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The effect of casting method on the magnetic properties of Sm(Co0.63Fe0.28Cu0.07Zr0.02)7.6 magnet has been investigated. The results show that the plate-mold ingot (PM) and strip-casting flake (SC) have the same phase composition. Compared with PM, the SC has a smaller grain size and larger fine-grain region due to its larger degree of undercooling. The magnetic properties of the PM magnet are Br = 11.63 kG, Hcj = 25.65 kOe, (BH)max = 30.97 MGOe, while the magnetic properties of SC magnet are Br = 11.45 kG, Hcj = 24.00 kOe, (BH)max = 30.03 MGOe. The reason for the low remanence of the SC magnet is revealed by the XRD and EBSD results. It shows that the PM magnet has a better easy-axis orientation than the SC magnet, due to the existence of fine grains in SC that are unfavorable for the alignment under a magnetic field. [ABSTRACT FROM AUTHOR]

The effect of Fe-rich content on the microstructure, phase structure, elements distribution, and magnetic properties of Sm(Co $_{0.91-\mathit {x}}$ FexCu0.07Zr0.02)7.6 ($x$ = 0.22, 0.30, and 0.35) magnets has been investigated systematically. With the increase of Fe content, the 2:17H, 2:17R, and 1:3R phases appeared in the Fe-rich solid solution. The different phase structures in the high-resolution transmission electron microscopy (HRTEM) images showed a locally short-range ordered state with dislocations. The presence of 2:17R phase and 1:3R phase was negative to the spinodal decomposition during the aging stage. In addition, the high Fe content caused Cu element enrichment in some area of the final state magnet, which further affected the formation of cellular structure. The Fe content increased from $x$ = 0.22 to $x$ = 0.35, the average cell size increased from 83.67 to 112.46 nm, the thickness of cell boundary increased from 9.6 to 18.25 nm, and the density of Zr-rich platelets increased from 0.036 to 0.06 nm. Furthermore, the defective cellular structures in the magnet ($x$ = 0.35) with incomplete and discontinuous cell boundaries had weak pinning field and poor coercivity. Moreover, the magnetooptical Kerr optical microscope observation revealed that the domain width of magnet ($x$ = 0.35) was significantly higher than that of magnet ($x$ = 0.22), and the reversal magnetic domain was formed first in the magnet ($x$ = 0.35), which caused a poor coercivity. [ABSTRACT FROM AUTHOR]

We achieved ultra-high coercivity of 5.65 kOe in L10-Mn1.33Ga alloy via the hot deformation (HD) method and revealed the hardening mechanism. Hot deformation led to recrystallization and grain refinement, where the average grain size was reduced to about 1.5 μm for HD-88% magnet. The coercivity mechanism indicated a weak pinning model by magnetic mini-loop analysis. It was found that small grains were formed, accompanied by a certain number of {111} ⟨11-2⟩ twins for HD magnets. The magnetic domain observation showed that both the sub-micro grain boundary and the twin boundary were acted as the pinning center of the domain wall, but the latter had weaker pinning effect. The ultra-high coercivity of the HD-88% Mn1.33Ga magnet originated mainly from the pinning of the grain boundary enhanced by grain refinement. Further grain refinement and twin structure inhibition will be promising approaches in order to obtain higher magnetic properties for L10-MnxGa bulk magnets. [ABSTRACT FROM AUTHOR]

The effect of doping Cu on the mechanical properties and magnetic properties of Sm(Co0.71Fe0.15Cu0.07Zr0.03)7.6 magnets was studied systematically. The results show that the Cu-lean grain boundaries and bending strength of the magnet can be improved by increasing of doping Cu content. The optimal magnetic properties of magnet with 1.0 wt% Cu doping are $B_{\mathrm {r}} =9.9$ kG, $H_{\mathrm {cj}} =23.0$ kOe, and (BH) $_{\mathrm {max}} = 22.2$ MGOe. With the doping content of Cu powders, the bending strength first reaches a peak value of 143.0 MPa at 1.0 wt% and then drops. The bending strength of the magnet with 1.0 wt% Cu doping is about 51.8% higher than that of the magnet with 0 wt% Cu doping. The coercivity and bending strength of the magnet are improved. [ABSTRACT FROM AUTHOR]

Phase and texture evolution of the hot-deformed Sm(Co,Fe,Cu,Zr)z magnet prepared by spark plasma sintering (SPS) have been investigated. The effects of hot deformation temperature and height reduction on the phase structure and magnetic properties of the magnet were studied. The results show that with 90% height reduction at 900 °C, the hot-deformed magnet with TbCu7 structure obtains an obvious $c$ -axis texture. However, with increasing hot deformation temperature, some 1:7H phases decompose into 2:17R, 1:5H, and Zr-rich particle phases in the hot deformation process. The hot-deformed magnet with 85% height reduction possesses a remanence ($M_{r}$) of 6.9 kG, which is higher than that of the isotopic precursor. [ABSTRACT FROM AUTHOR]

The changes in magnetic properties of LaFe11.5Al1.5Hx and LaFe11.5Al1.5By have been investigated. By introducing interstitial atoms H or B, the magnetic ground state is changed from the antiferromagnetic to the ferromagnetic state, accompanied by significant increases in the saturated magnetization (Ms) and the Curie temperature (TC). An attractive feature is that the magnetic transition from the second-order to the weakly first-order with increasing hydrogen content compared to the magnetic transition from the weakly first-order to the second-order with increasing boron content. The maximum magnetic entropy change (-ΔSM) under a field change of 0-5 T increases from 10.1 J/kg ·K for hydrogen content x=0.12 to 12.3 J/kg ·K for x=1.3, while decreases from 9.6 J/kg ·K for boron content y=0.1 to 9.2 J/kg ·K for y=0.3. [ABSTRACT FROM AUTHOR]

The Sm(CobalFe0.28Cu0.07Zr0.03)7.6 magnets were made by a casting process with two different cooling rates. X-ray diffraction analysis shows that the main phase of the two as-cast alloys consist of 1:5, 1:7, and 2:17 (hexagonal) phase. While a few of rhombohedral 2:17 phases appear in the ingots with the lower cooling rate. The electron probe micro-analysis and corresponding wavelength dispersive x-ray results indicate that a higher cooling rate of the as-cast alloy is helpful to the uniformity of Cu element distribution in the ingots and magnets, especially for suppressing the formation of 2:17 R phase in ingots. The coercivity and squareness of magnet prepared from ingot with higher cooling rate increase by 72 and 48 percentage, respectively. The microstructure observation shows that some cell boundaries are destroyed in the magnet made by lower cooling rate, while the cell boundaries are well developed in the magnet made by higher cooling rate. [ABSTRACT FROM AUTHOR]

The correlation between microstructure and magnetic properties of 2:17 SmCo commercial magnets 32 H and 32 L is studied. The 32 H magnet with high coercivity has an excellent ($00l$) orientation texture, and its magnetic properties are (BH) $_{\mathrm {max}}= 29.47$ MGOe, $B_{\mathrm {r}} = 11.20$ kG, and $H_{\mathrm {cj}} = 29.45$ kOe. The magnetic properties of the 32 L magnet with low coercivity are (BH) $_{\mathrm {max}}= 29.28$ MGOe, $B_{\mathrm {r}} = 11.40$ kG, and $H_{\mathrm {cj}} = 9.829$ kOe. The electron probe microanalysis results show that a Cu-lean grain boundary region is obvious in the 32 H magnet, which affects the squareness of the demagnetization curve. The transmission electron microscope result shows that the cell size and cell boundary thickness of high and low coercivity magnets are 129.32 and 9.83, and 90.94 and 7.87 nm, respectively. But the cell structure of the 32 H magnet is more complete and clearer than that of the 32 L magnet. The difference of the Cu concentration between the cell boundary phase and cell phase in the 32 H magnet is bigger than that of the 32 L magnet, which is really responsible for the high coercivity. [ABSTRACT FROM AUTHOR]

Shaping process is crucial for the application of MM′X systems which are commonly fragile due to the large volume effect during phase transition. We adopted spark plasma sintering as a new method to produce MnNiSi-based bulks and investigated the variations of both structural and magnetic properties. The sintering process creates many micro-cracks inside the large particles and changes the residual strain in the small particles. It leads to the reduction of the entropy change, while the relative cooling power is increased by 7%. This work provides reference for further investigations about the effects of different shaping processes on the performance of MM′X systems. [ABSTRACT FROM AUTHOR]

Electronic structure and magnetic properties for MnRhP have been studied from a first-principles density functional calculation. The calculated lattice constants, a=6.228 Å and c=3.571Å, are in good agreement with the experimental values of a=6.223 Å and c=3.585Å. The calculated moment of Mn is 3.1 μB/atom, resulting in a total moment of 3.0 μB/atom due to small moments induced at Rh and P sites. The magnetic moment of Mn decreases with unit cell size. The exchange interactions are dominated by positive Mn-Mn exchange coupling (JMn-Mn), implying a stable ferromagnetic ordering in Mn sublattice. In particular, JMn-Mn shows a maximum value (1.5 mRy) at the the optimized unit cell size. The structural distortion or unit cell size change will affect JMn-Mn, which is intimately related to the magneto-elastic and magneto-caloric effect. [ABSTRACT FROM AUTHOR]

Anisotropic MnBi/SmFeN (MnBi=0, 20, 40, 60, 80, and 100 wt. %) hybrid bonded magnets were prepared using MnBi powders and commercial SmFeN powders. With the increase in MnBi content from 0 to 100 wt. %, the density of the hybrid magnets improves linearly from 4.27 g/cm3 to 6.3 g/cm3, while the coercivity of the hybrid magnets does not change much at 293 K. For the pure MnBi magnet, the coercivity is increased from 10.76 kOe at 293K to 16.5 kOe at 373 K. For the hybrid magnet with 40 wt. % MnBi, the coercivity is increased by 19% compared to pure SmFeN magnet at 373 K. In the temperature range of 293 K-373 K, the coercivity temperature coefficient of the hybrid magnets changes gradually from -0.42%/K for the pure SmFeN magnet to -0.11%/K for the magnet with 80 wt. % MnBi, and becomes 0.67%/K for the pure MnBi magnet. [ABSTRACT FROM AUTHOR]

In this paper, Mn3Ga2 alloys with high saturation magnetization and high Curie temperatures were prepared by levitation melting high pure Mn and Ga elements followed by annealing. The effect of annealing temperature on phase structure and magnetic properties was investigated by means of x-ray diffraction and a vibrating sample magnetometer. A single phase alloy Mn3Ga2, which has tetragonal P4/mmm structure, was obtained with an annealing temperature of 773K and annealing time of 24 h. The hysteresis curve of its easy axis for this single phase alloy shows that the room temperature coercivity and saturation magnetization are 4.18 kOe and 50.81 emu/g, respectively. The thermomagnetic curves indicate that the Curie temperature is about 650K and a phase transformation occurs above 823K. [ABSTRACT FROM AUTHOR]

Nd-Fe-B permanent magnets with a small amount of CuZn5 powders doping were prepared by conventional sintered method. The effects of CuZn5 contents on magnetic properties and microstructure, electrochemical corrosion resistance of sintered Nd-Fe-B magnets were systematically studied. The results show that the magnetic properties of magnets do not have a significant variation by CuZn5 powders doping; the coercivity of magnets rises gradually, while the remanence of the magnets decreases a little with increasing of the CuZn5 amount. The CuZn5 doped magnets have more positive corrosion potential, Ecorr, and much lower corrosion current density, icorr, than the magnets without CuZn5 doping, indicating CuZn5 doping could improve the corrosion resistance. Both Zn and Cu enrich mainly into the Nd-rich phase, fully improve the wettability between the Nd-rich phase and the Nd2Fe14B phase, and repair the defects of the main phase, so the coercivity of magnets doped with CuZn5 powders rises. Such microstructure modification effectively restrains the aggressive inter-granular corrosion. As a result, the CuZn5 doped magnet possesses excellent corrosion resistance in NaCl electrolyte. [ABSTRACT FROM AUTHOR]

Effect of homogenization of the chemical composition and crystal structure on the magnetocaloric effects have been studied for bulk Mn1.1Fe1.9P1.8Ge0.2 alloy prepared by mechanical alloying and subsequent spark plasma sintering method. After optimal homogenization treatment, the ferromagnetic impurity, Ge6Fe3Mn4 phase was completely eliminated from the alloy; furthermore, the crystal lattice constant of the MnFePGe main phase, which possesses a hexagonal Fe2P-type structure, varies obviously compared with that of the sintered sample. As a result, the Curie temperature, TC, of the alloy increases from 253 to 267.5 K and the maximum magnetic entropy change, /ΔSm/, also increases from 36.36 to 44.35 J /kg K under 3 T magnetic field. Furthermore, the thermal hysteresis of M-T curves around TC upon heating and cooling, a signature of a first-order magnetic phase transition, reduces from 15 K for as-sintered sample to 9 K for annealed sample. [ABSTRACT FROM AUTHOR]

Spark plasma sintering technique had been applied to prepare bulk isotropic and anisotropic nanostructured Nd-Fe-B permanent magnets via hot pressing and subsequent hot deformation process. Influences of processing conditions and deformation height reduction on the structure and magnetic properties of the magnets were investigated. For the hot deformed magnet with 80% height reduction, XRD patterns of the anisotropic magnets show dominant (00l) diffraction peaks indicating evident c-axis crystallographic alignment in the magnet. Under the optimal processing conditions, the anisotropic magnet with 80% height reduction exhibits excellent magnetic properties as remanence (Br) of 1.492 T, coercive force (Hci) of 1004 kA/m, and the maximum energy product [(BH)max] of 400 kJ/m3, which are among the highest reported magnetic properties of nanostructured Nd-Fe-B permanent magnets. [ABSTRACT FROM AUTHOR]

The structure, magnetization and exchange interaction in Y(Co1-xFex)5 with x=0 to 0.3 are studied from a first-principles density functional calculation. The cohesive energy calculations indicate that Fe prefers to occupy the 3g site and the lattice constants increase with Fe Content. The magnetization increases from 7.50 to 8.97`B with increasing x from 0 to 0.3 as the calculations show that Fe has a much larger moment (about 2.4`B) than that of Co (about 1.5`B). The exchange parameters between Fe and Co are larger than those for Co-Co and Fe-Fe pairs, and are responsible for the higher TC of Y(Co1-xFex)5. The estimated TC from the calculated exchange parameters increases from about 1065 to 1298 K with increasing x from 0 to 0.3 using a multisublattices mean-field model. [ABSTRACT FROM AUTHOR]

Structure and magnetic properties were studied for Tm2(Co1-xFex)17 bulk nanocrystalline magnet synthesized by spark plasma sintering technique. X-ray diffraction results indicate both ingot and sintered magnet of Tm2(Co0.7Fe0.3)17 alloy exhibit hexagonal Th2Ni17 type structure. The microstructure of the magnet is composed of Th2Ni17 type nanograins with an average size of 35 nm detected by transmission electron microscopy and selected area electron diffraction patterns. Magnetic measurement shows that the remanence of the magnet is higher at 573 K than at 300 K, indicating there is a positive remanence temperature coefficient in the magnet. The anisotropy field of Tm2(Co0.7Fe0.3)17 alloy is 3.8 T, which is much higher than the HA of 2.3 T for the pure Tm2Co17alloy. The coercivity of the sintered magnet increases from 0.25 to 0.354 T after optimal annealing. [ABSTRACT FROM AUTHOR]

The correlation between preparation conditions and microstructure as well as magnetic properties were studied for Sm(Co 0.665 Fe 0.25 Cu 0.06 Zr 0.025 ) 7 magnets. Increase of sintering temperature from 1468 to 1493 K promotes the amalgamation of small grains into big ones, resulting in an enlargement of average grain size from 10 to 25 μm and diffusion of Cu from inner grains to Cu-lean grain boundaries. As a result, the demagnetization curve squareness of the magnets improves substantially, leading to a remarkable enhancement of the maximum energy product from 21.3 to 27.1 MGOe. The coercivity of the magnets drops from 25.3 to 16.0 kOe at the same time, which was verified by the increase of the average domain width from 1.1 μm in small grains to 2.5 μm in big grains. It is therefore concluded that tuning of the preparation conditions causes a more homogeneous distribution of Cu, which is crucial for the improvement of magnetic properties. [ABSTRACT FROM AUTHOR]

Sm1-xPrxCo5 (x=0-0.6) nanoflakes with CaCu5 structure were successfully prepared by surfactant-assisted high-energy ball milling (SAHEBM). The crystal structure and magnetic properties of Sm1-xPrxCo5 (x=0-0.6) nanoflakes were studied by X-ray diffraction and vibrating sample magnetometer. Effects of Pr addition on the structure, magnetic properties and coercivity mechanism of Sm1-xPrxCo5 nanoflakes were systematically investigated. XRD results show that all the nanoflakes have a hexagonal CaCu5-type (Sm, Pr)1Co5 main phase and the (Sm, Pr)2Co7 impurity phase, and all of the samples exhibit a strong (00l) texture after magnetic alignment. As the Pr content increases, remanence firstly increases, then slightly reduced, while anisotropy field (HA) and Hci of decrease monotonically. Maximum energy product [(BH)max] of the flakes increases first, peaks at 24.4 MGOe with Pr content of x = 0.4, then drops again. Magnetization behavior analysis indicate that the coercivity mechanism is mainly controlled by inhomogeneous domain wall pinning, and the pinning strength weakens with the increased Pr content, suggesting the great influence of HA on the coercivity of flakes. [ABSTRACT FROM AUTHOR]

Commercial NdFeB powders mixed with DyH x nanoparticles are hot pressed and hot deformed into anisotropic magnets by Spark Plasma Sintering (SPS). The hot deformed magnet exhibits strong c -axis crystallographic texture. The coercivity of the magnet doped with 1.0 wt% DyH x is increased by 66.7%, compared with the magnet without DyH x , while the remanence decreases only by 3%. TEM observation shows that there exists a continuous (Nd,Dy) 2 Fe 14 B layer between Nd-rich phase and NdFeB main phase. [ABSTRACT FROM AUTHOR]

Demagnetization curves of anisotropic nanocomposite MnBi/Co and MnBi/Fe 65 Co 35 permanent magnets were investigated by micro-magnetic finite element method. Effects of volume ratio, deviation degree of orientation and intrinsic magnetic properties of the soft magnetic phase on the magnetic properties of the magnets were investigated. From the viewpoint of practical applications, to meet the requirement of hardness parameters, ĸ = K /( μ 0 M S 2 ) 1/2 >1, the calculation maximum (BH)max of MnBi/Co and MnBi/Fe 65 Co 35 magnets are about 199 kJ/m 3 (V(Co)=22 vol%) and 196 kJ/m 3 (V(FeCo)=14 vol%), respectively, indicating their good potential in application. Compared with single phase MnBi magnet, the (BH) max of nanocomposite MnBi/Co and MnBi/Fe 65 Co 35 magnets increases by 66% and 63%, respectively. The remanence and coercivity of MnBi/Co nanocomposite magnets reduce as appearing a deviation degree of orientation, result of greatly decrease of the magnetic energy product. [ABSTRACT FROM AUTHOR]

Crystal structure and magnetic properties have been studied for bulk MnFePSi compounds prepared by the spark plasma sintering method. The effect of Si content on the crystal structure and the magnetic properties of the compounds were investigated. The MnFePSi compounds crystallize in a hexagonal Fe2P-type structure without obvious secondary phase. Magnetic measurements indicate that the compounds undergo a ferromagnetic to paramagnetic first-order transition near their Curie temperature ( TC) . With the increase in Si content, the TC rises from 343 to 381 K, while \Delta T\mathrm{ hys} decreases simultaneously from 27 to 15 K. For MnFeP0.5Si0.5 compound, the magnetic entropy change ( - \Delta SM) for a magnetic field change from 0 to 3 T is 12 J/kg \cdot \textK , demonstrating its good potential for practical application. [ABSTRACT FROM AUTHOR]

First principles calculation for the energies and magnetic moments of Fe2CrAl with various structures has been carried out. The contradiction between theoretical and experimental magnetic moment of Fe2CrAl has been illustrated. The L21-based structure has the lowest energy and thus should be formed during synthesis, while the native magnetic Cr-clusters are responsible for the extra large magnetic moment. Based on these calculations, a metastable and partially disordered B2CD structure has been achieved in a ball-milled Fe2CrAl alloy. It shows a 300 K higher TC and a 1.5 \mu {B} higher MS, respectively, compared with the arc-melted samples with L21-based structures. [ABSTRACT FROM AUTHOR]

Nanocomposite Nd2Fe14B/SmCo5 permanent magnets with different weight ratios have been prepared by spark plasma sintering mixtures of homemade amorphous SmCo5 powders and commercially available Nd2Fe14B powders. The magnetic properties of the nanocomposite magnets are sensitive to the ratio of the two hard phases. The peak (BH)max value of 14.4 MGOe is obtained at the SmCo5/Nd2Fe14B ratio of 4:1, which is $\sim 50$ % higher than that of the single-phase SmCo5 magnet prepared under the same preparation conditions. Hysteresis loop of the nanocomposite magnet shows the characteristics of single-phase magnet due to strong exchange coupling between the two phase grains. At high temperatures, the nanocomposite magnets exhibit greatly improved thermal stability compared with the single-phase Nd2Fe14B magnet. [ABSTRACT FROM AUTHOR]

La substitution for Ce inhibits the growth of the CeFe2 phase and promotes the formation of the single 2:14:1 phase, leading to an improvement in the magnetic properties of melt-spun (La/Ce)3Fe14B ribbons. Among which, the (La0.3Ce0.7)3Fe14B ribbon produced a high remanence of 6.86 kG, a coercivity of 5.51 kOe, and a maximum energy product (BH)max of 7.68 MGOe. After spark plasma sintering, the compacted (La0.3Ce0.7)3Fe14B magnet with good remanence and coercivity was successfully prepared, and these properties were enhanced to 5.14 kG and 5.60 kOe, respectively, leading to an energy product of 4.59 MGOe for the magnet with 5 wt % NdCu addition. [ABSTRACT FROM AUTHOR]

Magnetic properties and magnetocaloric effect (MCE) in LaFeSi B have been investigated by substituting 30 % Pr for La. It is found that the substitution of 30 % Pr for La leads to a reduction in Curie temperature ( T) from 200 to 190 K. The characteristic of the itinerant electron metamagnetic (IEM) transition above T becomes more prominent with the substitution of 30 % Pr for La. The maximum magnetic entropy change (−Δ S) is remarkably enhanced from 13.0 to 17.9 J/kg·K under a field change of 0-3 T, and correspondingly, the values of refrigerant capacity (RC) for LaFeSi B and LaPrFeSi B are 167 and 224 J/kg, respectively. The large −Δ S and the high RC in a low magnetic field indicate that LaPrFeSi B may be a promising candidate for magnetic refrigeration material near 200 K [ABSTRACT FROM AUTHOR]

Tetragonal polycrystalline Mn-Ga nanoflakes with a nominal composition of Mn1.33Ga were prepared by the surfactant-assisted high-energy ball milling method, and the effects of milling time and annealing treatment on structure and the magnetic properties were also investigated in detail. The irregular Mn1.33Ga flakes show typical shape anisotropy and a high aspect ratio with thicknesses in the range of 100 nm \sim 3 \mu m. Crystalline grain is reduced to 10 nm when increasing the milling time above 4 h. Coercivity is greatly improved, and the highest coercivity of 7.2 kOe is obtained for flakes milled for 2 h, but the saturation magnetization, Ms , and remanence, Mr , decrease sharply during the ball milling process. Medium-temperature annealing is beneficial to the crystallization and the enhancement of magnetization. After annealing at 773 K for 30 min, Ms and Mr are recovered to 68 and 41 emu/g, respectively; and the (BH)\mathrm {max} can reach 2.3 MGOe which is comparable with that of 2.5 MGOe for films or microparticles. [ABSTRACT FROM AUTHOR]

Melt spun ribbons of Nd4·5Fe77B18·5 alloy were consolidated into bulk permanent magnets by spark plasma sintering (SPS) method. Effects of heat treatment on the density, microstructure and magnetic properties of the magnets are studied. Further observation shows that the sample consolidated by SPS possesses ultrafine nanocrystalline structure and small fraction of amorphous phase. After proper heat treatment, magnets with fine crystal structure and good magnetic properties were obtained simultaneously. On the other hand, excessive grains growth, which will lead to undesirable magnetic properties, can occur due to improper heat treatment. [ABSTRACT FROM AUTHOR]

Sm2Fe17Nx sintered magnets were fabricated by spark plasma sintering (SPS) technique. Effects of sintering pressure, sintering temperature and heating rate on the magnetic properties and crystal structures of the magnets were investigated. The results showed that the density of the magnet was obviously improved with increasing sintering pressure, but the coercivity dropped simultaneously because Sm2Fe17Nx decomposed into SmN, α-Fe and N2. The coercivity decreased rapidly when sintering temperature was above 200°C under 1 GPa sintering pressure, which indicated that high pressure promoted the decomposition of Sm2Fe17Nx even at low temperature. In addition, the decomposition could not be effectively restrained even if the heating rate reached 450°C min-1. [ABSTRACT FROM AUTHOR]

In the present study, the demagnetization curves of MnBi/\alpha-Fe nanocomposite permanent magnets were calculated by the micro-magnetic finite element method. The effect of volume ratio between magnetically soft \alpha-Fe phase and MnBi hard phase on the magnetic properties of magnets was investigated. The sample used in the present simulation was consisted of 91 spherical fourteen faces units of hard phase grains with diameter of 20 nm, and the soft matrix phase with the thickness (t) ranging from 1 to 6 nm. For the isotropic MnBi/\alpha-Fe magnets, as t increases, the remanence (Br) increases first, peaks at 0.855 T for t = 3 nm, then decreases again, while the coercivity (Hci) drops monotonically from 691 kA/m for t = 1 nm to 94 kA/m for t = 6 nm. The sample with t = 2 nm has the optimal maximum energy product (BH)max = 55.15 kJ/m^3. For the anisotropic magnets, the Br and Hci exhibit their t-dependent behavior similar to that of the isotropic ones. The optimal values of Br, \rm Hci, and (BH)max are 1.47 T, 3200 kA/m, and 322 kJ/m^3 when t = 5, 1, and 3 nm, respectively, indicating a good potential of the anisotropic MnBi/\alpha-Fe nanocomposite as practical permanent magnets. [ABSTRACT FROM AUTHOR]

The structure and magnetic properties were studied for the ternary Tb-Fe-B nanoparticles and nanoflakes prepared by surfactant-aid high energy ball milling and subsequent size-selection. For the nanoparticles, significant room-temperature coercivity up to 10.6 kOe was achieved with the average particle size of 31.4 nm, but it decreases substantially to 400 Oe as the size is down to 8.2 nm. For the nanoflakes, the thickness is in the range of 50-80 nm while the length is about 1.1 μm, and high coercivity of 22.1 kOe and strong magnetic anisotropy were obtained simultaneously, indicating that the nanoflakes possess excellent permanent magnetic properties. [ABSTRACT FROM AUTHOR]

The microstructure and magnetic properties were studied for the sintered Nd–Fe–B permanent magnet doped with terbium (Tb) nanoparticles. Investigation shows that Tb is enriched as Tb2Fe14B and/or (Nd,Tb)2Fe14B phase in the surface region of the Nd2Fe14B matrix grains indicated by the remarkable enhancement in the magnetocrystalline anisotropy field of the magnet. Furthermore, the Tb-rich grain surface region with high crystal anisotropy increases the nucleation field of reverse domains in the demagnetization process. As a result, the magnet doped with a small amount of Tb nanoparticles possesses enhanced coercivity without sacrificing its magnetization. [ABSTRACT FROM AUTHOR]

The structure and magnetic properties were studied for bulk nanocrystalline dysprosium (Dy) metal prepared by spark plasma sintering method. All the as-prepared samples have hexagonal close packed structure. A decrease in grain size results in remarkable changes in magnetic ordering temperature of the nanocrystalline Dy metal. At 5 K, the magnetization drops by 3.35%, and the coercive force increases by three times for nanocrystalline Dy compared to those of coarse-grained bulk Dy sample. These results indicate the remarkable influence of the nanostructure on the magnetism of Dy due to finite size effect. [ABSTRACT FROM AUTHOR]

The crystal structure and magnetic properties were studied for the bulk nanostructural permanent magnet SmCo6.6Nb0.4 prepared by spark plasma sintering method. The magnet crystallizes in a single phase with a hexagonal TbCu7-type crystal structure after the sintering process. Rietveld fitting results show that the alloying element of Nb prefers to occupy the 3g site. Microstructure observation indicates that the average crystal grain size is about 30 nm. The coercivity decreases almost linearly from 2.8 to 0.5 T with increasing temperature from 300 to 773 K. A remanence enhancement resulting from intergrain exchange coupling among the fine grains was also observed. [ABSTRACT FROM AUTHOR]

• The magnetization mechanism is clarified based on Cu distribution at multi-scales. • The micrometer scale Cu distribution influences on the cell structure. • XRD characterization is not sufficient for determination of the solution temperature. Correlation between Cu distribution and magnetic properties was studied for Sm(Co bal Fe 0.28 Cu 0.07 Zr 0.02) 7.6 magnets prepared by conventional powder metallurgical techniques. It reveals that the micrometer scale Cu distribution homogeneity before aging treatment has a profound influence on the cell structure, nanometer scale Cu distribution, which determines the magnetization and demagnetization behavior as well as magnetic properties of the magnets. By tuning the solution treatment conditions, magnet with optimal magnetic properties (remanence of 11.5 kG, coercivity of 23.4 kOe, and maximum energy product of 30.3 MGOe) was prepared. [ABSTRACT FROM AUTHOR]

In this paper, bulk nanocomposite permanent magnets are prepared by spark plasma sintering (SPS) technique using melt-spun powders with a nominated composition of Pr4.2Tb0.3 Fe78B17.5. Effect of processing conditions on the density, microstructure, and magnetic properties of the magnets are studied. Higher sintering temperature improves the densification of the magnets, while deteriorates their magnetic properties simultaneously due to the excess crystal grain growth. An increased compressive pressure leads to better magnetic properties and higher density for the magnets. Magnet possesses a Br of 10.4 kGs and a Hci of 2.76 kOe under the optimal sintering condition. Observation shows the microstructure of the magnet contains fine grains with an average size of about 20 nm. The fine grain size in the microstructure and good magnetic properties are ascribed to the rapidly sintering speed and high compressive pressure of SPS, which effectively restrains the grain growth and allows the formation of fine crystalline materials with full dense in a short time. [ABSTRACT FROM AUTHOR]

Anisotropic Nd15.5Dy1.0FeBalCo3.0B6.8Al1.0 magnets were produced by the spark plasma sintering (SPS) technique. The effects of processing conditions on the microstructure, magnetic properties, dimensional precision and density of the magnets were studied. The magnetic properties, microstructure and constituents were investigated by means of a magnetic flux density - magnetic field strength (B-H) loopline instrument, scanning electron microscopy and energy dispersive X-ray analysis. The density of the magnets was determined by the Archimedes method, and the dimensional precision of the magnets was measured by micrometer. It was found that the microstructure of SPS processed Nd-Fe-B magnets is unique; the grain size is fine and uniform while distribution of the neodymium rich phase is heterogeneous. The optimal magnetic properties of SPS processed Nd-Fe-B magnets obtained so far are maximum energy product of 240 kJ m-3 and coercive force of 1260 kA m-1. The dimensional precision of the magnets is ~ 20 μm, and the density of the magnets reaches 7.58 g cm-3. [ABSTRACT FROM AUTHOR]

The microstructure, crystal structure, and magnetic properties were studied for Nd-Fe-B nanoflakes prepared by surfactant-assisted high-energy ball milling (HEBM) with heptane and oleic acid as the milling medium. The microstructure, crystal structure, and magnetic properties of the nanoflakes were examined with scanning electronic microscopy, x ray diffraction, and vibrating sample magnetometer, respectively. Effect of ball-milling time on the c-axis crystallographic alignment and coercivity of Nd-Fe-B nanoflakes were systematically investigated. Microstructure observation shows that the Nd-Fe-B nanoflakes have an average thickness of tens of nanometers, an average diameter in the range of 500 ∼ 1000 nm, and an aspect ratio as high as 100. As the ball-milling time increases from 2 h to 12 h, the intensity ratio between (006) and (105) reflection peaks, which indicates the degree of c-axis crystal texture of the Nd2Fe14B phase, drops gradually, indicating that the long time-milling process undermines the c-axis crystal texture of Nd2Fe14B phase in the nanoflakes. On the other hand, the coercivity of the nanoflakes firstly increases, peaks at 3.8 kOe for 8 h, and then decreases again along with the ball milling. [ABSTRACT FROM AUTHOR]

Magnetic properties and thermal stability were investigated for the MnBi/NdFeB (MnBi = 0, 20, 40, 60, 80, and 100 wt.%) bonded hybrid magnets prepared by spark plasma sintering (SPS) technique. Effect of MnBi content on the magnetic properties of the hybrid magnets was studied. With increasing MnBi content, the coercivity of the MnBi/NdFeB hybrid magnets increases rapidly, while the remanence and maximum energy product drops simultaneously. Thermal stability measurement on MnBi magnet, NdFeB magnet, and the hybrid magnet with 20 wt.% MnBi indicates that both the NdFeB magnet and the MnBi/NdFeB hybrid magnet have a negative temperature coefficient of coercivity, while the MnBi magnet has a positive one. The (BH)max of the MnBi/NdFeB magnet (MnBi = 20 wt.%) is 5.71 MGOe at 423 K, which is much higher than 3.67 MGOe of the NdFeB magnet, indicating a remarkable improvement of thermal stability. [ABSTRACT FROM AUTHOR]

The structure and magnetic properties were studied for ternary Tb-Fe-B melt-spun ribbons with nominal composition of Tb14Fe86-xBx (x = 5.2-6.8). Effect of boron content and melt-spun wheel speed on the coercivity of the ribbons was investigated. With the increase of boron content, the coercivity of the Tb-Fe-B ribbons increases first, and then decreases. XRD results show that the impurities of TbFe2 phase and FeB phase exist in low boron content and high boron content ribbons, respectively, resulting in the coercivity degradation of the ribbons. For the Tb14Fe79.6B6.4 ribbons, the wheel speed plays an important role in their magnetic properties. As the wheel speed increases from 5 to 25 m/s, the saturation magnetization and the remanence of the ribbons drop monotonically, while the coercivity increases first, peaks at 77.4 kOe, and then decreases. Further SEM observation indicates that the microstructure of the optimal ribbons was composed of fine and uniform crystal grains, which was responsible for the ultrahigh intrinsic coercivity of the ribbons. [ABSTRACT FROM AUTHOR]

Structural and magnetic properties of bulk nanostructural Mn100-xBix (x = 40, 45, 52) permanent magnets prepared by spark plasma sintering technique were studied. The effect of the Mn/Bi ratio on the MnBi low temperature phase (LTP) formation and its magnetic properties were investigated. An increase of the bismuth amount in the magnets leads to better formation of LTP, resulting in the improvement of both magnetization (Ms) and remanence (Mr), but decreasing the coercivity (Hc) of the magnets. At room temperature, Ms increases from 27.87 emu/g for Mn60Bi40 to 45.31 emu/g for Mn48Bi52, whereas Hc decreases from 12 to 7.9 kOe. The microstructure of Mn48Bi52 magnet is composed of fine and uniform grains with an average size of 140 nm as shown in the TEM image. The Mn48Bi52 magnet shows a high Hc of 19 kOe at 423 K, indicating a strong positive temperature coefficient of coercivity for the MnBi magnet. [ABSTRACT FROM AUTHOR]

Bulk anisotropic PrCo5 nanostructured magnets were prepared by hot deformation technique. The effects of height reduction on the structure and magnetic properties of the magnets were studied. It is found that the height reduction plays an important role in the formation of c-axis crystal texture of PrCo5 phase during hot deformation process. With the increase of height reduction, the c-axis crystal texture becomes more and more dominant, indicating strong magnetic anisotropy in the magnets. As a result, the saturated magnetization (Ms) of the magnets increases gradually, while the coercivity (Hci) of the magnets drops simultaneously, resulting in the remanence (Mr) of the magnets rising first, peaking at 80% height reduction, then dropping again. Under optimal height reduction of 80%, the PrCo5 magnet bears magnetic properties of Ms of 1.00 T, Mr of 0.86 T, Hci of 488.5 kA/m, and (BH)max of 96.87 kJ/m3. [ABSTRACT FROM AUTHOR]

Chemical coating, hot compaction, and hot deformation techniques have been applied to prepare bulk anisotropic SmCo5/α-Fe nanocomposite magnets. The effects of α-Fe content on the structure and magnetic properties of the magnets were studied. With the increase of the α-Fe content, both the saturation magnetization (Ms) and remanence (Mr) of the magnets rise first, peak at 10 vol. % α-Fe content and then fall while the coercivity (Hci) of the magnets drops simultaneously. Crystal structure analysis shows that the magnets exhibit a strong c-axis crystal texture of the SmCo5 phase, which, however, weakens gradually as the α-Fe content increases. Microstructure observation also shows that there are many SmCo5 equiaxial grains even after hot deformation in the magnets with 15 vol. % α-Fe. [ABSTRACT FROM AUTHOR]

Highlights • The Sm(Co bal Fe x Cu 0.06 Zr 0.025) z magnets with different Fe content and z value were investigated. • The correlation of Fe content and z value was established to achieve excellent magnetic properties. • Increasing Fe content promoted the irreversible microstructure evolution in magnets. • Magnetic domain patterns of magnets affected by increasing Fe content indirectly. Abstract Correlation between Fe content and z value on the structural and magnetic properties of the Sm(Co bal Fe x Cu 0.06 Zr 0.025) z magnets (x = 0.20, 0.25, 0.28, and z = 7, 9.5) has been investigated. It is found that the cellular phases in the magnets grow up with increasing Fe content, so the cell boundary phases could hardly form well without enough Sm atoms, resulting in coercivity decreasing. After supplement of Sm content by decreasing z value, cell boundary phases formed continuously, and coercivity was strongly enhanced due to the remarkable concentration gradient of Cu between the 1:5H cell boundary phase and 2:17R cellular phase. It is thus suggested that as the Fe content increases, the z value of magnets need reducing simultaneously in order to keep high coercivity of the magnets. [ABSTRACT FROM AUTHOR]

In present study, sodium silicate, a kind of heat-resistant binder, was used to prepare bonded Nd-Fe-B magnets with improved thermal stability and mechanical strength. Effect of curing temperature and curing time of the new binder to the magnetic properties, microstructure, and mechanical strength of the magnets was systematically investigated. Fracture surface morphology observation show that sodium silicate in bonded magnets could completely be cured at 175 °C for 40 min, and the magnets prepared under this condition exhibit optimal properties. They exhibit usable magnetic properties of B r of 4.66 kGs, H cj of 4.84 kOe, and (BH) max of 4.06 MGOe at 200 °C. Moreover, the magnets possess high compressive strength of 63 MPa. [ABSTRACT FROM AUTHOR]

• A large mass rotating diffusion with 2500 pieces of small-sized magnets was conducted to enhance coercivity. • The optimal parameters of Tb strips rotating diffusion were obtained. • The excellent uniformity of the properties in this massive rotating diffusion could realize. Rotating diffusion technology is especially suitable for mass production of small-sized magnets. In this paper, a large mass rotating diffusion with 2500 pieces of small-sized magnets was conducted to enhance coercivity. At the same time, the uniformity of the properties was studied. Taking both magnetic properties and yield rate into account, we obtained the optimal parameters of the rotating diffusion at 710 ℃ for 5 h, following a two-stage annealing process at 940 ℃ for 5 h and at 500 ℃ for 3 h. Thus, the coercivity of the magnet could increase from 14.05 kOe to 23.06 kOe. EPMA results show that most Tb enriches the surface of the magnets, and some Tb is diffused into the grain boundary phase forming magnetic isolation during the rotating diffusion process. After the two-stage annealing process, many (Nd,Tb) 2 Fe 14 B substitutional phases with higher anisotropy field are formed around the epitaxial layer of the main phase increasing the coercivity of the magnet. Discrete analysis and a linear fit show excellent uniformity of the properties in this massive rotating diffusion process. [ABSTRACT FROM AUTHOR]

Highlights • Hot deformation technology via spark plasma sintering effectively realized the magnetic hardening in L1 0 -MnGa alloy. • Recrystallization and grain size refinements were observed without changing the crystal structure, which led to the magnetic hardening and improvement of the magnetic properties. • The highest remanence of 2.92 kG and a coercivity of 4.73 kOe, for L1 0 -ordered MnGa alloy bulk, were achieved for the deformed magnets sintered at 873 K with a height reduction of 92% and a homogeneous average grain size of about 1.5 µm. Abstract Hot deformation (HD) technology via spark plasma sintering effectively realized the magnetic hardening in L1 0 -Mn 1.8 Ga alloy. During the HD process, recrystallization and grain size refinements were observed without changing the crystal structure, which led to the magnetic hardening and improvement of the magnetic properties. By optimizing the HD parameters, maximum height reduction of up to 92% can be achieved where full recrystallization with few defects were observed from EBSD and TEM measurements. The highest remanence of 2.92 kG and a coercivity of 4.73 kOe were achieved for the deformed L1 0 -Mn 1.8 Ga magnet sintered at 873 K with a height reduction of 92% and a homogeneous average grain size of about 1.4 µm. [ABSTRACT FROM AUTHOR]

Abstract Mn 2 CrGa is a newly found Heusler compound with most of its properties remain unknown. We investigated this system using first-principles calculation and found that it can show a martensitic transformation with a highly ordered L2 1 structure. However, the experimental results of melt-spun Mn 2 CrGa ribbons show a disordered A2-type structure which tends to decompose into D0 19 and D0 3 -type phases during annealing. These characters prohibit the predicted martensitic transformation from happening. This system also shows interesting features like relatively high Curie temperature and strong magnetic interactions, which deserve further studies. Highlights • Anti-sites occupation impacts the possible martensitic phase transformation in Mn 2 CrGa. • Mn 2 CrGa with A2 structure is easy to decompose into Mn-rich D0 19 and Cr-rich D0 3 phases. • Mn 2 CrGa has strong order-disorder transitions, high Tc and complicated magnetic structure. [ABSTRACT FROM AUTHOR]

FeCoB films with gradient B doping were deposited by a composition gradient sputtering method under different sputtering pressure. Good soft magnetic performances with magnetic anisotropy field of 142 Oe and ferromagnetic resonance frequency of 4.82 GHz were obtained at zero bias field. It is interesting to note that the magnetic anisotropy of the films rotates by 90° by changing the sputtering pressure from 0.2 to 0.5 Pa, which can be attributed to the stress transition from compressive to tensile. This provides a possible method to in-situ construct complex magnetic anisotropy by controlling the sputtering pressure. [ABSTRACT FROM AUTHOR]

• Multiple pinning model with H-phase and Z-phase as pinning sites was proposed. • Uneven pinning in H-phase is inevitable for its orientation and distribution. • Z-phase cut off the domain wall, intensified inhomogeneous magnetization reversal. Domain-wall-pinning is one of the ways to realize magnetic hardening for permanent magnet materials. The sintered 2:17 Sm-Co magnets, a most typical pinning-controlled magnet, have complex nano-scaled cellular structures including cellular matrix phase, cell wall phase, and lamellar Zr-rich phase. In this paper, a multiple domain-wall-pinning with cell wall phase dominating and Zr-rich phase participating was proposed through micromagnetic simulation. The simulation results were supported by magnetic domain observation and macroscopic magnetic measurement analysis, which provided a key reference for the correlation between the magnetic properties and microstructure of this kind of magnet. Furthermore, the squareness of the demagnetization curve for the magnet was affected by multiple pinning, including multiple pinning phases and the internal inhomogeneity inside a pinning phase. Our finding can enrich the magnetic hardening mechanism and provide theoretical guidance for the optimization of magnetic properties of the pinning-controlled permanent magnets. [ABSTRACT FROM AUTHOR]