Ferrimagnetic Behavior Research Articles

Functional glass-ceramic foams from ‘inorganic gel casting’ and sintering of glass/slag mixtures

Abstract The here described investigation was essentially aimed at exploring the chemical stabilization and reutilization of iron-rich slag from copper metallurgy, by the manufacturing of glass-ceramic foams. The foams were developed according to a new method, recently reported for pure recycled soda-lime glass. Mixtures of soda-lime glass/slag powders (with slag content ranging from 10 to 30 wt%), suspended in alkaline aqueous solution, underwent progressive low temperature (80 °C) hardening, owing to the formation of hydrated calcium silicate compounds (C S H). Before complete setting, an extensive foaming could be achieved by vigorous mechanical stirring, with the help of a surfactant. After foaming, glass/slag mixtures could be sintered at 800–1000 °C; the mutual interaction caused an extensive crystallization, with precipitation of Ca Fe silicates and iron oxides (hematite and magnetite), promoting the mechanical properties (up to 4.4 MPa, with a porosity of about 80%). Leaching test confirmed the stabilization of pollutants, from the slag, in the final ceramics. Owing to the separation of iron oxides, particularly magnetite, the newly obtained foams exhibited a ferrimagnetic behavior, that could be exploited in electromagnetic shielding applications.

Electronic and Crystalline Structure, Magnetic Response, and Optical Characterization of Rare-Earth Ruthenate Sr2HoRuO6

Sr2HoRuO6 ceramic has been synthesized and its structural, morphological, magnetic, optical, and electronic properties studied. Rietveld refinement of x-ray diffraction patterns revealed that this oxide material crystallizes in monoclinic perovskite structure in space group P2 1 /n (no. 14). Scanning electron microscopy revealed polycrystalline surface morphology. x-Ray dispersive spectroscopy suggested that Sr2HoRuO6 was obtained with expected stoichiometry. Magnetic susceptibility curves as a function of temperature revealed ferrimagnetic feature of this material below the Neel temperature TN of 14 K. Evidence of magnetic disorder was provided by the irreversibility observed in the zero-field-cooled and field-cooled responses of the susceptibility below Tirr = 169 K. Analysis of the diffuse reflectance spectrum suggested that this material behaves as a semiconductor with energy gap Eg of 1.38 eV. Results of band structure and density-of-states calculations are in agreement with the interpretation of Sr2HoRuO6 as a semiconductor. The ferrimagnetic behavior is interpreted as due to exchange mechanisms of d–f (Ru–O–Ho) electrons. The effective magnetic moment calculated from density functional theory was 93.5% of the experimental value obtained from Curie–Weiss fitting of the susceptibility curve.

Ferrimagnetism in cobalt ferrite (CoFe2O4) nanoparticles

Ferrimagnetic cobalt ferrite (CoFe2O4) nanoparticles were synthesized by employing co-precipitation method. Product physico-chemical and magnetic properties with respect to cetyl trimethylammonium bromide (CTAB), hexamethylenetetramine (HMT) and polyethylene glycol (PEG-400) surfactants were investigated. XRD pattern and Raman characteristic active modes revealed the cubic cobalt ferrite structure formation. SEM images explored spherical shaped product with different particle size. Identified strong PL emission peaks confirmed the product quality. IR metal oxygen vibration at 615 and 426 cm−1 revealed tetrahedral and octahedral site of cobalt ferrite system. Product electrochemical behavior was found to be size dependent and high specific capacitance was observed using CTAB. Room temperature ferrimagnetic behavior was confirmed through VSM studies. High saturation value as 66 emu/g was found using PEG. Particles with larger crystallite and particle size exhibited improved magnetic behavior.

Structural, surface and magnetic properties of chalcogenide Co9S8 nanoparticles prepared by mechanochemical synthesis

In this study, the mechanochemical synthesis of Co9S8 nanoparticles from cobalt and sulphur by high-energy milling in a planetary mill in an argon atmosphere is reported. Structural characterization of the synthesized nanoparticles by XRD was performed. Co9S8 nanoparticles crystallize in the cubic structure with the crystallite size of about 16 nm. The microstructure of the Co9S8 nanoparticles was further studied using TEM, HRTEM and EDS-HAADF-STEM techniques. Co9S8 nanoparticles consist of nanocrystals exhibiting size in the range of 10–30 nm that are densely aggregated into spherical-like objects. The highest specific surface area value observed was 4 m2g-1 and the pore properties of this sample are quite poor. The magnetic properties of mechanochemically synthesized nanoparticles were investigated using SQUID magnetometer. The room temperature magnetic data supported the paramagnetic spin structure of Co9S8 nanoparticles. The transition from paramagnetic to weak ferromagnetic or ferrimagnetic behaviour was indicated from temperature dependence of magnetization at cryogenic temperatures. It is demonstrated that mechanochemical synthesis can be successfully employed in the one-step solid-state preparation of Co9S8 nanoparticles.

Mössbauer and electrical studies of NixCo1-xFe2O4 nanoparticles

Nanocrystalline nickel substituted cobalt spinel ferrites with chemical formula NixCo1-xFe2O4 (0 ≤ x ≤ 1.0) have been synthesized by the glycol-thermal technique under low reaction temperature of 200 °C. The crystallite size ranges from about 8 nm to 14 nm across the composition range. Strong correlation between particle size and sample reaction pressure has been observed. This shows dependence of the magnetic properties on the synthesis conditions. 57Fe Mössbauer spectra recorded at room temperature (∼300 K) show ferrimagnetic behaviour of the compounds and have been explained on the bases of composition and crystallite size. Mӧssbauer data recorded at 80 K are indicative of enhanced hyperfine fields and isomer shifts due to increased magnetic order. Magnetization results reveal superparamagnetic nature of the compounds investigated. Resistivity measurements on the pellet samples annealed at 1100 °C show evidence of semiconducting behaviour. The current results also show significant differences in the resistivity determined from each face of a pellet.

Microstructure and magnetic properties of cobalt ferrite nano powder prepared by solution combustion synthesis

In this study, cobalt ferrite nanoparticles (CoFe2O4NPs) were prepared by solution combustion synthesis using urea and glycine as fuels. The magnetic properties of the CoFe2O4 powders were modified by using various amounts of extra fuel (above the stoichiometric value). Thermodynamic calculations indicates that as the extra fuel increases, the amount of gases produced and the adiabatic flame temperature (Tad) rise. To investigate effect of urea, glycine and amount of extra fuel on the structural and magnetic properties of CoFe2O4 powders, the produced samples were studied by using X-ray diffraction (XRD), vibrating sample magnetometer (VSM), field emission scanning electron microscopy (FESEM), thermogravimetric analysis and differential scanning calorimetry (TGA-DSC), and Brunauer-Emmett-Teller (BET) technique. XRD results of the produced sample indicated that the single phase CoFe2O4with an average crystallite size between 17 and 33 nm was synthesized. By using two different type of fuel, the specific surface area of the produced powders were increased from 1.6 (glycine fuel) to 56.2 m2/g (urea fuel). By changing the type of fuel and the amount of extra fuel, the CoFe2O4 coercivity (Hc) ranges between 870 and 1667.8Oe and the saturation magnetization (Ms) varies between 31.6 and 83.7 emu/g. The solution combustion synthesized CoFe2O4 powders exhibit a hard ferrimagnetic behavior. Based on the results, Urea is the proper fuel for producing cobalt ferrite nanoparticles (with a particle size less than 100 nm) and in case of using glycine, the minimum amount of this fuel should be 2 times the stoichiometric amount.

Inorganic antiferromagnetic semiconductors A2MnWO6 (A = Ba2+, Pb2+) as promising materials for optospintronics applications

Based on density functional theory (DFT), the structural, electronic, magnetic and optical properties of Mn2+ (3d5)–W6+ (5d0) based double perovskite oxides A2MnWO6 (A = Ba2+, Pb2+) were studied using the generalized gradient approximation (GGA) and by adding the exchange correlation effect (GGA + U). The crystal structures of two compounds were found to have cubic symmetry, space group Fm-3m, no 225, at room temperature. Both GGA and GGA + U calculations predicted a semiconducting-antiferromagnetic (AF-type1) behavior in A2MnWO6 compounds with energy gaps (Eg) in spin-up and spin-down except for (A = Pb2+), it exhibits ferrimagnetic (FI) metallic behavior within GGA. The value of Eg decreases with structure changing; Eg in (A = Pb2+; Eg = 0.54–2.11 eV) is smaller than in (A = Ba2+; Eg = 0.85–2.80 eV). Optical calculations show that the AF A2MnWO6 compounds have a good ability to absorb the incident photons due to their narrow Eg. The real and imaginary parts of the dielectric function show that these compounds also possess a great ability to retain the photon energy that it absorbed. It is believed that these materials could be synthesized experimentally, and they would prove useful for optospintronics applications.

Magnetization reversal and tunable exchange bias behavior in Mn-substituted NiCr2O4

Single phase samples of Ni(Cr1−xMn x )2O4 (x = 0–0.50) were synthesized by using sol–gel route. Investigation of structural, magnetic, exchange bias and magnetization reversal properties was carried out in the bulk samples of Ni(Cr1−xMn x )2O4. Rietveld refinement of the X-ray diffraction patterns recorded at room temperature reveals the tetragonal structure for x = 0 sample with I41/amd space group and cubic structure for x ≥ 0.05 samples with \( {\text{Fd}\bar{3}\text{m}} \) space group. Magnetization measurements show that all samples exhibit ferrimagnetic behavior, and the transition temperature (TC) is found to increase from 73 K for x = 0 to 138 K for x = 0.50. Mn substitution induces magnetization reversal behavior especially for 30 at% of Mn in NiCr2O4 system with a magnetic compensation temperature of 45 K. This magnetization reversal is explained in terms of different site occupation of Mn ions and the different temperature dependence of the magnetic moments of different sublattices. Study of exchange bias behavior in x = 0.10 and 0.30 samples reveals that they exhibit negative and tunable positive and negative exchange bias behavior, respectively. The magnitudes of maximum exchange bias field of these samples are found to be 640 and 5306 Oe, respectively. Exchange bias in x = 0.10 sample originates from the anisotropic exchange interaction between the ferrimagnetic and the antiferromagnetic components of magnetic moment. The tunable exchange bias behavior in x = 0.30 sample is explained in terms of change in domination of one sublattice moment over the other as the temperature is varied.

Mn2VAl Heusler alloy thin films: appearance of antiferromagnetism and exchange bias in a layered structure with Fe

Mn2VAl Heusler alloy films were epitaxially grown on MgO(1 0 0) single-crystal substrates by ultra-high-vacuum magnetron sputtering. A2- and L21-type Mn2VAl order was controlled by the deposition temperature. A2-type Mn2VAl films showed no spontaneous magnetization, while L21-type Mn2VAl films showed ferrimagnetic behaviour with a maximum saturation magnetization of 220 emu cm−3 at room temperature (RT). An antiferromagnetic reflection was observed with neutron diffraction at RT for an A2-type Mn2VAl film deposited at 400 °C. A bilayer sample of the antiferromagnetic A2-type Mn2VAl and Fe showed an exchange bias of 120 Oe at 10 K.

Magnetism in Heterobimetallic and Heterotrimetallic Chains Based on the Use of [WV(bipy)(CN)6]– as a Metalloligand

Two new heterobi‐ and trimetallic chains of formula ∞1[{MnII(pyim)2}{(µ‐NC)2WV(bipy)(CN)4}][WV(bipy)(CN)6] (1) and ∞1[{CuIIMnIIL}{(µ‐NC)3WV(bipy)(CN)3}][WV(bipy)(CN)6]·0.75H2O·2MeCN (2) were obtained by reacting the cyanido‐based AsPh4[W(bipy)(CN)6] heteroleptic complex with the pre‐formed [MnII(pyim)2]2+ (1) and [CuIIMnIIL]2+ (2) complexes [bipy = 2,2′‐bipyridine, pyim = 2‐(1H‐imidazol‐2‐yl)pyridine and H2L = macrocyclic Schiff‐base resulting from the stepwise condensation of 2,6‐diformyl‐p‐cresol with ethylenediamine and diethylenetriamine]. The structure of 1 consists of cationic cyanido‐bridged {MnIIWV} chains, assembled from [WV(bipy)(CN)6]– spacers, each one coordinating in a bis‐monodentate fashion, two [MnII(pyim)2]2+ nodes, and [WV(bipy)(CN)6]– counteranions. Compound 2 comprises a positively charged 1D coordination polymer, built from [WV(bipy)(CN)6]– cyanido metalloligands that act as tris‐monodentate spacers towards [CuIIMnIIL]2+ complexes, the entire assembly being neutralized by [WV(bipy)(CN)6]– anions. Each manganese(II) ion in 1 is six‐coordinate in a somewhat distorted octahedral surrounding. Five‐coordinate copper(II) and seven‐coordinate manganese(II) ions exhibiting distorted square pyramidal and monocapped trigonal prism environments respectively, occur in each {CuIIMnII} node of 2. The magnetic susceptibility of 1 and 2 investigated down to 1.9 K is characteristic of 1D ferrimagnetic behavior with minima in the χMT vs. T plots at 35 (1) and 20 K (2) (χM is the magnetic susceptibility per one MnII plus two WV ions). The magnetic data of 1 in the whole temperature range were analyzed through a model considering SMn = 5/2 as a classical spin and SW = 1/2 as a quantum spin, with two interaction parameters J1 = J(1 – α) and J2 = J(1 + α) {the spin Hamiltonian being defined as H = –JΣiSW,i[(1 + α)SMn,j + (1 – α)SMn,i+1] + Σi(gWSW,i + gMnSMn,i)βH}. The values of the intrachain antiferromagnetic interactions for 1 through this model were –3.0(1) (J1) and –32.0(1) cm–1 (J2). The complexity of the spin topology in 2, a branched chain with four different intrachain antiferromagnetic interactions (double phenoxido bridge between MnII and CuII, two single cyanido bridges between MnII and CuII, and one single cyanido bridge between CuII and WV) precluded any simulation of its magnetic data.

Superparamagnetic and ferrimagnetic behavior of nanocrystalline ZnO(MnO)

We have studied the magnetic properties of nanocrystals of ZnO:MnO prepared by traditional wet chemistry method. The detailed structural and morphological characterization was performed. The results of systematic measurements of AC magnetic susceptibility as a function of temperature and frequency as well as DC magnetization are reported. We observed two different types of magnetic behavior depending on the concentration doping. For samples with low nominal content (up to 30 wt% of MnO), superparamagnetic behavior was observed. We attribute the observed superparamagnetism to the presence of nanosized ZnMnO3 phase. For nanocrystals doped above nominal 60 wt% of MnO ferrimagnetism was detected with TC at around 42 K. This magnetic behavior we assign to the presence of nanosized Mn3O4 phase.

Thermodynamic and magnetic properties of magnesium-gallium ferrite ceramics

A comparative study of the thermodynamic and magnetic properties of the Ga-substituted magnesium ferrite polycrystalline samples Mg(Fe1-xGax)2O4 with x = 0.2 and x = 0.4 was carried out. The low-temperature heat capacity of the sample with x = 0.2 was measured by adiabatic calorimetry. Based on the smoothed heat capacity data Cp,m°(T) for Mg(Fe0.8Ga0.2)2O4, the standard thermodynamic functions were determined in a temperature range 2–800K. A broad heat capacity anomaly below 60K, which can be attributable to the magnetic order-disorder transition, was observed for both samples. The field-dependence of magnetizations in an applied magnetic field up to ± 50kOe revealed the ferrimagnetic behaviour of the samples. The values of Curie temperature (TC) and the blocking temperature (TB) were determined from ZFC-FC magnetization measurements. Based on the results of heat capacity and magnetic measurements, the low temperature state in the Mg(Fe0.6Ga0.4)2O4 sample may be attributed to a spin glass-like state.

Effect of γ- rays irradiation on structural, electrical and magnetic properties of Dy3+ substituted nanocrystalline Ni-Zn ferrites

Nanocrystalline NixZn1-xDyyFe2-yO4 (x ≤ 0 ≤ 1.0; y = 0.0, 0.1) ferrites were prepared by solution combustion method. Structural investigation was studied using XRD, FTIR, SEM and EDAX techniques. All samples were irradiated with 60Co gamma source with total exposure dose of 310 kGy. XRD patterns revealed the formation of cubic spinel structure. FTIR spectra confirm the presence of two prominent vibrational bands. DC conductivity was found to obey the Arrhenius relation with a change in slope at Curie temperature and impedes with Dy3+ ion content. ZnFe2O4 nanoparticles exhibit a weak ferrimagnetic behavior at 300 K. The saturation magnetization, remanence magnetization, coercivity, remanence ratio, magneton number and Yaffet–Kittle angle were found to decrease in Dy3+ ion substituted samples attributed to redistribution of cations amongst the sites and weakening the A-B exchange interactions. The enhancement of DC conductivity and magnetic parameters on γ-irradiation attributed to surface states pinning of domains released.

Characterization and magnetic properties study for magnetite nanoparticles obtained by pulsed laser ablation in water

Magnetite (Fe3O4) nanoparticles of 1–10 nm (with the maximum at 2 nm) were obtained via pulsed laser ablation of iron target in water in form of a stable dispersion without addition of surfactants and stabilizers. The structure of the material obtained was investigated using transmission electron microscopy, scanning electron microscopy, and Brunauer–Emmett–Teller methods. To investigate the composition of the particles in the sample, such methods as Fourier transform infrared spectroscopy, Raman spectroscopy, differential scanning calorimetry, and X-ray diffraction, were applied. Magnetite phase was found to be sufficiently pure, it was not contaminated by other iron oxide phases and contained not more than 0.5% of metallic iron in form of large particles. The study of the magnetic properties of the magnetite nanoparticles obtained has shown that they exhibit ferrimagnetic behavior at room temperature with the paramagnetic contribution explained by the presence of fine superparamagnetic particles.

Electric Transport Characteristics of Gallium Iron Oxide Epitaxial Thin Film

ABSTRACTA Ga0.8Fe1.2O3 epitaxial thin film was fabricated on a SrTiO3(111) substrate using pulsed laser deposition. The film is c-axis-oriented and has multiple in-plane domains. In-plane magnetization measurements show that it exhibits ferrimagnetic behavior with a Curie temperature (TC) of 290 K. The insulating film exhibits hopping conduction with a resistivity (ρ) of 4 × 105 Ωcm at 300 K. The ρ value is four orders lower than that of a BiFeO3 film, probably owing to the formation of multiple in-plane domains in the Ga0.8Fe1.2O3 film. Positive magnetoresistance with a maximum value of 3.5% near TC was observed, suggesting that antiferromagnetic interaction between Fe3+ ions decreases carrier transfer between the ions.

The diversity of five metal–organic complexes based on an unsymmetrical biphenyl tetracarboxylate: Synthesis, structures, magnetism and luminescence

Careful investigation of the effects of metal ions and pH value resulted in five multi-dimensional metal−organic complexes, [Co5(μ3-OH)2(α-bptc)2(H2O)6]n (1), {(H3O)2[Co4(μ3-O)(α-bptc)2(H2O)]·4H2O}n (2), {K2[Zn4(μ3-OH)2(α-bptc)2(H2O)3]}n (3), [Zn4(α-bptc)2(H2O)3]n (4), and {[Cd4(α-bptc)2(H2O)7]·2H2O}n (5) (α-H4bptc = 2,3,3',4'-biphenyl tetracarboxylic acid). The complexes consisted of different highly connected secondary building units (SBUs) assembled via hydrothermal in situ routes. The pH value as well as the kinds of metal ions influenced the coordination modes of α-H4bptc and also introduced the hydroxyl ligand at high pH value, resulting in the diversity of SBUs and dimensionality. Variable temperature magnetic measurements indicated the antiferromagnetic behavior in the Co5 core in 1, and the intra-chain ferrimagnetic behavior in complex 2. Moreover, the luminescent properties of the complexes 3−5 indicated the existence of intra-ligand charge transfer.

Effect of CNTs blending on the structural, dielectric and magnetic properties of nanosized cobalt ferrite

Preparation of Cobalt ferrite (CoFe2O4) blended multiwalled carbon nanotubes (CNTs); synthesised by solvothermal method is reported. Formation of single phase cubic CoFe2O4nanoparticles restrained on the external surfaces of CNTs was confirmed by FTIR and XRD analysis. SEM, FESEM and TEM images reveal visible evidence of CoFe2O4 nanoparticles intimately connected to the surface of CNTs. Selected area electron diffraction (SAED), High-Resolution Transmission Electron Microscopy (HRTEM), energy dispersive X-ray (EDX) spectroscopy inveterate the presence of CoFe2O4nanoparticles on CNTs surfaces. Dielectric study reveals the dielectric behaviours of the specimen to be much higher than unblended CoFe2O4nanoparticles stipulating the improvement in the dielectric properties of the specimen which favours these specimens to be used in high-frequency applications. Room temperature vibrating sample magnetometer (VSM) measurements indicated nanocomposites displaying ferrimagnetic behaviour. The specific goal of this study is to enhance the dielectric properties of CoFe2O4 nanoparticles by blending them with highly conducting CNTs.

Effect of Preparation Conditions on the Structure and Magnetic Properties of Metal-Doped Magnesium Ferrites Synthesized From Laterite Leaching Solutions

In this paper, metal-doped magnesium ferrites (MgFe2O4) were synthesized from laterite leaching solutions using a coprecipitation-calcination method. The as-synthesized samples were characterized by x-ray diffraction (XRD), Fourier transform infrared spectrometer (FTIR), and physical property measurement system (PPMS) to determine the structure and magnetic properties. The effects of preparation conditions including precipitant reagents and metal ion concentrations in the laterite leaching solutions on the as-prepared spinel ferrites were investigated systematically. It is indicated that Ni–Co–Mn-doped MgFe2O4 and Mn–Al–Cr-doped MgFe2O4 could be synthesized from laterite leaching solutions by using sodium hydroxide (NaOH) and ammonia solution (NH3⋅H2O) as precipitant reagent, respectively. By adjusting the metal ion concentrations in the laterite leaching solutions, Ni–Co–Mn-doped MgFe2O4 with different substitution contents were obtained. With the Ni and Mn substitution content increasing, the lattice constant and average grain size decreased, while x-ray density increased correspondingly. Magnetic property tests indicated that all the as-prepared samples exhibited typical ferrimagnetic behavior at room temperature, and the saturation magnetization (Ms) depended on the Ni, Co, and Mn substitution content. Specifically, the Ms and Hc values of the as-prepared metal-doped MgFe2O4 sample with optimum substitution content of 0.185 could reach 33.22 emu g−1 and 53 Oe, respectively.

Lattice constant changes leading to significant changes of the spin-gapless features and physical nature in a inverse Heusler compound Zr2MnGa

The spin-gapless semiconductors with parabolic energy dispersions [1–3] have been recently proposed as a new class of materials for potential applications in spintronic devices. In this work, according to the Slater-Pauling rule, we report the fully-compensated ferrimagnetic (FCF) behavior and spin-gapless semiconducting (SGS) properties for a new inverse Heusler compound Zr2MnGa by means of the plane-wave pseudo-potential method based on density functional theory. With the help of GGA-PBE, the electronic structures and the magnetism of Zr2MnGa compound at its equilibrium and strained lattice constants are systematically studied. The calculated results show that the Zr2MnGa is a new SGS at its equilibrium lattice constant: there is an energy gap between the conduction and valence bands for both the majority and minority electrons, while there is no gap between the majority electrons in the valence band and the minority electrons in the conduction band. Remarkably, not only a diverse physical nature transition, but also different types of spin-gapless features can be observed with the change of the lattice constants. Our calculated results of Zr2MnGa compound indicate that this material has great application potential in spintronic devices.

First-Principle Study of Half-Metallic Ferrimagnet Behavior in Titanium-Based Heusler Alloys Ti2FeZ (Z = Al, Ga, and In)

Using density functional theory with the full-potential linearized augmented plane-wave method (FP-LAPW), we have study the structural, electronic, and magnetic properties of Ti2FeZ (Z = Al, Ga, and In) alloys with Hg2CuTi-type structure. The magnetic stabilities reveal that all our compounds exhibit ferrimagnetic (FiM) behaviors. The electronic structure report the existence of a gap energy equal to 0.56, 0.60, and 0.64 eV for Ti2FeAl, Ti2FeGa, and Ti2FeIn, respectively, in the spin-down state and divulge metallic intersections at the Fermi level for the spin-up state. These results indicate that our compounds have a half-metallic (HM) nature. In addition to this, the total magnetic moments are in agreement with the obtained one by the Slater-Pauling rule (M tot = Z tot − 18), which indicates the 100% spin polarization for these compounds.