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In recent years, MnFePGe magnetocaloric materials have been widely studied as promising candidates for magnetic refrigeration materials. The Curie temperature of MnFePGe can be adjusted to around room temperature by changing the element ratio or doping with other elements. Due to its first-order magnetic and structural transition, it engenders a large entropy change but unfortunately also exhibits a large thermal hysteresis during the phase transition, which leads to energy loss and lower refrigeration capability. In this paper, we establish a correlation between the in-plane covalent bonding and Curie temperature (TC), thermal hysteresis (ΔThys), two-phase coexistence zone (ΔTcoex), and entropy change (ΔSDSC) using 54 Mn2−xFexPyGe1−yMz (where M is a metallic or nonmetallic doped element) samples with different components. Neutron diffraction and XRD diffraction data and refinements have been employed to allow a detailed electron density reconstruction of six typical samples with the maximum entropy method. We find that the length of the in-plane bonding is closely correlated with the TC and ΔThys, while the TC, ΔThys, ΔTcoex, and ΔSDSC have no significant correlation with the length of the interlayer covalent bond. Moreover, we find that the ΔThys correlates most strongly with the change in the bond length when undergoing the paramagnetic-to-ferromagnetic phase transition rather than the absolute value of the bond length. These results provide an understanding of how to control the properties, enabling effective ways to tune the composition of magnetic refrigeration materials to tailor magnetocaloric properties for optimal performance. [ABSTRACT FROM AUTHOR]

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]

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]

Site preference of doped Mn ions in CoCr2-xMnxO4 (x=0-2) series has been derived separately from structure and magnetic measurement. It shows that parts of the doped Mn ions occupy the A (Co) sites when x<0.5. And then, it takes the two B (Cr) sites in turn before and after x=1.3. This site preference behavior results in a role conversion of the magnetic contributors and, thus, leads to the composition dependent magnetic compensation. Temperature induced compensation and negative magnetization have also been found in several samples, which is attributed to the large energy barrier between the ferromagnetic and antiferromagnetic spin arrangement. A structure transition from cubic to tetragonal symmetry has been detected. [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]

MnCoGe1-xVx (x = 0.005, 0.01, 0.015, 0.02, 0.03, and 0.04) compounds were synthesized and investigated in view of the effect of transition metals on main-group-element sites to the magnetostructural transition. A small amount of V doping results in a decrease of the martensitic transformation temperature, while a further increase of V disturbs the Co-Ge bonds hence destabilizing the MM'X phase. Therefore, the transformation temperature returns to high temperature, and the expected Curie temperature window becomes incomplete. Accordingly, a large magnetic entropy change of about 10 J/kg·K and a refrigerant capacity of about 129.5 J/kg is obtained in the series. [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]

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]

In this paper, we studied the magnetic hardening mechanism of SmCo6.6Nb0.4 nanoflakes prepared by surfactant-assisted high energy ball milling. The hysteresis loop with the initial magnetization curve and the corresponding differential susceptibility curve of thermally demagnetized SmCo6.6Nb0.4 nanoflakes were studied. It is concluded that the magnetization reversal process of the specimen is determined by domain wall motion, i.e., the magnetic hardening mechanism of the magnetic powders is dominated by domain wall pinning. Moreover, the dependence of coercive field of the nanoflakes on the maximum applied field derived from minor hysteresis loops also confirms the pinning effect in the magnetization reversal. [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 structure and magnetic properties were studied for bulk nanocrystalline SmCo5 sintered magnet produced by spark plasma sintering technique. X-ray diffraction patterns show that the sintered magnet exhibits CaCu5 crystal structures. Transmission electron microscopy (TEM) observation indicates the average grain size of the magnet of about 40 nm. Magnetic measurement shows that the coercivity reaches as high as 2.85 T; the saturation magnetization and the remanence are 0.71 and 0.5 T, respectively. The magnet exhibits good thermal stability with a coercivity of 0.9 T at 773 K and a coercivity coefficientβ of -0.15%/K. [ABSTRACT FROM AUTHOR]

The crystal structure and magnetic transition were studied for the bulk Mn1.1Fe0.9P0.8Ge0.2 compound prepared by a simple blending and subsequent spark plasma sintering route. X-ray diffraction analysis and refinement show that the compound crystallizes in the hexagonal Fe2P-type structure, in which the Mn atoms occupy all the 3g sites and some 3f sites, the Fe atoms occupy the rest of the 3f sites, and P and the Ge atoms randomly occupy the 2c and 1b sites. Magnetic measurement indicates that the Curie temperature TC is at 253 K and the thermal hysteresis of M-T curves at TC upon heating and cooling, a signature of a first-order magnetic phase transition, is about 15 K. The maximum magnetic entropy change of the compound reaches as high as 49.2 J/kg K in a field change from 0 to 5 T at 253 K, while the adiabatic temperature change of the compound reaches only 1.2 K in a field change from 0 to 1.5 T at the same temperature. [ABSTRACT FROM AUTHOR]

Nd–Fe–B nanoparticles have been obtained by using surfactant-assisted ball milling and subsequent size-selection technique. Structural analyses show that nanoparticles with two particle sizes around 10 and 100 nm were obtained. The partially amorphous Nd–Fe–B nanoparticles give their room-temperature coercivities around 0.1 and 1.5 kOe for the small and large nanoparticles, respectively. As the temperature decreases to 200 K, the coercive force of the large nanoparticles increases by 50% due to the enhancement of the magnetocrystalline anisotropy of the Nd2Fe14B phase in the particles. [ABSTRACT FROM AUTHOR]

Polarization curve and electrochemical impedance spectroscopy tests have been applied to investigate the corrosion kinetics for both spark plasma sintered (SPS) and conventional sintered Nd–Fe–B magnets in different electrolytes. Effect of microstructure modification on the chemical stability of the magnets was discussed. Both magnets exhibit evident passive behavior in alkaline electrolyte but are susceptible to corrosion in weak acid and saline electrolytes. SPS magnets are more corrosion resistant than conventional sintered magnets due to a remarkable microstructure modification formed in the SPS process. Further investigation shows that the unique microstructure in SPS magnets effectively restrains the aggressive intergranular corrosion which takes place along Nd-rich phases in conventional magnets. [ABSTRACT FROM AUTHOR]

Chemical coating, hot compaction, and hot deformation techniques have been applied to prepare bulk isotropic and anisotropic Nd2Fe14B/α-Fe nanocomposite magnets. The effect of α-Fe content on the structure and magnetic properties of the magnets were studied. For the isotropic magnets, the remanence (Br) increases as the α-Fe content increases, while the coercive force (Hci) drops simultaneously. For the anisotropic magnets, the Br rises first, peaking at 2 vol % of α-Fe content, then falls as the α-Fe content increases, and Hci drops significantly for all the α-Fe containing anisotropic magnets. Crystal structure analysis shows that only the magnets with no more than 2 vol % α-Fe exhibit strong c-axis crystal texture of Nd2Fe14B phase after deformation. Microstructure observation also shows that there are many Nd2Fe14B equiaxial grains even after hot deformation in the magnets with α-Fe more than 2 vol %. [ABSTRACT FROM AUTHOR]

Oxidation kinetics of Nd–Fe–B permanent magnets prepared by both spark plasma sintering (SPS) and conventional sintering techniques has been studied at elevated temperature in dry air environment. Compared with the conventional sintered magnet, the SPS magnet possesses much lower oxidation rate, which leads to less reduction of magnetic properties of the SPS magnet than that of the conventional sintered magnet. Microstructure observation shows that the SPS magnet possesses unique microstructure due to the special sintering mechanism of SPS technique. In detail, the grain size of the Nd2Fe14B main phase is fine and uniform, only a few Nd-rich phases form along the grain boundaries of Nd2Fe14B phase, while most of them agglomerate into triple junctions as small particles. Such microstructure modification restrains effectively the intergranular corrosion along Nd-rich phase in the SPS magnet. As a result, the SPS magnet possesses excellent corrosion resistance at elevated temperature. [ABSTRACT FROM AUTHOR]

The phase evolution, microstructure, and magnetic properties of PrxFe80-xTi2Co10B4C4 (x=9,10.5) melt-spun ribbons were studied. All these ribbons consist mainly of three phases, namely, 2:14:1, α-(Fe,Co), and 2:17 phases. The iHc significantly increases and Br slightly decreases with increasing Pr content. It was found that increasing Pr content from 9 to 10.5 at. % leads to marked grain refinement in the ribbons. Increasing Pr content also helps suppress the formation of metastable 2:17 phase and the grain growth of the α-(Fe,Co) phase during the annealing treatment, thus avoiding the formation of extensive soft magnetic regions. The refined and uniform structure tends to enhance the exchange-coupling interaction between magnetic grains, which results in a significant improvement of the demagnetization-curve shape and magnetic properties accordingly. High coercivity iHc of 10.2 kOe, remanence Br of 9.6 kG, and maximum energy product (BH)max of 17.4 MG Oe have been achieved in Pr10.5Fe69.5Ti2Co10B4C4 ribbons after optimal annealing. [ABSTRACT FROM AUTHOR]

The influence of Nb addition on the magnetic properties and microstructure for nanocomposite Nd9.5Fe79-xCo5NbxB6.5 (x=0,1,2,3) magnets was investigated. The results showed that Nb additon improved the coercivity obviously. An intergranular Nb–Fe–B phase with a chemical composition near the Nb:Fe:B stoichiometry of 1:2:1 between the Nd2Fe14B interface was found for Nd9.5Fe77Co5Nb2B6.5 by a three-dimensional atom probe technique, which provides direct evidence of the improvement of magnetic properties. [ABSTRACT FROM AUTHOR]

A series of layer structural composite magnetic refrigerant materials with composition of (Gd5Si2Ge2)x(Gd)y(Gd5Si1.85Ge2.15)z was synthesized via spark plasma sintering technique. The adiabatic temperature change (ΔTad) of the composites and of the three individual components was measured directly from 245 to 315 K with a magnetic field change of 1.5 T using a homemade magnetocaloric effect measuring apparatus. For all composites with different x:y:z ratios, their resultant ΔTad uniformly peaks at 246, 276, and 296 K, respectively, corresponding to the magnetic transition temperature of the three components. In addition, proper x:y:z ratio can improve both the value and the constancy of ΔTad of the composite. Compared with the three components, the value of ΔTad of the composites exhibits a more constant tendency, which is more suitable for practical application in room temperature refrigeration, when compared to those of the three components. [ABSTRACT FROM AUTHOR]

PrCo5 magnet can have excellent magnetic properties and good thermal stability. In this paper, anisotropic nanograin PrCo5 hot deformed magnets with and without PrCu eutectic alloy were prepared by the spark plasma sintering technique. For the 70% hot deformed magnet with 6 wt.% PrCu, the coercivity of the magnet achieves 10.1 kOe, and is increased to be 14.6 kOe after annealed at 550°C, more than twice that of the undoped magnet (6.7 kOe). The nonmagnetic PrCu phase is mainly distributed in the interface of the grains, introducing a demagnetization coupling effect among the hard magnetic grains, resulting in large enhancement of the coercivity. [ABSTRACT FROM AUTHOR]

Spark plasma sintering technique has been applied to synthesize composite Gdx(Gd5Si2Ge2)1-x (x=0.3, 0.5, and 0.7) with layer structure using high-purity gadolinium (Gd) metal and Gd5Si2Ge2 alloys. The magnetocaloric effect of the composites was studied by directly measuring adiabatic temperature change (ΔTad) with a magnetic-field change of 1.5 T using a homemade magnetocaloric effect measuring apparatus. With increasing x from 0.3 to 0.7, ΔTad peak temperature shifted from 286 to 293 K and the peak values of ΔTad slowly increased from 1.6 to 2.0 K at a magnetic-field change of 1.5 T. Meanwhile, the ΔTad peak of the composite broadened as Gd content was increased. For x=0.7, the composite showed a ΔTad ranging from 1.1 to 2.0 K at a magnetic-field change of 1.5 T in a temperature range of 260–300 K, which adapted to work as a room-temperature refrigerant. [ABSTRACT FROM AUTHOR]

An attempt was made to tailor the magnetostructural transitions over a wide temperature range under the principle of isostructural alloying. A series of wide Curie-temperature windows (CTWs) with a maximal width of 377 K between 69 and 446 K were established in the Mn1-y CoyNiGe1-xSix system. Throughout the CTWs, the magnetic-field-induced metamagnetic behavior and giant magnetocaloric effects are obtained. The (Mn,Co)Ni(Ge,Si) system shows great potential as multi-functional phase-transition materials that work in a wide range covering liquid-nitrogen and above water-boiling temperatures. Moreover, general understanding of isostructural alloying and CTWs constructed in (Mn, Co)Ni(Ge, Si) as well as (Mn, Fe)Ni(Ge, Si) is provided. [ABSTRACT FROM AUTHOR]

In this paper, the recoil loops of SmCo6.6Nb0.4 nanoflakes prepared by the surfactant-assisted high energy ball milling (SA-HEBM) were systematically studied. The recoil loop openness was observed in both the aligned and non-aligned samples. Reversible and irreversible portions of the demagnetization process derived from the recoil loop were also investigated. For both the aligned and non-aligned samples, reversible portion (Δmrev) is too small to determine the coercivity. Irreversible portion (Δmirrev) shows similar tendency, i.e. increasing slowly at low reverse field and then growing up rapidly after a critical field (nucleation field Hno). The demagnetization process can be described as following: the reversible demagnetization is dominant when the applied reverse field is lower than 8 kOe, under which the irreversible nucleation also occurs. The reverse domain walls are pinned by the grain boundaries until the reverse field is larger than 8 kOe. With increasing field, the pinning effects are weakened and the rapid reversible demagnetization starts. Finally, the demagnetization process is accomplished. The values of AM in the Henkel plots are totally opposite for the aligned and non-aligned SmCo6.6Nb0.4 nanoflakes. [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]

A new approach has been proposed in this work, which provides an effective way for tuning the structural transition in MM'X systems with relatively high transition temperature. With this method, a temperature window as wide as 275 K for the magnetostructural transition has been achieved in the MnNiSi alloy system. The maximum magnetic entropy change of the system is as high as 13.3 J/kgK, which, together with the large temperature window, enables the Mn0.4Fe0.6NiSi1-xGax system to be a promising candidate for magnetic refrigerant applications. [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]

Bulk nanocrystalline gadolinium metal was prepared using spark plasma sintering (SPS) and subsequent annealing process. The SPS Gd metal had a single phase with a mean grain size of about 10 nm. A pressure-induced C-axis crystal texture was found in the SPS Gd sample. With the decrease of Gd grains from micrometer to nanometer range, the Curie temperature TC decreased by 10.7 K and the magnetic moment per Gd atom at 5 K dropped noticeably from 7.81μB to 6.31μB. These results indicate the remarkable influence of the nanostructure on the magnetism of Gd due to the finite size effect. [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]

Bulk anisotropic nanocrystalline SmCo5 magnets have been prepared by hot deformation method. The height reduction of the magnets plays a key role in inducing the crystallographic alignment in the magnet. Increase of height reduction to 90% leads to the formation of platelet shape grains perpendicular to the press direction; correspondingly c-axis crystallographic texture and magnetic anisotropy were developed in the deformed magnets. The coercivity of the magnets increases first,and then decreases again with the increase of the height reduction. The magnet with 70% height reduction exhibits a high coercivity over 5 T. [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]

Nd-Fe-B permanent magnets doped with a small amount of praseodymium (Pr) nanoparticles were prepared by conventional sintering method. Effects of the Pr nanoparticles doping amount and the sintering temperature on the magnetic properties of the magnets were studied. As the doping amount increases, the coercivity of the magnets rises gradually, while the remanence and the maximum energy product of the magnets rise first, peak at 1.0 wt. % of Pr nanoparticles doping, then drop. The optimal sintering temperature was determined as 1040 °C. Under optimal doping amount and sintering temperature, the Nd-Fe-B magnet bears good magnetic properties of Br of 1.386 T, Hci of 1170 kA/m and (BH)max of 371 kJ/m3, which are better than the Pr-free magnet's magnetic properties of Br of 1.358 T, Hci of 1097 kA/m and (BH)max of 354 kJ/m3, suggesting the doping of Pr nanoparticles is a promising way to enhance the magnetic properties of sintered Nd-Fe-B magnets. [ABSTRACT FROM AUTHOR]