Curie Temperature Behavior Research Articles

Experimental realization of CoFeRuSn quaternary Heusler alloy for room temperature spintronic applications

We synthesize CoFeRuSn equiatomic quaternary Heusler alloy using arc-melt technique and investigate its structural, magnetic, and transport properties. The room temperature powder x-ray diffraction analysis reveals that CoFeRuSn crystallizes in cubic crystal structure with small amount of DO3-disorder. The field dependence of magnetization shows non-zero but small hysteresis and saturation behavior up to room temperature, indicating soft ferromagnetic nature of CoFeRuSn. The magnetic moment estimated from the magnetization data is found to be 4.15 μB/f.u., which is slightly less than the expected Slater–Pauling rule. The deviation in the value of experimentally observed moment from the theoretical value might be due to small disorder in the crystal. The low temperature fit to electrical resistivity data shows the absence of quadratic temperature dependence of resistivity, suggesting half-metallic behavior of CoFeRuSn. The high Curie temperature and possible half-metallic behavior of CoFeRuSn make it a highly promising candidate for room temperature spintronic applications.

First principle study of Curie temperature, spin polarization, ferromagnetism and transport behavior of Sr2CrXO6 (X = Ta, W, Re, Os) for spintronic

The double perovskites have outstanding properties for spintronic devices as they are stable, non-toxic, and accomplish the spin polarization. This article studies the function of 5d-electrons of Ta, W, Re and Os to regulate the magnetic properties of Sr2CrXO6. The tolerance factors and formation energies confirm the stability of the structures and the thermodynamics. The half-metallic ferromagnetic nature is found by analyzing the density of states and band structures described by the double exchange model, exchange energy, and exchange constants. According calculations, ferromagnetism is induced by the electron spin due to hybridization process, magnetic moments, exchange energies, and crystal field energy. The thermoelectric applications are further explored by computing and discussing the thermal and electrical conductivities, and Seebeck coefficients. The power factor has also been elaborated for the performance of studied DPs.

Tuning in optical, magnetic and Curie temperature behaviour of nickel ferrite by substitution of monovalent K+1 ion of Ni0·8K0·2Fe2O4 nanomaterials for multifunctional applications

The synthesis of nickel potasium ferrite (Ni0·8K0·2Fe2O4) nanoparticles with the doping of Monovalent K1+ ions has been synthesized by sol-gel auto combustion method. Differential Thermal Analysis (DTA) was performed to analyze the phase formation of the prepared sample. The crystal phase formation has been confirmed by employing the XRD (X-ray diffraction) technique. The crystallite size and Strain were calculated by using the W–H (Williamson-Hall) plot. The crystallite of nanoparticles of K1+ doped nickel ferrite is ~30 nm. The FTIR spectra were recorded in the range of 560–590 cm−1 to analyze the changes in nickel ferrite due to K1+ ion manipulation. The optical property was studied in the field of 200 nm–1000 nm using UV visible spectrometer, and the results show that band gap was improved as in the case for nickel ferrite and the observed value was 2.20 eV, which was furthered decreased to 1.91 eV. The strong photoluminescence was observed in the visible range, and substitutions of monovalent potassium ion are improving its luminescence property. Its intensity peaks get shifted towards orange range 610 nm (2.03 eV). This shows that the monovalent ion may creates defects, leading to porosity and oxygen vacancy in the nanomaterial. The porous structure was confirmed by scanning electron microscope. The magnetic hysteresis loop has been recorded by employing the VSM (Vibrating Sample Magnetometer). The saturation magnetization and Curie temperature were found to increase with the substitution of monovalent potassium. Thus prepared material is soft magnetic nature, possess strong luminescence in the visible range, and high Curie temperature (798 K). Hence the present materials may be used as functional nanomaterials for various technological applications.

Random electric field strength distribution in lead-free relaxor ferroelectrics caused by barium content

Curie temperature behavior of BaxSr[Formula: see text]TiO3 ferroelectrics ceramic ([Formula: see text]) in dependence on bias field is detected by means of acoustic emission. Curie temperature exhibits nontrivial V-shape effect with threshold field of 0.3[Formula: see text]kV/cm, equivalent to random electric fields strength. This random field strength is compared with those in BaxSr[Formula: see text]TiO3 relaxor ferroelectrics ([Formula: see text], 0.7, 0.8) obtained previously, as well as with those determined from mean domain sizes in BaxSr[Formula: see text]Nb2O6 relaxor ferroelectrics ([Formula: see text], 0.39, 0.6). It is estimated that the random field strength of Ba[Formula: see text]Sr[Formula: see text]TiO3 is 30 times stronger than those of Ba[Formula: see text]Sr[Formula: see text]Nb2O6 and it is shown that the random field strengths of both BaxSr[Formula: see text]TiO3 and BaxSr[Formula: see text]Nb2O6 obey the same exponential law in dependence on barium content.

Structural, Magnetic, and Mössbauer Studies of Transition Metal-Doped Gd2Fe16Ga0.5TM0.5 Intermetallic Compounds (TM = Cr, Mn, Co, Ni, Cu, and Zn)

The effect of transition metal substitution for Fe and the structural and magnetic properties of Gd2Fe16Ga0.5TM0.5 (TM = Cr, Mn, Co, Ni, Cu, and Zn) compounds were investigated in this study. Rietveld analysis of X-ray data indicates that all the samples crystallize in the hexagonal Th2Ni17 structure. The lattice parameters a, c, and the unit cell volume show TM ionic radii dependence. Both Ga and TM atoms show preferred site occupancy for 12j and 12k sites. The saturation magnetization at room temperature was observed for Co, Ni, and Cu of 69, 73, and 77 emu/g, respectively, while a minimum value was observed for Zn (62 emu/g) doping in Gd2Fe16Ga0.5TM0.5. The highest Curie temperature of 590 K was observed for Cu doping which is 15 and 5% higher than Gd2Fe17 and Gd2Fe16Ga compounds, respectively. The hyperfine parameters viz. hyperfine field and isomer shift show systematic dependence on the TM atomic number. The observed magnetic and Curie temperature behavior in Gd2Fe16Ga0.5TM0.5 is explained on the basis of Fe(3d)-TM(3d) hybridization. The superior Curie temperature and magnetization value of Co-, Ni-, and Cu-doped Gd2Fe16Ga0.5TM0.5 compounds as compared to pure Gd2Fe17 or Gd2Fe16Ga makes Gd2Fe16Ga0.5TM0.5 a potential candidate for high-temperature industrial magnet applications.

Curie temperature behavior in half-metallic ferromagnetic double perovskites within the electronic correlation picture

Curie temperature behavior in half-metallic ferromagnetic double perovskites within the electronic correlation picture

Increase of Curie temperature with La doping in the double perovskite Sr2-LayFeMoO6 within an electronic correlation approach

The double perovskite compound Sr2FeMoO6 has a half-metallic ferromagnetic character and ahigh Curie temperature (420 K). Fe-Mo usually present some degree of disorder in either Fe orMo ions, it is therefore fundamental to understand the role of electronic and structural parameterscontrolling the half-metallic character together with a Curie temperature as high as possible. We replaceddivalent Sr2+ by trivalent La3+ ions in Sr2FeMoO6 system to observe the Curie temperaturebehavior. We present an electronic approach using the Green's functions and the renormalizationperturbation expansion method, with localized Fe-spins and conduction Mo-electrons interactingwith the local spins via a double-exchange-type mechanism. We also include the electronic correlationsamong the conduction electrons within a mean-eld approximation. Our results showthe density of states and the Curie temperature behavior when La concentration increases for theSr2y-yLayFeMoO6 system

Tunable Dielectric Properties of Poly(vinylidenefluoride-co-hexafluoropropylene) Films with Embedded Fluorinated Barium Strontium Titanate Nanoparticles

Fluoropolymer nanocomposites of poly(vinylidene fluoride-co-hexafluoropropylene) (PVdF-HFP) were prepared using fluorinated barium strontium titanate (Ba1−xSrxTiO3, BSTO) nanoparticles (NPs) by low-temperature synthesis using a modified liquid–solid solution process. The exact stoichiometry of as-synthesized BSTO NPs was confirmed by X-ray diffraction analysis along with lattice parameter calculations. The synthesized BSTO NPs were fluorinated using 2,2,2-trifluoroacetic acid as a fluorous ligand. The BSTO NPs showed high solubility in the fluorous system (polymer and solvent) on account of their modified surface. The root-mean-square roughness of the fluorinated BSTO/PVdF-HFP nanocomposite was 76 times lower than that of the nonfluorinated BSTO/PVdF-HFP nanocomposite. The dielectric constant of the fluorinated BSTO/PVdF-HFP nanocomposite exhibited Curie temperature behavior. The dielectric constant of the nanocomposite predicted using the modified Kerner model at room temperature agreed well with the experimental values.

Corrigendum to ‘‘Abnormal Curie temperature behavior and enhanced strain property by controlling substitution site of Ce ions in BaTiO3 ceramics’’ [Ceramics International 43 (2017) 10683–10690

Corrigendum to ‘‘Abnormal Curie temperature behavior and enhanced strain property by controlling substitution site of Ce ions in BaTiO3 ceramics’’ [Ceramics International 43 (2017) 10683–10690

Abnormal Curie temperature behavior and enhanced strain property by controlling substitution site of Ce ions in BaTiO3 ceramics

Abstract Dopants have a great effect on the phase transition behavior and the properties of the ferroelectrics. Here we report an abnormal Curie temperature ( T c ) behavior and enhanced strain property by controlling the doping site of Ce ions in the BaTiO 3 ceramics. The Ce doped A-site and B-site BaTiO 3 ceramics (BT-xCe-A and BT-xCe-B, x=2, 4, 6, 8 mol%) were prepared by a conventional solid state reaction method through a different sintering temperature. The Raman test and the XPS results give evidence that Ce is successfully incorporated into Ba-site as Ce 3+ in the BT-xCe-A samples, and into Ti-site as Ce 4+ in the BT-xCe-B samples. Different doping sites have distinct phase transition behavior. Compared with the BT-xCe-A ceramics, the BT-xCe-B ceramics show higher T c , and the T c show abnormal increasing behavior with the increase of the Ce content. In the Ce doped BaTiO 3 system, this phenomenon has not been reported before. The origin of the higher T c and its increasing behavior is discussed from the viewpoint of the larger local strain field generated by the Ce 4+ ions entering into B-site. Besides, the BT-xCe-B ceramics show a stronger diffuse phase transition behavior. The reason is considered that the Ce substituting B-site leads to a multiphase coexistence, which induces more frustration states for the polarization according to the random defect field theory. Due to such distinct phase transition behavior, the BT-xCe-B ceramics show the enhanced maximum polarization ( P max ) and enhanced strain properties compared with the BT-xCe-A ceramics. This work may provide a promising way to design high performance materials by controlling the substituting site of the dopant in other lead-free systems.

Thermal Expansion and Second Harmonic Generation Response of the Tungsten Bronze Pb2AgNb5O15.

The incorporation of transition metal element Ag was performed to explore negative thermal expansion (NTE) materials with tetragonal tungsten bronze (TTB) structures. In this study, the structure and thermal expansion behaviors of a polar TTB oxide, Pb2AgNb5O15 (PAN), were systematically investigated by high-resolution synchrotron powder diffraction, high-resolution neutron powder diffraction, transmission electron microscope (TEM), and high-temperature X-ray diffractions. The TEM and Rietveld refinements revealed that the compound PAN displays (√2a(TTB), √2b(TTB), 2c(TTB))-type superstructure. This superstructure within the a-b plane is caused by the ordering of A-site cations, while the doubling of the c axis is mainly induced by a slight tilt distortion of the NbO6 octahedra. The transition metal Ag has larger spontaneous polarization displacements than Pb, but the Pb-O covalence seems to be weakened compared to the potassium counterpart Pb2KNb5O15 (PKN), which may account for the similar Curie temperature and uniaxial NTE behavior for PAN and PKN. Powder second harmonic generation (SHG) measurement indicates that PAN displays a moderate SHG response of ∼0.2 × LiNbO3 (or ∼100 × α-SiO2) under 1064 nm laser radiation. The magnitudes of the local dipole moments in NbO6 and PbOx polyhedra were quantified using bond-valence approach. We show that the SHG response stems from the superposition of dipole moments of both the PbO(x) and NbO6 polyhedra.

Thickness dependent Curie temperature and power-law behavior of layering transitions in ferromagnetic classical and quantum thin films described by Ising, XY and Heisenberg models

Ferromagnetic–paramagnetic phase transitions in classical and quantum thin films have been studied up to 50 mono-layers using effective field theory with two-site cluster approximation. Variation of the Curie temperature as a function of film thickness has been examined. The relative shift of the Curie temperature from the corresponding bulk value has been investigated in terms of the shift exponent λ. We have found that shift exponent λ clearly depends on the strength of the ferromagnetic exchange coupling of the surface. Moreover, we have not observed any significant difference between classical and quantum exponents for a particular model.

The variation of Curie temperature and dielectric relaxor behaviour in the nominal (1-x)BaTiO3-xBiAlO3 system

BiAlO3 is a perovskite ferroelectric with a high Curie temperature above 520°C. However, it is difficult to prepare pure perovskite phase by the conventional method. In this experiment, BaTiO3 has been selected as host to incorporate BiAlO3, and the nominal binary system of (1-x)BaTiO3-xBiAlO3 has been investigated with regard to its Curie temperature (T c) and dielectric relax behaviors. It was found that the pure perovskite phase can be retained below x = 0.08. However, the value of T c in the system doesn’t follow the normal Vegard’s law, on the contrary, shows the decreasing trend with the increase of x. According to the compared experiments about Bi3+ and Al3+ doping in BaTiO3, it can be safely concluded that the combined substitution of Bi3+ and Al3+ played the dominant role to decrease the T c and increase the relaxor behavior in (1-x)BaTiO3-xBiAlO3 system.

Fe 3O 4 inverse spinal super paramagnetic nanoparticles

The present article reports an energy efficient method for the synthesis of superparamagnetic ferrite (Fe 3O 4) nanoparticles (10–40 nm) and their annealing effect on the morphology, size, curie temperature and magnetic behavior at 50, 300, 400 and 500 °C. The synthesized nanoparticles were characterized by various spectroscopic techniques like FT-IR and UV–visible. The crystalline structure and particle size were estimated through solid phase as well as the liquid phase using XRD, TEM and DLS techniques. Superparamagnetic behavior of nanoparticles was confirmed by VSM. The EPR study reveals that the main feature of X-Band solid state EPR spectrum has strong transition at g eff ∼ 3.23 (2100G) and a relatively weak transition at g eff ∼ 2.05 (3300G). The later transition further confirms the super paramagnetic nature of these nano ferrites. The activation energy and order of weight losses of nano ferrites were found to be: 39.6 KJ mol −1 and 0.21 orders (600–800 °C), respectively, analyze with the help of TGA while the specific surface area (23.1 m 2 g −1) and pore size (9 Å) were determined by Quanta chrome BET instrument.

Effect of Co on the martensitic transformation, crystal structure and magnetization of Ni52.5Mn23.5Ga24 based ferromagnetic shape memory alloys

Five (Ni52.5Mn23.5Ga24)100−xCox (x = 0, 2, 4, 6, 8) alloys were prepared by arc melting, and the effects of Co addition on the martensitic phase transformation, crystal structure and magnetization were investigated. The phase transformation temperatures Ms, Mf, As and Af are proportional to the content of Co in the (Ni52.5Mn23.5Ga24)100−xCox alloys, which appears to be due to the variation in the valance electron concentration. The Curie temperature is sensitive to the composition of the alloy. As the amount of Co changes, both the Co-Mn exchange interaction and the distance between Mn atoms change. These, in turn, affect the Curie temperature and magnetization behavior of the alloy. The martensite phases in all the alloys are domained in three different orientations, the domain boundary was determined to belong to the family of {1 1 2} lattice planes.

Anomalous Curie temperature behavior of A-site Gd-doped BaTiO3 ceramics: The influence of strain

The influence of A-site Gd3+ doping on the c/a ratio, cell volume and Curie temperature (Tc) of ferroelectric BaTiO3 according to the titanium vacancy mechanism, viz., Ba1−xGdxTi1−x/4O3 has been investigated and compared to that of La3+-doping. The c/a ratio and cell volume of Gd-doped samples are larger than the equivalent La-doped samples and Tc decreases at a rate of only ∼8 °C/at. % for Gd3+ substitution compared to ∼24 °C/at. % for La3+ substitution. These trends are opposite to that expected based on ionic-radii and tolerance factor arguments. This anomalous behavior is attributed to an ion-size mismatch (cation variance) effect on the A-site between the Ba2+ and Gd3+ ions that induces local strain in the lattice that suppresses the reduction in the c/a ratio and cell volume, and as a consequence in the rate of decrease in Tc.

Curie temperature behaviour at relaxation and nanocrystallization of Finemet alloys

Dependence of Curie temperature (Tc) on time and temperature of annealing for Finemet-type amorphous alloys is studied by DSC. Structural relaxation of an amorphous phase at annealing is accompanied by increase of Tc. The σ-shaped time dependencies, however, are not characterized by the definite final value of Tc: long-term annealing of amorphous phase results in continuation of slow increase of Tc for every temperature. Apparent values of activation energy of relaxation were evaluated from the Tc time–temperature dependencies. It is found that the average value of activation energy increases with progress of the relaxation process. Correlation of the Tc data with structural alterations reflects redistribution of components in amorphous phase during annealing. Further increase of the annealing temperature results in precipitation of α-Fe(Si) nanograins in an amorphous matrix, that accompanied by gradual degradation of corresponding to Tc heat capacity peak. DSC measurements of Tc allow to detect the starting moment of amorphous phase crystallization.

Magnetic properties of nano-sized 5 at.%Fe–Al systems

High energy ball milling is a promising materials processing technique that is widely used to produce nanocrystalline structures. However, when stainless steel or hardened steel containers and balls are used for milling, contamination from the milling medium can influence the material properties of the final nanostructured products due to intercalation of iron (Fe) as an impurity. This study reports the effect of iron contamination on nanocrystalline aluminum (Al) powder. 57Fe Mossbauer spectroscopy and bulk magnetization studies using a vibrating sample magnetometer show that pure Al powder milled in hard steel media is strongly ferromagnetic at room temperature due to Fe contamination of about 5 at.% from the milling medium. TEM studies indicate that the system consists mainly of nano-sized Fe interspersed in Al with average crystallite sizes of ~2 and ~5 nm for Fe and Al, respectively. A comparative study of this system made with a mechanically alloyed Fe–Al system with the same percentage of Fe mixed with pure Al and mechanically alloyed using tungsten carbide vials and balls shows that the saturation magnetization, coercivity, Curie temperature, and low temperature behavior (field cooled–zero field cooled) are very different in the two cases. The different magnetic properties of the two systems can be attributed to the presence of magnetic and non-magnetic phases present.

ChemInform Abstract: Modification of the Magnetic Properties and Corrosion Resistance of Nd- Fe-B Permanent Magnets with Addition of Cobalt.

Abstract The effect of partial substitution of iron by cobalt on the Curie temperature, demagnetization curves and corrosion behaviour under various conditions of sintered Nd 16 Fe 76−x Co x B 8 ( O ⩽ x ⩽ 30) permanent magnets was investigated. The microstructure and chemical composition of phase structures were also determined. A new intergranular Nd(Fe, Co) 2 B 2 phase was found for x ⩾ 20.

Novel Ferromagnetic Mn-Doped ZnSiAs<sub>2</sub> Chalcopyrite with Curie Point Exceeded Room Temperature

Based on Mn-doped chalcopyrite ZnSiAs2 the new dilute magnetic semiconductor with p-type conductivity was produced. The Curie temperature behavior of the produced semiconductor is distinctly dependent on the Mn concentration: 325 K for 1 wt.% and 337 K for 2 wt.% of Mn, consequently. Magnetization, electrical resistance, magnetic resistance and Hall effect of mentioned compositions were studied. Temperature dependence of magnetization M(T) have complicate behavior. For T  15 K the M(T) dependence is characteristic for superparamagnetic and at T > 15 K magnetization is sum of magnetizations of ensemble of superparamagnetic clusters and ferromagnetic phase contained frustration regions.