nd–Fe–B thick film magnets prepared by using arc deposition

Nd–Fe–B thick film magnets with the thickness of several 10 μm were prepared by using an arc-deposition method with the high vacuum of 2×10−5 Pa. Good transference for the compositions could be confirmed between a Nd–Fe–B target and a film. In addition, the highest deposition rate reached approximately 10 μm/h. The structure of as-deposited films was amorphous, therefore a pulse-annealing method was adopted as a high-speed crystallization method. The average grain diameters of crystallized films prepared under the annealing time for approximately 3.5 s were 35 nm. The values of coercivity, remanence, and (BH)max for a Nd–Fe–B thick film with a stoichiometric composition were approximately 710 kA/m, 0.75 T, and 56 kJ/m3, respectively.

Improvement of corrosion resistance and magnetic properties of Nd–Fe–B sintered magnets by Al 85Cu 15 intergranular addition

To improve the corrosion resistance and magnetic properties, Al 85Cu 15 (at.%) compound powders were added to (Pr, Nd) 14.8Fe 78.7B 6.5 sintered magnets as grain boundary modifiers. The corrosion resistance was found to be remarkably improved by small additions of Al 85Cu 15 powders. When 1.2 wt% Al 85Cu 15 was added, the corrosion rate of magnets in humid environments was reduced by two orders of magnitude. This is partly due to the stability enhancement of the (Pr, Nd)-rich intergranular phase by Cu and Al. In addition, the occurrence of the Cu-rich phase ((Pr, Nd) 22Fe 56Cu 10Al 2O 10), whose open-circuit potential is higher than the (Pr, Nd)-rich intergranular phase, may be another reason for the improvement of the corrosion resistance. Furthermore, the magnetic properties of (Pr, Nd) 14.8Fe 78.7B 6.5 were also improved by adding 0.3–1.2 wt% Al 85Cu 15. Optimum addition amount was 0.6 wt%. The improvement of the magnetic properties may be related to the microstructural modification and the increase of magnet density.

Effect of yttrium substitution on magnetic properties and microstructure of Nd-Y-Fe-B nanocomposite magnets

The phase evolution, microstructure and magnetic properties of Nd 9– x Y x Fe 72Ti 2Zr 2B 15 ( x=0, 0.5, 1, 2) nanocomposite ribbons were investigated. It was found that substitution of Y enhanced glass forming ability of the over-quenched ribbons and stabilized the amorphous phase during post annealing treatment. Appropriate content of Y substitution effectively refined the microstructure and enhanced the remanence of the annealed samples. The residual amorphous intergranular phase in the annealed sample improved the squareness of loops, resulting in enhanced maximum energy product. The optimum annealing treatment significantly improved magnetic properties of the Y substituted ribbons. Best magnetic properties, J r=0.78 T, H ci=923.4 kA/m, ( BH) max=98.5 kJ/m 3 were obtained from Nd 8YFe 72Ti 2Zr 2B 15 ribbon spun at V s = 4 m/s, and annealed at 700 °C for 10 min.

Mechanism of the enhancement of discharge rate property for Nd 0.8Mg 0.2(Ni 0.8Co 0.2) 3.8 hydrogen storage alloy by magnetic annealing

For further improving the rate properties of Nd 0.8Mg 0.2(Ni 0.8Co 0.2) 3.8 hydrogen storage alloy, the alloy was annealed in high magnetic fields (10 T). The results showed that the electrochemical properties and magnetic properties of Nd 0.8Mg 0.2(Ni 0.8Co 0.2) 3.8 hydrogen storage alloy were considerably enhanced. And there was no change of the phase composition. The lattice constants of c and c/a ratio increased for the sample magnetically annealed, yielding uniaxial magnetic anisotropy along the c axis. The increase of c and c/a ratio enlarged interstitial volume, leading to a larger diffusion channel for hydrogen atoms, and resulted in high hydrogen storage capacity and rate properties.

Crystal structure and magnetic properties of Nd(Mn1–xFex)2Si2 compounds

X-ray powder diffraction, resistivity and magnetization studies have been performed on polycrystalline Nd(FexMn1–x)2Si2 (0 ≤ x ≤ 1) compounds which crystallize in a ThCr2Si2-type structure with the space group I4/mmm. The field-cooled temperature dependence of the magnetization curves shows that, at low temperatures, NdFe2Si2 is antiferromagnetic, while the other compounds show ferromagnetic behaviour. The substitution of Fe for Mn leads to a decrease in lattice parameters a, c and unit-cell volume V. The Curie temperature of the compounds first increases, reaches a maximum around x = 0.7, then decreases with Fe content. However, the saturation magnetization decreases monotonically with increasing Fe content. This Fe concentration dependent magnetization of Nd(FexMn1–x)2Si2 compounds can be well explained by taking into account the complex effect on magnetic properties due to the substitution of Mn by Fe. The temperature's square dependence on electrical resistivity indicates that the curve of Nd(Fe0.6Mn0.4)2Si2 has a quasi-linear character above its Curie temperature, which is typical of simple metals.

Complex ferromagnetic state transformation in single crystal [formula omitted

The magnetic properties of Nd 0.5 Pb 0.5 MnO 3 single crystal have been studied by dc magnetization and magnetotransport data. The ferromagnetic (FM) to paramagnetic (PM) transition temperature T C and the metal–insulator transition temperature are 177 and 194 K, respectively. The deviation of the inverse susceptibility from the Curie–Weiss law indicates the presence of a Griffiths-like phase in this system, viz., an inverse susceptibility characterized by χ - 1 ∝ ( T - T C Rand ) 1 - λ with λ = 0.81 and T C Rand = 183 K close to the T C 177 K. The slopes of H / M vs. M 2 isotherms are negative between 300 and 194 K and positive above 300 K and below 194 K. The transition cannot be regarded as first or second order on the basis of the Banerjee criterion. The above interesting and complex magnetic transition is a manifestation of competition between the double exchange mechanism and correlations arising from coupled spin and lattice degrees of freedom present in studied system. To analyze the magnetism around T C , the critical behavior of Nd 0.5 Pb 0.5 MnO 3 is investigated based on the data of static magnetization measurements. It is seen that the critical behavior of Nd 0.5 Pb 0.5 MnO 3 belongs to the mean-field model and shows a second-order like magnetic transition at high fields, however, the poor scaling is found toward low fields, which suggest that the critical behavior is related to the observed complicated magnetic transition. The possible origin of observed complex FM state has been discussed based on the competition between the charge/orbital order clusters and the A site disorder.

Magnetic properties of Nd–Fe–B/FeMn multilayer films

[Nd–Fe–B( x nm)/FeMn( d nm)] n thin films were deposited by magnetron sputtering on Si (100) substrates heated at 650 °C. The influence of the composition and thickness of FeMn layer on the structure and magnetic properties of Nd–Fe–B films are investigated. The Nd–Fe–B/FeMn multilayer films present an enhanced coercivity and a reduced saturation magnetization, in comparison with those of a Nd–Fe–B single layer. The coercivity of [Nd–Fe–B( x nm)/FeMn(5 nm)] n films increases with increasing the period number of FeMn layer for the same thickness of magnetic layer, while the coercivity in [Nd–Fe–B(50 nm)/FeMn(5 nm)] n films increases with decreasing the period number of Nd–Fe–B/FeMn bilayers. The coercivity H c of about 17.2 kOe is achieved in the Nd–Fe–B(50 nm)/FeMn(5 nm) film.

Surface quality, microstructure and magnetic properties of Nd 2(Fe,Zr,Co) 14B/α-Fe alloys prepared by different melt-spinning equipments

The effects of melt-spinning equipments on the surface quality, microstructure and magnetic properties of Nd 2(Fe,Zr,Co) 14B/α-Fe magnets have been studied. The ribbons prepared by the induction-melt spurt-spinning equipment have smooth surfaces and uniform thickness. However, the ribbons prepared by the arc-melt overflow-spinning equipment have rough surfaces and inhomogeneous thickness, which makes the cooling rate nonuniform through the thickness of ribbons and causes the occurrence of coarse grains. The ribbons prepared by induction-melt spurt-spinning equipment show better magnetic properties than the ribbons prepared by arc-melt overflow-spinning equipment, even using the same alloy composition. By properly increasing the Zr content, the glass forming ability of alloy is improved, which can lessen the detrimental effect of cooling rate fluctuation, thus enhancing the magnetic properties of ribbons prepared by the arc-melt overflow-spinning equipment.

Magnetic properties of Nd 1−xK xMnO 3 compounds

Polycrystalline Nd 1− x K x MnO 3 ( x=0.10–0.20) compounds have been prepared in single phase form with Pbnm space group. The magnetic properties were studied by measuring dc magnetization and ac susceptibility. They exhibit paramagnetic to ferromagnetic transition with transition temperature ranging from 116 to 128 K. The magnetization data have been analyzed by using Brillouin function model and by taking into account the ferromagnetic interaction. The effective spin contribution towards ferromagnetic interaction and spin canting angle have been estimated. The spin canting angle is found to decrease with increase in doping. Magneto-caloric effect (MCE) has been studied and the maximum change in entropy was found to be 1.76 J/kg K for 1 T field. Metal–insulator transition and colossal magnetoresistance of the order of 60% for 1 T field have been observed for x=0.20 sample.

Improvement of the magnetic properties of Nd 9.5Fe 81Zr 3B 6.5 nanocomposite magnets by semi-melt spinning

Nd 9.5Fe 81Zr 3B 6.5 ribbons are prepared by single roller melt-spinning technique at 1150 °C which is in the solid and liquid coexistence zone. The phase evolution and magnetic properties were studied by X-ray diffraction, differential scanning calorimetry, transmission electron microscopy observations, and magnetization measurements. The experimental results show that in comparison to the ribbons quenching at higher temperature, the thickness of ribbons prepared at 1150 °C are insensitive to the wheel speed and an uniform nanoscale structure with fine grains can be obtained directly from the semi-melt and the exchange coupling interaction between the grains was enhanced for the nanocomposite permanent alloy which can contributed to excellent magnetic properties.

Effects of Ti Addition on Microstructure and Magnetic Properties of B-rich Nd9.4Fe79.6-xTixB11 Nanocrystalline Alloys

The effects of Ti addition on the microstructure and magnetic properties of Nd 9.4 Fe 79.6- x Ti x B 11 ( x =0, 1, 2, 4, 6) nanocrystalline alloys were investigated. The results show that Ti addition suppresses the formation of unfavorable soft Nd 2 Fe 23 B 3 and Fe 3 B phases, and promotes the formation of Nd 2 Fe 14 B phases. When the Ti content reaches a certain amount, Ti may precipitate as TiB 2 from the alloys. TiB 2 may serve as inoculants and promotes uniform nucleation, and thus increases the exchange coupling between the hard and soft phases. As a result, excellent magnetic properties of B r =0.87 T, H cj =931 kA/m and ( BH ) max =115.4 kJ/m 3 are achieved in Nd 9.4 Fe 75.6 Ti 4 B 11 alloy ribbons.

Grain Interface Modification and Magnetic Properties of Nd–Fe–B Sintered Magnets

Effective grain interface modification was conducted to increase the coercivity of Nd–Fe–B sintered magnets without degrading their magnetic properties seriously. The surface of magnet pieces (3.0×3.0×2.8 mm3) was uniformly coated with a Dy or Tb metal film, and then each metal was introduced inside the magnets through the Nd-rich grain boundary regions for enriching them on the surface around the Nd2Fe14B grain particles. The coercivities of the Dy- and Tb-metal-treated magnets (HcJ = 1.45 and 1.81 MA/m, respectively) were considerably improved compared with that of the untreated magnet (HcJ = 0.98 MA/m), suggesting that the aligned magnetic domain structure was effectively stabilized by such a Dy- or Tb-enriched interface around the Nd2Fe14B grain particles.