Fabrication and magnetic transformation from paramagnetic to ferrimagnetic of ZnFe2O4 hollow spheres

ZnFe2O4 hollow spheres (ZFHs) with sizes of 200-302 nm were synthesized by simple impregnating method using the as-prepared phenolic formaldehyde (PF) spheres as templates and subsequent annealing at 500-700 ℃. The prepared ZFHs are assembled by a large number of small nanoparticles with sizes of 15-20 nm, and many mesopores exist among these nanoparticles. The samples annealed at 500-550℃ exhibit a single cubic spinel structure, while higher annealing temperature leads to the formation of hexagonal ZnO and rhombohedral α-Fe2O3 secondary phases. The size of the assembled nanoparticles increases with the increase in annealing temperature. Novel magnetic transformation from paramagnetic to ferrimagnetic is induced by the reduction of annealing temperature and the saturation magnetization significantly increases from 2.3 to 13.5 A·m^2/kg. The effect of the formation of hollow sphere structure on the redistribution of Fe^3+ and Zn^2+ in the spinel structure was studied.

Magnetic transformation of Mn from anti-ferromagnetism to ferromagnetism in FeCoNiZMn_(x)(Z=Si,Al,Sn,Ge)high entropy alloys

We design high entropy alloys(HEAs) with different induction elements(Si/Al/Sn).In order to keep the crystal structure invariant and to investigate how the increment in saturation magnetization(Ms)is caused only by the change of electron spin state,each set of HEAs contains a different amount of Mn.Synergistic effects among induction elements that induce the magnetic transformation of Mn from anti-ferromagnetism to ferromagnetism are found.Ms of added Mn reduces when a particular induction element(Si_(0.4)/Al_(0.4)/Sn_(0.4)) exists,while a larger increment of Ms appears when two induction elements coexist,Si_(0.4)Al_(0.4)(25.79 emu/g) and Sn_(0.4)Al_(0.4)(15.43 emu/g).This is reflected in the microcosmic magnetic structure for the emergence of closed domains due to large demagnetization energy,which is confirmed by the Lorentz transmission electron microscope(LTEM) data.The calculated magnetic moments and the exchange integral constants from density functional theory based on the Exact Muffin-Tin Orbits fo rmalism reveal that the magnetic state and the strength of fe rromagnetic and anti-ferromagnetic coupling determine the variation of Ms in different chemical environments.The difference in energy levels of coexisting multiple induction elements also leads to a larger increment of Ms,Si_(0.4)Al_(0.4)Sn_(0.4)(29.78 emu/g),and Si_(0.4)Al_(0.4)Ge_(0.4)Sn_(0.4)(31.00 emu/g).

Three-dimensional transformation of magnetization direction and magnetic field component at low latitudes based on vertical relationship

The transformation of the magnetization direction and the magnetic fi eld component is one of the important methods in magnetic data processing and transformation,which can be conducted in both wavenumber and spatial domains.The transformation method in the wavenumber domain has simpler processing expression and higher processing effi ciency than in the spatial domain;however,they are unstable at low latitude.In this paper,the conclusion that the sum is 0 of two vertical magnetic fi eld components(magnetization inclinations are also perpendicular)in 2D is used for the 3D transformation of the magnetization direction and the magnetic field component.In addition,the transformation method at low latitudes based on vertical relationship(VMT)is proposed,which is an iterative algorithm that converts the transformation of the magnetization direction and the magnetic field component at the low latitude into the high latitude.This method restrains the instability of transformation of constant and variable magnetization direction and magnetic fi eld components in low latitudes.The accuracy,stability,and practicality are verifi ed from synthetic models and real data.

Transformation behaviors,structural and magnetic characteristics of Ni-Mn-Ga films on MgO(001)

Ferromagnetic Ni-Mn-Ga films were fabricated by depositing on MgO （001） substrates at temperatures from 673 K to 923 K. Microstructure, crystal structure, martensitic transformation behavior, and magnetic properties of the films were studied. With increasing deposition temperature, the surface morphology of the films transforms from granular to continu- ous. The martensitic transformation temperature is not dependent on deposition temperature; while transformation behavior is affected substantially by deposition temperature. X-ray analysis reveals that the film deposited at 873 K has a 7M marten- site phase, and its magnetization curve provides a typical step-increase, indicating the occurrence of magnetically induced reorientation （MIR）. In situ magnetic domain structure observation on the film deposited at 873 K reflects that the marten- sitic transformation could be divided into two periods： nucleation and growth, in the form of stripe domains. The MIR occurs at the temperature at which martensitic transformation starts, and the switching field increases with the decrease of temperature due to damped thermal activation. The magnetically induced martensitic transformation is related to the difference of magnetization between martensite and austenite. A shift of martensite temperature of dT/dH = 0.43 K/T is observed, consistent with the theoretical value, 0.41 K/T.

EFFECT OF MAGNETIC FIELD ON MARTENSITIC TRANSFORMATION IN Fe-21Ni-4Mn ALLOY

The pulsed magnetic field induced martensitic transformation with isothermal and athermal kinetics in Fe-2Ni-4Mn(wt-%)alloy has been studied by means of magnetization measurements,optical microscopy and thermodymical analyses.It is shown that there exits a critical magnetic intensity for induing martensitic transformation at a given temperature above Ms.The critical magnetic field increases linearly with increasing ΔT= T-M_S.The magnetic field strongly promotes the athermal martensitic transforamtion and restrains the isothermal one.The entropy change ΔS for athermal transformation at Ms is 4.13 J/mol· K.The effect of magnetic field on martensitic transformation in Fe-21Ni-4Mn alloy is main- ly due to Zeeman effect.Lath,plate and butterfly martensities were observed under magnetic field.

Influence of Ni/Mn ratio on magnetostructural transformation and magnetocaloric effect in Ni48-xCo2Mn38+xSn12(x=0,1.0,1.5,2.0,and 2.5)ferromagnetic shape memory alloys

An investigation on the magnetostructural transformation and magnetocaloric properties of Ni48-xCo2Mn38＋xSn12（x = 0, 1.0, 1.5, 2.0, and 2.5） ferromagnetic shape memory alloys is carried out. With the partial replacement of Ni by Mn in the Ni_（48）Co2Mn38Sn12 alloy, the electron concentration decreases. As a result, the martensitic transformation temperature is decreased into the temperature window between the Curie-temperatures of austenite and martensite. Thus, the samples with x = 1.5 and 2.0 exhibit the magnetostructural transformation between the weak-magnetization martensite and ferromagnetic austenite at room temperature. The structural transformation can be induced not only by the temperature,but also by the magnetic field. Accompanied by the magnetic-field-induced magnetostructural transformation, a considerable magnetocaloric effect is observed. With the increase of x, the maximum entropy change decreases, but the effective magnetic cooling capacity increases.

Magnetic properties and magnetocaloric effects in HoPd intermetallic

A large reversible magnetocaloric effect accompanied by a second order magnetic phase transition from PM to FM is observed in the Ho Pd compound. Under the magnetic field change of 0–5 T, the magnetic entropy change-ΔS max M and the refrigerant capacity RC for the compound are evaluated to be 20 J/（kg·K） and 342 J/kg, respectively. In particular,large-ΔS max M（11.3 J/（kg·K）） and RC（142 J/kg） are achieved under a low magnetic field change of 0–2 T with no thermal hysteresis and magnetic hysteresis loss. The large reversible magnetocaloric effect（both the large-ΔS M and the high RC）indicates that Ho Pd is a promising material for magnetic refrigeration at low temperature.

Magnetic properties and magnetocaloric effects in Er_(1-x)Gd_xCoAl intermetallic compounds

The magnetism and magnetocaloric effect in Er1-xGdxCoAl（x = 0, 0.1, 0.2, 0.4, 0.6, 0.8, 1） were investigated. The Er1-xGdxCoAl compounds were synthesized by arc melting. With the increasing Gd content, the N′eel temperature（T N）linearly increases from 14 K to 102 K, while the magnetic entropy change（-？S M） tends to decrease nonmonotonously.Under the field change from 0 T to 5 T, the-？S M of the compounds with x = 0.2–1 are stable around 10 J/kg·K, then a cooling platform between 20 K and 100 K can be formed by combining these compounds. For x = 0.6, 0.8, 1.0, the compounds undergo two successive magnetic transitions, one antiferromagnetism to ferromagnetism and the other ferromagnetism to paramagnetism, with increasing temperature. The two continuous magnetic transitions in this series are advantageous to broaden the temperature span of half-peak width（δT） in the-？S M–T curve and improve the refrigeration capacity.

Observation of giant magnetocaloric effect under low magnetic fields in EuTi_(1-x)Co_xO_3

The magnetic properties and magnetocaloric effect（MCE） in EuTi1-xCoxO3（x = 0, 0.025, 0.05, 0.075, 0.1） compounds have been investigated. When the Ti^4＋ ions were substituted by Co2＋ions, the delicate balance was changed between antiferromagnetic（AFM） and ferromagnetic（FM） phases in the EuTiO3 compound. In EuTi1-xCoxO3 system, a giant reversible MCE and large refrigerant capacity（RC） were observed without hysteresis. The values of -△SM^max were evaluated to be around 10 J·kg^-1·K^-1 for EuTi0.95Co0.05O3 under a magnetic field change of 10 kOe. The giant reversible MCE and large RC suggests that EuTi1-xCoxO3 series could be considered as good candidate materials for low-temperature and low-field magnetic refrigerant.

Mechanism of microwave assisted suspension magnetization roasting of oolitic hematite ore

Oolitic hematite is an iron ore resource with rich reserves,complex composition,low grade,fine disseminated particle sizes,and a unique oolitic structure.In this study,a microwave-assisted suspension magnetization roasting technology was proposed to recover and utilize the ore.The results showed that under the conditions of microwave pretreatment temperature of 1050℃ for 2 min,a magnetic concentrate with an iron grade of 58.72%at a recovery of 89.32%was obtained by microwave suspension magnetization roasting and magnetic separation.Moreover,compared with the no microwave pretreatment case,the iron grade and recovery increased by 3.17%and 1.58%,respectively.Microwave pretreatment increased the saturation magnetization of the roasted products from 24.974 to 39.236(A∙m^(2))/kg and the saturation susceptibility from 0.179×10^(−3) m^(3)/kg to 0.283×10^(−3) m^(3)/kg.Microcracks were formed between the iron and gangue minerals,and they gradually extended to the core of oolite with the increase in the pretreatment time.The reducing gas diffused from outside to inside along the microcracks,which promoted the selective transformation of the weak magnetic hematite into the strong magnetic magnetite.

Effect of bastnaesite as reductant on hematite reduction during in-situ suspension magnetization roasting of refractory iron ore under neutral atmosphere

The iron tailings of Bayan Obo mines are solid waste,which occupies land area and also causes environmental pollution;however,this waste can be recycled.In this study,based on the characteristics of iron minerals and fluorocarbonate contained in Bayan Obo iron tailings,clean magnetization roasting of iron minerals by bastnaesite from iron tailings during in-situ suspension magnetization roasting in a neutral atmosphere was explored.The results show that for iron tailings with a mass of 12 g,a N_(2) gas flow rate of 600 mL/min,and roasting for 5 min at 800℃,iron concentrate with a 60.44%iron grade at an iron recovery of 76.04%could be obtained.X-ray diffraction analysis showed that the weak magnetic hematite was reduced to strong magnetic magnetite in the neutral atmosphere,without additional reductant.The kinetics of the magnetization roasting of mineral mixtures(bastnaesite and hematite)in a neutral atmosphere showed that the optimal reaction mechanism function was the three-dimensional diffusion model with activation energy of 161.8838 kJ·mol^(-1);this indicates that the reaction was a heterogeneous,diffusion-controlled solid-state reaction.

Magnetocaloric and barocaloric effects in a Gd_5Si_2Ge_2 compound

The first-order phase transition in GdsSi2Ge2 is sensitive to both magnetic field and pressure. It may indicate that the influences of the magnetic field and the pressure on the phase transition are virtually equivalent. Moreover, theoretical analyses reveal that the total entropy change is almost definite at a certain Curie temperature no matter whether the applied external field is a magnetic field or a pressure. The entropy change curve can be broadened dramatically under pressure, and the refrigerant capacity is improved from 284.7 J/kg to 447.0 J/kg.

Influences of La and Ce doping on giant magnetocaloric effect of EuTiO

Giant reversible magnetocaloric effects and magnetic properties in Euo.9Ro.lTiO3 （R = La, Ce） are investigated. The antiferromagnetic ordering of pure EuTiO3 can significantly change to be ferromagnetic as substitution of La （x = 0.1） and Ce （x = 0.1） ions for Eu2＋ ions. The values of -ASM and RC are evaluated to be 10.8 J/（kg.K） and 51.8 J/kg for Euo.gCeo.lTiO3 and 11 J/（kg.K） and 39.3 J/kg for Euo.9Lao.lTiO3 at a magnetic field change of I0 kOe, respectively. The large low-field enhancements of --ASM and RC can be attributed to magnetic phase transition. The giant reversible MCE and large RC suggest that Euo.9Ro.ITiO3 （R = La, Ce） compounds could be promising materials in low temperature and low magnetic field refrigerants.

Orthogonal transformation operation theorem of a spatial universal uniform rotating magnetic field and its application in capsule endoscopy

According to the anti-phase sine current superposition theorem, the orientation, the magnetic flux density, the angular speed and the rotational direction of the spatial universal rotating magnetic field (SURMF) can be controlled within the tri-axial orthogonal square Helmholtz coils (TOSHC). Nevertheless, three coupling direction angles of the normal vector of the SURMF in the Descartes coordinate system cannot be separately controlled, thus the adjustment of the orientation of the SURMF is difficult and the flexibility of the robotic posture control is restricted. For the dimension reduction and the decoupling of control variables, the orthogonal transformation operation theorem of the SURMF is proposed based on two independent rotation angular variables, which employs azimuth and altitude angles as two variables of the three-phase sine current superposition formula derived by the orthogonal rotation inverse transformation. Then the unique control rules of the orientation and the rotational direction of the SURMF are generalized in each spatial quadrant, thus the scanning of the normal vector of the SURMF along the horizontal or vertical direction can be achieved through changing only one variable, which simplifies the control process of the orientation of the SURMF greatly. To validate its feasibility and maneuverability, experiments were conducted in the animal intestine utilizing the innovative dual hemisphere capsule robot (DHCR) with active and passive modes. It was demonstrated that the posture adjustment and the steering rolling locomotion of the DHCR can be realized through single variable control, thus the orthogonal transformation operation theorem makes the control of the orientation of the SURMF convenient and flexible significantly. This breakthrough will lay a foundation for the human-machine interaction control of the SURMF.

Synthesis,Structure and Polymorphism of a Novel Two-dimensional Cobalt(Ⅱ)Coordination Polymer Constructed from Citrazinate Ligand

The polymeric Co（Ⅱ） complex[Co（Hdhpc）（py）]n（1）（py = pyridine,H3dhpc =2,6-dihydroxypyridine-4-carboxyl acid） was prepared and characterized.X-ray diffraction data revealed that the compound crystallizes in dimorphic 1α and 1β forms at room and low temperature,respectively.The former crystallizes in the orthorhombic crystal system,space group Pbcm with a =7.209（1）,b = 14.834（3）,c = 15.376（3） A°,V= 1644.3（5）A°3,Z = 4,C（16）H（13）CoN3O4,Mr = 370.22,Dc= 1.496 g/cm^3,F（000） = 756,μ = 1.068 mm^-1,R = 0.0633 and wR = 0.1192.While 1β is attributed to the monoclinic space group C2/c with a = 32.102（4）,b = 7.022,c = 14.945（2）A°,β = 109.052（5）°,V= 3184.4（6） A°3,Z= 8,Dc= 1.544 g/cm^3,F（000） = 1512,μ = 1.103 mm^-1,R = 0.0428 and wR =0.0797.The conformation changes of pyridines between Co-citrazinate planes leading to a reversible single-crystal to single-crystal transformation.The variable temperature magnetic data indicate a weak ferrimagnetism.

Improvement of the low-field-induced magnetocaloric effect in EuTiO3 compounds

The magnetocaloric effect of Mn,Ni,and Mn-Ni-doped EuTiO3 compounds are studied in the near-liquid-helium-temperature range.The Eu(Ti0.9375Mn0.0625)O3,Eu(Ti0.975Ni0.025)O3,and Eu(Ti0.9125Mn0.0625Ni0.025)O3 are prepared by the sol-gel method.The Eu(Ti0.9375Mn0.0625)O3 and Eu(Ti0.9125Mn0.0625Ni0.025)O3 exhibit ferromagnetism with second-order phase transition,and the Eu(Ti0.975Ni0.025)O3 displays antiferromagnetic behavior.Under the magnetic field change of 10 kOe(1 Oe=79.5775 Am-1),the values of magnetic entropy change are 8.8 Jkg-1K-1,12 Jkg-1K-1,and 10.9 Jkg-1K-1 for Eu(Ti0.9375Mn0.0625)O3,Eu(Ti0.975Ni0.025)O3,and Eu(Ti0.9125Mn0.0625Ni0.025)O3,respectively.The co-substitution of Mn and Ni can not only improve the magnetic entropy change,but also widen the refrigeration temperature window,which greatly enhances the magnetic refrigeration capacity.Under the magnetic field change of 10 kOe,the refrigerant capacity value of Eu(Ti0.9125Mn0.0625Ni0.025)O3 is 62.6 Jkg-1 more than twice that of EuTiO3(27 Jkg-1),indicating that multi-component substitution can lead to better magnetocaloric performance.

Microstructure and Magnetic Property Variation with Addition of Rare Earth Element Dy in Co-Ni-Al Ferromagnetic Shape Memory Alloy

The influence of rare earth element Dy on martensitic transformation and magnetic properties of Co-Ni-Al alloy was studied.The results showed that the microstructure of the sample has a dual-phase structure（γ-phase and martensite）.The rare earth element Dy was segregated in Co-richγ-phase and took the place of Co after its addition into the Co-Ni-Al alloy.As Dy content increased to over 0.5at.%,the grain was refined and the rare earth intermetallic compounds Co5 Dy were precipitated inγ-phase.Meanwhile,one-step thermo-elastic martensitic transformation occurred in the sample,wherein the phase transformation temperature significantly increased with rising Dy content.The martensite had a tetragonal L10 structure with a（111）twinning plane.Furthermore,the sample exhibited obvious hysteresis behaviors in the magnetic hysteresis loops.In addition,the saturation magnetization,coercivity,retentivity and magnetocrystalline anisotropy were significantly enhanced owing to the bigger radius of Dy which took the place of Co in the alloy.

Magnetically assisted gas-solid fluidization in a tapered vessel:Part II Dimensionless bed expansion scaling

The article presents an effort to create dimensionless scaling correlations of the overall bed porosity in the case of magnetically assisted fluidization in a tapered vessel with external transverse magnetic field. This is a stand of portion of new branch in the magnetically assisted fluidization recently created concerning employment of tapered vessels. Dimensional analysis based on ＂pressure transform＂ of the initial set of variables and involving the magnetic granular Bond number has been applied to develop scaling relationships of dimensionless groups representing ratios of pressures created by the fluid flow, gravity and the magnetic field over an elementary volume of the fluidized bed. Special attention has been paid on the existing data correlations developed for non-magnetic beds and the links to the new ones especially developed for tapered magnetic counterparts. A special dimensionless variable Xp = （Ar△Dbt）1/3√RgMQ combining Archimedes and Rosensweig numbers has been conceived for porosity correlation. Data correlations have been performed by power-law, exponential decay and asymptotic functions with analysis of their adequacies and accuracies of approximation.

Correlation Between Magnetic Properties and Allotropic Phase Transition of Fe–Co–V Alloy

In this study, the allotropic phase transition and its effect on the magnetic behavior of Fe Co–7 wt%V alloy were investigated. It was found that c phase is observed in the microstructure in the as-cast condition, and it diminishes after severe cold rolling（90% reduction）. After annealing at temperatures higher than 500 up to 750 ℃, the c phase is observed in the structure, again. But, this phase is disappeared by annealing at temperatures above 750 ℃ due to the formation of vanadium-rich precipitates. Thermocalc software was used in order to elucidate the influence of vanadium percent on the stability of c phase in Fe–Co alloys. Also, magnetic studies showed that the saturation induction is reduced by annealing at temperatures from 500 up to 750 ℃, which is related to the formation of residual non-magnetic γ phase.

IEC61850 standard-based harmonic blocking scheme for power transformers

Transformer Differential and overcurrent schemes are traditionally used as main and backup protection respectively. The differential protection relay (SEL487E) has dedicated harmonic restraint function which blocks the relay tripping during the transformer magnetizing inrush conditions. However, the backup overcurrent relay (SEL751A) applied to the transformer protection does not have harmonic restraint element and trip the overcurrent relay during the inrush conditions. Therefore, major contribution of this research work is the developed harmonic blocking scheme for transformer which uses element (87HB) of the transformer differential relay (SEL487E) to send an IEC61850 GOOSE-based harmonic blocking signal to the backup overcurrent relay (SEL751A) to inhibit from tripping during the transformer magnetizing inrush current conditions. The simulation results proved that IEC61850 standard-based protection scheme is faster than the hardwired signals. Therefore, the speed and reliability of the transformer scheme are improved using the IEC61850 standard-based GOOSE applications.