Structural and magnetic properties of BaFe12 ? 2x Co x Sn x O19 modified M-type hexaferrites

We have studied the effect of heterovalent substitution of a Co²⁺ + Sn⁴⁺ combination for Fe³⁺ on the crystal chemistry and magnetic properties of M-type barium hexaferrite (BHF). The results demonstrate that 2Fe³⁺ ?? Co²⁺ + Sn⁴⁺ heterovalent substitution allows one to tune the magnetic properties of M-type BHF (to reduce its coercive force (H _c), while maintaining its magnetization (M _s) at the level of unsubstituted BHF (x = 0)).     

Crystal structure and magnetic properties of Sr1 − x Sm x Fe12 − x Co x O19 solid solutions

Sr_{1 ? x} Sm _x Fe_{12 ? x} Co _x O₁₉ (0 ≤ x ≤ 0.5) ferrites have been prepared by solid-state reactions in air at 1470 K using mixtures of samarium oxide, ferric oxide, Co₃O₄, and strontium carbonate. X-ray diffraction characterization showed that the samples with x < 0.2 were single-phase, whereas the samples with 0.2 ≤ x ≤ 0.5 contained α-Fe₂O₃ and those with 0.3 ≤ x ≤ 0.5 contained SmFeO₃, CoFe₂O₄, and Sm₂O₃ as well. The highest degree of Sm³⁺ and Co²⁺ substitutions for Sr²⁺ and Fe³⁺ (x) in the SrFe₁₂O₁₉ ferrite at 1470 K was determined to be slightly less than 0.2. This substitution only slightly decreases the a and c parameters of the hexagonal lattice and the Curie temperature (T _C) of the material. At temperatures of 5 and 300 K in magnetic fields of up to 14 T, we obtained magnetic hysteresis loops, which were used to evaluate the spontaneous magnetization (σ₀), specific saturation magnetization (σ_s), and coercive force (_σ H _c) of the ferrites. The experimentally determined 5-K spontaneous magnetization per formula unit (n ₀) of the x = 0.1 ferrite is 20.86μ_B, which coincides with the theoretical value calculated as n ₀ = (8 × 5) ? (3.9 × 5 ? 0.1 × 3) = 20.8μ_B. At 300 K, the n ₀ and _σ H _c of Sr_0.9Sm_0.1Fe_11.9Co_0.1O₁₉ exceed those of SrFe₁₂O₁₉ by 7.7 and 9.9%, respectively.     

Structural and dielectric relaxor properties of A-site deficient samarium-doped (Ba1−x Sm2x/3)(Zr0.3Ti0.7O3) ceramics

Rare earth samarium (Sm)-doped barium zirconate titanate (Ba_1?x Sm_2x/3)(Zr_0.3Ti_0.7)O₃ (x = 0.00, 0.02, 0.04, 0.06, 0.08, 0.10) ceramics were prepared using solid state reaction (SSR) route. The structural and microstructural characterizations of the materials were done by using X-ray diffraction and SEM analysis, respectively. Rietveld refinement technique employed to investigate the details of crystal structure revealed single-phase cubic perovskite structure belonging to space group Pm-3m. Microstructure of the doped ceramics were found to be porous and of irregular shape and size along with aggregative characteristic. FTIR technique was employed to study the influence of additives in ceramics compositions and to investigate the displacement of M–O bonds. Raman spectroscopic study revealed that the substitution of Ba²⁺ ions by Sm³⁺ ions shifted the Raman-active modes toward higher energy, which indicated that these materials undergo an increase in average cubicity with increase in Sm³⁺ ion concentration. The temperature dependence of dielectric properties was investigated in the frequency range from 1 kHz to 1 MHz. The dielectric measurement indicated a diffuse type of phase transition (DPT). The broadening in the dielectric permittivity and frequency dependence behavior with increase in frequency indicated a relaxor behavior of these materials. The relaxation strength of these materials was well adjusted by using the Vogel–Fulcher relation.     

Studies on magnetic and magnetoelectric properties of the NiFe2O4–Ba0.7Sr0.3TiO3 composites

The magnetic and magnetoelectric properties of magnetoelectric (ME) composites consisting of with nickel ferrite (NiFe₂O₄) and barium strontium titanate (Ba_0.7Sr_0.3TiO₃) were investigated. The composites were prepared by standard double sintering ceramic method. The X-ray diffraction analysis was carried out to confirm the phases formed during sintering and also to calculate the lattice parameters. The hysteresis measurements were done to determine saturation magnetization (M_s), remenance magnetization (M_r) and coercivity (H_c) of the samples. The magnetoelectric voltage coefficient (dE/dH)_H was studied as a function of intensity of the magnetic field. The measured magnetoelectric (ME) response demonstrated strong dependence on the volume fraction of NiFe₂O₄ and the applied magnetic field. A large ME voltage coefficient of about 560 μVcm⁻¹Oe⁻¹ was observed for 15% NiFe₂O₄ + 85% Ba_0.7Sr_0.3TiO₃ composite.     

Structural, optical, magnetic and electrical properties of Zn1−x Co x O thin films

Despite a considerable effort aiming at elucidating the nature of ferromagnetism in ZnO-based magnetic semiconductor, its origin still remains debatable. Although the observation of above room temperature ferromagnetism has been reported frequently in the literature by magnetometry measurement, so far there has been no report on correlated ferromagnetism in magnetic, optical and electrical measurements. In this paper, we investigate systematically the structural, optical, magnetic and electrical properties of Zn_1−x Co _x O:Al thin films prepared by sputtering with x ranging from 0 to 0.33. We show that correlated ferromagnetism is present only in samples with x > 0.25. In contrast, samples with x < 0.2 exhibit weak ferromagnetism only in magnetometry measurement which is absent in optical and electrical measurements. We demonstrate, by systematic electrical transport studies that carrier localization indeed occurs below 20–50 K for samples with x < 0.2; however, this does not lead to the formation of ferromagnetic phase in these samples with an electron concentration in the range of 6 × 10¹⁹ cm⁻³ ∼1 × 10²⁰ cm⁻³. Detailed structural and optical transmission spectroscopy analyses revealed that the anomalous Hall effect observed in samples with x > 0.25 is due to the formation of secondary phases and Co clusters.     

Magnetic and dielectric properties of the M-type barium strontium hexaferrite (Ba x Sr1−x Fe12O19) in the RF and microwave (MW) frequency range

This paper presents results for the dielectric permittivity (ε′), dielectric loss (tg δ _E) dielectric permeability (μ′) and magnetic loss (tg δ _M) in the radio-frequency and microwave frequency range of Ba _x Sr_1−x Fe₁₂O₁₉ hexaferrite (0 ≤ x ≤ 1). The samples were prepared by a new route of the ceramic method. The magnetic permeability (μ′) and magnetic loss (tg δ _M) measurements in the range 100 MHz to 1.5 GHz, reveals that 1.32 ≤ μ′ ≤ 1.68 for the permeability of BFO100 (BaFe₁₂O₁₉) and 1.16 < μ′ ≤ 1.88 for SFO100 (SrFe₁₂O₁₉) in the range of studied frequencies. The BFO100 sample presented lower loss (tg δ _M = 4.10⁻³ at 1.5 GHz). The permittivity of BFO100 and SFO100 in 1.5 GHz are, respectively 8.18 and 8.19, and in the 1 MHz are, respectively 52.04 and 19.09. The samples presented coercive field in the range of 3–5 kOe and remanence magnetization in the range of 33–36 emu/g. The subjects of paper were study the dielectric and magnetic properties of the barium and strontium hexaferrite, in view of applications as a material for permanent magnets, high density magnetic recording and microwave devices.     

Structural,electrical, and magnetic properties of La0.7Ca0.3 − x Na x MnO3 ± γ solid solutions

La_0.7Ca_{0.3 − x} Na _x MnO_{3 ± γ} (LCNM) solid solutions with x = 0, 0.04, 0.06, 0.08, and 0.10 have been synthesized (rhombohedral structure, sp. gr. R c). Sodium volatility during sintering is shown to lead to the formation of vacancies on the lanthanum and oxygen sites. Ca²⁺ → Na⁺ substitution does not increase the fraction of Mn⁴⁺ in LCNM, but the increase in the concentration of lanthanum vacancies with increasing sodium content leads to an increase in ferromagnetic ordering temperature T _C and magnetoresistance, which depend, in addition, on heat-treatment conditions on account of the sodium volatility. Original Russian Text ? O.Z. Yanchevskii, A.I. Tovstolytkin, O.I. V’yunov, A.G. Belous, 2008, published in Neorganicheskie Materialy, 2008, Vol. 44, No. 2, pp. 226–233.     

Synthesis and magnetic properties of polycrystalline films of Co x Fe y Cr3 − x − y O4 and Cr2O3/CoFe2O4 multiferroics

Magnetic properties of first obtained polycrystalline films of FeCr₂O₄, CoCr₂O₄, and CoFe_0.5Cr_1.5O₄ multiferroics and films of a Cr₂O₃/CoFe₂O₄ composite multiferroic have been studied. In particular, magnetization curves and temperature dependences of the magnetic moment of the samples were measured in the temperature range 4.2–300 K in fields of up to 10 kOe. It was shown that the Curie point of a multiferroic depends on its cation composition. It was found that an exchange bias of the hysteresis loop exists in films of the Cr₂O₃/CoFe₂O₄ composite multiferroic at temperatures below the Néel point of Cr₂O₃ (330 K).     

Structural,optical, magnetic,and photoluminescence properties of Sn0.7−xMo0.3 NdxO2+δ (0.0 ≤ x ≤ 0.3)

Journal of Materials Science: Materials in Electronics - In this study, the properties of a series of (Sn0.7?xMo0.3 NdxO2+δ) (0.0?≤?x?≤?0.3) Nd3+ thin...     

Room-temperature multiferroic properties and magnetoelectric coupling in Bi4−x Sm x Ti3−x Co x O12−δ ceramics

We present the structural, dielectric, ferroelectric, magnetic and magnetoelectric studies of lead free; single phase Bi_4?x Sm _x Ti_3?x Co _x O_12?δ (0 ≤ x ≤ 0.07) ceramics, synthesized using a standard solid-state reaction technique. Raman spectroscopy analysis reveals the relaxation of distortion in TiO₆ octahedron. Field emission scanning electron microscopy confirmed the growth of plate-like grains. It is observed that with the substitution of Sm³⁺ and Co³⁺ ions the dielectric constant, loss tangent and ferroelectric transition temperature decreases. Electrical dc resistivity, remnant polarization and magnetization increases with increasing Sm³⁺ and Co³⁺ contents. The magnetoelectric coupling co-efficient, α = 0.65 mV cm^?1 Oe^?1 is realized for Bi_4?x Sm _x Ti_3?x Co _x O_12?δ (x = 0.07) ceramic sample. Our results clearly demonstrate the lead free, multiferroic nature of Sm/Co-substituted Bi₄Ti₃O₁₂, which may find useful application in designing cost-effective electromagnetic devices.     

Dielectric properties of the Sr1−x La x Sn1−x Co x O3 system

The possibility of the formation of a solid solution in the Sr_1–x La _x Sn_1–x Co _x O₃ system has been explored. Single-phase solid solution forms in the compositions for x0.10. All single-phase solid solution compositions have a cubic structure similar to SrSnO₃. The dielectric behaviour of these solid solution compositions has been studied as a function of temperature and frequency. The frequency dependence of dielectric constant and dielectric loss in these materials indicates that space charge polarization contributes significantly to their observed dielectric parameters. Microstructural studies show the presence of well-faceted grains. The average grain size in these samples is small.     

Mössbauer spectra and magnetic properties of Tm0.65Sr0.35Fe x Mn1 − x O3 (x = 0.3, 0.35, 0.4)

We report Mössbauer spectroscopy results for Tm_0.65Sr_0.35Fe _x Mn_{1 ? x} O₃ (x = 0.3?0.4) at 300 and 80 K. Like in the case of lighter lanthanide ferromanganites, we observe phase separation of the magnetic sub- system: a magnetic phase shows up in the spectra in the form of a Zeeman sextet and “paramagnetic” dou- blets.     

Effect of Ti on glass-forming ability and magnetic properties of Fe81Si4B12−x P2Cu1Ti x (x = 0–3) soft magnetic alloys

The effect of Ti substitution for B on the glass-forming ability, microstructure and soft magnetic properties of Fe₈₁Si₄B_12?x P₂Cu₁Ti _x (x = 0–3) alloy ribbons made by single roller melt spinning method were investigated. The experimental results demonstrate that proper doping of Ti effectively improves the glass-forming ability, widening the optimum annealing temperature range, decreasing the sensitivity of coercivity on annealing temperature, increasing the volume fraction of nanocrystalline α-Fe phase and suppressing the grain growth in this alloy system. For alloy ribbons Fe₈₁Si₄B_12?x P₂Cu₁Ti _x (x = 0.5–2.5) annealed at 475 °C for 5 min, the saturation magnetostriction λ _s and the magnetic flux density B ₈₀₀₀ gradually decrease with increasing x, while the coercivity H _c decreases with increasing x until x = 2.0 and then increases. Nanocrystalline alloy Fe₈₁Si₄B₁₀P₂Cu₁Ti₂ shows excellent magnetic properties with low λ _s of 7 ppm, low H _c of 7.5 A/m and high B ₈₀₀₀ of 1.73 T which is promising for the future industrial applications.     

The effect of zinc doping on the structural and magnetic properties of Ni1−x Zn x Fe2O4

Nanoparticles of Ni_1?x Zn _x Fe₂O₄ (x = 0.0, 0.1, 0.3, 0.5, 0.7, and 1.0) were synthesized by the sol–gel auto-combustion method using ethylenediamine tetra acetic acid as a complexion agent. The detailed analysis of X-ray diffraction revealed that the crystalline structure was cubic spinel and by increasing x, it underwent a phase transition from normal to inverse spinel. The crystal lattice constant was increased gradually with increasing zinc substitution from 0.8339 nm (x = 0.0) to 0.8443 nm (x = 1.0). Also, the average crystallite size, which is determined from Scherrer formula, was about 14–35 nm. The spinel phase formation was further monitored by the FTIR analysis. The vibration sample magnetometer data showed that by increasing Zn doping level up to x = 0.3, the magnetization was increased and it was decreased by further increase in x. This effect was discussed by metal cations distribution into the tetrahedral and octahedral sites. Also, the coercivity was decreased by increasing Zn content due to the decrease of magnetocrystalline anisotropy constant of the samples.     

Structural elastic and thermal properties of Sr x Cd1−x O mixed compounds — a theoretical approach

In the present paper, the structural and mechanical properties of alkaline earth oxides mixed compound Sr _x Cd_1?x O (0 ? x ? 1) under high pressure have been reported. An extended interaction potential (EIP) model, including the zero point vibrational energy effect, has been developed for this study. Phase transition pressures are associated with a sudden collapse in volume. Phase transition pressure and associated volume collapses [ΔV (Pt)/V(0)] calculated from this approach are in good agreement with the experimental values for the parent compounds (x = 0 and x = 1). The results for the mixed crystal counterparts are also in fair agreement with experimental data generated from the application of Vegard’s law to the data for the parent compounds.