Controllable high Curie temperature through 5d transition metal atom doping in CrI_(3)

Two-dimensional(2D) CrI_(3) is a ferromagnetic semiconductor with potential for applications in spintronics. However,its low Curie temperature(T_(c)) hinders realistic applications of CrI3. Based on first-principles calculations, 5d transition metal(TM) atom doping of CrI_(3)(TM@CrI_(3)) is a universally effective way to increase T_(c), which stems from the increased magnetic moment induced by doping with TM atoms. T_(c) of W@CrI_(3) reaches 254 K, nearly six times higher than that of the host CrI_(3). When the doping concentration of W atoms is increased to above 5.9%, W@CrI_(3) shows room-temperature ferromagnetism. Intriguingly, the large magnetic anisotropy energy of W@CrI_(3) can stabilize the long-range ferromagnetic order. Moreover, TM@CrI_(3) has a strong ferromagnetic stability. All TM@CrI_(3) change from a semiconductor to a halfmetal, except doping with Au atom. These results provide information relevant to potential applications of CrI_(3) monolayers in spintronics.

Piezoelectric properties of low loss and high Curie temperature (Bi, La)FeO_3-Pb(Ti, Mn)O_3 ceramics with Mn doping

Piezoelectric ceramics of 0.6(Bi0.9La0.1)FeO3-0.4Pb(Ti1-xMnx)O3 (BLF-PTM) for x=0, 0.01, 0.02, and 0.03 were prepared by sol-gel process combined with a solid-state reaction method. The tan? for BLF-PTM of x=0.01 is just 0.006 at 1 kHz, drastically decreasing by using Mn dopants. The TC increases to 490 ℃ for BLF-PTM of x=0.02. Furthermore, Mn modification effectively enhances the poling state and the piezoelectric properties of BLF-PTM. The kp, Qm, d33, and g33 of 0.34, 403, and 124 pC1·N-1 and 37×10-3 Vm·N-1 are achieved for BLF-PTM of x=0.01. The results indicate that Mn modified BLF-PTM is a competitive high power and high temperature piezoelectric material with excellent piezoelectric properties.

Magnetic entropy change and magnetic properties of LaFe_(11.5)Si_(1.5) after controlling the Curie temperature by partial substitution of Mn and hydrogenation

Magnetic properties and magnetic entropy changes of La（Fe_（1-x）Mn_x）_（11.5）Si_（1.5）H_y compounds are investigated. Their Curie temperatures are adjusted to room temperature by partial Mn substitution for Fe and hydrogen absorption in 1-atm（1 atm = 1.01325×10~5Pa） hydrogen gas. Under a field change from 0 T to 2 T, the maximum magnetic entropy change for La（Fe_（0.99）Mn_（0.01））_（11.5）Si_（1.5）H_（1.61）is-11.5 J/kg. The suitable Curie temperature and large value of ？S_m make it an attractive potential candidate for the room temperature magnetic refrigeration application.

ANOMALOUS EFFECT OF PRESSURE ON THE CURIE TEMPERATURE IN MECHANICALLY ALLOYED Fe-Ni INVAR

Measurements of magnetic susceptibility in mechanically alloyed Fe-Ni Invar alloys were taken under pressures up to 7.5GPa. The rate of decrease in the Curie temperature for 700℃ annealed specimen was larger than that annealed at 1000℃. This result can be explained by considering the fact that the width of the concentration fluctuation becomes larger in the specimen annealed at lower temperature.

MAGNETIC MOMENT,CURIE TEMPERATURE AND SPIN WAVE EXCITATION FOR AMORPHOUS Fe_(90-x)Si_xZr_(10) ALLOYS

The magnetization curves at 1.5 K and thermomagnetic curves for amorphous Fe_(90-x)Si_xZr_(10)(x=0,4,7 and 10)alloys prepared by the drum spinning technique have been measured with an extracting sample magnetometer.It is obtained that the average magnetic moment,,per magnetic atom and Curie temperature,T_c,in the amorphous FeSiZr alloys increase with increasing Si content.The and T_c are found to be quite small,compared with amorphous FeSiB alloys.This unusual behavior is suggested to be due to the presence of the Fe—Fe antiferromagnetic interactions.The temperature dependence of magnetization at lower temperature is in accordance with Bloch's T^(3/2) law.Calculation shows that the spin wave stiffness constant,D,increases with increasing Si content from 0.37 meV·nm^2 for x=0 to 0.538 meV·nm^2 for x=10.The values of<r^2>indicate that the range of the exchange interaction is roughly the mean atomic distance of nearest neighbours.

Influence of Non-Magnetic Substitutional Atoms on Spontaneous Moment and Curie Temperature of Ce_2Co_(17) Compounds

The structure and magnetic properties of Ce 2Co 17-xM x(M=Ga,Al and Si) compounds for M concentrations up to x=5 were studied by means of X-ray diffraction and magnetic measurements. The experimental results show that the Curie temperatures and Co spontaneous magnetization decrease significantly with increasing the addition of non-magnetic substitutional atoms, and that Si which has a minimum solid solubility in Ce 2Co 17 causes a largest reduction of Curie temperature, spontaneous magnetization and moment per Co atom compared with Ga and Al.

Curie Temperature of the Intergranular Amorphous Phase in Nanocrystalline Fe_(89)Zr_7B_4 Alloy

The FeZrB amorphous alloys for simulating the intergranular amorphous phase in the nanocrystalline Fe 89 Zr 7B 4 soft magnetic materials were obtained by mechanical alloying of a mixture of elemental Fe, Zr and B powders for 25 h. It is shown that the Curie temperature of the simulated intergranular phase alloy is much lower than that of the intergranular phase with the same chemical composition in the nanocrystalline Fe 89 Zr 7B 4 alloy. The possible mechanism is mainly due to the strong ferromagnetic exchange force among the nanocrystalline α Fe grains.

High Ferroelectricities and High Curie Temperature of BiInO3PbTiO3Thin Films Deposited by RF Magnetron Sputtering Method

Properties of ferroelectric xBiInO3-（1-x）PbTiO3（xBI-（1-x）PT） thin films deposited on（101） SrRuO3/（200）Pt/（200） MgO substrates by rf magnetron sputtering method and effects of deposition conditions are investigated.The structures of the xBI-（1-x）PT films are characterized by x-ray diffraction and scanning electron microscopy.The results indicate that the thin films are grown with mainly（001） orientation. The chemical compositions of the films are analyzed by scanning electron probe and the results indicate that the loss phenomena of Pb and Bi elements depend on the pressure and temperature during the sputtering process.The sputtering parameters including target composition, substrate temperature, and gas pressure are adjusted to obtain optimum sputtering conditions. To decrease leakage currents,2 mol% La2 O3 is doped in the targets. The P-E hysteresis loops show that the optimized xBI-（1-x）PT（x = 0.24） film has high ferroelectricities with remnant polarization2 Pr = 80μC/cm2 and coercive electric field 2 EC = 300 kV/cm. The Curie temperature is about 640℃. The results show that the films have optimum performance and will have wide applications.

PHASE COMPONENT AND CURIE TEMPERATURE OFNd_4(Fe_(1-x)Cr_x)_(77.5)B_(18.5)ALLOYS

The phase component and Curie tempemture of Nd4(Fe1-xCrx)77.5B18.5 (0 <x <0.25) alloys have been studied. X-ray diffraction analysis shows the presence of α-Fe and Fe3B phases in the samples with x < 0.1 and the presence of α-Fe, Nd2Fe14B and Fe2B phases in the samples with x > 0.1. The magnetic measurement shows that Curie temperutures of Fe3B and Nd2Fe14B phases decrease with increasing Cr content. The influence of the substitution of Cr for Fe was discussed.

Studies on the Relation between the Composition of Thermal Sensitive MnZn Ferrite and Curie Temperature

Thermal sensitive MnZn ferrite is a kind of soft magnetic ferrite material with lower Curie temperature (Tc) and can be used to make many kinds of magnetic thermal sensitive sensors with high sensitivity. In this paper, the relation between the composition of thermal sensitive ferrite and TC was studied. It was found that TC changes linearly with ZnO extent when the content of Fe2O3 is fixed. Based on lots of experiments, an experimential formula to determine was given out.

BiAlO_(3)-modified BiFeO_(3)-BaTiO_(3) high Curie temperature lead-free piezoelectric ceramics with enhanced performance

BiFeO_(3)-BaTiO_(3)(BF-BT)lead-free piezoelectric ceramics have high piezoelectricity and high Curie temperature(T_(C)),but the mixed-valence Fe ions and Bi^(3+)volatilization would promote the formation of Bi_(25)FeO_(40)/Bi_(2)Fe_(4)O_9 and oxygen vacancy,which greatly degrade the insulation properties required for polarization.In this study,it was found that the modification of BiAlO_(3)(BA)in BF-BT ceramics could effectively solve these problems,reducing the leakage current to 1×10^(-9)A·cm^(-2)and transiting the space charge-limited conduction to ohmic conduction.Because of the enhanced insulation properties and appropriate rhombohedral-pseudocubic phase ratio(C_R/C_(PC)),BF-BT-xBA ceramics in an optimized composition obtain enhanced piezoelectric performance:piezoelectric charge coefficient(d_(33))=196 pC·N^(-1),planar electromechanical coupling coefficient(k_(p))=31.1%,T_(C)=487℃and depolarization temperature(T_d)=250°C;unipolar strain(S_(uni))=0.17%and piezoelectric strain coefficient(d_(33)^(*))=335 pm·V^(-1)at 100℃.Especially,d_(33)exceeds 283 pC·N^(-1)at 233℃and d_(33)^(*)is 335 pm·V^(-1)at100℃,showing an excellent high-temperature piezoelectricity and high depolarization temperature.The results are attributed to the domain structure of rhombohedral-pseudocubic phase coexistence and its high-temperature switching behavior.This work provides a feasible and effective approach to improve the high temperature piezoelectric properties of BF-BT-xBA ceramics,making them more suitable for high temperature applications.

Relating atomic local structures and Curie temperature of NdFeB permanent magnets:an X-ray absorption spectroscopic study

Relationship between atomic local structures and Curie temperature of NdFeB permanent magnets was investigated semi-quantitatively using synchrotron radiation technique. Fe K-edge X-ray absorption spectroscopy(XAS) was employed to study the local structure of Fe atoms for samples before and after doping Dy, Tb or Gd. It is found that the bond lengths and coordination numbers are changed. Thus, the exchange interaction between Fe atoms increases with Dy, Tb or Gd doping, resulting in the improvement of Curie temperature of NdFeB permanent magnets. The doping effect is proven by experimental measurement of the magnetic properties. Microstructural characterization using scanning electron microscopy(SEM) was also used to further analyze the effect of different rare earth elements doping on Curie temperature of NdFeB permanent magnets.

Critical temperature below the Curie temperature of ferroelectric ceramics PZT

The article presents the results of research the pre-transitional features of the behavior of solid solutions based on lead zirconate-titanate.The presence of a“special”critical temperature T_(d)on the temperature dependences of the permittivityε(T)and the remanent polarization P_(r)(T),preceding the temperature of the paraelectric phase transition at the Curie temperature T_(C),is noted.In the temperature range T<T_(d),the P_(r)(T)dependence obeys a power law.In the temperature range T_(d)<T<T_(C),this law is not fulfilled.The results of X-ray experiments make it possible to associate this behavior with reversible disordering at T<T_(d)of an ordered domain structure formed during the polarization of piezoelectric ceramics and with its irreversible disordering in the temperature range T_(d)<T<T_(C).This is due to the appearance of internal mechanical stresses in a polycrystalline ferroelectric due to irreversible depolarization of the samples at temperatures T_(d)<T<T_(C).

The effect of Ba/Sr ratio on the Curie temperature for ferroelectric barium strontium titanate ceramics

The powders of lead-free material namely(nonhazardous)barium strontium titanate(BST)with different stoichiometric compo-sitions have been synthesized by the sol-gel method.Ba_(1−x)Sr_(x)TiO_(3)(BST)materials possess the properties of both ferroelectric and dielectric materials.These materials have spontaneous polarization that can be reversed by an applied electric field and they remain polarized even when the applied external electric field is removed.Synthesized samples have been subjected to structural,morphological,and dielectric characterizations.In this study,BST nanopowders with different substitutions of x(where x=0.2,0.3,0.4,0.5,and 0.6)were prepared by the sol-gel method,which is an easy method with low power consumption and low tem-perature requirement and produces higher yield.Nanopowders had average particle sizes of 12-24 nm and particles sizes after sintering at 1000°C for 3 h were 197,267,79.80,63.09,and 63 nm.All resulting pellets had a polycrystalline structure.Crystal structure,space group,morphological characterization,and particle size were determined from the structural analysis using X-ray powder diffraction(XRD),energy-dispersive X-ray spectroscopy(EDX),and scanning electron microscopy(SEM).The dielec-tric measurements were made for BST pellets under different frequencies(1-200 kHz)from room temperature to 250℃.The dielectric constants for the bulk were 743,1566,1091,766,and 626 for x=0.2,0.3,0.4,0.5,and 0.6,respectively.From dielectric measurements,samples with x=0.2 and 0.3 had the Curie temperatures of 70℃ and 28.5℃,respectively,and remained intact below 0℃.The sample with x=0.3 had a good dielectric measurement and moderate dissipation factor;it may be used in capac-itance application as energy stores.

Enhanced piezoelectric properties of (Ba_(0.3)Bi_(0.7))(Mg_(0.05)Fe_(0.6)Ti_(0.35))O_(3) piezoelectric ceramics with high Curie temperature

(Ba_(0.3)Bi_(0.7))(Mg_(0.05)Fe_(0.6)Ti_(0.35))O_(3) ceramics were either doped with vanadium or sintered in calcined powder with the same composition.Compared to an undoped ceramic sintered without the calcined powder,both ceramics showed reduced leakage current densities(lower than 1×10^(-7) A/cm^(2))and absence of dielectric relaxation behaviors observed in frequency-and temperaturedependent dielectric measurements.The Curie temperatures of both samples were higher than 460℃.The maximum field-induced strain over the applied field,S_(max)/E_(max),of 366 pm/V of the undoped ceramic sintered without the calcined powder increased to 455 and 799 pm/V for the V-doped ceramics and the ceramics sintered with the calcined powder,respectively.The increase was related to a reduced concentration of bismuth vacancy-oxygen vacancy defect dipoles.

Curie Temperature of Amorphous Fe-Si-B and Fe-W-Si-B Alloys

オhe effects of composition, annealing temperature and time, annealing heating rate on the Curie temperature of amorphous FeSiB and FeWSiB alloys were studied. The results indicate that the Curie temperature of these alloys increases with the increase of the metalloid content when it is <25 at%, then decreases with the further increase of the metalloid content. For amorphous FeSiB and FeWSiB alloys with the low metalloid content, the Curie temperature increases with the annealing temperature and the annealing time. However, for the amorphous FeWSiB alloys with the high metalloid content, the Curie temperature increases at low annealing temperature and with short annealing time, and decreases at high annealing temperature and with long annealing time. The heating rate in measuring Curie temperature also influences the Curie temperature of the alloys. The Curie temperature is higher at lower heating rates.

Crystal structure and dielectric properties of layered perovskite-like solid solutions Bi_(3-x)Gd_(x)TiNbO_(9)(x=0,0.1,0.2,0.3)with high Curie temperature

The Aurivillius phases(APs)[Bi_(2)O_(2)]2t[A_(m-1)B_(m)O_(3m+1)]2-are well-known ferroelectrics with high Curie temperatures.Hightemperature piezoceramics Bi_(3-x)Gd_(x)TiNbO_(9)(BiGdTiNb,x=0,0.1,0.2,0.3)were prepared by a solid-state reaction method.The structural and electrophysical characteristics of BiGdTiNb ceramics have been studied.According to the data of powder X-ray diffraction,all the compounds are single-phase with the structures of two-layer APs(m=2)with the orthorhombic crystal lattice(space group A21am).The temperature dependence of the relative permittivityε/ε_(0)(T)of the compounds was measured and showed that the Curie temperature of perovskite-like oxides Bi_(3-x)Gd_(x)TiNbO_(9) increases linearly with an increase in the substitution parameter x to T_(C)=950℃.The activation energies of charge carriers have been found in different temperature ranges.

Crystal structure and dielectric properties of layered perovskite-like solid solutions Bi_(3-x)Gd_(x)TiTaO_(9)(x=0.0,0.1,0.2,0.3)with high Curie temperature

The Aurivillius phases[Bi_(2)O_(2)][A_(n−1)B_(n)O3_(n+1)]are well-known ferroelectrics with high Curie temperatures T_(C).High-temperature piezoceramics Bi_(3-x)Gd_(x)TiTaO_(9)(BGdTTa,x=0.0,0.1,0.2,0.3)were prepared by a solid-state reaction method.The structural and electrophysical characteristics of BGdTTa ceramics have been studied.According to the data of powder X-ray diffraction,all the compounds are single-phase with the structures of two-layer Aurivillius phases(m=2)with the orthorhombic crystal lattice(space group A2_(1)am).The temperature dependence of the relative permittivity ε/ε_(o)(T)of the compounds was measured and showed that the Curie temperature T_(C) of perovskite-like oxides Bi_(3-x)Gd_(x)TiTaO_(9)increases linearly with an increase in the substitution parameter x to TC=925℃.The activation energies of charge carriers have been found in different temperature ranges.

Influence of the substitution of Sm, Gd, and Dy for La in La_(0.7)Sr_(0.3)MnO_3 on its magnetic and electric properties and strengthening effect on room-temperature CMR

A series of La0.7-xSmxSr0.3MnO3, La0.7-xGdxSr0.3MnO3, and La0.7-xDyxSr0.3MnO3 （x=0.00, 0.10, 0.20, 0.30） samples were prepared by the solid-state reaction method. The influence of the substitution of Sm, Gd, and Dy for La on the magnetic and electric properties and on the magnetoresistance （MR） was studied through measurements of M-T curves and p-T curves. The results showed that： lattice distortion induced by substitution of Sm, Gd, and Dy for La and extra magnetism of substitution had great influence on the magnetic and electric properties of pcrovskite manganites; substitution of magnetic rare earth element for La was an effective way to change Curie temperature and to strengthen MR in perovskite manganites; and appropriate substitution proportion would generate large MR near room temperature.

Adiabatic Temperature Changes in (Gd_(1-x)Ho_x)_5Si_4 Magnetic Refrigeration Materials

A series of alloys (Gd1-xHox)5Si4(x=0, 0.05, 0.15, 0.25) have been prepared. Adiabatic temperature changes of(Gd1-xHox)5Si4 alloys is exactly investigated by a control and analysis system for ΔH=1.4 T, and the measurement results are trustworthy. Curie temperatures of these alloys are tunable in a wide temperature region, and decrease almost linearly with the increasing of Ho content. Magnetic entropy changes in the (Gd1-xHox)Si4 compounds are about 2.35 J/(kg·K) when magnetic field change are 0～1.4 T. The adiabatic temperatures of these alloys at Curie Points are larger than 1 K about 40% of that of Gd in a field change 0～1.4 T, and the curves of ΔTad are as wide as that of Gd. The relative cooling power RCP(S) or RCP(T) of these alloys are about 0.5～0.7 J·cm-3 and 42～50 K2 on the field 0～1.4 T, about 58% and 55% of that of Gd respectively. These alloys are potential magnetic refrigerants working in a refrigerator at room temperatures.