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.     

Microstructure and magnetic characterization of the Sm-CoMn co-substituted SrCaM hexagonal ferrites

A series of Sm-CoMn substituted hexagonal ferrites with chemical composition of Sr_0.85-xCa_0.15Sm_xFe_12-y(Co_0.5Mn_0.5)_yO₁₉ (0.00?≤?x?≤?0.60, (0.00?≤?y?≤?0.50) were synthesized by the solid-state reaction method. Microstructure and magnetic properties of the hexaferrites have been investigated by the X-ray diffraction, field emission scanning electron microscopy and a permanent magnetic measuring system. A single magnetoplumbite phase is exhibited in the hexaferrites with the substitutiom of Sm (0.00?≤?x?≤?0.12) and CoMn (0.00?≤?y?≤?0.10) contents. For the hexaferrites containing Sm (x?≥?0.24) and CoMn (y?≥?0.20), impurity phases are observed in the structure. The FESEM micrographs exhibit that the hexaferrites with different Sm-CoMn contents have formed hexagonal structures and the grain size of the hexaferrites remains unchanged with increasing Sm-CoMn content. The remanence (B_r), H_k/H_cj ratios, and maximum energy product [(BH)_max] decrease with increasing Sm-CoMn content (0.00?≤?x?≤?0.60, (0.00?≤?y?≤?0.50). Instrinsic coercivity (H_cj) and magnetic induction coercivity (H_cb) increase with increasing Sm-CoMn content (0.00?≤?x?≤?0.12, 0.00?≤?y?≤?0.10), and then decrease with increasing Sm-CoMn content (0.12?≤?x?≤?0.36, 0.10?≤?y?≤?0.30), while for the hexaferrites with Sm (x?≥?0.36) and CoMn (y?≥?0.30), with increasing Sm-CoMn content, H_cj increases and H_cb decreases.     

An investigation on microstructural,spectral and magnetic properties of Pr–Cu double-substituted M-type Ba–Sr hexaferrites

This is first report on Pr–Cu double-substituted M-type Ba–Sr hexaferrites with nominal compositions Ba_0.3Sr_0.7−xPr_xFe_12.0−xCu_xO₁₉ (x = 0.00–0.35) fabricated by the solid-state reaction route. X-ray diffraction (XRD), Fourier transform infrared (FTIR) spectroscopy, field emission scanning electron microscopy (FE-SEM) and Hysteresis graph meter were used to characterize the synthesized M-type Ba–Sr hexaferrites. XRD results show that the hexaferrites with x ≤ 0.21 exhibited single M-type phase, while the hexaferrites with x ≥ 0.28 exhibited the M-type phase and impurity phases. FE-SEM images proposed that all particles with hexagonal platelet-like shape were homogeneously dispersed. The remanence (B_r) first increased with Pr–Cu content (x) from 0.00 to 0.14, and then decreased when x ≥ 0.14. The intrinsic coercivity (H_cj) and magnetic induction coercivity (H_cb) first decreased with x from 0.00 to 0.14, and then increased when x ≥ 0.14. Maximum energy product [(BH)_max] reached the maximum value at x = 0.14.     

Effects of Pr-Al co-substitution on the magnetic and structural properties of M-type Ca-Sr hexaferrites

In this research, a series of Pr-Al co-substituted M-type hexaferrites with the chemical composition of Ca_0.4Sr_0.6-xPr_xFe_12.0-yAl_yO₁₉ (0.00 ≤ x ≤ 0.40, 0.00 ≤ y ≤ 0.60) were synthesized by the standard ceramic method. The phase identification of the samples was confirmed by X-ray diffraction analysis. A single magnetoplumbite phase is exhibited in the hexaferrites with the substitutiom of Pr (0.00 ≤ x ≤ 0.32) and Al (0.00 ≤ y ≤ 0.48) contents. For the hexaferrite containing Pr (x = 0.40) and Al (y = 0.60), an impurity phase α-Fe₂O₃ is observed in the structure. The morphology of the hexaferrites was analyzed by field emission scanning electron microscopy (FE-SEM). FE-SEM micrographs show that the hexaferrites with different Pr-Al contents have formed hexagonal structures, and the grain size of the magnets decreases with increasing Pr-Al content. A magnetic property measurement system was used to measure the magnetic properties of the hexaferrites. The remanence (B_r) and maximum energy product [(BH)_max] decrease with increasing Pr-Al content (0.00 ≤ x ≤ 0.40, (0.00 ≤ y ≤ 0.60). The intrinsic coercivity (H_cj) increases with increasing Pr-Al content (0.00 ≤ x ≤ 0.40, (0.00 ≤ y ≤ 0.60). The magnetic induction coercivity (H_cb) and H_k/H_cj ratio first increase with increasing Pr-Al content (0.00 ≤ x ≤ 0.24, 0.00 ≤ y ≤ 0.36) and then decrease with increasing Pr-Al content (0.24 ≤ x ≤ 0.40, 0.36 ≤ y ≤ 0.60).     

Magnetic and microstructural properties of M-type strontium hexaferrites with Pr–ZnAl substitution

We have investigated the influence of Pr–ZnAl substitution on the magnetic and microstructural properties of M-type strontium hexaferrites Sr_1.0-xPr_xFe_12.0-x(Zn_0.5Al_0.5)_xO₁₉ (0.0 ≤ x ≤ 0.5) synthesized by the standard ceramic method. X-ray diffraction (XRD) was carried out to determine the crystal structure and the phase identification of the hexaferrites showed that a single magnetoplumbite phase was exhibited in the hexaferrites with Pr–ZnAl content (x) from 0.0 to 0.4 and impurity phase α-Fe₂O₃ was observed in the structure when Pr–ZnAl content (x)?=?0.5. The morphology of the hexaferrites was analyzed by a field emission scanning electron microscopy (FE-SEM). The representative FE-SEM micrographs showed that the particles were regular hexagonal platelets and the average grain size basically kept unchanged with increasing Pr–ZnAl content (x). A magnetic property measurement system was used to measure the magnetic properties of the hexaferrites. The remanence (B_r), maximum energy product [(BH)_max] and H_k/H_cj ratio decreased with increasing Pr–ZnAl content (x) from 0.0 to 0.5. The intrinsic coercivity (H_cj) and magnetic induction coercivity (H_cb) first increased with increasing Pr–ZnAl content (x) from 0.0 to 0.1, and decreased with increasing Pr–ZnAl content (x) from 0.1 to 0.2, and then increased when Pr–ZnAl content (x) ≥ 0.2.     

The tunable magnetic properties and microstructures of Co–Ni double-substituted M-type Casrla hexaferrites

M-type hexaferrites with Co²⁺ and Ni²⁺ions substituting for Fe³⁺ ions (Ca_0.30Sr_0.35La_0.35Fe_12.0−x(Co_0.5Ni_0.5)_xO₁₉, 0.0 ≤ x ≤ 1.0) were prepared by the traditional solid state method. X-ray diffractometer (XRD), field emission scanning electron microscopy (FE-SEM), physical property measurement system-vibrating sample magnetometer (PPMS-VSM) have been employed to study the microstructures and magnetic properties of hexaferrites. XRD patterns showed that the single magnetoplumbite phase is obtained if Co–Ni content (x) ≤ 0.4 and impurity phases are observed in the structure when Co–Ni content (x) ≥ 0.4. FE-SEM micrographs showed that the hexaferrites with hexagonal platelet-like grains is obtained. The saturation magnetization (M_s), remanent magnetization (M_r), M_r/M_s ratio, magneton number (n_B), coercivity (H_c), magnetic anisotropy field (H_a) and first anisotropy constant (K₁) decrease with increasing Co–Ni content (x) from 0.0 to 1.0. And our reported results with tunable H_c and M_r can be used for recording applications.     

Structure and magnetic properties of (Nd,Dy)16(Fe,Co)76−xTixB8 powders prepared by mechanical alloying

Nanocrystalline (Nd,Dy)₁₆(Fe,Co)_76−xTi_xB₈ magnets were prepared by mechanical alloying and respective heat treatment at 973–1073 K/30–60 min. An addition of 0.5 at % of Ti results in an increase of coercivity from 796 to 1115 kA m⁻¹. Partial substitution of Nd by Dy results in an additional increase of coercivity up to 1234 kA m⁻¹. Mössbauer investigations shows that for x?1 the (Nd,Dy)₁₆(Fe,Co)_76−xTi_xB₈ powders are single phase. For higher Ti contents (x>1) the mechanically alloyed powders heat treated at 973 K are no more single phase, and the coercivity decreases due to the presence of an amorphous phase. A heat treatment at a higher temperature (1073 K) for longer time (1 h) results in the full recrystallisation of powders. The mean hyperfine field of the Nd₂Fe₁₄B phase decreases for titanium contents of 0?x?1, and remains constant for x>1. This indicates that the Ti content in the Nd₂Fe₁₄B phase reaches its maximum value.     

Microstructure of sintered ND-Fe-Ga-B magnets with Mo and MoS2 addition

The effect of Mo and MoS₂ additions on the magnetic and microstructure properties has been investigated in Nd-Fe-Ga-B sintered magnets. Coercivity can be increased by both the additions, but the MoS₂ addition provides the larger increase per Mo atom for up to 0.6 at.% Mo. Microstructure investigation reveals a new amorphous intergranular Ga rich phase. This phase forms a thin layer in the grain boundaries and leads to a wetting behavior of the grain boundary phase, therefore increasing the coercivity. Molybdenum addition in the form of MoS₂ is found to modify the Nd₂Fe₁₄B phase, rather than form new minority phases, and the coercivity enhancement of the magnet is due to the increased anisotropy field of the hard magnetic phase.     

Highly anisotropic resin-bonded magnets processed with surfactant-coated SmCo5 nanocrystalline powders

Highly anisotropic SmCo₅ nanocrystalline powders with grain size in the range 5-20 nm were processed through surfactant and magnetic field-assisted milling. The SmCo₅ nanocrystalline powders so obtained by this method possess unusual characteristics such as reduction in particle size, platelet-structure and high remanence values. A possible mechanism for achieving remanence enhancement with the surfactant-coated SmCo₅ powders has been discussed. Besides, the resin-bonded magnets processed with the surfactant-coated SmCo₅ powders showed relatively higher density, induction remanence and energy product with strong anisotropic behavior than those of the magnets processed with the conventionally milled SmCo₅ powders. Maximum values of H_ci (16 kOe), B_r (4.66 kG) and (BH)_max (5.5 MG Oe) were achieved for the resin-bonded magnets processed with the surfactant-coated powders.     

Microstructural and magnetic properties of Pr–BiCo co-substituted M-type Sr–Ca hexaferrites

We have synthesized the Pr–BiCo substituted hexaferrites with compositions of Sr_0.8-xCa_0.2Pr_xFe_12.0-x(Bi_0.5Co_0.5)_xO₁₉ (0.0?≤?x?≤?0.5) by the standard ceramic method. Results of X-ray diffraction analysis exhibits that the synthesized hexaferrites with x from 0.0 to 0.3 are in single magetoplumbite structure, and impurity phases are observed when x?≥?0.4. The surface morphology of magnets shows that hexaferrite grains have a hexagonal platelet shape with clear grain boundaries. The remanence first increases with x from 0.0 to 0.1, and then decreases when x?≥?0.1. The intrinsic coercivity decreases with x from 0.0 to 0.1, and then increases when x?≥?0.1. With x from 0.0 to 0.4, the changing trend of magnetic induction coercivity is in agreement with that of H_cj, while at x?≥?0.4, H_cb decreases. The maximum energy product initially increases with x from 0.0 to 0.2, and then decreases when x?≥?0.2.     

High magnetostriction at low fields of (Tb1−xDyx)0.2Pr0.8(Fe0.4Co0.6)1.88C0.05 intermetallic compounds

The structure and magnetostriction of the (Tb_1−xDy_x)_0.2Pr_0.8(Fe_0.4Co_0.6)_1.88C_0.05 intermetallic compounds (0≤x≤1) were studied by X-ray diffraction and magnetic measurements. The formation of an approximate single Laves phase with a MgCu2-type cubic structure was observed in this series of compounds. It was found that the Curie temperature and the saturation magnetization of the compounds would decrease with increase in the Dy content up to x=1. The magnetostriction λ_a (λ_a=λ_‖-λ_⊥) gently rises when x≤0.6, and follows with a precipitous fall when x exceeds 0.6, with the highest value of λ_a being reached in the compounds with x=0.6. The magnetostriction of all the samples was observed to approach their own saturation in the magnetic fields higher than 4 kOe. This indicates that the addition of a small amount of Dy could effectively improve the low-field magnetostriction of the Tb_0.2Pr_0.8(Fe_0.4Co_0.6)_1.88C_0.05 compounds, which could become a kind of promising magnetostrictive material.     

Structure and magnetostriction of Tb0.2Pr0.8(Fe0.4Co0.6)1.93−xCx intermetallic compounds

The structure and magnetostriction of Tb_0.2Pr_0.8(Fe_0.4Co_0.6)_1.93−xC_x intermetallic compounds were studied by X-ray diffraction and magnetic measurements. Almost a single cubic Laves phase forms in the alloys for x ≤0.20, and a small amount of C can inhibit the formation of the 1:3 phase. The lattice parameter increases when 0≤x≤0.15, while the T_c and the spontaneous magnetization decreases with increasing x. The lattice parameter decreases slowly when 0.15≤x≤0.30, while the T_c decreases evidently with increasing x. The magnetostriction λ_a (=λ_∥-λ_⊥) is improved at low magnetic fields at room temperature for the compounds with 0.05≤x≤0.10, indicating that these C-containing compounds are promising magnetostrictive materials.     

Structure and magnetostrictive properties of melt-spun Pr(Fe0.4Co0.6)1.93 alloys

Pr(Fe_0.4Co_0.6)_1.93 ribbons were prepared by a melt-spinning method. Their structure and magnetic properties are investigated as functions of wheel speed and annealing temperature. The as-spun ribbon consists of a Pr(Fe, Co)₂ cubic Laves phase and an amorphous phase at a wheel speed of v≥35 m/s, while the non-cubic phases of PuNi₃-type and rare earth appear when the speed lower than 30 m/s. A single Pr(Fe, Co)₂ phase with MgCu₂-type structure has been synthesized by the process for the wheel speed of v≥35 m/s and subsequent annealing at 500 °C for 30 min. The epoxy/Pr(Fe_0.4Co_0.6)_1.93 composite has been produced by a cold isostatic pressing technique, and the magnetic properties have been investigated. The composite rod sample possesses good magnetostrictive properties, i.e., a large magnetostriction (λ_a=λ_∥−λ_⊥) of 710 ppm at 800 kA/m and a dynamic coefficient d₃₃ of 0.67 nm/A at 100 kA/m, and is of practical value.     

Fe65B22Nd9Mo4 bulk nanocomposite permanent magnets produced by crystallizing amorphous precursors

The Fe₆₅B₂₂Nd₉Mo₄ nanocomposite permanent magnets in the form of a rectangular cross sectioned rod have been prepared by annealing the amorphous precursors. The thermal behavior, structure and magnetic properties of the magnets have been investigated by differential scanning calorimetry, X-ray diffractometry, electron microscopy and magnetometry techniques. The as-cast Fe₆₅B₂₂Nd₉Mo₄ alloy showed soft magnetic properties, which changed into magnetically hard after annealing. Results provoke that the magnetic properties of the alloy are sensitive to thermal processing conditions. The optimum hard magnetic properties with a remanence (B_r) of 0.56 T, coercivity (_iH_c) of 920.7 kA/m and maximum energy product (BH)_max of 50.15 kJ/m³ were achieved after annealing the alloy at 983 K for 10 min. The good magnetic properties of Fe₆₅B₂₂Nd₉Mo₄ magnets are ascribed to the exchange coupling between the nano-scaled soft α-Fe, Fe₃B and hard Nd₂Fe₁₄B magnetic grains.     

熔体快淬Pr(Fe1-xCox)2合金的结构和磁性

通过熔体快淬方法获得Pr(Fe_1-xCo_x)₂合金条带,经过X射线衍射、差示扫描量热计和磁性测量对其结构、磁性和热稳定性进行了研究.发现当Co的含量x大于0.2时才可能获得Pr(Fe,Co)₂立方Laves相化合物.对Pr(Fe_0.6Co_0.4)₂合金,在快淬速度为30m/s时,条带由Pr₂(Fe,Co)₁₇,Pr(Fe,Co)₂和富稀土相组成;在速度为40m/s时,获得了几乎单相的Pr(Fe_0.6Co_0.4)₂化合物,其居里温度为305℃;在速度为45m/s时,除了Pr(Fe_0.6Co_0.4)₂化合物外,还存在少量的非晶相.Pr(Fe_0.6Co_0.4)₂化合物在770℃以上发生分解.用40m/s快淬纳米晶粉胶粘磁体有大的磁致伸缩系数（λ_∥-λ_⊥=140×10^-6)和高的硬磁性能（_iH_c=398kA/m). 关键词：     

The effect of compound addition Dy2O3 and Sn on the structure and properties of NdFeNbB magnets

NdFeNbB with the additions of Dy₂O₃ and Sn permanent magnets have been attained by means of powder-blending technique, and their magnetic properties, temperature performance and microstructure were studied in this paper. The addition of just 2.0 wt% Dy₂O₃ or 0.3 wt% Sn proved to be very effective in improving the permanent magnetic properties of NdFeNbB magnets. Dy₂O₃ additions result in the increase in the H_ci and temperature dependence due to the increase of T_c, formation of (NdDy)-rich phase and grain refinement of Φ phase. This improvement of the coercivity stability of the magnets from the addition of Sn is attributed to the smoothing effect of the Sn addition at the grain boundaries. The magnetic properties, the temperature dependence and Curie temperature of NdFeNbB with Dy₂O₃ and Sn combined addition were found to be considerably improved. From the X-ray diffraction, SEM-EDAX studies and the thermo-magnetic study, the improved properties due to the solution of Dy and Sn to the Φ phase, the reduced N_eff and the smaller Φ phase.     

Structural and magnetic properties of SmCo5.6Ti0.4 alloy

Three series of SmCo_5.6Ti_0.4 samples were prepared by quenching, melt spinning, and ball milling, respectively. Annealing at different temperatures was carried out for the three series. The influence of the processing routes on the structural and magnetic properties was systematically investigated for this alloy. The as-quenched bulk sample consisted of three phases with a rather coarse grain microstructure. Low intrinsic coercivity (_iH_c) of 0.12 T was obtained in this sample. While the as-spun ribbons and as-milled/annealed powders showed the CaCu₅-type phase (1:5) plus Th₂Zn₁₇-type phase (2:17), and the 1:5 phase plus TbCu₇-type phase (1:7), respectively, with nanograin microstructure. The _iH_c of as-spun ribbons and as-milled/annealed (700 °C for 2 h) powders was found to be 0.59 and 2.23 T, respectively. Coercivity mechanism of these as-spun ribbons is mainly of nucleation type. In the as-milled/annealed powders, the network of the nanograin boundaries is believed to provide strong pinning sites for the domain wall movement.     

Simultaneous variations of microstructure and magnetic properties of Ni58Fe12Zr20B10 nanostructure/amorphous alloy prepared by mechanical alloying

This study aims to evaluate magnetic and micro-structural properties of amorphous/nanocrystalline mechanically alloyed Ni₅₈Fe₁₂Zr₂₀B₁₀ powders with ball-milling time up to 190 h. Structural, micro-structural and thermal evaluations of the milled powders were carried out by X-ray diffraction (XRD), scanning electron microscope (SEM), transmission electron microscope (TEM) and differential scanning calorimetry (DSC) methods. Magnetic properties were also measured by a vibrating sample magnetometer (VSM) instrument. Results showed that the amorphous phase reached maximum value of 95% and the crystallite size was about 3 nm at the end of the milling. Magnetization saturation (M_s) decreased slightly and coercivity (H_c) reached to the highest value at 72 h of the milling time. At the 190 h of milling, the coercivity and saturation magnetization reached 18 Oe and 20 emu/g, respectively. While, after an appropriate amount of heat treatment, these two variables became approximately 2 Oe and 32 emu/g.     

Magnetic and Microwave Absorbing Properties of Electrospun Ba(1−x)LaxFe12O19 Nanofibers

Ba_(1−x)La_xFe₁₂O₁₉ (0.00≤x≤0.10) nanofibers were fabricated via the electrospinning technique followed by heat treatment at different temperatures for 2 h. Various characterization methods including scanning electron microscopy (SEM), X-ray diffraction (XRD), vibrating sample magnetometer (VSM), and microwave vector network analyzer were employed to investigate the morphologies, crystalline phases, magnetic properties, and complex electromagnetic parameters of nanofibers. The SEM images indicate that samples with various values of x are of a continuous fiber-like morphology with an average diameter of 110±20 nm. The XRD patterns show that the main phase is M-type barium hexaferrite without other impurity phases when calcined at 1100 °C. The VSM results show that coercive force (H_c) decreases first and then increases, while saturation magnetization (M_s) reveals an increase at first and then decreases with La³⁺ ions content increase. Both the magnetic and dielectric losses are significantly enhanced by partial substitution of La³⁺ for Ba²⁺ in the M-type barium hexaferrites. The microwave absorption performance of Ba_0.95La_0.05Fe₁₂O₁₉ nanofibers gets significant improvement: The bandwidth below −10 dB expands from 0 GHz to 12.6 GHz, and the peak value of reflection loss decreases from −9.65 dB to −23.02 dB with the layer thickness of 2.0 mm.     

Magnetic properties and grain-boundary structure transition of melt-spun (Sm0.12Co0.87Cu0.01)97(VC)3 under annealing

Effects of annealing treatment on the magnetic properties and microstructure of SmCo₇-based magnets doped with VC and Cu were investigated. The coercivity of the as-spun ribbons (Sm_0.12Co_0.87Cu_0.01)₉₇(VC)₃ was 3.6 kOe. It was increased to 7.3 kOe after annealing at 800 °C for 15 min. A fixed single 1:7H structure and regular 1:7H dendrite grains with long axes preferentially parallel to each other had been attained during rapid solidification and subsequent annealing treatment. However, TEM results revealed that there was grain-boundary phase rich in C and Cu besides 1:7H phase in the as-solidified ribbon. After annealing, the grain-boundary phase decomposed to Cu-, Sm- and C-rich intergranular phases. Cu-, Sm- and C-rich regions formed at the grain boundaries after annealing improved the coercivity of (Sm_0.12Co_0.87Cu_0.01)₉₇(VC)₃ by decreasing the magnetostatic interactions and act as effective domain wall pinning sites.