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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]

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]

Several first-principles density calculations are conducted to explain the structure, magnetization and the exchange interactions taking place in the Y[(Co,Fe).ub.5] compounds. An increase in the Fe content is shown to highly increase the lattice constants of the compounds.

The article explains the structure, as well as the various magnetic properties of the different isotropic and anisotropic Nd-Fe-B permanent magnets that are prepared by the spark plasma sintering technology. The various effects of the processing conditions and deformation height reduction on these properties are also discussed.

The spark plasma sintering technique is employed to explain the structure, as well as the magnetic properties of the bulk nanocrystalline [Tm.sub.2][([Co.sub.1 - x][Fe.sub.x]).sub.17] permanent magnet. Optimal annealing is shown to lead to a sharp increase in the coercivity of the sintered magnet.

The article explains the structure, as well as the magnetic properties of the different nanocrystalline Sm[Co.sub.5] magnet synthesized by spark plasma sintering technique. The magnet is shown to demonstrate excellent thermal stability.

The various effects of annealing and homogenization on the structure, as well as the magnetic properties of the [Mn.sub.1.1][Fe.sub.0.9][P.sub.0.8][Ge.sub.0.2] compounds are analyzed. Annealing is shown to lead to a significant increase in the Curie temperature and the magnetic entropy changes of the compounds.

The crystal structure and magnetic transition are analyzed for the bulk [Mn.sub.1.1][Fe.sub.0.9][P.sub.0.8][Ge.sub.0.2] compound, which is prepared by a simple blending and subsequent spark plasma sintering route. X-ray diffraction analysis and refinement has shown that the compound is crystallized in the hexagonal [Fe.sub.2]P-type structure, in which the Mn atoms have occupied all the 3g sites and some 3f sites, the Fe atoms have occupied the rest of the 3f sites, and P and the Ge atoms have randomly occupied the 2c and 1b sites.

Surfactant-assisted ball milling and subsequent size-selection method are used for preparing Nd-Fe-B nanoparticles. The structural analysis has shown that nanoparticles with two particle sizes are obtained and the partially amorphous Nd-Fe-B nanoparticles have given their room-temperature coercivities around 0.1 and 1.5 kOe for the small and large nanoparticles.

Polarization curve and electrochemical impedance spectroscopy tests are used for examining the corrosion kinetics for both spark plasma sintered (SPS) and conventional sintered Nd-Fe-B magnets in different electrolytes. The studies have shown that the unique microstructure in SPS magnets has restrained the aggressive intergranular corrosion taking place along Nd-rich phases in conventional magnets.

The effect of Nb addition on the magnetic properties and microstructure for nanocomposite [Nd.sub.9.5][Fe.sub.79-x][Co.sub.5][Nb.sub.x][B.sub.6.5] (x = 0, 1, 2, 3) magnets is examined. The results have shown that Nb addition has improved the coercivity and also the magnetic properties.

Oxidation kinetics of Nd-Fe-B permanent magnets prepared by both spark plasma sintering (SPS) and conventional sintering methods is analyzed at elevated temperature in dry air environment. The results have shown that the SPS magnet possesses excellent corrosion resistance at elevated temperature.

The phase evolution, microstructure, and magnetic properties of [Pr.sub.x][Fe.sub.80-x][Ti.sub.2][Co.sub.10][B.sub.4][C.sub.4] (x = 9, 10.5) melt-spun ribbons are analyzed. The refined structure has enhanced the exchange-coupling interaction between magnetic grains, which has improved the demagnetization-curve shape and the maximum energy product for the ribbons accordingly.

The effect of [alpha]-Fe content on the structure and magnetic properties of bulk isotropic and anisotropic[Nd.sub.2][Fe.sub.14]B/[alpha]-Fe nanocomposite magnets is analyzed. It is shown that the addition of [alpha]-Fe more than 2 vol% content has led to deterioration of [Nd.sub.2][Fe.sub.14]B crystallographic texture in the magnets, which has resulted in the degradation of the magnetic properties of the magnets.

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]

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]

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]

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]

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]

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]