Honglin Du

Structure and magnetic properties of Pr2Fe14(C,B)-type ribbons with high coercivity

The effect of the substitution of B for C on the structure and magnetic properties of the Pr15Fe77C8−xBx (x=0–8) ribbons has been investigated. Microstructure analysis shows that the grain size and size distribution of the ribbons with x⩾2 do not change with B substitution. It is found that B substitution significantly improves the hard magnetic properties of the samples. The coercivity, remanence, and energy product increase from 0.0002 and 0.19 T and 0.001 MGOe for x=0 to 2.19 and 0.76 T and 14.3 MGOe for x=8, respectively. Without heat treatment, Pr2Fe14C-type ribbons with high coercivity of greater than 2 T have been prepared by melt spinning. The introduction of B changes the phase components, and leads to a substantial difference in coercivity mechanisms of the B-poor ribbons (x=2) and B-rich (x=8) ribbons.

Anisotropic ternary Pr13Fe80B7 powders prepared by hydrogenation disproportionation desorption recombination process

High-purity ternary Pr13Fe80B7 magnetic powder with high anisotropy is obtained by a modified hydrogenation disproportionation desorption recombination (HDDR) process in this work. This powder exhibits a record-high Br of 1.05T, and has a good crystal texture along the c axis. It is found that the formation of HDDR Pr13Fe80B7 anisotropy is related to a rodlike disproportionation microstructure. We also show that by changing the HDDR conditions, an intrinsic coercivity of 800kA∕m and an energy product of 144kJ∕m3 are obtained on this powder. The details of the modified HDDR process are also presented in this paper.

Neutron powder diffraction study on the structures of LaNi5−xAlxDy compounds

Abstract The structures of LaNi5−xAlxDy ( x=0.75, 0.25, y=1.01, 1.10, 1.91 and 3.1) were systematically investigated by neutron and X-ray diffraction. D atoms are found to enter the 6m site of the α-phase but not the reported 12n site, while the 6m and 12n sites of the β-phase. In the case of LaNi4.75Al0.25Dy with lower Al content and symmetry, D atoms do not enter the α-phase but occupy the 4h site besides the 6m and 12n sites of the β-phase. The relationship between structures and properties is also discussed.

High-performance Pr2Fe14C-type magnets prepared by melt spinning

Without annealing, Pr13Fe80-xCoxC5B2 (x = 0-20) ribbons, with a coercive force. of more than 1.0 T have been prepared by melt spinning. Due to Co addition, rectangularity of demagnetization curves is significantly improved. The remanence and maximum energy product of the samples are obviously increased with the increase of x (x less than or equal to 15). A 3 maximum energy product of 145.7 kJ/m(3) which is the highest value among all that previously reported in the R2Fe14C-type (R = Nd or Pr) ribbons, has been achieved in the ribbons (x = 15) prepared directly by melt spinning. The Curie temperatures of 2:14:1 carbides of the ribbons in the as-quenched state increase linearly with X at an average rate 12K/at%Co. Similar to B and Cu, Co addition is found to accelerate the formation of 2:14:1 carbides

Coercivity enhancement in Pr9.5Fe83Zr2B5.5 magnetic nanomaterials

The coercivity of Pr2Fe14B/α-Fe magnetic nanomaterial has been drastically improved from 6.8 kOe to 26 kOe by the diffusion of the Pr68Cu32 alloy. Pr68Cu32 alloy reacts with α-Fe to form boundary phases among Pr2Fe14B grains. The boundary phases have weak magnetic properties and have a thickness comparable to the domain wall thickness of Pr2Fe14B phase. So boundary layers are very effective in pinning the motion of domain walls, leading to an increased coercivity. The coercivity of this material at 160 °C is improved from 2.7 kOe to 10 kOe by diffusion treatment.

Magnetic frustration and magnetocaloric effect in AlFe2-xMnxB2 (x = 0-0.5) ribbons

The crystal structure and magnetic properties of AlFe2−x Mn x B2 (x = 0–0.5) compounds were investigated. With increasing Mn content, the magnetic properties of these compounds evolve gradually and the lattice parameters change continuously: Curie temperature (T c) decreases from 312 K (x = 0) to 220 K (x = 0.5) and a new phase transition from the ferromagnetic state (FM) to spin-glass state (SPG) appears upon cooling. The lattice shrinks in the ab plane while it expands in the c direction. The formation of re-entrant SPG around 50 K was studied via temperature dependent ac and dc magnetization as well as the initial magnetization curves in 5 K. The reason for this glass state is the triangular configuration of magnetic atoms and the antiferromagnetic interactions introduced by Mn substitutions. The Curie transition leads to a conventional magnetocaloric effect (MCE). The Mn doping leads to a decrease in the MCE near room temperature, but there is a plane in entropy change (ΔS) for the x = 0.1 compound under low field which makes these compounds good candidates to produce composites used for magnetic refrigeration application in a wide temperature span.

Magnetic properties of AlFe2B2 and CeMn2Si2 synthesized by melt spinning of stoichiometric compositions

By suppressing the growth of impurities, a melt spinning method was successfully applied to the synthesis of typical layered CeMn2Si2 and AlFe2B2 compounds. X-ray diffraction analysis showed that CeMn2Si2 and AlFe2B2 had good purity and crystallized in ThCr2Si2- and AlFe2B2-type structures, respectively. The differences among three -type structures were also analyzed. The magnetic properties were investigated by magnetic measurements and electronic structure calculations. It was found that the Fe moment of AlFe2B2 reaches 1.32 μB at 5 K, which fits well with the calculated result of 1.44 μB at 0 K, and that the isothermal magnetic entropy change reaches 7.2 J kg−1 K−1 at 5 T, which shows great potential for room-temperature refrigeration applications.

Magnetic properties and magnetocaloric effect in Nd5Si3 compound

The structure and magnetic properties of Nd5Si3 compound have been investigated. A reversible magnetic entropy change was observed at about 112 K accompanied with a second-order magnetic transition from the ferromagnetic to paramagnetic state. The maximum value of −ΔSM is 5.0 J kg−1 K−1 at 112 K for a magnetic field change of 50 kOe. The relatively large magnetic entropy change and broad working-temperature span (about 57 K) of the reversible magnetocaloric effect make the present compound a potential candidate for the practical magnetic refrigeration in this temperature range.

Microstructural evolutions in NdFe10.5Mo1.5NX and Pr13Fe80B7 compounds during hydrogenation-disproportionation desorption recombination process

Microstructural changes of NdFe10.5Mo1.5 and Pr13Fe80B7 compounds during the solid-hydrogenation disproportionation desorption recombination process are investigated in this paper. It is found that the early disproportionated microstructure of NdFe10.5Mo1.5 and Pr13Fe80B7 alloys shows similar rodlike morphology. All the NdH2+X and PrH2+X rods have the same orientation and grow with a definite orientation related to the α-Fe matrix. However, it is different that Mo atoms are found to dissolve in the α-Fe matrix of the NdFe10.5Mo1.5 disproportionated products while the PrH2+X rods are enriched with B in the case of Pr13Fe80B7 alloys. No special crystallographic relationship between the recombined NdFe10.5Mo1.5 or Pr13Fe80B7 and its disproportionated products is observed. A preferred nucleation and growth of recombined Pr2Fe14B grains is found while that of recombined NdFe10.5Mo1.5 grains is not. Thus, the final hydrogenation-disproportionation desorption recombination (HDDR) NdFe10.5Mo1.5NX powder is isotro...

Nitrogenation effect of Sm2Fe17 alloys prepared by strip casting technique

Sm2Fe17 alloys prepared by strip casting technique can be directly nitrided to prepare interstitial Sm2Fe17NX compounds without pre-crushing. A phenomenon of spontaneous pulverization in the Sm2Fe17 strips induced by nitrogenation is found. This kind of pulverization may arise from the inter-granular fracture along the Sm-rich grain boundary phase as well as trans-granular fracture of Sm2Fe17 primary phase. Anisotropic Sm2Fe17N2.85 powders with a remanence (Br) of 14.1 kGs, a coercive force (iHc) of 12.1 kOe, and a maximum energy product ((BH)max) of 33 MGOe can be prepared using the nitrided strips.