Enhancement of magnetic properties and thermal stability of nanocrystalline (NdDyTb)_(12.3)(FeZrNbCu)_(81.7)B_(6.0) alloy with Co substitution

The major drawbacks of Nd-Fe-B magnets are relatively low Curie temperature and poor thermal stability. Ribbons with the near stoichiometric 2：14：1 composition of Nd10.8Dy0.75Tb0.75Fe79.7-xCoxZr0.8Nb0.8Cu0.4B6.0 （x=0, 3, 6, 9, 12, 15） were prepared by rapid quenching and subsequent heat treatment. The effect of Co element on the magnetic properties, thermal stability, and microstructure of the ribbons was systematically studied by vibrating sample magnetometer （VSM）, thermal magnetic analysis, atomic force microscopy （AFM）, and transmission electron microscopy （TEM）. It was found that Co substitution was significantly effective in improving the magnetic properties and the thermal stability of nanocrystalline ribbons. Although the intrinsic coercivity decreased from 1308.7 kA/m for x=0 to 817.4 kA/m for x=15, the remanence polarization and maximum energy product increased from 0.839 T and 116.5 kJ/m^3 for the Co-free samples to 1.041 T and 155.1 kJ/m^3 for the 12at% Co-substituted samples, respectively. About 10 K increase in Curie temperature was observed for the 2：14：1 phase with 1at% Co substitution. The absolute values of temperature coefficients of induction and coercivity were significantly decreased with Co substitution, which may be attractive for high operational temperature applications. The microstructure of nanocrystalline ribbons was slightly refined with Co substitution.

Effects of Cu and Co Substitution on the Properties of NiZn Ferrite Thin Films

Cu- and Co-substituted NiZn ferrite thin films, Ni0.4-xZn0.6CuxFe2O4 and Ni0.5Zn0.5CoxFe2-xO4 （0≤x≤0.2）, are synthesized by sol-gel process. The crystallographic and magnetic properties of Cu- and Co-substituted NiZn ferrite thin films have been investigated. The lattice parameter decreases with Cu substitution and increases with Co substitution. The saturation magnetization decreases and the coereivity increases with the increase of Cu substitution. Moreover, the saturation magnetization gradually increases with the increase of Co substitution when x≤0.10, but decreases when x〉0.10. Meanwhile, the coereivity initially decreases with the increase of Co substitution when x≤0.10, but increases when x〉0.10.

Impact of Co^(2+)substitution on structure and magnetic properties of M-type strontium ferrite with different Fe/Sr ratios

Ion substitution has significantly improved the performance of ferrite magnets,and cobalt remains a key area of research.Studies on the mechanism of Co^(2+)in strontium ferrite,especially SrFe_(2n-x)Co_(x)O_(19-d)(n=6.1-5.4;x=0.05-0.20)synthesized using the ceramic method,showed that Co^(2+)preferentially enters the lattice as the Fe/Sr ratio decreases.This results in a decrease in the lattice constants a and c due to oxygen vacancies and iron ion deficiency.The impact of Co substitution on morphology is minor compared to the effect of the Fe/Sr ratio.As the Fe/Sr ratio decreases and the Co content increases,the saturation magnetization decreases.The magnetic anisotropy field exhibits a nonlinear change,generally increasing with higher Fe/Sr ratios and Co content.These changes in the performance of permanent magnets are attributed to the absence of Fe^(3+)ions at the 12k+2a and 2b sites and the substitution of Co^(2+)at the 2b site.This suggests that by adjusting the Fe/Sr ratio and appropriate Co substitution,the magnetic anisotropy field of M-type strontium ferrite can be effectively optimized.

Effect of Co substitution on the glass forming ability and magnetocaloric effect of Fe88Zr8B4 amorphous alloys

As greater attention is paid to energy consumption and global warming, magnetic refrigeration （MR） technologies based on the magneto-caloric effect （MCE） have been developed. Systems based on MR are expected to be more compact, energy efficient, and environmentally safe compared with traditional vapor-cycle refrigeration technologies .

Effect of cobalt substitution on magnetic properties and microstructure of nanocrystalline(NdDyTb)_(12.3)(FeZrNbCu)_(81.7)B_(6.0) ribbons

Effect of Co substitution and annealing treatment on the formation, magnetic properties and microstructure of （NdDyTb）12.3（FeZrNbCu）81.7.xCoxB6 （x=0-15） ribbons prepared by rapid quenching and subsequent annealing was systematically investigated by means of differential scanning calorimeter （DSC）, X-ray diffraction （XRD）, high resolution scanning electron microscopy （HRSEM） and vibrating sample magnetometer （VSM）. Phase analysis revealed single-phase material. The remanence polarization Jr and maximum energy product （BH）max increased with increasing x from 0 to 12 and then decreased for x=15. The intrinsic coercivity Hci of （NdOyTb）12.3 （FeZrNbCu）81.7-xCoxB6 ribbons optimally processed decreased from 1308.7 kA/m for x=0 to 817.4 kA/m for x=15. Optimum magnetic properties with Jr=1.041 T, Hci=944.9 EA/m and （BH）max=155.1 kJ/m^3 were achieved by annealing melt-spun ribbon （x=12） at 675 ℃ for 10 min. There was no significant influence of Co substitution on microstructure.

Effect of cobalt substitution for nickel on microstructural evolution and hydrogen storage properties of La_(0.66)Mg_(0.34)Ni_(3.5-x)Co_(x) alloys

Superlattice hydrogen storage alloys offer a compelling advantage with rapid hydriding rate and high storage capacity.However,its practical applications face challenges including complex structure,low dehydriding capacity,and cyclic instability.In this work,we successfully prepared La_(0.66)Mg_(0.34)Ni_(3.5-x)Co_(x) superlattice hydrogen storage alloys with enhanced dehydriding capacity and stability by partially substituting Co for Ni.X-ray diffraction(XRD)refinements analysis reveals the presence of(La,Mg)_(3)Ni_(9),(La,Mg)_5Ni_(19),and LaNi_(5) phases within the alloy.Following Co substitution in the La_(0.06)Mg_(0.34)Ni_(3.4)Co_(0.1)alloy,there is a significant increase in content of the(La,Mg)_(3)Ni_(9) phase and a reduction in the hysteresis factor,resulting in an improved reversible hydrogen storage capacity from 1.45 wt%to 1.60 wt%.The dehydriding kinetics of the alloy is controlled by diffusion model with an activation energy of 8.40 kJ/mol.Furthermore,the dehydriding enthalpy value of the Co-substituted alloy decreases from 30.84 to 29.85 kJ/mol.Impressively,the cycling performance of the alloy after Co substitution exhibits excellent stability,with a capacity retention rate of 92.3%after 100 cycles.These findings provide valuable insights for the development of cost-effective hydrogen storage materials.

Reversible Mn^(2+)/Mn^(4+)double-electron redox in P3-type layer-structured sodium-ion cathode

The balance between cationic redox and oxygen redox in layer-structured cathode materials is an important issue for sodium batteries to obtain high energy density and considerable cycle stability.Oxygen redox can contribute extra capacity to increase energy density,but results in lattice instability and capacity fading caused by lattice oxygen gliding and oxygen release.In this work,reversible Mn^(2+)/Mn^(4+)redox is realized in a P3-Na_(0.65)Li_(0.2)Co_(0.05)Mn_(0.75)O_(2)cathode material with high specific capacity and structure stability via Co substitution.The contribution of oxygen redox is suppressed significantly by reversible Mn^(2+)/Mn^(4+)redox without sacrificing capacity,thus reducing lattice oxygen release and improving the structure stability.Synchrotron X-ray techniques reveal that P3 phase is well maintained in a wide voltage window of 1.5-4.5 V vs.Na^(+)/Na even at 10 C and after long-term cycling.It is disclosed that charge compensation from Co/Mn-ions contributes to the voltage region below 4.2 V and O-ions contribute to the whole voltage range.The synergistic contributions of Mn^(2+)/Mn^(4+),Co^(2+)/Co^(3+),and O^(2-)/(O_n)^(2-)redox in P3-Na_(0.65)Li_(0.2)Co_(0.05)Mn_(0.75)O_(2)lead to a high reversible capacity of 215.0 m A h g^(-1)at 0.1 C with considerable cycle stability.The strategy opens up new opportunities for the design of high capacity cathode materials for rechargeable batteries.

Effects of cobalt substitution on structure and microwave absorption properties of PrNi_5 alloy

The polycrystalline samples PrNi5_xCox （x=0.0, 0.1, 0.2, 0.3, 0.4） were synthesized by arc smelting and high energy ball milling method. The phase structure, morphology, saturation magnetization and electromagnetic parameters of the alloy powders were characterized by X-ray diffraction （XRD）, scanning electron microscopy （SEM）, vibrating sample magnetomctry （VSM） and vector network analyzer （VNA）, respectively. The results revealed that the lattice parameter a and c and unit-cell volume V increased with the increasing amount of Co substitution. The saturation magnetization increased as Co content increased. The minimum absorp- tion peak frequency shifted towards lower frequency region with the increasing amount of Co substitution. And the minimum reflec- tion loss of the PrNi5 xCox powders increased first and then decreased with the increasing amount of Co substitution. The PrNisCox alloys possessed the excellent microwave absorbing properties. The minimum reflection loss of the PrNi4.gCo0,1 alloy all could reach 20.0 all3 with the coating thickness ranging from 1.8 to 3 ram. The minimum reflection loss of PrNi4.gCoo.l powders was -36.20 d13 at 7.76 GHz, and the frequency bandwidth ofR〈10 dB reached about 1.50 GHz with the best matching condition d=2.0 ram.