Magnetic Properties Of Nd Research Articles

Magnetic phase transitions in Nd 1− xY xMn 2Ge 2 (0 ≤ x ≤ 0.6)

The structure and magnetic properties of Nd 1− x Y x Mn 2Ge 2 (0.0≤ x≤0.6) were studied by X-ray powder diffraction and magnetization measurements. All compounds crystallize in the ThCr 2Si 2-type structure with space group I4/ mmm. Substitution of Y for Mn led to a linear decrease in the lattice constants and the unit cell volume. Increasing substitution of Y for Nd in NdMn 2Ge 2 shows a depression of ferromagnetic ordering and the gradual development of antiferromagnetic ordering.

Effect of Y addition on the microstructure and magnetic properties of Nd 60− xY xFe 30Al 10 mould-cast alloys

The effect of Y addition on the phase formation, microstructure, and magnetic properties of Nd 60− x Y x Fe 30Al 10 (0≤ x≤30) mould-cast alloys has been investigated. The X-ray diffraction (XRD) patterns of the x=0 rods exhibit Nd peaks superimposed on a diffuse background and the rods show hard magnetic properties at room temperature with a coercivity in the range of 3–4 kOe. The diffuse background in the XRD patterns of the x=0 rods and the hard magnetic properties are attributed to the amorphous-like A 1 structure. The A 1 structure is a mixture of Fe- and Nd-rich regions. The formation of the A 1 structure can be related to the absence of the MgCu 2-type NdFe 2 Laves phase. The XRD patterns and micrographs of the x=10 and 30 rods show that partial substitution of Nd by Y promotes the formation of the MgCu 2-type RFe 2 (R≡Nd or Y) phase. The formation of the MgCu 2-type RFe 2 phase is manifested by the vanishing room temperature coercivity of the as-cast rods with x=10 and 30.

Specific heat and magnetic properties of Nd0.5Sr0.5MnO3 and R0.5Ca0.5MnO3 (R=Nd, Sm, Dy, and Ho)

Magnetization and specific heat measurements of Nd0.5Sr0.5MnO3, Nd0.5Ca0.5MnO3, Sm0.5Ca0.5MnO3, Dy0.5Ca0.5MnO3, and Ho0.5Ca0.5MnO3 samples were performed. Near the charge ordering (CO) and ferromagnetic transition temperatures, the specific heat curves showed peaks superimposed to the characteristic response of the lattice oscillations. These peaks allowed us to estimate the entropy variation for each phase transition. The entropy variation corresponding to the CO transition was higher than the one corresponding to the ferromagnetic transition. Furthermore, specific heat measurements in presence of a 9 T magnetic field showed that this field was not strong enough to affect the specific heat in the CO phase transition region. Our results suggest that the CO phase is very stable and almost independent of magnetic fields.

Magnetic properties of Nd–Fe–B system anisotropic HDDR powder made from segregated master ingots

In order to examine the possibility of applying the HDDR process to segregated master ingots, Nd–Fe–B system HDDR powders were made from ingots with different levels of homogeneity, and their structures and magnetic properties were evaluated in detail. HDDR powders made from segregated as-cast ingots displayed anisotropy and large coercivity. They had a nearly homogeneous Nd 2Fe 14B phase, although some large areas with α-Fe and Nd-rich regions of 30 μm in size were present after the HD process. With increasing in the homogeneity level of the master ingots, the anisotropy of HDDR-processed powders decreased and their coercivity increased. In addition, an intermediate Ar treatment was applied between the HD and DR processes to improve the magnetic properties. As a result, the effect of the IA treatment was clearly confirmed, and good magnetic properties of B r=1.23 T, H c J =848 kA/m and ( BH) max=238 kJ/m 3 were obtained.

The effect of nitrogen insertion in the Nd 2− xGd xFe 17N y gadolinium substituted compounds

The structural and magnetic properties of Nd 2− x Gd x Fe 17N y ( x=0–2 and y≈3) gadolinium substituted compounds were studied. X-Ray diffraction characterization showed that all our samples are single phase and crystallize in the rhombohedral Th 2Zn 17-type structure. Nitrogen insertion in Nd 2− x Gd x Fe 17 samples induced an increase in the unit-cell volume. This increase was found to be about 5.6% for all gadolinium contents. Magnetization measurements showed that nitrogen insertion induced a strong increase in the Curie temperature, Δ T c= T cy− T c0, which depends on the gadolinium content. The values of Δ T c decrease with increasing gadolinium concentration. It was found to decrease from 125% for x=0 to 70% for x=2. Nitrogen insertion leads to an increase in the saturated magnetization, μ s( y)− μ s(0)/ μ s(0), which increases with increasing gadolinium content. It was found to increase from 26% for x=0 to 53% for x=2. The volume effects on the Curie temperature of our samples have been studied. The evolution of Grüneisen parameter defined by Γ versus gadolinium contents was linear.

Effects of cooling rate on microstructures and magnetic properties of Nd–Fe–B alloys

The microstructures and magnetic properties of Nd–Fe–B alloys produced by rapid solidification processing techniques were examined by X-ray diffraction, scanning electron microscopy, differential scanning calorimetry, and in a vibrating sample magnetometer. Two rapid solidification processing techniques, metallic mold casting and melt-spinning, were used to investigate the influences of cooling rates on the microstructure and magnetic properties of the Nd–Fe–B alloys. The Nd–Fe–B alloys had equiaxed Nd 2Fe 14B grains together with α-Fe dendrites when produced by the metallic mold casting technique with moderately high cooling rates (3.3×10 2 to 1.2×10 3 K s −1). The Nd–Fe–B alloys had fine equiaxed Nd 2Fe 14B grains with or without amorphous phase when produced by the melt-spinning technique with high cooling rates (4.3×10 5 K s −1 to 1.5×10 6 K s −1). The relationships among the cooling rate, microstructure, and coercivity of the Nd–Fe–B alloys were determined.

Effect of carbon substitution on the magnetic properties of Nd–Fe–(B,C) nanocomposite magnets

The purpose of the present work is to study the effect of carbon substitution for boron on the magnetic and structural properties in nanocomposite Nd 10Fe 82B 8− x C x , ( x=0, 2, 4, 5, 6, 7) ribbons in correlation with their crystallization behavior. Four different structural states were observed in as-spun ribbons depending on the carbon content x and the wheel speed: (i) Nd 2Fe 14(B,C)+α-Fe, (ii) Nd 2Fe 14(B,C)+Nd 2Fe 17C x +α-Fe, (iii) Nd 2Fe 17C x +α-Fe and (iv) amorphous. In annealed ribbons, the 2:17:C x phase transforms into the 2:14:1, whereas the amount of α-Fe phase increases with x. The coercivity has a maximum of 8.7 kOe for x=2, followed by a gradual decrease with further increase of carbon concentration. The deterioration of the magnetic properties with x can be associated with the change in the crystallization behavior and the coarsening of the microstructure for x>4.

Structure, magnetic properties and phase separation of [formula omitted

Structure and magnetic properties of Nd 0.5Ca 0.5Mn 1− x Ga x O 3 (0⩽ x⩽0.1) were investigated systematically through X-ray diffraction, magnetization and electron spin resonance (ESR) measurements. It was found that substituting Mn with Ga reduces the charge ordering temperature ( T CO) and induces an additional peak in magnetization–temperature curve at low temperature. Both the temperature and magnetic field dependence of the magnetization in zero-field-cooling and field-cooling modes suggest that, in the Ga-doped samples, spin-glass-like phase induced by Ga-doping and antiferromagnetic charge-orbital-ordered (COO) phase coexist at low temperature. Furthermore, the ESR spectra indicate that, when the temperature is between the Neel temperature T N and the T CO, the paramagnetic phase and antiferromagnetic COO phase coexist and the volume fraction of the former increases with temperature at the expense of the latter. In addition, magnetization evidences for the interaction between Nd and Mn ions are present.

Investigation of high saturation magnetization of low rare-earth content α-Fe/Nd2Fe14B bulk exchange-spring magnets

An investigation was made of the magnetic properties of Nd–Fe–Co–V bulk exchange-spring magnets fabricated by spark plasma sintering and consisting of a hard Nd2Fe14B phase and a soft α-Fe phase and having a low rare-earth content of Nd=2–7 at. %. The high saturation magnetization of the bulk exchange-spring magnets was confirmed experimentally, and the measured data agreed well with the saturation magnetization values estimated from their respective rare-earth content. The saturation magnetization values were nearly uniform and were not dependent on changes in the grain size. Additionally, the specific resistance of the samples nearly coincided with the values interpolated from the specific resistances of an ordinary sintered pure Fe bulk compact and a sintered Nd–Fe–B magnet. These results suggest that the α-Fe/Nd2Fe14B bulk exchange-spring magnets did not contain any appreciable grain boundary phase between the fine nanoscale-size grains or tertiary phase.

Phase diagram and magneto-transport properties in Nd 1− xSr xMnO 3 crystals

We have investigated electronic transport and magnetic properties of Nd 1− x Sr x MnO 3 crystals with controlled band filling (0.5⩽ x⩽0.8) grown by the floating zone method. The detailed phase diagram of over-doped Nd 1− x Sr x MnO 3 was obtained through magnetization, resistivity, and crystal structure measurements. We have found the phase boundary from an insulator with tetragonal symmetry to a metal with pseudocubic one at high temperatures ≈450 K . The observed insulator–metal phase transition is attributed to the orbital order–disorder transition.

Structure and magnetic properties of Nd xFe 83− xB 17 alloys

The crystallization, crystal structure, microstructure and magnetic properties of Nd x Fe 83− x B 17 alloys have been investigated. It is found that with increasing Nd content, the crystallization temperature of amorphous Nd x Fe 83− x B 17 alloys increases, but the magnetization decreases. On annealing, amorphous alloys crystallize to different crystalline phases and the coercivity increases, depending strongly on Nd content. A new hard magnetic alloy of Nd 3Fe 80B 17 has been obtained. This alloy consists of α-Fe and Fe 3B phase containing a small amount of Nd. The hard magnetic properties originate from the Fe 3B phase containing Nd.

Transport and magnetic properties of Nd0.67Sr0.33MnO3/YBa2Cu3O7 multilayers

We have fabricated perovskite superlattices consisting of ferromagnetic metallic oxide Nd0.67Sr0.33MnO3 (NSMO) and superconducting YBa2Cu3O7 (YBCO). We have investigated structural, transport and magnetic properties of a series of multilayers, in which the layer thickness of NSMO is fixed and that of YBCO varied from 2 to 6 unit cells. We find that the superconducting phase is suppressed for YBCO layer thickness lower than 3 unit cells in NSMO/YBCO multilayered structure. Magnetic moment versus external magnetic field hysteresis curves shows a coexistence of ferromagnetism and superconductivity nearly in the scale of their characteristic lengths.

Structure and magnetic properties of Nd0.5Sr0.4Pb0.1MnO3 manganites

Structure,magnetic and transport properties of polycrystalline Nd0.5S r0.4Pb0.1MnO3 were experimentally studied by ne utron powder diffraction at room temperature and magnetic measurement.The neutron diffraction shows that the space group of this orthorhombic structure is Pnma,i.e.its structure exhibits crystal field distortion.Its Curie temperature TC equals 273K by the M-T curve.According to the R-T curve,it shows a ferromagnetic metal- paramagnetic semiconductor transition as temperature increases and Tp =225 K.Using the competing between manganites crystal field and double exchange inter action explains the metal property at room temperature.

Effects of Zn coating on the microstructure and magnetic properties of Nd–Fe–B magnets

Recent work at Birmingham has shown that the use of a low-pressure pack sublimation (LPPS) process produces Zn-coatings on Nd–Fe–B magnets, which result in dramatic improvements in corrosion resistance. In the present work we have studied the microstructures of the LPPS coatings and their effects on the magnetic properties of the magnets. It was found that the coating process had a small detrimental effect upon the magnetic properties of the magnets. For example, in one case, production of a 12 μm LPPS Zn coating led to a decrease of ∼3% in both coercivity and remanence. Microstructural changes were, however, confined to the near-surface regions with three microstructural ‘layers’ identified: A surface region saturated in Zn consisting mainly of Fe–Zn compounds which resemble those observed previously for galvanised steel (layer 1). A transition region in which grain boundary films of the Fe–Zn compounds surround the hard magnetic Nd 2Fe 14B grains (layer 2). An unaffected substrate with no ingress of Zn (layer 3). It can be inferred from these observations that there are microstructural differences between the LPPS coatings on Nd–Fe–B magnets and those for galvanised steel. Moreover, it is shown that the change in magnetic properties is consistent with an effective reduction in the volume fraction of the Nd 2Fe 14B phase, rather than with any change in the inherent characteristics of the phase.

HDDR Characteristics and Magnetic Properties of Nd15(Fe1-xCox)77B8(x=0-0.6) Alloys

HDDR characteristics and magnetic properties of Nd_(15)(Fe_(1-x)Co_x)_(77)B_8 (x = 0-0.6) alloys were investigated. The effect of applying magnetic field during the recombination step on the anisotropic nature of the HDDR-treated material was also examined. The Nd₂(Fe, Co)₁₄B phase in the Nd-Fe-B alloys with high Co-substitution alloy had remarkably enhanced phase stability. The Nd_(15)(Fe_(1-x)Co_x)_(77)B_8 alloys with high Co-substitution could be HDDR-treated successfully by only using high pressure hydrogen. However, these alloys had no appreciable coercivity. The poor coercivity of the HDDR-treated Nd_(15)(Fe_(1-x)Co_x)_(77)B_8 alloys with high Co-substitution was attributed to the Nd(Fe, Co)₂ phase in the alloys. The magnetic filed applied during the recombination step had little effect on the anisotropic nature of the HDDR-treated powder.

Enhanced magnetic properties of Nd–Fe–B thin films crystallized by heat treatment

Nd 2Fe 14B Φ phase crystallites were formed in Nd 16.7Fe 65.5B 17.8 thin films prepared by RF sputtering with subsequent heat treatment. The 2 μm-thick films were deposited onto 0.1 mm Mo sheets at an average substrate temperature ( T s) of 365°C. The enhanced magnetic properties of the magnetically anisotropic thin films were investigated using different heating rates ( h r) of 10°C, 20°C, 50°C and 100°C/min in an annealing experiment. Transformation from the amorphous phase to the crystalline phase is clearly manifested by the formation of fine crystallites embedded as a columnar matrix of Nd 2Fe 14B phase. High-resolution scanning electron microscope data of the cross-section of the annealed films show columnar stacking of Nd 2Fe 14B crystallites with sizes <500 nm. Transmission electron microscope observations revealed that the microstructure of these films having out-of-plane magnetization consists of uniformly distributed Φ phase with grain size around 400 nm together with small Nd rich particles. This grain size of Φ phase is comparable to the single domain particle diameter of Nd 2Fe 14B. Significant change in i H c, 4 πM r⊥ and 4 πM s⊥ with h r was confirmed. Annealing conditions with a heating rate of 50°C/min to an annealing temperature ( T a) of 650°C for 30 min was consequently found to give optimum properties for the NdFeB thin films. The resulting magnetic properties, considered to be the effect of varying h r were i H c= 1307–1357 kA/m, 4 πM r⊥=0.78–1.06 T and 4 πM s⊥=0.81–1.07 T.

Effects of post-sintering annealing on magnetic properties of Nd–Fe–B sintered magnets

Dependence of the coercive force of (Nd, Dy)–Fe–B magnets on annealing time, temperature and the order of annealing step were investigated. The two schemes of heat treatment were used: HT1—cooling at 925°C to 20°C before annealing and HT2—cooling at 925°C to annealing temperature. The annealing temperature dependences of H ci for HT1 and HT2 are substantially different. These dependences reveal three phase's transformations in microstructure of magnets, which corresponded the maxima of H ci around 450°C, 535°C, 590°C. The correlation between annealing behavior of H ci and hypothetic metastable Fe–Nd diagram was found. We supposed that below eutectic point at 640°C (L⇌A+Nd) the series of consecutive eutectoid decompositions of A phase take place. The origin of new Fe-rich phases occurs preferentially at the surface of Nd 2Fe 14B grains. The size, morphology and number of initial precipitates are determined by temperature of annealing. At high temperature the separate large precipitates form “roughness” on the surfaces of Nd 2Fe 14B grains and decrease H ci. At low temperature continuous thin layers make “smoothing” better and increase H ci.

Crystal growth, structural and magnetic properties of Nd 1− xPb xMnO 3

Single crystals of Nd 1− x Pb x MnO 3 with various dopant concentrations ( x=0.15, 0.2, 0.3, 0.4 and 0.5) are grown by high temperature solution growth technique using PbO–PbF 2 flux. Charge-to-flux ratio and PbO–PbF 2 composition are optimized to grow good quality crystals at lower temperature. When the PbO:PbF 2 ratio is close to the eutectic composition, crystal yield has improved. Powder X-ray diffraction studies reveal that the crystals exhibit tetragonal symmetry. Super-lattice structure obtained from transmission electron microscopic investigations suggests lattice doubling. Magnetization measurements show that the Curie temperature ( T C) increases with dopant concentration. A second transition observed below 30 K is probably due to ordering of the Nd 3+ ions. The magnetization does not saturate up to a field of 50 kOe at 20 K suggesting a non-collinear (canting) ordering of Nd-spins.

Magnetic transitions in Nd 1− xDy xMn 2Ge 2

The various magnetic structures of the ThCr 2Si 2 structured RMn 2Ge 2 (R: rare-earth) compounds can lead to numerous magnetic configurations by gradually substituting the rare-earth element by another lanthanide. In this study, the magnetic properties of Nd 1− x Dy x Mn 2Ge 2 (0⩽ x⩽1) compounds were investigated by means of temperature-dependent DC magnetization measurements in low external magnetic fields. The substitution of Dy for Nd leads to a linear decrease in the lattice constants, and the magnetic interactions in the Mn sublattice cross over from a ferromagnetic character to an antiferromagnetic one. At low temperatures, the rare-earth sublattice orders in various configurations that depend on the composition. The results are collected in a phase diagram.

Phase transformation and magnetic properties of Nd–Fe–V–Nb alloys prepared by mechanical alloying

The phase transformation and magnetic properties of the NdFe 11.35− x V x Nb 0.65 ( x=0–1.35) alloys prepared by mechanical alloying (MA) have been studied. Phases of 2:17, 1:7 and 1:12 are formed in the as-annealed alloys with x=0, 0.3–0.7 and 1.0–1.35, respectively. With increasing V content in the NdFe 11.35− x V x Nb 0.65 ( x=0.3–0.7) alloys, the Curie temperatures of the matrix 1:7 phases monotonically increase. Upon nitrogenation, with increasing V content, the intrinsic coercivity μ 0 H c of the nitrided alloys monotonically increases. The increase becomes sharp at x=1.0 due to the formation of a great amount of Nd(Fe, V) 12N δ . The remanence J r and the maximum magnetic energy product (BH) max of the nitrided alloys monotonically decrease with increasing V content. The 1:12 phases are formed in all the NdFe 11− x Nb x V 1 ( x=0, 0.3, 0.65, 1.0) alloys annealed at 850 oC for 20 min. With increasing Nb content, the crystallization of the 1:12 phase is improved and the relative volume fraction of the 1:12 phase tends to be higher. While μ 0 H c of the nitrided alloys monotonically increase, and J r and (BH) max of the nitrided alloys monotonically decrease. With increasing Nb content in the nitrided alloys, the average grain size of α-Fe decrease while the nitrogen content increases.