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Post-sinter annealing process plays an important role in the microstructures and magnetic properties of the Nd-Fe-B sintered magnets. In this paper, systematically investigated are the magnetic properties and microstructures of the as-sintered and post-sinter annealed Nd-Fe-B magnets with Pr-Fe-Ga boundary addition. Two choice consecutive annealing methods are adopted at high and low temperatures, namely the 1st annealing at 880 oC for 2 h and then the 2nd annealing at 440 oC for 3 h. It is exceptional to find out that both the remanence and coercivity are improved after 2nd annealing process for this type of magnet. The coercivity is hugely increased from 10.09 kOe for the as-sintered sample to 17.19 kOe for the 2nd annealed magnet, with a significant increment of 70.37% in coercivity. The extraordinary magnetic properties of Br=14.44 kGs, Hcj=17.19 kOe and (BH)max=51.08 MGOe are obtained for the designated Nd-Fe-B sintered magnets without heavy rare earth (HRE) elements manufactured by dual alloy method. The Curie temperature is monotonically decreased from 634 K to 602 K while the c-axis alignment degree is optimized after annealing. Microstructural observation and analysis indicate that the elemental distribution patterns are altered after the 2nd annealing. The diffusion of the aggregate (Pr,Nd,Cu,Ga)-rich phase from triple junctions into the grain boundary regions is ascribed to the formation of thin and continuous grain boundary layer, which is critical to improve the microstructures and magnetic properties.

SmCo5 magnets were prepared by spark plasma sintering (SPS) technique. The phase constitutions, magnetic properties, and microstructures of magnets prepared under different sintering temperatures were investigated systematically. It is observed that the 1:5 phase and 2:7 phase coexist in the magnet, and 2:17 phase appears when the temperature rises to 1050 °C. The best magnetic properties were obtained for the magnets prepared at 1000 °C, with remanence Jr = 0.45 T, intrinsic coercivity Hcj = 985 kA/m, and maximum energy density (BH)max = 37 kJ/m3. It is shown that the SPSed magnet prepared at 1000 °C exhibits excellent thermal stability which is described in terms of temperature coefficient of remanence (α) = −0.15%/°C and temperature coefficient of coercivity (β) = −0.25%/°C in the temperature range of 27–400 °C. The microstructure analysis showed that the high density of the magnet and the uniform distribution of the hard magnetic phase are the main reasons for the excellent magnetic properties.

NdFeB hot-pressed and hot-deformed magnets were prepared by hot-pressed (HP) sintering and spark plasma sintering (SPS). The effects of sintering mechanisms of SPS and HP on the microstructure of hot deformation magnets were studied. The temperature of the mold surface is much higher than that of the sample in the cavity in HP, but lower than that of the sample in SPS. The Nd-rich phase is uniformly distributed and the grain size is smaller in the hot-deformed magnets prepared by HP, while the Nd-rich phase is excessively enriched and the grain size in the liquid-enriched region is abnormal in the hot-deformed magnets prepared by SPS. The comprehensive magnetic properties of hot deformed magnets prepared by SPS are significantly lower than those prepared by HP.

The magnetic properties, magnetocaloric effect and magnetoresistance in ErNi single crystal have been investigated in detail. With decreasing temperature, ErNi single crystal undergoes two successive magnetic transitions: a paramagnetic to ferromagnetic transition at TC =11 K and a spin-reorientation transition at TSR = 5 K. Meanwhile, a sharp field-induced metamagnetic transition is observed below the TC along the a axis. ErNi single crystal possesses a giant magnetocaloric effect around TC. The maximum magnetic entropy change is -36.1 J (kg K)−1 along the a axis under the field change of 0−50 kOe. In particular, the rotating magnetocaloric effect in ErNi single crystal reaches its maximum under a relatively low field, and the maximum rotating entropy change with a value of 9.3 J (kg K)−1 is obtained by rotating the applied field from the [011] to [100] directions under 13 kOe. These results suggest that ErNi could be a promising candidate for magnetic refrigeration working at liquid-helium temperature region. Moreover, a complicated transport behavior is uncovered in ErNi single crystal, which is attributed to the complex magnetic states and magnetic polaronic effect. Both positive and negative magnetoresistance are observed. A considerable large magnetoresistance with the value of -34.5 % is acquired at 8 K under 50 kOe when the field is along the [100] direction.

Solid-state refrigeration based on the magneto- or mechano-caloric effect, including elasto- and baro-caloric in ferroic phase transition materials is promising to replace the current vapor compression refrigeration in consideration of environmental-friendliness and energy-saving. However, both high driven field and small thermal changes in all of these caloric materials hinder the development of solid-state refrigeration. Here we report a giant baro-caloric effect near room temperature induced by a low hydrostatic pressure in Co-based Co51Fe1V33Ga15 Heusler alloy. The maximum adiabatic temperature change under the applied pressure change of Δp = 0.1–100 MPa can be as high as Δ T ad M a x = 7.7 K ( Δ T ad M a x / Δ p reaches up to ∼7.7 K kbar−1), surpassing the Δ T ad M a x / Δ p value reported hitherto in baro-caloric alloys. In addition, the microstructure is also studied by using the electron microscopes. Along with the austenite and martensite, the submicron V-rich particles are precipitated in this alloy, which are believed to account for enhancing mechanical properties.

Nowadays, searching for the materials with multiple magneto-functional properties and good mechanical properties is vital in various fields, such as solid-state refrigeration, magnetic actuators, magnetic sensors and intelligent/smart devices. In this work, the magnetic-field-induced metamagnetic reverse martensitic transformation (MFIRMT) from paramagnetic martensite to ferromagnetic austenite with multiple magneto-responsive effects is realized in Fe-doped Co-V-Ga Heusler alloys by manipulating the magnetic ordering. The martensitic transformation temperature Tm reduces quasi-linearly with increasing Fe-content. In strikingly contrast with the Fe-free alloys, the magnetization difference (ΔM') across martensitic transformation increases by three orders of magnitude for Fe-doped alloys. The increased ΔM' should be ascribed to the reduction of Tm, almost unchanged Curie temperature of austenite and the increased magnetic moment in the samples with higher Fe-content. The large ΔM' provides strong driving force to realize the MFIRMT and accordingly multiple magneto-responsive effects, such as magnetocaloric, magnetoresistance and magnetostriction effects. Meanwhile, giant Vickers hardness of 518 HV and compressive strength of 1423 MPa are achieved. Multiple magneto-responsive effects with exceptional mechanical properties make these alloys great potential candidates for applications in many fields.

Recently it is a hot topic to make full use of high abundant Y element in Nd2Fe14B-type permanent magnets. In contrast to Pr and Nd elements, Y shows different metallurgical behaviors during preparation process. In this paper, we have explored the magnetic properties, microstructures and corrosion performance of Pr-Nd-Y-Fe-B magnets fabricated by spark plasma sintering (SPS) technique from the ribbons of nanocrystalline and amorphous precursors, respectively. The coercivity and maximum energy product were improved for the magnets prepared from amorphous precursor materials (denoted as SPS-A hereafter) compared with the magnets prepared from crystalline precursor materials (denoted as SPS-C hereafter). Magnetic properties of Jr = 0.79 T, Hci = 864 kA/m, and (BH)max = 102 kJ/m3 were obtained for SPS-A magnets. In contrast with SPS-C magnets, the magnetic properties of SPS-A magnets are not so sensitive to the preparation conditions, which is quite beneficial to the homogeneity of microstructure and enhancement of coercivity for large-scale production of the designated magnets. Aggregated (Pr,Nd,Y)-rich phase was found out in SPS-C magnets. Pr and Nd elements are rich at grain boundary while Y is distributed uniformly at main phase and grain boundary phase. The strip grains and equiaxed grains exist in SPS-C and SPS-A magnets, respectively. The enhanced magnetic properties for SPS-A magnets are accredited to the uniform distribution of rare-earth-rich phase and low demagnetization factor. It is revealed by electrochemical test and dipping test that the corrosion potential is more positive and the corrosion rate is slower for the SPS-A magnets in 3.5 wt.% NaCl solution. The work is also expected to shed light on developing the nanocrystalline Pr-Nd-Y-Fe-B SPSed high-performance magnets in industry.

In the present work, we reveal a novel finding, that is, self-assembled grain boundary precipitates for realizing the magnetic-field-induced metamagnetic transition by employing low melting point metal in materials. This strategy has been experimentally verified in a well-established ferrimagnetic compound Mn2Sb by doping the bismuth (Bi) element with a low melting point of just 271.3°C. Bi solidifies later than the Mn2(Sb,Bi) main phase in (Mn2Sb)1-xBix system (the melting point of ~948°C for Mn2Sb), and aggregates spontaneously along the grain boundaries, forming Bi-rich grain boundary precipitates to coat main phase grains. This is very similar to the Nd-rich grain boundary phase in Nd-Fe-B permanent magnets. The fraction of Bi-rich grain boundary phase can be controlled by Bi-content. As a result, the magnetic field induced steep magnetoelastic transition from antiferromagnetic to ferrimagnetic is achieved in (Mn2Sb)0.89Bi0.11 alloy with giant multiple functional properties in Bi-doped Mn2Sb. Especially, the magnetic entropy change maximum nearly quadruples when Bi-doping increases from 0.03 to 0.11. Giant negative magnetoresistance of more than 65% under μ0∆H = 0–5 T, and magnetostrain of ~1802 ppm under μ0H = 8.5 T are obtained in (Mn2Sb)0.89Bi0.11. It should pave a way to achieve the magnetic transition and enhance the magnetoresponsive effects in designing similar coherent materials by employing low melting point metal doping to form the dual-phase heterogeneous structure.

The purpose of this paper is to study the influence of Mo addition on the phase morphologies, microstructures and magnetic properties of the designated alloys. It is found out that the coercivity Hcj increases unevenly from 12.2 kOe for (Nd0.8Ce0.2)13Fe82B5 to the maximum value of 13.3 kOe for (Nd0.8Ce0.2)13Fe80B5Mo2. The transmission electron microscopy images demonstrate that the grain size decreases with the addition of Mo, which indicates that Mo has grain refinement effect. The correlative analysis gives rise to the conclusion that the coercivity mechanism of the investigated alloys is dominated by pinning type. All in all, the enhancement of the magnetic properties is mainly attributed to the synergistic impact of grain refinement, pinning effects and the microstructural homogenization. The research may shed light on the potential development and application of rare earth-based counterpart magnets.

Grain boundary diffusion process (GBDP) serves as a promising approach in improving magnetic properties and thermal stability of NdFeB permanent magnets. Herein, non-heavy rare earth Pr-Zn films deposited on the magnet surface using DC-magnetron sputtering system are reported. The thermal stability and coercivity enhancement mechanism of Pr-Zn GBDP magnets were investigated. Results show that the coercivity of Pr-Zn GBDP magnet increases from 963.96 kA m−1 to 1317.14 kA m−1 without any remanence reduction. Notably, the demagnetization curve of Pr-Zn GBDP magnet still remains a high squareness ratio. The temperature coefficient of coercivity and anti-demagnetization ability of Pr-Zn GBDP magnet under high temperatures are improved after GBDP treatment. The well-optimized rare earth-rich (RE-rich) grain boundary phases and high effective anisotropy field of (Nd,RE)2Fe14B magnetic hardening layers surrounding main grains are the key factors to impact the magnetic properties and thermal stability of NdFeB permanent magnets via GBDP treatment.

The magnetic properties of alnico alloys are highly dependent on the spinodally decomposed nanostructure. In this article, we report the fabrication of alnico nanoribbons and the effects of various heat treatments on the magnetic properties, spinodal decomposition, microstructure, and temperature stability. It is found that the spinodal decomposition occurs in a wider range of temperatures from 800 °C to 860 °C. The scanning electron microscopy (SEM) and transmission electron microscopy (TEM) analyses of the microstructure confirmed that the nanostructure phases develop in a wide temperature range. Aspect ratio of the order of ~20 is obtained by optimizing the heat treatment conditions. Magnetic properties of H cj = 815 Oe, B r = 6.70 kG, and (BH) max = 1.88 MGOe are obtained after simplified heat treatment. The magnetic properties of the alloys are measured at low (10 K) and at high (800 K) temperature, and it is shown by calculating temperature coefficient of remanence (α) and temperature coefficient of coercivity (β) that alnico ribbons possess extraordinary temperature stability at low and high temperatures.

The effects of Ta doping on the magnetic properties, temperature stabilities, phase constituents, intergranular exchange interactions, and microstructures of (Nd0.8Ce0.2)13.5Fe80.5−xTaxB6 (x = 0–1.5) nanoribbons are investigated in this paper. It is found that Ta doping increased the coercivity of the alloys, while the remanence remained nearly unchanged. The temperature stability of the alloys improved significantly as the absolute value of temperature coefficient of coercivity β enhanced from 0.48%/K for Ta-free alloy to 0.38%/K for the alloys with 0.3–1.5 at.% Ta addition. The lattice constants (a, c), unit cell volume, and phase transition temperatures (Tsr, TC) of the alloys changed by adding Ta into the alloys. Comprehensive best magnetic properties of Hcj = 16.0 kOe, Br = 7.65 kG, and (BH)max = 12.60 MGOe are obtained in (Nd0.8Ce0.2)13.5Fe79.6Ta0.9B6 ribbon. The improvement in magnetic properties is mainly attributed to refined and uniform microstructure of the Ta-doped alloys.

The formation of the paramagnetic CeFe2 phase has deleterious effects on the magnetic properties of Ce Fe B type alloys. In order to reduce the volume fraction of the CeFe2 phase and improve the magnetic properties of cost efficient Ce Fe B magnetic alloys, Ce17Fe77-xGexB6 (x = 0.0–1.5) alloys were fabricated by melt spinning technique. The crystal structures, magnetic properties, intergranular exchange interactions and phase transition temperatures of CeFe2 and Ce2Fe14B phases were investigated. The critical amount of Ge doping enhanced the magnetic properties of the alloys by partially decreasing the formation of paramagnetic CeFe2 phase and refining the nano-grains. The optimized magnetic properties of coercivity Hcj = 467 kA/m, remanence Br = 0.51 T and energy density (BH)max = 40.6 kJ/m3 were obtained for Ce17Fe76.4Ge0.6B6 alloy. The analysis of Henkel plots confirmed that the exchange interaction among nano-grains was greatly improved for the optimized doping of Ge. The improved magnetic properties of the investigated alloys are attributed to the refined grains, enhanced intergranular exchange interactions and the decrease of paramagnetic phase for the critical amount of Ge.

Nanocrystalline Ce–Fe–B based rare earth permanent magnets are prepared by spark plasma sintering (SPS) method using grounded ribbons as raw material. The phase compositions, microstructure, magnetic properties, intergranular magnetic interactions, recoil loops, and corrosion resistance of the magnets are investigated systemically. The relationship among sintering processes, microstructures, and magnetic characteristics are discussed in depth by mainly using transmission electron microscope (TEM) and Physical Property Measurement System (PPMS) techniques. It is demonstrated that the sintering temperature has a significant influence on the average grain size and width of coarse grain areas. The optimized magnetic properties of remanent magnetization $J_{r}= 0.37$ T, coercivity $H_{\mathrm {ci}} = 227$ kA/m, and maximum energy product $(BH)_{\mathrm {max}}= 16$ kJ/m3 are obtained at 650 °C under 50 MPa for 2 min. Their exchanging coupling interactions are quite weak compared with those of the counterpart alloys. The exchanged decoupled of soft magnetic materials and inhomogeneous magnetic anisotropy result in open and steep recoil loops. The electrochemical experiment results display that the corrosion resistance of the magnets is improved by sintering at high temperature. This paper plays a role in guiding the future research and development of nanocrystalline Ce–Fe–B based permanent magnetic materials.

FeSiCr nanoparticles were fabricated by plasma arc-discharging method. The particle size is controlled by regulating the ratio of Ar and H 2 . The proper particle size improves the microwave attenuation capability and optimizes the impedance matching of the FeSiCr nanoparticles. When the ratio of Ar:H 2 = 80:20, the calculated reflectivity of the FeSiCr nanoparticle reaches −50.7 dB at 17.3 GHz ( d = 1.5 mm). By regulating the proportion of heat source gas H 2 and changing the coating thickness from 1.0 to 4.0 mm, the effective absorbing bandwidth ( 2 is a feasible way to control the nanoparticle size.

In this work, Ni-Co-Mn-Ti ferromagnetic shape memory alloy thin films, which consists of all 3d metals, are well prepared by direct-current (DC) double targets magnetron co-sputtering method. The deposition temperature (DT) dependence of microstructure and magnetic properties is studied in these thin films. The elemental compositions of these thin films are almost invariable, while the average grain size increases with the increasing DT. Micro-morphology shows that the crystal grains of films are spherical and homogeneous. For the samples deposited at 523 K and 573 K, an unusual magnetization reversal behavior is observed at ∼342 K and ∼225 K, respectively, in the thermomagnetic curves at the applied field μ0H = 1 T. Meanwhile, the hysteresis loops at ambient temperature demonstrate that in Ni-Co-Mn-Ti thin films the ferromagnetic contribution increases at the expense of diamagnetic one as DT increases. The reasons for these results are discussed.

The magnetic properties, thermal stabilities and microstructures of misch-metal (MM) alloys with nominal composition of MM2.0+xFe14B (x = 0–0.6) prepared using melt-spun technique are investigated. The XRD pattern showed that the ribbons consist of the MM2Fe14B main phase, α-Fe, Fe3B and ReFe7 phases. The coercivity of all ribbons enhances with increasing the content of MM, while the remanence gradually decreases. Interestingly, there is an increase in remanence of MM2.2Fe14B ribbon, which is attributed to the strong intergranular exchange coupling effect. The Curie temperature of all the ribbons is around 546 K, which does not change with the content of MM. By the EDS analysis, we have clarified that the changes of the temperature stability are mainly related to the distribution of rare earth content in the main phase. This study shows that the magnetic properties of the alloys can be improved by optimizing the content of rare earth elements. The ribbons in the optimum condition exhibit a coercivity of 899 kA/m and a (BH)max of 116 kJ/m3, which can be used to produce high cost performance MM-Fe-B magnets.

The all-d-metal Ni50-xCoxMn35Ti15 (x = 13,13.5) ferromagnetic shape memory alloy ribbons are successfully fabricated. The intermartensitic transformation and martensitic transformation arrest phenomenon are systematically investigated. In contrast to melt-spun ribbons, the annealed ribbons reveal an intermartensitic transformation from five-fold (5 M) modulated to non-modulated (L10) martensite below B2→5 M martensitic transformation. The XRD, TEM, DSC and temperature dependence of electrical resistivity measurements validate the occurrence of intermartensitic transformation. On the other hand, the magnetic-field-induced martensitic transformation arrest is achieved in these all-d-metal ribbons like other normal Ni-Mn-based Heusler alloys consisting of p-group and d-group elements. Strikingly, a kinetic de-arrest phenomenon is brought about in all-d-metal ribbons with the increasing heat treatment temperatures. The associated origins are discussed in these ribbons, which is very significant for deeply understanding the arrest and de-arrest phenomenon in ferromagnetic shape memory alloys. What's important, excellent magneto-functional and mechanical properties are obtained in these ribbons. Ni36.5Co13.5Mn35Ti15 annealed ribbon displays the best integrated properties, such as large magnetoresistance (∼34.9%), magnetic entropy change peak value (∼24.9 Jkg−1K−1) and effective refrigerant capacity (∼122.5 Jkg−1) under the field change of Δμ0H = 0–5 T, and large Vickers hardness [2.75 GPa (280.7HV)]. These make the all-d-metal Ni-Mn-based Heusler alloy ribbons attractive in the practical applications.

In this work, the exchange bias behavior and magnetocaloric effect have been studied in Mn7Sn4 alloy. The X-ray powder diffraction pattern recorded at room temperature indicates that the sample crystallizes in a single phase with Ni2In-type hexagonal structure (space group P 6 3 / mmc ). The maximum magnetic entropy change value across paramagnetic/ferrimagnetic transition is about 3.3 J kg−1 K−1 under the magnetic field change of μ 0 Δ H = 0 - 5 T . With further cooling, the reentrant spin-glass-like state is obtained below 150 K, for which the exchange bias effect has been observed. The exchange bias field is ∼7.8 mT and ∼6.7 mT at T = 10 K when the cooling field is μ 0 H CF = 0.1 T and 0.5 T, respectively. The magnetic behavior and the origin of exchange bias in Mn7Sn4 are discussed.

The carbon coated core-shell C@Fe3C/Fe nanocomposites were prepared by plasma arc-discharging method. The core-shell and graphite network structures were obtained, which could improve the absorbing properties by optimizing the impedance matching and increase the internal reflections of the propagated microwave. By varying the coating thickness from 1.0 to 5.0 mm, the reflectivity of C@Fe3C/Fe nanocomposites prepared in 30% CH4 is less than −20 dB nearly in the whole range of 2–18 GHz. The minimum reflection loss value reaches −32.9 dB at 14.2 GHz and the effective bandwidth (

Ce-Fe-B spark plasma sintered (SPSed) magnets prepared with different ratio of alloys of Ce-Fe-B and Pr-Nd-Fe-B by dual alloy method are investigated in this paper. As expected, the remanent magnetization Jr, coercivity Hci and maximum energy product (BH)max of SPSed magnets increase obviously with increasing weight percentage of Pr-Nd-Fe-B alloy. The magnetic properties of Jr = 0.71 T, Hci = 915 kA/m, (BH)max = 72 kJ/m3 are obtained for the SPSed magnets with 80 wt% Pr-Nd-Fe-B alloy. There are three Curie temperatures in this type magnet, which implies the coexistence of three hard magnetic phases. The second Curie temperature depends on the Pr-Nd-Fe-B content. With increasing Pr-Nd-Fe-B alloy content, the volume fraction and width of coarse grain zone decrease. It is shown by the microstructure analysis that the rare earth elements diffuse during sintering process resulting in the formation of Pr-Nd-Ce-Fe-B hard magnetic phase. The intergranular exchange coupling strength is enhanced with increasing Pr-Nd-Fe-B content. The present research may be a potential reference for further research and development of this type Ce-containing nanocrystalline permanent magnetic materials.

Al film, which was coated in sintered Nd-Fe-B magnets prepared by magnetron sputtering, was employed for grain boundary diffusion source. Effects of the grain boundary diffusion processes (GBDP) on the microstructure evolution and properties were investigated in detail. Through grain boundary diffusion processes, the highest coercivity of 1184 kA/m and maximum energy product of 238 kJ/m3 could be obtained, increasing by 21.8% and 3.9%, respectively, compared with the initial magnet. Meanwhile, our results showed that fine, uniform and continuous intergranular phase induced by Al diffusion, was the main reason for properties improvement, while a weak ferromagnetic phase and the vague interface between main phase and RE-rich phase should be responsible to the deterioration of coercivity when the diffused temperature exceed 600 °C. Besides, the corrosion resistance of Al-diffused magnets was also greatly improved, owing to the fact that the Al element could promote the electrochemical potential of RE-rich phase and the more thin, continuous intergranular phase would also narrow the corrosion channel.

MnBi alloys with high content of low temperature phase (LTP) MnBi and excellent magnetic properties were prepared by surfactant assistant ball milling (SABM), using annealed ribbons as precursors. Effects of the SABM processes on the phase constituent, microstructure, and magnetic properties were investigated in detail. It is found that the reduction of saturation magnetization is mainly attribute to the decomposition of LTP MnBi into Mn phase, Bi phase and MnO phase, with increasing the ball milling time. Meanwhile, due to the fine grain size and increased magnetic isolation effects between LTP MnBi grains, the coercivity increases monotonously with prolonging the ball milling time to 10 h for Mn55Bi45 powders. Through compression molding under the magnetic field, based on the SABM powders, the optimum anisotropic bonded magnet displays the maximum energy product (BH)max of 9.06 MGOe at room temperature, and a value of 7.05 MGOe at 380 K can be still achieved. In addition, the magnetic hardening mechanism of bonded magnets can be well explained by the strong pinning model. Strongly favorable magnetic properties make bonded MnBi magnets an attractive candidate material for small permanent magnets used for temperature applications up to 380 K.

In this paper Hf doped (Nd0.8Ce0.2)13Fe82−xB5Hfx (x = 0, 0.5, 1.0, 2.0, 3.0) ribbons were fabricated by melt-spinning technique, and their microstructure, magnetic properties and coercivity mechanism have been investigated methodically. It is found that the coercivity of (Nd0.8Ce0.2)13Fe82−xB5Hfx ribbons is enhanced for 0 ≤ x ≤ 2.0 at.% while the remanence decreases slightly. The optimal comprehensive magnetic properties Jr = 7.5 kG, Hcj = 12.7 kOe, and (BH)max = 12.3 MGOe, are obtained at x = 1.0 at.%. The grain size decreased with the addition of Hf and more uniform microstructure evolved. The coercivity mechanism of the (Nd0.8Ce0.2)13Fe82−xB5Hfx (x = 0–3.0) ribbons is found to be the pinning mechanism based on the systematic investigations and analysis. The synchronization of the grain refinement and the pinning effect lead to the improvement of magnetic properties.

Ce-Fe-B-based rare earth permanent magnets are prepared by spark plasma sintering (SPS) technique, and low melting NdCu alloy is added to improve its magnetic properties and thermal stabilities. The X-ray diffraction (XRD) result indicates that the lattice constants of the unit cell of 2:14:1 phase increase with NdCu addition. The remanent magnetization, coercivity and maximum energy product are enhanced remarkably from 0.37 T, 227 kA/m, 16 kJ/m3 for the sintered magnets without NdCu addition to 0.47 T, 476 kA/m, 30 kJ/m3 for those with 20 wt% NdCu addition. The temperature coefficients of remanence (α) and coercivity (β) of the spark plasma sintered magnets (denoted as SPSed magnets thereafter) are improved from −0.46%/K, −0.60%/K to −0.34%/K, −0.55%/K in the range of 300–400 K. There are two Curie temperatures in the Ce-based magnets with NdCu addition, which implies the coexistence of two hard magnetic phases. The second Curie temperature depends on the NdCu content. It is shown by the microstructure analysis that a typical core-shell structure is formed with Ce-rich core and Ce-lean shell by NdCu addition. Furthermore, it is displayed that Nd atoms prefer to diffuse into the Ce-lean flakes. The Nd-Ce exchange mechanism and immigration behavior of elements are finally investigated. The intergranular exchange coupling strength is enhanced in NdCu-added magnet. It is found out that the core-shell structure plays an important role in the special microstructure evolution and the enhancement of the magnetic properties for the typical Ce-Fe-B-based SPSed magnets by NdCu addition.

The substituted Mn2Sb-based ferrimagnetic (FIM) alloys by other elements have attracted much attention recently due to excellent magneto-functional properties. However, almost all investigations have been concentrated on the first-order phase transition between antiferromagnetic and FIM state. In this work, a large topological Hall effect (THE) associated with the spin reorientation transition is observed in the Mn2Sb0.9Bi0.1 alloy. Strikingly, the sign reversal of topological Hall resistivity ([Formula: see text]) is found before and after the SRT temperature TSR ∼260 K. Above the TSR, a positive [Formula: see text] is observed, e.g., ∼0.52 μΩ cm at 320 K. By reducing temperature to 275 K, the [Formula: see text] value decreases to ∼0.42 μΩ cm. It is interesting that, however, the negative [Formula: see text] value is found below the TSR, e.g., ∼−0.66 μΩ cm at 175 K. The physical mechanism about this peculiar THE is discussed in Bi-doped Mn2Sb-based alloys.

There is a close relationship between the magnetic properties of alnico permanent magnetic alloys and the nano-scaled spinodally decomposed structure which results from various heat treatment cycles. In this paper, different heat treatment cycles are employed to cast alnico 8 alloys with composition 32.3Fe-37.5Co-13.7Ni-6.2Al-5.8Ti-3.4Cu-0.2Zr-0.1S-0.8Nb. It is observed that magnetic field treatment at high temperature for specific time is the most effective method to obtain better microstructure and magnetic properties. The mosaic structures consisting of Fe-Co phase and Al-Ni rich phase are best separated during thermomagnetic treatment for 4–5 min and refined during low temperature treatments. The bias growth of the ferromagnetic phase does not develop in absence of magnetic field, and hence the phases are not refined and separated completely. This produces isotropic alnico alloys with low magnetic properties. However, continuous cooling of the alloys in magnetic field followed by isothermal treatment without magnetic field provides moderate magnetic properties. Treatment at high temperatures in field and without field for longer time leads to the coarsening of spinodal phases and poor magnetic properties. The optimum magnetic properties of Hcj = 1.7 kOe, Br = 8.0 kGs and (BH)max = 5.02 MGOe are attributed to the refined microstructure of the thermomagnetically treated alloys.

In this work, the Mn1-xNixCoGe (0.01 ≤ x ≤ 0.075) alloys are prepared. By slight substitution of Mn upon Ni element, the magnetic transition and structural transformation of stoichiometric MnCoGe ferromagnet are controlled to coincide. Accordingly, the coupled magnetostructural transformation occurs during the wide temperature window of ∼91.5 K covering room temperature from the ferromagnetic TiNiSi-type to paramagnetic Ni2In-type state. Strikingly, a magnetic-field-driven metamagnetic martensitic transformation is observed in Mn0.975Ni0.025CoGe alloy. As a result, large room temperature magnetocaloric effects are obtained including large magnetic entropy change of ∼30.3 Jkg−1K−1 for sample with x = 0.025 and large refrigeration capacity of ∼276.8 Jkg−1 for x = 0.035 under the applied field change of ΔH = 0–7 T. The influence of slight Ni-substitution for Mn on the magnetic and magnetocaloric properties of MnCoGe alloy is studied and the origins are discussed.