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FeCo thin films with high saturation magnetization (4 πMs) can be applied in high-frequency electronic devices such as thin film inductors and microwave noise suppressors. However, due to its large magnetocrystalline anisotropy constant and magnetostrictive coefficient of FeCo, the coercivity (Hc) of FeCo films is generally high, which is detrimental to the soft magnetic properties. Meanwhile, the thickness and deposition temperature have significant effects on the coercivity and saturation magnetization of FeCo films. In this paper, FeCo thin films with different thicknesses were prepared by magnetron sputtering at different temperatures. The effects of thickness and deposition temperature on the microstructure and magnetic properties of FeCo thin films were systematically studied. When the film thickness increases from 50 nm to 800 nm, the coercivity would decrease from 309 Oe to 160 Oe. However, the saturation magnetization decreases from 22.1 kG to 15.3 kG. After that, we try to further increase the deposition temperature from room temperature (RT) to 475 °C. It is intriguing to find that the coercivity greatly decreased from 160 Oe to 3 Oe (decreased by 98%), and the saturation magnetization increased from 15.3 kG to 23.5 kG (increased by 53%) for the film with thickness of 800 nm. For the film with thickness of 50 nm, the coercivity also greatly decreased from 309 Oe to 10 Oe (decreased by 96%), but the saturation magnetization did not change significantly. It is contributed to the increase of deposition temperature, which will lead to the increase of grain size and the decrease of the number of grain boundaries. And the coercivity decreases as the number of grain boundaries decreases. Meanwhile, for the thicker films, when increasing the deposition temperature the thermal stress increases, which changes the appearance of (200) texture, and the saturation magnetization increases. Whereas, it has a negligible effect on the orientation of thin films with small thickness (50 nm). This indicates that high-temperature deposition is beneficial to the soft magnetic properties of FeCo thin films, particularly for the films with larger thickness. This FeCo thin film with high saturation magnetization and low coercivity could be an ideal candidate for high-frequency electronic devices.

To obtain dense Al-based quasicrystalline (QC) coatings with high content of quasicrystal phase, the QCs were deposited by the high-velocity air fuel spray process with different feedstock powder sizes. The phase composition, microstructure, chemical composition, tribological, and mechanical properties of the coatings were analyzed using x-ray diffraction, scanning electron microscopy, energy-dispersive x-ray spectroscopy, a pin-on-disk wear tester, and a nanohardness tester. The results indicated that smaller particle sizes produced denser structures with lower coating porosities, while the coarser powder helped maintain the desired quasicrystalline phase. In addition, the coatings sprayed with coarser powders exhibited a lower sensitivity to the sliding velocity due to a stronger bonding strength between the splats and a lower oxidation degree. The coating first exhibited abrasive wear coupled with oxidative wear, which was then converted to delamination, abrasive wear, and intensified oxidative wear.

Ni–Mn–Sn-based magnetic refrigeration materials have a coupling ability of structure transformation and magnetic transition to improve their magnetocaloric effects. In this work, the influence of the Co doping on Curie temperature, structure and magnetocaloric properties of Ni43-xCoxMn46Sn11 (x = 0, 1, 2, 3) alloys prepared by melt-spinning were investigated by means of X-ray diffraction, Differential Scanning Calorimetry and Vibrating Sample Magnetometry. It was found that the crystal structure of samples changes from 4O modulated martensite to L21 cubic austenite with increasing temperature. The magnetic phase diagram of Ni43-xCoxMn46Sn11 system was constructed from thermomagnetic curves. Increasing Co content enhanced the Curie temperature of L21 cubic austenite from 279 K to 354 K, however, shifted the transition temperature of martensitic down to lower temperature, 170 K. As for the sample with x = 3, it only has ferromagnetic–paramagnetic second order magnetic transition, and no structural transformation was observed. The sensitivity of martensitic transformation induced by magnetic field can be improved up to − 3.52 K · T−1. Under 0–5 T, the maximum values of magnetic entropy change, refrigerant capacity and the adiabatic temperature change are improved by 60.5%, 59.0% and 17.5%, respectively. The results indicate that the relatively large martensitic transformation sensitivity and magnetocaloric effects make these alloys good candidates in the range of 150–300 K.

Agglomerated 8YSZ nano-powders for thermal barrier coating (TBC) were prepared by spray drying method. The morphology and diameter of 8YSZ powders were adjusted through controlling the solid content of the suspensions. Using prepared agglomerated 8YSZ nano-powders, columnar-structured coatings were obtained on Ni-based superalloy substrates by plasma spray-physical vapor deposition (PS-PVD). The experimental results proved that the spray dried powders characteristics were related to the solid content of suspensions. During the PS-PVD process, the deposition efficiency of the powders was improved with the increase of powder diameter due to the existence of thermophoresis. Moreover, it can be concluded by mathematical derivations that the top area of the plasma flame was sufficient for powder evaporation.

Titanium powders and hydroxyapatite powders were used to fabricate the titanium and hydroxyapatite composite coating (Ti/Ti/HA) on the Polyetheretherketone (PEEK) by vacuum plasma spraying (VPS). The phase composition and morphology of the Ti/Ti/HA coating were analyzed by XRD, SEM, industrial CT, and three-dimensional contour profiler (DEKTAK XT). The results showed that the phase composition of the Ti/Ti/HA coating was dominated by the HA phase and a small amount of the Ti phase. The Ti/Ti/HA composite coating presented an obvious three-layer structure with different roughness and porosity. The bottom was Ti coating with a porosity less than 10%; the middle was porous Ti coating with a porosity of 35% ± 10%; the surface coating was HA coating with the crystallinity near 95%, a porosity of 32% ± 10%, a roughness Ra = 30 ± 10 μm. Moreover, the TG-DSC and ATR-FTIR results showed that VPS coating has no effect on thermochemical properties of PEEK material. The average bond strength of the composite coating was achieved 32 MPa.

Large thermal hysteresis in the (Mn,Fe)2(P,Si) system hinders an efficient heat exchange and thus limits the magnetocaloric applications. Substitution of manganese by vanadium in the Mn1-x1Vx1Fe0.95P0.593Si0.33B0.077 and Mn1-x2Vx2Fe0.95P0.563Si0.36B0.077 compounds enable a significant reduction in the thermal hysteresis without losing the giant magnetocaloric effect. For the composition closest to the critical one, where first-order crossovers to second-order phase transition in the series of x2 = 0.02, Mn0.98V0.02Fe0.95P0.563Si0.36B0.077 exhibits a thermal hysteresis that is reduced from 1.5 to 0.5 K by 67%, yielding an adiabatic temperature change of 2.3 K and magnetic entropy change of 5.6 J/kgK for an applied field of 1 T, which demonstrates its potential for highly efficient magnetic heat pumps utilizing low-cost permanent magnets.

The relation of microstructure and mechanical property in cathodic arc evaporated (CAE) Cr 33 Al 67 N coatings have not yet been fully understood despite their extensive applications. In this work, we prepared Cr 33 Al 67 N coatings using CAE, a more industrially favored technique. The as-deposited coatings show superhardness (41 GPa), superior fracture resistance, adhesion strength and high compressive stress (6.3 GPa). Phase and bonding analyses show that the coatings comprise single fcc -solid solution structure with (111) orientation. Transmission electron microscope investigation revealed a microstructure evolution of the coatings: columnar grains with a diameter of 20–40 nm ripen from nano-composite structure with grain diameter of about 6 nm. The resulting densification of grain boundary (GB) facilitates growth of compressive stress, confirming the GB adatom pinning mechanism. Compressive stress plays a significant role in the concomitant hardening and toughening of the coatings by impeding grain boundary glide. Hall-Petch effect and low-angle grain boundary also contribute to the hardening-toughening. These findings reveal the relation of structural mechanism between hardening and toughening in PVD nitride coatings, and supplement the measures to tune microstructure towards superhard yet tough coatings.

The Fe15−xMn40Al45+x (x = 0, 1, 2 and 3) and Fe15Mn40−yAl45+y (y = 1, 2 and 3) alloys were prepared by arc melting and annealed at 1000 °C for 7 days. The microstructure and magnetic properties are characterized by XRD and VSM. Corresponding corrosion potential and hardness are measured by electrochemical workstation and Vickers hardness tester. All samples have CsCl type Cubic structure. And for Fe15Mn40−yAl45+y alloys, with increasing Mn content, the lattice parameters increase from 2.9613 A to 2.9678 A, while the curie temperatures can be tuned from 288 K to 330 K. As for Fe15−xMn40Al45+x alloys, the curie temperatures rise from 315 K to 340 K with lattice parameters increasing from 2.9658 A to 2.9689 A. The peak values of magnetic entropy change under 5 T are −2.4 and −3.1 J·kg−1K−1 for Fe15Mn40Al45 and Fe14Mn40Al44 respectively. The values of refrigerant capacity power are 223.4 and 232.5 J·kg−1 under 5 T. The Arrott plots are also employed to investigate the magnetic phase transition, showing all samples undergo second order ferro-paramagnetic phase transition. Furthermore, these alloys have good hardness and corrosion resistance properties. The potential applications of these alloys as magnetic refrigerant will be also discussed in this paper.

A rotary active magnetic regeneration refrigerator prototype named FAME Cooler was developed for studying the performance of different magnetocaloric materials in a realistic practical environment. The rotary magnetic field source generates an average magnetic field of 0.875 T within a volume of 0.71 l The regenerator is designed asymmetrically and holds in total 1.18 kg of gadolinium spheres for a first performance test. Combined with a real-time controlled programmable solenoid-valves system, different working parameters or thermodynamic cycles can be applied. In the performance test, while the temperature of system hot side was fixed at 295 K, under a utilization condition of 0.25, this prototype achieved a maximum zero-span cooling power of 162.4 W, and a zero-power temperature span of 11.6 K. Under a utilization condition of 0.15, a maximum COP of 1.85 was reached. These performance metrics are comparable with existing magnetic heat pump devices of the same scale.

The nucleation and growth processes during α 2 ' → α 2 + γ transformation that leads to fully lamellar TiAl alloys were investigated by phase-field simulations. Since both α2 and γ are ordered solid solutions with a complex superlattice structure, it is still a great challenge describing the phase transition under different temperature conditions. In this article, sublattice model combined with gradient descent method was proposed for free energy calculation of the ordered phases. To verify the accuracy of this model, the formation of fully lamellar TiAl alloys was simulated. The simulation results demonstrated that the formation of lamellar structure is under the action of elastic energy and different variants show preferred orientation. It was also indicated that the distribution of lamellar structure at different temperatures is different. For example, at 1100 K, the lamellae are dense and small, but they are coarse at 1300 K, 1200 K, 1000 K and 900 K, which is consistent with the experimental observations. These findings can verify the correctness of our free energy model and overcome the defect that the traditional polynomial free energy model can only simulate isothermal temperature conditions, thus greatly simplifies the computational complexity and gives us the opportunity to expand to other ordered phase systems.

The Mn1.2Fe0.8P0.6Si0.4B0.05 alloys were prepared by ball milling and melt-spinning methods. The structure and magnetic characteristics of all samples were examined by X-ray diffraction, vibrating sample magnetometer and SEM. Results show that both the ribbon and bulk alloys can crystallize in a hexagonal Fe2P-type phase with some impurity phase. The lattice parameters, a and c, of Fe2P-type phase are 6.02960 A, 6.03033 A, and 3.42310 A, 3.44431 A for ribbon and bulk Mn1.2Fe0.8P0.6Si0.4B0.05 alloys, respectively. The Curie temperature increased by 20% from 165 K in bulk to 197 K in ribbon while thermal hysteresis and magnetic hysteresis decreased by 28% and 80% for ribbon sample, respectively. Moreover, the values of magnetic entropy change can be tuned from 15.7 J⋅kg−1⋅K−1 in bulk to 21.8 J⋅kg−1⋅K−1 in ribbon under 0–5 T, resulting in the effective refrigerant capacity (RCE) increasing from 238 to 286 J⋅kg−1. The nature of the phase transitions was studied through the Arrott plots, indicating that the samples undergo first-order ferro-paramagnetic phase transitions. The origin of magnetic hysteresis losses is also discussed deeply. Furthermore, this alloys with large magnetic entropy change could be an interest potential for future magnetic refrigeration applications.

Rare earth (RE) permanent magnetic thin films, such as SmCo-based films, are promising candidates for future thermal-assisted magnetic recording media because of their supreme thermal stability and fine superparamagnetic critical size. Phase compositional distributions and crystallographic orientations can directly influence the magnetic domain evolutions and magnetic performance of SmCo films. However, these films often exist in multi-phases without well-defined distinct magnetic anisotropy, thereby causing difficulties in analyzing their functions. The effects of atomic diffusions induced by annealing on crystallization and magnetic anisotropy energy are poorly understood. In this work, the influence of doping Cu atoms via introducing Cu layer on magnetic anisotropy of Cr/SmCo/(Cu)/Cr films is investigated. Introducing a Cu layer and post-annealing lead to tunable magnetic anisotropy from isotropy to anisotropy and domain structure formation. Micromagnetic simulation is used to further analyze the effects of crystallization, anisotropy field and compositional distribution on the magnetization reversal behavior and coercivity variations in SmCo films. It reveals that the differences of anisotropy field of Co and amorphous phases could affect the domain wall motions and coercivity, which shows the analogous trend as an experimental result. Moreover, the elevated anisotropy constant of Sm(Co,Cu) alloy and the small fractions of SmCo5 boundary phases are also beneficial to the enhancement of coercivity derived by calculating domain wall energy. In-plane magnetic anisotropy is improved by the SmCo5 phase, which has an in-plane preferred orientation of the c axis. This work provides theoretical and experimental bases for the future fabrication of SmCo-based films by controlling atomic diffusion with optimized grain boundary phase distribution.

The magnetic anisotropy of SmCo-based permanent magnetic thin films are generally controlled by introducing buffer layer or heating substrate. However, the design for the multi-layer thin film system is complicated and the thickness of SmCo is limited due to a short range of interfacial stress/strain between the buffer layer and SmCo layer. In this work, the effects of temperature gradients, generated by RTP (rapid thermal process), on the magnetic anisotropy of the SmCo-based films were systematically investigated. The results show that the as-deposited films exhibit amorphous state. The out-of-plane coercivity of RTP-treated films is strongly correlated with the heating rate, and its optimum value (2810 Oe) is larger than that of the CTA (conventional thermal annealing) treated films (1670 Oe). For the RTP-treated films, the intensity of characteristic diffraction peaks for in-plane oriented SmCo5 (200) and Sm2Co17 (300) decreases, together with reducing the roughness. Besides, the grain size is finer and the contrast of magnetic domains becomes stronger for the RTP-treated films due to that the easy axis of SmCo5/Sm2Co17 phase gradually changes from in-plane to out-of-plane direction. It is suggested that the RTP treatment with a shorter annealing time has beneficial effects on obtaining finer microstructure and improving the out-of-plane magnetic anisotropy of the SmCo-based films. This work provides a novel way to control the magnetic anisotropy via annealing temperature gradients for permanent magnetic thin films, compared with conventional methods, to induce the magnetic anisotropy.

TiB2-Metal composite coatings with excellent oxidation resistance become ideal candidates using at high temperature ranging from 600 to 1000 °C. In order to maintain both the superior mechanical properties and oxidation resistance in severe working conditions, the nanostructured NiCrCoAlY-TiB2 coating was fabricated by the activated combustion high velocity air-fuel spraying (AC-HVAF) with the composite powders prepared by ball milling and plasma spheroidization. X-ray diffraction (XRD), scanning electron microscopy (SEM) and transmission electron microscopy (TEM) were used to observe the phase constituents and microstructure. It was found that the coating with nanostructured TiB2 particles uniformly distributed in the NiCrCoAlY matrix has the same structure as the composite powders. The coating shows excellent mechanical properties, such as high microhardness (991.43 HV0.3), good fracture toughness (4.12 MPa m−1/2) and large bonding strength (75.43 MPa), and excellent oxidation resistance with low weight gain (1.56 × 10−6 mg2 cm−4 s−1). The cyclic oxidation behavior is in accordance with the parabolic law.

The soft magnetic alloys Fe73.5Cu1B13Si9.5Nb3-xVx (x = 0, 0.5, 1.0, 1.5) were prepared by melt-spinning. The effects of doping V and annealing process on the microstructure, magnetic properties and bending ductility of the alloys were investigated. Results show that doping V can improve the glass formation ability for the alloys. It is found that the large thermal stability value (ΔT), which is beneficial to enhance the soft magnetic properties, can be obtained by tuning the first crystallization temperature and the second crystallization temperature with doping V. The alloys exhibit high saturation magnetization of about 155.9 emu/g. Furthermore, the coercivity (Hc) of 1.9 A/m and permeability of 152500 measured at 10-170 KHz near room temperature are obtained. Moreover, the good bending ductility makes Fe73.5Cu1B13Si9.5Nb2V1 alloy as a candidate for widely used in the fields of mechanical, chemistry and medicine.

BiFeO3 nanoparticles (BFO-NPs) have been successfully synthesized through modified microwave-assisted hydrothermal method. The obtained BFO-NP was hexagonal phase with R3c structure and covered with a large number of surface hydroxyl groups. Compared with the bulk BiFeO3 microsphere, BFO-NP has much higher purity and similar band gap energy, about 2.10 eV. The photocatalytic performance of BFO-NP was evaluated by Rhodamine B (RhB) removal without any sacrificial agent under visible-light irradiation. A fivefold increase in the rate of RhB degradation and mineralization was obtained, which should result from effective separation of the electron-hole pairs. Furthermore, the scavenger-experiments reveal that photo-generated holes and hydroxyl radicals were the primary reactive species. This study opens a new pathway to synthesize BiFeO3 nanoparticle by hydrothermal method and provides a referential route for other perovskite photocatalysts.

Sm-Co multilayer films are deposited by plasma sputtering with a Cr underlayer and a Cu buffer layer, followed by annealing at different temperatures. The as-deposited films show low hard magnetic properties due to the existing amorphous Sm-Co phase. After annealing, for the films without Cu buffer layer, there is only Sm2Co17 phase in the films even at high annealing temperature and the coercivity is less than 12kOe. When inserting a Cu buffer layer, the well-crystalline SmCo5 single phase is obtained at relatively lower annealing temperature (500 °C and 550 °C) and extremely high in-plane coercivity (38kOe) is achieved. An analysis of Transmission electron microscopy (TEM) and Auger electron spectroscopy (AES) reveals that Cu atoms started to diffuse during the annealing process induced by thermal dynamics, concentration gradient and microstructure variations, and eventually uniformly distribute in SmCo layer and form Sm(Co,Cu)5 phase. The exchange interaction energy calculation indicates that small fraction of Cu atoms preferentially substitute the Co(2c) site in SmCo5 lattice, which reduces the exchange coupling effects of Sm-Co and gives rise to the coercivity. The results provide a guidance to fabrication of single-phase Sm(Co,Cu)5 multilayer films with superior performance that have applications in advanced electromagnetic and electronic devices.

The relation between the microstructure and the magnetic properties of Fe2P-type (Mn,Fe)2(P,Si,B) based materials has been systematically investigated by changing the annealing temperature and time. X-ray diffraction, Scanning Electron Microscopy and Energy Dispersive X-ray Spectroscopy measurements show that the alloys contain the main Fe2P-type phase and two impurity phases of (Fe,Mn)5Si3-type and Fe2MnSi-type. Boron appears to facilitate the formation of the Fe2P-type phase during the arc-melting progress. Upon increasing the annealing temperatures from 1123 to 1423 K, the Curie temperature (TC) decreases from 302.0 to 270.5 K in the Mn1.15Fe0.85P0.55Si0.45 alloys and the magnetic-entropy change (ΔSM) increases linearly with annealing temperature. For the Mn1.15Fe0.85P0.52Si0.45B0.03 alloys annealed at 1423 K for different times, TC decreases from 263.8 and 232.8 K with increasing annealing time and ΔSM reaches a maximum value after annealing for 48 h. The differences in the annealing temperature and time influence the Si content in the Fe2P-type phase of the alloys and determine TC, the thermal hysteresis and the magneto-elastic transition.

TiC-Fe based cermet coating with high hardness and superior wear resistance together with low price and environmental friendliness was developed. Initially, the TiC-Fe composite particles were prepared by high energy ball milling, spray drying and plasma spheroidization. These cermet powders not only showed high sphericity and dense microstructure but also presented homogeneous distribution of TiC. Then, the TiC-Fe cermet coating was deposited by high velocity air fuel (HVAF). The results indicated that introducing ceramics would increase the deformation degree of the splats and eliminate the layered structure, which effectively enhanced the microhardness and wear resistance of composite coating. Compared with pure metallic coating, the microhardness of cermet coating increased to 887.5 HV0.3, while the wear rates of cermet coating reduced by 40% and 60% at 10 N and 25 N, respectively. Besides, the TiC-Fe cermet coating showed much less sensitive to the heavy load. The primary wear mechanism of single 316 L coating was a combination of adhesive wear and severe oxidation, while the TiC-Fe cermet coating showed slight abrasive wear combined with oxidation. The excellent wear resistance together with its harmless to human body make the TiC-Fe based composite coating a potential candidate when using at kitchen ware surface.

Deformation mechanisms especially grain boundary(GB)-related plastic behaviors are essential for understanding and designing advanced hard coatings. This work systematically studied mechanical behaviors and the underlying interfacial mechanisms in Ti-Mo-N coatings, which is predicted to have both high hardness and toughness according to first-principle calculation. Mo-doped TiN coatings were prepared by multi-arc plating technique as a function of N2 pressure. The as-deposited coatings demonstrate a bct-Ti2N + fcc-TiN dual-phase structure below 1.2 Pa, and single-fcc structure at above 1.2 Pa. Single-fcc phase Ti-Mo-N coatings show considerable higher hardness and load-bearing capacity compared to pure TiN coating due to alloying effect of Mo. Transmission electron microscope (TEM) study unveil that GB plays the key role in the deformation behaviors. The Mo-doped TiN coatings exhibit enhanced plastic deformation ability of GBs, including substantial plastic flow and twinning, which retard intergranular cracking that is geometry necessary during GB glide and rotation. While the appearance of the bct-Ti(Mo)2N phase leads to stress concentration at bct-fcc interface during deformation because of the large lattice misfit, considerably lowering load-bearing capacity. In addition, Ti-Mo-N coatings have lower friction coefficient (COF) and wear rate than TiN coating in reciprocal tribology tests, which is attributed to the higher hardness and toughness, as well as tribochemistry-induced solid lubricant effect.

Fe-based metallic glass has been reported to exhibit high degradation ability for azo dye due to its unique atomic structure. In this work, we show that the degradation efficiency of Fe-based alloy can be further improved via simple heat treatment. Fe82Si2.5B12P2.5C amorphous ribbons were prepared by arc melting and melt spinning and then annealed from 100 °C to 850 °C for 5 min. A crystallization process from single α-Fe at 500 °C, to α-Fe + Fe3B at 520 °C, to α-Fe + Fe3B + Fe2C at 850 °C, took place. The degradation efficiency of the heat-treated ribbons decreased monolithically when annealed at 100-600 °C, but increased dramatically at 850 °C. The underlying degradation mechanisms were analyzed, that the formation and interaction of nanocrystals after annealing were considered mainly responsible for the differences in their degradation performances.

Tribological properties and wear mechanisms of ex-situ additively manufactured FeCrMoCB/Cu bulk metallic glass composite (BMGC) under different normal loads and sliding speeds were investigated. The unique amorphous/crystalline microstructure provided FeCrMoCB/Cu BMGC with well wear resistance including low wear rate and coefficient of friction (COF). Both the wear rate and COF showed the same tendency as the variation of normal load. However, the COF decreased but the wear rate increased with the increasing sliding speed. Moreover, the wear mechanisms changed from abrasive wear to oxidation wear and adhesive wear when increasing the normal load, while the adhesive wear and fatigue wear became dominated as the sliding speed increased.

Mn 1.15 Fe 0.85 P 0.50 Si 0.45 B 0.05 alloys were prepared by copper mold suction casting method. Subsequent annealing processes were employed to tune the microstructures and magnetocaloric effects. Results show that Mn 1.15 Fe 0.85 P 0.50 Si 0.45 B 0.05 alloys crystallize in a hexagonal phase with the Fe 2 P structure type. With increasing annealing temperature, the lattice parameters of a and c of Fe 2 P-type phase increase from 5.7988(1)A to 6.0785(2)A and from 3.3218(1)A to 3.4727(2)A for the Mn 1.15 Fe 0.85 P 0.50 Si 0.45 B 0.05 alloys according to XRD. At the same time the Curie temperature and magnetic entropy change increase from 233 K to 244 K and from 8.8 J kg −1 K −1 to 17.0 J kg −1 K −1 (Δ H = 2 T), respectively, while the thermal hysteresis decreases. The entropy changes of these alloys are also estimated from the Clausius-Clapeyron equation, Landau theory and heat capacity, respectively. The nature of the phase transitions were studied through the Arrott plots, which indicate that the samples undergo first-order ferro-paramagnetic phase transitions. However, the universal curve of scaled magnetic entropy change reveals that during the magnetic phase transition, there exists a critical magnetic field, about 1.25 T, below which the sample undergoes a second-order phase transition and above which it displays a first-order phase transition. Furthermore, mechanisms for the large magnetic entropy change and possibilities for the room-temperature magnetic refrigeration are discussed.

In this paper, the grain boundary diffusion process (GBDP) using a Dy70Cu30 (at.%) alloy as the diffusion source was performed in a commercial sintered Nd–Fe–B magnet, and the effect of heat treatment time on the microstructure and magnetic properties of the magnet was investigated in detail. For the processed magnets heat-treated at 860 °C, as heat treatment time increased, the coercivity and the depth of (Nd,Dy)2Fe14B core–shell structure increased first and then decreased. However, when the heat treatment time was more than 2 h, the diffusion path of Dy from the Dy-rich shell phase into the Nd2Fe14B grains was revealed, and a nearly homogeneous (Nd,Dy)2Fe14B phase was formed, which brought on the decrease in both the depth of visible core–shell structure and the coercivity of Nd–Fe–B magnet.

This paper focuses on improving the permeability of Fe-Si-B based amorphous magnetic powder cores by addition of micron-sized ferromagnetic crystalline metal particles (Permalloy). The effects of Permalloy content, size and the amount of insulation on magnetic properties and density were investigated. The results showed that the Fe based amorphous powder cores prepared with 15 wt.% Permalloy (

A strain-driven orthorhombic (O) to rhombohedral (R) phase transition is reported in La-doped BiFeO3 thin films on silicon substrates. Biaxial compressive epitaxial strain is found to stabilize the rhombohedral phase at La concentrations beyond the morphotropic phase boundary (MPB). By tailoring the residual strain with film thickness, we demonstrate a mixed O/R phase structure consisting of O phase domains measuring tens of nanometers wide within a predominant R phase matrix. A combination of piezoresponse force microscopy (PFM), transmission electron microscopy (TEM), polarization–electric field hysteresis loop (P–E loop), and polarization maps reveal that the O-R structural change is an antiferroelectric to ferroelectric (AFE-FE) phase transition. Using scanning transmission electron microscopy (STEM), an atomically sharp O/R MPB is observed. Moreover, X-ray absorption spectra (XAS) and X-ray linear dichroism (XLD) measurements reveal a change in the antiferromagnetic axis orientation from out of plane...

The critical cooling rate ( R c ) calculated on the basis of the time-temperature-transformation (TTT) curve was taken as the intrinsic criteria of reflecting the glass forming ability (GFA) for the amorphous alloy. The TTT curves were plotted based on the isothermal Wheeler-Boettinger-McFadden (WBM) phase field method (PFM). By analyzing the TTT curves, the influence of different activation energy parameters E and Q for the interface mobility M and nucleation rate P respectively on R c and GFA were investigated for Fe-25%B (mole fraction) binary amorphous alloy in present paper. The results showed that the activation energy E for the interface mobility M had litter influence on the nose temperature and time for the TTT curves. Under the different thermal activation energy Q 1 , Q 2 and Q 3 for the nucleation rate P , the temperatures and times corresponding to the nose tip were 500 K, 600 K, 775 K and 6.2 × 10 − 4 s, 4.5 × 10 − 4 s, 9.5 × 10 − 4 s, respectively, and the calculated values of R c were 1.57 × 10 6 K/s, 1.93 × 10 6 K/s, 7.35 × 10 5 K/s, respectively, which were in the range of 6.4 × 10 5 ~ 6.8 × 10 6 K/s from the experimental measurements. Under the influence of thermal activation energy Q , the nose tip temperature increased, which meant Q controlled the nose tip temperature, while the higher Q would not get the perfect C shape. It was found that the values of R c calculated based on the TTT curves by the PFM were in good agreement with the reported experimental values, which verified the feasibility of the glass prediction and the research of the intrinsic physical mechanism of the GFA by the PFM.