Magnetic and electromagnetic properties of RuZn and RuCo substituted BaFe12O19

Polycrystalline samples of M-type hexaferrites BaFe_12−2xRu_xZn_xO₁₉ and BaFe_12−2xRu_xCo_xO₁₉ with 0x0.45 have been prepared by a classical sintering method. The evolutions with x of the cell parameters, the saturation magnetization and the magnetic transition temperature have been measured; in this range of small doping ratios, saturation magnetization and Curie temperature of substituted hexaferrites remain close to those of the undoped BaFe₁₂O₁₉. X-ray diffraction measurements on oriented powders show that a change of magnetocrystalline anisotropy from axial to planar occurs in both cases for a small substituting ratio x_c=0.375. Microwave electromagnetic characteristics have been studied on the ceramic samples from 0.1 to 10 GHz. The behaviour of the magnetic losses (μ″) corroborates the anisotropy change when doping; a convolution of the dissipation mechanisms (domain wall motions and gyromagnetism) is obtained for x_c. The level of the magnetic losses is discussed in relation with others substituted Ba-hexaferrites.     

Magnetic order in M2Mo3O8 single crystals (M = Mn, Fe, Co, Ni)

Magnetic measurements on hexagonal single crystals of M₂Mo₃O₈ (M = Mn, Fe, Co and Ni) are reported. The Mn compound orders ferrimagnetically at T_c = 41.5 K; the Fe and Co compounds antiferrimagnetically at T_N = 59.5 K and 40.8 K, respectively. No magnetic ordering was found in the Ni compound down to 2 K. All the compounds showed strong magnetic anisotropy when ordered, the results indicating that the magnetic spins' preferred orientation is along the hexagonal axis. Mn₂Mo₃O₈ shows a temperature dependence of the spontaneous magnetization in the ferrimagnetic regime which is rarely observed: as T → 0, M_s → 0.     

Magnetic and microstructural properties of the Ti-doped Barium hexaferrite

A study of the magnetic and microstructural properties of the M-type Ti⁴⁺-doped Barium hexaferrite according to the stoichiometric formulation BaFe_{(12−(4/3)x)}Ti_xO₁₉ with x=0, 0.6, 0.8 and 1.0, has been reported. The XRD and magnetic analysis show a variation of the host lattice parameters and a decrease in the values of remnant magnetization and magnetic anisotropy with Ti⁴⁺ content. The behavior of magnetic properties of materials is explained by the combined effect of the coherent rotation of the magnetic domains and the replacements of Fe³⁺ by Ti⁴⁺ ions in the octahedral and tetrahedral sites.     

Magnetic properties and composition range of non-stoichiometric m-type hexagonal ferrites prepared by ion exchange

Single crystals of Ba, Sr M-type hexagonal ferrites were prepared by ion exchange in Ba, Sr containing molten salts from single crystals of β″ -ferrites. A fast diffusion of the divalent Ba²⁺, Sr²⁺ is observed leading to a non-stoichiometric M-type ferrite with chemical formula: Ba_1+xFe_10.5Co_0.25O_17+x (0 ≤ x ≤ 0.25). x depending on the exchange reaction time. Saturation magnetization ranges from 19 to 64 emu/g depending on exchange conditions. The Curie temperature is (470 ± 5)°C. An easy axis direction (M_s c) has been determined in all cases. The observed anisotropy is considerably lower than that of M ferrite. The calculated anisotropy constants are, in 10⁶ erg/cm³, K₁ = 0.8 and K₂ = 1.0 at room temperature.     

Formation and decay kinetics of nickel nitrides resulting from nitrogen ion implantation. The nickel–nitrogen phase diagram

Structural transformations in nickel films exposed to N⁺ ions were investigated through the use of electron diffraction, electron microscopy, Rutherford backscattering (RBS) of He⁺ ions, thermal desorption spectroscopy (TDS).

With an increasing exposure dose, there occurred a smooth transition of the FCC structure of Ni to the HCP phase -Ni₃N with the lattice parameters a=0.266 nm and c=0.430 nm. The completion of the transition was observed once the implanted nitrogen concentration corresponding to the stoichiometric ratio of Ni₃N was attained, this giving evidence for the chemical nature of the structural change observed.

During annealing, structure variations were traced, enabling one to observe the following four nickel nitrides: (1) -Ni₃N with a disordered arrangement of nitrogen atoms (HCP-phase with a=0.266 nm and c=0.430 nm), (2) β-Ni₃N with an ordered arrangement of nitrogen atoms (two hexagonal lattices: one with a=0.266 nm, c=0.430 nm, and the other with a=0.466 nm and c=0.43 nm), (3) Ni₄N having a primitive cubic lattice structure with a=0.377 nm, (4) Ni₈N having the FCC structure with a=0.725 nm.

The results of an investigation have led to building up a phase diagram for the Ni–N system.     

Influence of magnetization on lattice constants of 3d transition metal alloys

A simple relation is found in 3d transitional metal alloys between the lattice constant and the magnetization, which can be described with an equation: a(x) = a₀^A· (1 − x) + a₀^B. x + C μ(x). It is proposed that studies of lattice constants at high temperatures may serve as an experimental method to detect the existence of localized moments above T_c. The anomalous thermal expansion of the Invar alloy is explained as a result of the collapse of localized moments above T_c.     

过渡金属与F共掺杂ZnO薄膜结构及磁、光特性

采用溶胶-凝胶法在玻璃衬底上制备了过渡金属元素与F共掺杂Zn_0.98-xTM_xF_0.02O (TM_x=Cu_0.02, Ni_0.01, Mn_0.05, Fe_0.02, Co_0.05)薄膜, 进而利用X射线衍射仪、扫描电子显微镜、紫外-可见透过谱、光致发光及振动样品磁强计等研究了薄膜的表面形貌、微结构、禁带宽度及光致发光(PL)和室温磁学特性. 研究表明: 掺杂离子都以替位的方式进入了ZnO晶格, 掺杂不会破坏ZnO的纤锌矿结构. 其中Zn_0.93Co_0.05F_0.02O薄膜样品的颗粒尺寸最大, 薄膜的结晶度最好且c轴择优取向明显; Zn_0.93Mn_0.05F_0.02O薄膜样品的颗粒尺寸最小, 薄膜结晶度最差且无明显的c轴择优取; Cu, Ni, Fe与F共掺杂样品的颗粒尺寸大小几乎相同. TM掺杂样品均表现出很高的透过率, 同时掺杂后的薄膜样品的禁带宽度都有不同程度的红移. PL谱观察到Zn_0.98-xTM_xF_0.02O薄膜的发射峰主要由较强的紫外发射峰和较弱的蓝光发射峰组成. Zn_0.93Mn_0.05F_0.02O薄膜样品的紫外发光峰最弱, 蓝光发射最强, 饱和磁化强度最大; 与之相反的是Zn_0.96Cu_0.02F_0.02O薄膜, 其紫外发光峰最强, 蓝光发射最弱, 饱和磁化强度最小. 结合微结构和光学性质对Zn_0.98-xTM_xF_0.02O薄膜的磁学性质进行了讨论.     

Magnetic moments and Fe hyperfine field interactions in Y(Fe1−xRux)2 ternaries

Measurements of magnetization and ⁵⁷Fe Mössbauer spectra have been made for Y(Fe_1−xRu_x)₂. The C15 type cubic structure is stabilized for xx 0.7. The C15 compounds is ferromagnetic with T_c200 K and its saturation moment decreases monotonically with increasing x, while the ⁵⁷Fe hyperfine field decreases only slightly with x. From these results, it is deduced that the Ru atoms have an induced moment of ≈1μ_B in the range x 0.2. In the C14 type phase, no magnetic ordering develops even at 4.2 K.     

Non-stoichiometric barium ferrite particles for high-density magnetic recording

The organometallic precursor method was employed for the synthesis of β” ferrites, from which non-stoichiometric Ba ferrite particles have been prepared by ionic exchange. The magnetic grains are hexagonal platelets with diameters as low as 50 nm and aspect ratio of 1.5. After annealing, the sample diameter increases to 200 nm while the grains remain single-domain. The Curie temperature is 455°C. Annealed samples show specific magnetization up to 62 emu/g, coercive fields _jH_c close to 2 kOe, and an SFD factor 1−S* of 0.55     

Magnetostriction and spin reorientation in ferromagnetic Laves phase Pr(Ga_xFe_(1-x))_(1.9) compounds

The magnetostriction, magnetization, and spin reorientation properties in Pr(Ga_xFe_(1-x))_(1.9) alloys have been investigated by high-precision x-ray diffraction(XRD) step scanning, magnetization, and Mo¨ssbauer spectra measurements. Ga substitution reduces the magnetostriction(λ_(||)) with magnetic field H ≥ 8 kOe(1 Oe = 1.33322×10~2 Pa), but it also increases the λ|| value when H ≤ 8 kOe at 5 K. Spin-reorientations(SR) are observed in all the alloys investigated, as determined by the step scanned XRD, Mo¨ssbauer spectra, and the abnormal temperature dependence of magnetization. An increase of the spin reorientation temperature(T_(SR)) due to Ga substitution is found in the phase diagram, which is different from the decrease one in many R(T_x Fe_(1-x))_(1.9)(T = Co, Al, Mn) alloys. The present work provides a method to control the easy magnetization direction(EMD) or T_(SR) for developing an anisotropic compensation system.     

Effect of Sn doping on the magnetic and transport properties of LaMnO3+δ

We report the influence of the Sn doping on the magnetotransport properties of the LaMnO_3+δ perovskite. Two series of samples with nominal LaSn_xMn_1−xO_3+δ (I series) and La_{(1−x)/(1+x)}Sn_xMn_1−xO_3+δ (II series) compositions (x=0, 0.025, 0.05 and 0.10) were prepared at T_s=750°C. The M(T) data under 0.01 and 0.5 T for the I series reveal a depressed magnetization as the Sn content increases suggesting the presence of magnetic clusters with a superparamagnetic behavior. Resistivity measurements indicate an insulator material for all Sn content independently of the applied magnetic field. On the contrary, for the II series the M(T) and M(H) data reveal FM behavior and an improvement of the magnetization as Sn increases. These samples show magnetoresistance. The magnetotransport properties are discussed in terms of the presence of A-site cation vacancies.     

Anomalous magnetotransport phenomena in θ-(BEDT-TTF)2I3

Anomalous magnetotransport phenomena have been observed in θ-(BEDT-TTF)₂I₃ crystals at temperatures below 15 K. The magnetoresistance M : (1) is a linear function of the magnetic field H, (2) is not affected by the angle between the electric current and the magnetic field, (3) but depends on the magnetic field orientation with respect to the crystal axis. Magnetoresistance is expressed as M = (aH²_a + bH²_b + cH²_c)₀^-3/2/H in terms of H = (H_a, H_b, H_c), the zero field resistivity ₀, and parameters a, b, and c which are independent of temperature and magnetic field. We have found that b a > c. Magnetoresistance up to 40 is observed for H = 7T along the b-axis at T = 1.5K.     

Continuous photoluminescence, time resolved photoluminescence and optically detected magnetic resonance measurements of PbI2 nanometer-sized particles, embedded in SiO2 films

The nanometer sized particles of PbI₂ were embedded in SiO₂ films. X-ray diffraction and the TEM pictures showed the preservation of the bulk layered structure and symmetry. The PL spectrum of the nano-particles exhibited a pronounced blue shift of the exciton band due to quantum size effect. The Lead Iodide represents an exceptionally small exciton Bohr radius (a_B = 19 Å) and a special case in which m_e m_h. The prepared samples contained particles with mean radii, a, in the range a_B < a < 3a_B. Within this limit (with m_e m_h), the experimental results suggest that the electron is localized nearly at the center of the particle, enabling the hole to move around it. Thus, the size confinement permits the creation of an acceptor-like exciton. The PL spectrum revealed additional states, associated with stoichiometric defects either at the interior or surface sites of the nano-particles. These defects act either as donor or acceptor states. The dynamics of the various recombination processes has been investigated by measuring the time resolved PL spectra. The results show a multiexponential behavior of the various recombination emission bands, indicating the occurrence of trapping and detrapping processes. Analysis of these results suggests that the existence of surface states give rise to these complex radiative decay processes. The correlation between donor-acceptor recombination emission bands in the aforementioned samples and lattice imperfections was examined, utilizing optically detected magnetic resonance (ODMR) spectroscopy. The results identified the following imperfection sites: an acceptor site associated with an isotropic Lead vacancy defect, [V⁻]_pb²⁺ and a donor site, associated with an anisotropic Iodine vacancy, [V⁰]_Iodine.     

Analysis of the Zeeman effect on D_α spectra on the EAST tokamak

Based on the passive spectroscopy,the D_α atomic emission spectra in the boundary region of the plasma have been measured by a high resolution optical spectroscopic multichannel analysis(OSMA) system in EAST tokamak.The Zeeman splitting of the D_α spectral lines has been observed.A fitting procedure by using a nonlinear least squares method was applied to fit and analyze all polarization π and ±σ components of the D_α atomic spectra to acquire the information of the local plasma.The spectral line shape was investigated according to emission spectra from different regions(e.g.,low-field side and high-field side) along the viewing chords.Each polarization component was fitted and classified into three energy categories(the cold,warm,and hot components) based on different atomic production processes,in consistent with the transition energy distribution by calculating the gradient of the D_α spectral profile.The emission position,magnetic field intensity,and flow velocity of a deuterium atom were also discussed in the context.     

Ferromagnetic Zr1−xMnxCo2 laves phase compounds

Structure and magnetic properties of the Zr_1−xMn_xCo_2+δ alloys were studied for 0 x <0.7, δ=0, 0.45. The cubic C15 Laves phase structure shows Mn solubility up to x≈0.4. The other Laves phase with the hexagonal C36 structure found for x0.5 apparently has a small region of Mn solubility in the vicinity of Zr_0.4Mn_0.6Co₂. Though the parent Mn-free compounds are known to be paramagnetic, the Mn-substituted alloys show ferromagnetic behavior with the Curie temperatures up to 625 K and the room-temperature saturation magnetization of about 100 emu/g. The onset of ferromagnetism with the Mn substitution for Zr may be caused by polarization of itinerant 3d electrons, like it was earlier supposed for the off-stoichiometric ZrCo_2+δ. The universal composition dependencies of the intrinsic magnetic properties for different δ can be obtained, if plotted against the amount of zirconium atoms missing in its sublattice. The room-temperature anisotropy with the noticeable anisotropy field of 24 kOe and the 1 1 0 easy magnetization direction laying in a basal plane was found in the hexagonal Zr_0.5Mn_0.5Co₂.     

Magnetic properties of the hexagonal NdNi5 and NdCu5 compounds

Magnetization and resistivity measurements performed on the hexagonal NdNi₅ and NdCu₅ compounds are presented. For NdNi₅, magnetization was measured on a single crystal along the three main axes of the orthohexagonal cell. This compound orders ferromagnetically at T_c = 7 K, a being the easy magnetization axis. Quantitative analysis of the experimental data led to the determination of the 4f-Nd and 3d-Ni contributions to the magnetization. In particular crystal field parameters were determined which account for inelastic neutron scattering data. Two original features of the compounds magnetic behaviour due to crystal field effects are noted: i) in the basal plane a large anisotropy of the magnetic moment which strongly increases with the magnetic field between 11 and 130 kOe; ii) a large decrease of the Nd moment during the rotation toward the c axis driven by the field. NdCu₅ orders also ferromagnetically at 15 K. The Nd moment lies perpendicular to c, and its reduction by the crystal field seems smaller than in NdNi₅.     

Effects of Mg substitution on the structural and magnetic properties of Co_(0.5)Ni_(0.5-x)Mg_xFe_2O_4 nanoparticle ferrites

In this study, nanocrystalline Co–Ni–Mg ferrite powders with composition Co_(0.5)Ni_(0.5-x)Mg_xFe_2O_4 are successfully synthesized by the co-precipitation method. A systematic investigation on the structural, morphological and magnetic properties of un-doped and Mg-doped Co–Ni ferrite nanoparticles is carried out. The prepared samples are characterized using x-ray diffraction(XRD) analysis, Fourier transform infrared spectroscopy(FTIR), field emission scanning electron microscopy(FESEM), and vibrating sample magnetometry(VSM). The XRD analyses of the synthesized samples confirm the formation of single-phase cubic spinel structures with crystallite sizes in a range of ~ 32 nm to ~ 36 nm. The lattice constant increases with increasing Mg content. FESEM images show that the synthesized samples are homogeneous with a uniformly distributed grain. The results of IR spectroscopy analysis indicate the formation of functional groups of spinel ferrite in the co-precipitation process. By increasing Mg2+substitution, room temperature magnetic measurement shows that maximum magnetization and coercivity increase from ~ 57.35 emu/g to~ 61.49 emu/g and ~ 603.26 Oe to~ 684.11 Oe(1 Oe = 79.5775 A·m-1), respectively. The higher values of magnetization Ms and Mr suggest that the optimum composition is Co_(0.5)N_(i0.4)Mg_(0.1)Fe_2O_4 that can be applied to high-density recording media and microwave devices.     

Shaped crystal growth and scintillating properties of Yb:(Gd,Lu)3Ga5O12 solid solutions

Shaped single crystals of (Lu_xGd_1−x)₃Ga₅O₁₂ (0.0x1.0) and (Yb_0.05Lu_xGd_0.95−x)₃Ga₅O₁₂ (0.0x0.9) were grown by the modified micro-pulling-down method. Continuous solid solutions with garnet structure and a linear compositional dependency of crystal lattice parameter in the system Yb:(Gd,Lu)₃Ga₅O₁₂ are formed. Measured optical absorption spectra of the samples show 4f–4f transitions related to Gd³⁺ ion at 275 and 310 nm, and also an onset of charge transfer transitions from oxygen ligands to Gd³⁺ or Yb³⁺ cations below 240 nm. A complete absence of Yb³⁺ charge transfer luminescence under X-ray excitation in any of the investigated samples was explained by the overlapping of charge transfer absorption of Yb³⁺ by that of Gd³⁺ ions. For specific composition of Lu_1.5Gd_1.5Ga₅O₁₂ an intense defect-host lattice-related emission, which achieve of about 40% integrated intensity compared with Bi₄Ge₃O₁₂, was found.     

Synthesis,crystal structure and magnetic characterization of Pr3+ and Zn2+ ions co-doped hexagonal ferrites via the ceramic process

M-type hexaferrites Ca_0.2Sr_0.8-xPr_xFe_12-yZn_yO₁₉ (0.00?≤?x?≤?0.40, 0.00?≤?y?≤?0.30) were synthesized by the ceramic process. The X-ray diffraction (XRD), field emission scanning electron microscopy (FE-SEM) and a vibrating sample magnetometer (VSM) were used to investigate microstructure and magnetic properties of the M-type hexaferrites. The single-phase with hexagonal structure was obtained in all Pr–Zn substituted M-type hexaferrites, and with increasing Pr–Zn content, the 2θ values of (107) and (114) peaks shifted towards higher angles. With increasing Pr–Zn content, the lattice constant a basically kept unchanged, while the lattice constant c decreased. FESEM images of the hexaferrites showed that the hexagonal platelets had formed in the hexaferrites and the average grain size increased with increasing Pr–Zn content. The saturation magnetization (M_s), remanent magnetization (M_r) and M_r/M_s ratio first increased with increasing Pr–Zn content (0.00?≤?x?≤?0.24, 0.00?≤?y?≤?0.18), and then decreased with further increasing Pr–Zn content. The coercivity (H_c), magnetic anisotropy field (H_a) and effective magnetic anisotropy constant (K_eff) increased with increasing Pr–Zn content (0.00?≤?x?≤?0.16, 0.00?≤?y?≤?0.12), and then decreased with further increasing Pr–Zn content.     

Magnetic doping in Zn7−xMxSb2O12 spinels (M=Ni and Co)

In this article we present a concise report on our studies on the magnetic behavior and structural arrangements of the inverse spinel Zn_7−xM_xSb₂O₁₂ system (M=Ni, Co). Studies on the temperature dependence of the magnetization (M) of several samples in this system showed the occurrence of a spin-glass-like state in temperatures around 10 K. The capability of this system to hold magnetic ions in either octahedral and/or tetrahedral positions is responsible for the occurrence of competing ferromagnetic and antiferromagnetic interactions. This condition is likely to cause the appearance of the observed spin-glass-like behavior.