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The Pr2Fe17−xCrx (x = 0.0, 0.1, 0.2, 0.4) powders were successfully prepared by arc melting and high-energy ball milling. The crystal structure, morphology, magnetic properties, and microwave absorption performance of the Pr2Fe17−xCrx alloys was studied by X-ray diffraction (XRD), scanning electron microscopy (SEM), vibrating sample magnetometer (VSM), and vector network analyzer (VNA), respectively. The results show that the saturation magnetization increases with the increase of Cr doping amount. The average particle sizes of Pr2Fe17−xCrx particulates are 1.56, 1.47, 1.67, and 1.71 μm, which correspond to x = 0.0, 0.1, 0.2, and 0.4, respectively, and the average particle size decreases first and then increases. The minimum absorption peak frequency of Pr2Fe17−xCrx shifts towards a lower frequency region with the increase of Cr doping amount. The minimum reflection loss (RL) of the Pr2Fe17−xCrx composite absorbers decreases first and then increases with the increase of Cr doping amount. The Pr2Fe16.9Cr0.1 composite absorber exhibits excellent microwave absorption properties, its minimum reflection loss value can reach up to − 33.81 dB at 7.28 GHz, and its effective absorption bandwidth (RL < − 10 dB) is 2.24 GHz with the best matching thickness of 2.2 mm. [ABSTRACT FROM AUTHOR]

In order to understand the intrinsic properties of high abundance permanent magnet materials, effects of Co element on the structure, magnetic, and microwave absorption properties of La12.5(Fe1-xCox)81.3B6.2 alloys have been investigated with x = 0, 0.1, 0.2, 0.3. The X-ray diffraction results revealed that compounds of La12.5(Fe1-xCox)81.3B6.2 crystallized the Nd2Fe14B-type structure with the space group P42/mnm. The saturation magnetization of the powders increases with the Co content increasing, 97.7 emu/g for x = 0.3. The minimum absorption peak value of La12.5(Fe1-xCox)81.3B6.2 alloy reaches about − 18.69 dB at 10.56 GHz with the matching thickness of 2.5 mm. [ABSTRACT FROM AUTHOR]

The crystal structure, magnetic, and microwave absorption properties of the (Nd1−xLax)2Fe14B system have been investigated. The La2Fe14B compound was successfully synthesized and refined, giving a tetragonal structure, space group P42/mnm with the Nd2Fe14B-type structure. The crystal structure parameters of the (Nd1−xLax)2Fe14B compounds were determined by full-profile Rietveld refinements. The results revealed that all intermediate alloys form a continuous solid solution. The normalized lattice parameters of the (Nd1−xLax)2Fe14B compounds increase linearly with an increase of La concentration. Based on the results of DSC measurements and X-ray powder diffraction examinations, the phase diagram of the Nd2Fe14B-La2Fe14B system has been constructed. The remanence (Mr) and coercivity (Hc) of (Nd1−xLax)2Fe14B (x = 0.00, 0.10, 0.20, 0.30, and 0.40) gradually decrease. The highest reflection loss is − 29.8, − 27.4, − 24.1, − 18.6, and − 14.2 dB at 9.8, 8.9, 7.5, 6.9, and 6.5 GHz, respectively. The absorption peak shifts toward from higher frequency region to lower frequency region and the absorption bandwidth widens with the increase of the La substitution. [ABSTRACT FROM AUTHOR]

The Sm-Ni-Fe ternary system has been investigated at 773 K by means of powder x-ray diffraction, metallography and scanning electron microscopy equipped with energy dispersive x-ray spectroscopy. The isothermal section consists of 16 single-phase regions, 29 two-phase regions and 14 three-phase regions. The influence of Fe-doping on the structure and the microwave absorption properties of the SmNi compound has been systematically studied. The homogeneity range in SmNiFe was determined as x = 16.67. The lattice parameters were found to gradually increase and the particle size become much finer with the increase of Fe concentration. All the samples exhibited good microwave absorption properties in the X-band (8-12 GHz). The highest reflection loss of the SmNiFe ( x = 0.0, 5.0, 10.0,15.0, 16.67) alloys are −10.12 dB, −10.39 dB, −16.44 dB, −20.69 dB, and −43.05 dB at 6.96 GHz, 7.92 GHz, 8.56 GHz, 10.04 GHz, and 11.08 GHz, respectively. The absorption peak shifted towards the higher frequency region with the increasing amount of Fe substitution. [ABSTRACT FROM AUTHOR]

• BaFe 12 O 19 /CeO 2 composites were prepared by solid-state reaction method. • BaFe 12 O 19 is a high magnetic ferrite and CeO 2 is a dielectric semiconductor. • The minimum reflection loss achieved − 51.2 dB. • The absorption ability was improved due to the synergistic effects of BaFe 12 O 19 &CeO 2. Hexagonal barium ferrite (BaFe 12 O 19) is a promising microwave absorption material, due to high magnetic loss and stable chemical state. However, the poor electrical performance of BaFe 12 O 19 will lead to impedance mismatch and poor absorption capacity. Compounding with other dielectric materials is a feasible way to solve the above problems. In this work, BaFe 12 O 19 + x% CeO 2 (x = 0, 0.16, 0.31, and 0.64) were prepared by conventional solid state reaction method. The microwave absorption performance of BaFe 12 O 19 /CeO 2 composites was significantly improved in comparison with single BaFe 12 O 19 , which is mainly correlated with the synergistic effects of magnetic loss, dielectric loss and multiple reflections. The x = 0.31 sample exhibited the minimum reflection loss of − 51.2 dB at 6.5 GHz and bandwidth with the loss above 10 dB is about 2.7 GHz. In addition, when x = 0.64, the reflection loss of - 23.6 dB could be achieved at only 1.8 mm and effective bandwidth is 3 GHz. Consequently, the facile preparation pathway and excellent performance make BaFe 12 O 19 /CeO 2 composite a promising candidate for efficient low-frequency electromagnetic wave absorbing. [ABSTRACT FROM AUTHOR]

• Nano-spinel powder samples of Co 1– x Ni x Fe 2 O 4 (x = 0, 0.1, 0.3, 0.5) were successfully synthesized by sol–gel method. • Ni doping changes the ion concentration at the [A][B] position and affects the magnetic properties of CoFe 2 O 4. • Different microwave absorption mechanisms of Co 1– x Ni x Fe 2 O 4 (x = 0, 0.1, 0.3, 0.5) samples. • The Co 1– x Ni x Fe 2 O 4 (x = 0, 0.1, 0.3, 0.5) samples exhibit excellent microwave absorption performance. In this paper, the Co 1− x Ni x Fe 2 O 4 (x = 0, 0.1, 0.3, 0.5) ferrite material sample was successfully synthesized by the sol–gel combustion method. Using XRD to detect the phase, it was found that a pure sample was prepared, and the corresponding unit cell model was established using XRD data. At the same time, using Raman spectroscopy analysis, the change of the T2g(1) peak in the Raman spectrum indicates that the doping of Ni2+ ions replaces the Co2+ ions in the tetrahedral position, and the high-frequency shoulder-like characteristics also indicate that the octahedral position has been replaced. The substitution of Ni2+ ions for Co2+ ions causes lattice distortion, which leads to the destruction of the ferromagnetic sequence and thus changes in magnetic properties. Microscopic observation was performed with SEM to observe the structure. It was found that with the doping of Ni2+ iron, the grain size gradually decreased, and the decrease of the grain size would have an impact on the space charge polarization. At the same time, the phenomenon of electronic polarization was found in the analysis of the microwave absorption mechanism. To explain the occurrence of this phenomenon, Raman detection was performed on the sample. The Raman detection is combined with the bond length and bond angle changes in the unit cell to analyze the Ni element. The reason for doping electron polarization. When the Ni doping amount is 0.1, the reflection loss of Co 1− x Ni x Fe 2 O 4 at 16.24 GHz is 37.66 dB, the corresponding thickness is 2.1 mm, and the effective frequency band is 2.64 GHz, which meets the requirements of light, thin and wide microwave absorbing materials. [ABSTRACT FROM AUTHOR]

This paper investigated the influence of Nd substitution on the microstructure, element valences, magnetic characteristics, and microwave absorption performances of Bi 1– x Nd x FeO 3 (x = 0.0, 0.05, 0.10, 0.15) nanopowders prepared via the sol-gel technique. The crystal structure of the nanopowders transformed from a twisted rhombohedral (R3c) for x ≤ 0.10 to cubic (Pm 3 ¯ m) for x = 0.15. When Nd substitution increased, the particle size gradually decreased and the surface morphology became uniform. Analysis of the results illustrate that Nd substitution can reduce the content of oxygen vacancies and effectively enhance magnetic performance. The results show that an appropriate amount of Nd doping can effectively enhance the microwave absorption performance of the Bi 1– x Nd x FeO 3 nanopowders. The sample with x = 0.10 demonstrates exceptionally good microwave absorption characteristics (RL min value of approximately −33.7 dB at 12.1 GHz and the maximum effective bandwidth of 2.8 GHz at 2.0 mm). Therefore, the Bi 1– x Nd x FeO 3 nanopowders have various potential applications due to outstanding microwave absorption performance and wide bandwidth. Image 1 • The Bi 1– x Nd x FeO 3 (x = 0.0, 0.05, 0.10, 0.15) nanopowders were readily prepared. • Nd-doping causes a transition from rhombohedral structure to cubic structure. • An decrease oxygen vacancies is observed with Nd doping. • Nd substitution can effectively improve the magnetic properties and microwave absorption properties of BiFeO 3. [ABSTRACT FROM AUTHOR]

LaNiO 3 is considered electromagnetic wave-absorbing material owing to its unique crystal structure and controllable dielectric constant. However, the effect of ion doping modification on microwave absorption performance remains to be thoroughly investigated. In this study, LaNi 1− x Ba x O 3 (x = 0, 0.02, 0.04, 0.06) was prepared through sol-gel methods. The reflection loss (RL) of the sample in the 2−18 GHz band was calculated using transmission line theory. Specifically, LaNi 0.96 Ba 0.04 O 3 exhibited superior results, with an RL value of −34.54 dB at d = 3 mm and f = 6.80 GHz, indicating effective absorption within the C-band. These results suggest that adding an appropriate amount of Ba ions to the material can effectively regulate the electromagnetic parameters and optimize impedance matching. Introducing Ba ions into the crystal interior produces abundant defects, which provide active sites for multipolarization and ultimately improve the wave-absorbing properties of the material. In addition, radar cross section(RCS) simulations simulation after coating the samples on original ideal conductor (PEC) substrates provide support for potential practical applications of the material. [ABSTRACT FROM AUTHOR]

In this paper, a high-purity NdFe 1-x Ni x O 3 perovskite-type material was prepared by a simple sol method. At the same time, adjust the substitution content of nickel to achieve the purpose of adjusting the dielectric properties and magnetic properties. According to the respective instruments, as Ni is substituted into the NdFeO 3 , the crystal microstructure will change to a certain extent, and there is a certain causal relationship between the magnetic properties and the bonding. Therefore, by adding a certain amount of nickel, the dielectric properties and magnetic properties can be adjusted to a certain balance point. NdFe 1-x Ni x O 3 material has excellent microwave absorption performance. When x = 0.2, the minimum reflection loss value is −49.32, and the corresponding impedance matching value is 1, and the effective bandwidth is 2.2 GHz when the thickness is 5.0 mm. The material that adjusts the perovskite structure by Ni element is beneficial to make the microwave absorption peak move from high frequency to low frequency, which has a wider application range and is closer to civil, commercial, military and aerospace. [ABSTRACT FROM AUTHOR]

Given the remarkable performances of rare earth multiferroic ortho-ferrites with magnetic optical and dielectric properties, the Y 1- x Sr x FeO 3 (x = 0, 0.05, 0.1, 0.15) perovskite structure microwave absorbing ferrite materials was successfully synthesized by Sr2+ ions A-site doping based on sol-gel technology in this paper. The XRD of all samples was refined with FullProf software, which confirmed the formation of the orthogonal perovskite structure (SG: Pnma). The SEM and TEM results display the average particles size of the samples is distributed between 110 and 160 nm. The increase of Sr doping concentration leads to the increase of particles size, which may be related to the growth of preferred orientation and incomplete substitution. The XPS analysis shows that Fe3+ was accompanied by the presence of Fe2+ with the doping of Sr2+ ions and oxygen vacancies increased significantly. The samples change from weak ferromagnetic state to paramagnetic state with the increase of Sr content. The minimum reflection loss (RL) of the Y 0.95 Sr 0.05 FeO 3 samples at 12.2 GHz reached −30.87 dB with thickness of 2.2 mm, where its effective absorption bandwidth (EAB, RL ≤ −10 dB) reached 2.4 GHz (11.3–13.7 GHz). Moreover, the EAB of the Y 0.85 Sr 0.15 FeO 3 samples reached 2.64 GHz, and the corresponding range is 9.0–11.6 GHz (X-band). [ABSTRACT FROM AUTHOR]

• Preparation of BaFe 12 O 19 and SmFeO 3 composite by sol–gel method. • Use the henkel diagram, the reciprocal curve of the hysteresis loop and the maximum magnetic energy product to explain the magnetic properties of the BaFe 12 O 19 @SmFeO 3 composite. • The addition of SmFeO 3 moves the microwave absorption frequency of the BaFe 12 O 19 @SmFeO 3 composite to low frequency. • While BaM + SmFeO 3 15% has the best absorbing performance, there are two reflection loss peaks, the maximum reflection loss is −48.5 dB, the bandwidth is 3.4 GHz. In this study, BaFe 12 O 19 (BaM)/SmFeO 3 10%, 15 %, and 20 % were synthesized via the sol–gel method. SmFeO 3 was uniformly attached to the BaM surface in the prepared composite. As the SmFeO 3 content increases, the weak magnetic properties of SmFeO 3 caused a gradual decrease in the saturation magnetization of the composite and a gradual increase in its coercive force. Based on the Henkel diagram, an exchange coupling between the two magnetic phases is observed. Similarly, the high permeability of BaM and the best dielectric properties of SmFeO 3 together improved the microwave absorption performance of the composite. The maximum reflection loss and bandwidth of BaM/15 %SmFeO 3 reached −48.5 dB and 3.4 GHz, respectively. [ABSTRACT FROM AUTHOR]

In this study, it is reported for the first time that porous Sm-doped CaFe 0.5 Mn 0.5 O 3-δ (CFMO) has good microwave absorption properties. In this paper, Sm x Ca 1−x Fe 0.5 Mn 0.5 O 3-δ (x = 0,0.05, 0.1, 0.15, 0.2) (Sm-CFMO) sample powders were prepared by the sol-gel method after calcination at 750 °C. Sm-CFMO was characterized using XRD, SEM, TEM, XPS and VSM, and mixed with paraffin wax for VNA testing. The addition of Sm elements increased the porous structure of CFMO, increased interfacial polarization and defect polarization, and increased oxygen vacancy content, resulting in enhanced charge polarization and dipole polarization, while greatly optimizing the impedance matching of CFMO, and the compounding with paraffin wax also increased the composite with paraffin also increases the interfacial polarization capacity of the material, thus improving the microwave absorption performance of the sample. Moreover, as a new type of absorbing material, this material has great potential for development in the field of absorbing materials and provides a new direction for the development of absorbing materials in the future. • A new oxide wave absorbing material. • Sm doping modulates the holes and oxygen vacancies thus changing the microwave absorption properties. • There is still much room for development in the field of wave absorbing materials. [ABSTRACT FROM AUTHOR]

• PrFeO 3 ceramics were prepared by the solid-state reaction method and the sol–gel method. • The magnetic properties of PrFeO 3 ceramic have obviously changed from antiferromagnetic to ferromagnetic by increasing the annealing temperature and time. • Possible mechanisms of structure, magnetic and microwave absorption properties have been analyzed. To investigate the magnetic and microwave absorption properties of PrFeO 3 ceramic, the traditional solid-state reaction and sol–gel methods were used. The results show that only an orthorhombic crystal structure was detected by X-ray diffraction and transmission electron microscopy. Interestingly, heat treatment can greatly improve the coercivity of PrFeO 3 ceramic and thus change the magnetic properties from antiferromagnetic to ferromagnetic. The high correlation between the magnetization parameters and bonding characteristics indicated that signifificant contracting of the Fe3+ O c 2− bonds and decrease in Fe3+ O d 2− Fe3+ linkage angles were the main origins of the strong ferromagnetism in the PrFeO 3 ceramic. The PrFeO 3 sample prepared by sol–gel method has good reflection loss. When the simulated thickness is 2 mm, the reflection loss reaches −36.87 dB at 15.92 GHz. The preparation process of the sol–gel method is simple and can be used to synthesize single phase at low temperature, but it is only suitable for the synthesis and performance testing of single phase. The solid-state reation method can be used to determine the phase relationship and phase properties, but it requires high temperature and long annealing time. The experimental results show that the sol–gel method is more suitable for the study of material properties. These results demonstrate the potential application of PrFeO 3 ceramics in magnetic materials and microwave absorbing field. [ABSTRACT FROM AUTHOR]

Perovskite LaCoO 3 has unique mixed ionic electronic and structural defects, which has high research value in microwave absorption field. LaCoO 3 precursor was prepared by sol-gel method, and LaCo 1− x Fe x O 3 (Fe-LCO, x = 0, 0.05, 0.1 and 0.15) with rhombic symmetric structure was successfully synthesized at 600 °C. By refinement of X-ray diffraction (XRD) (Rietveld analysis), it was found that Fe doping makes LaCoO 3 lattice constant and cell volume increase. As a dielectric loss microwave absorbing material, the electromagnetic attenuation of LaCoO 3 is mainly due to the conduction loss, while the interface and dipole polarization are secondary reasons. It finds that Fe doping can improve the wave absorption performance of LaCoO 3. The best absorbing performance was obtained when Fe content is x = 0.1, with the maximum reflection loss of − 38.99 dB at 10.8 GHz and the effective absorption bandwidth (RL<−10 dB) is 4.48 GHz, while the corresponding thickness was only 3 mm. In summary, LaCoO 3 has broad application prospects in X and Ku bands. • The study focus on rare earth perovskite can expand and popularized of their application in the field of absorption. • LaCo 1- x Fe x O 3 composites have tunable Impedance matching performance and high-performance microwave absorption by ions doping. • The influence of dielectric loss and magnetic loss on material is analyzed in detail. • Composites can still maintain the effective bandwidth at 4–5 GHz when the reflection loss reached − 30 dB and above. • This work develops the application potential of LaCoO 3 in the field of absorption other than photocatalytic field. [ABSTRACT FROM AUTHOR]

• The Bi 1–x Ca x FeO 3 (x = 0.0, 0.05, 0.10, 0.15) nanopowders were prepared by sol–gel method. • Study its performance changes by analyzing the unit cell parameters, bond length, bond angle and valence. • The possible mechanism of improving magnetic properties and microwave absorption properties via calcium doping bismuth ferrite was analyzed. Bi 1- x Ca x FeO 3 (x = 0.0, 0.05, 0.1, 0.15) nanopowders were prepared using the sol–gel self-diffusion combustion technology. The effects of structure and grain size changes during the substitution of Bi ions by Ca ions on the magnetic properties and wave absorbing properties of BCFO are discussed. Single-phase BiFeO 3 is a typical rhombohedral R 3 c structure. When the doping amount reaches 0.15, the Ca2+ induced BCFO structure gradually changes to the Pm -3 m phase. The small-sized alkaline earth metal ions Ca2+ (0.99 Å) can successfully replace the A-site Bi3+ ions in BiFeO 3. Ca2+ doping improves the BFO spin helical modulation structure and change the Fe-O-Fe bond angle, thus enhancing the magnetic properties of BCFO. When the doping amount of Ca2+ is 0.10 and the simulated thickness is 2 mm, the best absorption performance at 10.23 GHz is −36.91 dB, and its effective bandwidth reaches 2.81 GHz, which has a good broadband effect. This study provides a reliable candidate material for the synthesis of electromagnetically attenuating ceramic materials with excellent properties. [ABSTRACT FROM AUTHOR]

• Pure phase bismuth ferrite was prepared by sol–gel method. • Pr doping improves the magnetic properties and microwave absorption properties of bismuth ferrite. • Possible mechanisms of structure, magnetic and microwave absorption properties have been analyzed. Bi 1-x Pr x FeO 3 material with perovskite structure was prepared using organic tartaric acid-assisted sol–gel self-propagating combustion method to obtain high-efficiency microwave absorption materials. The influence of the introduction of Pr on dielectric properties and permeability was further studied. After 15% Pr introduced, the lowest reflection absorption loss reaches –32.34 dB, but the absorption bandwidth is only 2.25 GHz. When Pr is 5%, the lowest reflection absorption loss value of −27.31 dB is obtained, and the effective bandwidth which below −10 dB is 3.41 GHz. The structural changes in the process of Pr replacing Bi were analyzed to explore the properties of BPFO perovskite. The influence of strong interaction force, residual magnetization, and natural resonance of ceramic nanoparticles on microwave absorption performance was explored. This work supplies a reliable candidate material for making up electromagnetic attenuation ceramic materials with excellent properties. [ABSTRACT FROM AUTHOR]

• La 1– x Ca x FeO 3 microwave absorbing ferrite material was quickly synthesized by a simple sol-gel method. • The amount of Ca doping was crucial in determining the magnetic properties and electromagnetic parameters of LaFeO 3. • Conduction loss is the primary reason for microwave absorption. • The effective absorbing bandwidth of La 0.85 Ca 0.15 FeO 3 reaches 4.56 GHz and covering almost the entire Ku-band. Rare-earth orthoferrites (RFeO 3) is emerging as a type of microwave absorbing material (MAM) with development potential because of its excellent structural stability and moderate permittivity and amount of potential energy present. In this study, we employed a simple sol–gel technology to quickly synthesize La 1− x Ca x FeO 3 (x = 0, 0.05, 0.1, 0.15, and 0.2) ferrite MAMs. The FullProf X-ray diffraction refinement demonstrated that all samples formed single-phase LaFeO 3 (space group: Pnma). The amount of Ca doping was crucial in determining the particle size, magnetic properties, and electromagnetic parameters of LaFeO 3. As a dielectric loss type in MAM, conduction loss is the primary reason and interfacial as well as dipolar polarizations are the secondary reasons for the attenuation of the electromagnetic energy of the samples. The study discovered that an appropriate amount of Ca2+ doping improves LaFeO 3 microwave absorption. Therefore, the ideal microwave absorption is achieved in the La 1− x Ca x FeO 3 samples when Ca content x = 0.1 and 0.15, where the minimum reflection loss (RL min) of La 0.9 Ca 0.1 FeO 3 is − 39.90 dB at 6.72 GHz and the corresponding matching thickness is 4.0 mm. Although the RL min of La 0.85 Ca 0.15 FeO 3 is − 24.37 dB at 13.44 GHz, the effective absorption bandwidth is 4.56 GHz and the corresponding matching thickness is only 2.0 mm, which almost covers the entire Ku-band. This La 1− x Ca x FeO 3 is expected to be an industrially produced high-performance MAM owing to its excellent microwave absorption performance as well as its simple and rapid synthesis method. [ABSTRACT FROM AUTHOR]