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Soft magnetic composites (SMCs), consisting of micrometer-scale magnetic particles and insulating materials, are extensively used as microwave absorbing materials (MAMs) due to their advantages concerning the lightweight, low cost, manufacturing flexibility, and adjustable microwave properties. SMCs composed of rare earth-iron intermetallics for MAMs are rarely studied. Here we show that Sm substituted (Nd 1-x Sm x) 2 Fe 14 B/paraffin composites exhibit excellent microwave absorption properties with an average value of reflection loss (RL) being below −10 dB at 6–18 GHz. The Sm substitution for Nd not only increases the complex permeability by 23%, decreases the permittivity by 24%, but also improves the characteristic impedance matching, due to their easy magnetization directions (EMDs) change from easy c- axis to c- cone, then to ab- plane with Sm concentration increasing. Thus the microwave absorption properties of these composites are greatly enhanced. Besides, (Nd 0.7 Sm 0.3) 2 Fe 14 B/paraffin composite exhibits the strongest microwave absorption with an RL value of −43.8 dB and a small thickness of 1.5 mm at a frequency of 9.1 GHz, which can be one of the promising microwave absorbing materials. • The Sm substitution for Nd in Nd 2 Fe 14 B can tune the easy magnetization directions (EMD) of the compounds from easy c- axis to c- cone, then to ab- plane. • The Sm sbustitution leaves a vital effect on the electromagnetic parameters and effectively improves the characteristic impedance matching of the composites. • (Nd 0.7 Sm 0.3) 2 Fe 14 B/paraffin composite, with an EMD of c -cone, exhibits the strongest microwave absorption with a reflection loss (RL) value of −43.8 dB and a small thickness of 1.5 mm at a frequency of 9.1 GHz, which can be one of the promising microwave absorbing materials. [ABSTRACT FROM AUTHOR]

The carbon doped RMn 1.7 Cr 0.3 Si 2 C (R = Nd, Sm, Dy) compounds were prepared by arc melting and investigated using room temperature (RT) X-ray diffraction (XRD), neutron powder diffraction (NPD) and magnetic measurements. Carbon atoms were found to occupy the interstitial site (0, 0, 0.125) in a superstructure with the space group P 4/ mmm at room temperature. There exists a disordered substitution between the R atoms and corresponding Si dumbbells on the same layer perpendicular to c direction in the carbides. The Mn/Cr sublattice of the carbides exhibits ferromagnetic characteristics at room temperature despite of a very short intralayer interatomic distance ( d Mn-Mn  = 2.796 Å for R = Dy), which is far below the critical distance for a ferromagnetic ( d Mn-Mn >2.87 Å) ordering of Mn sublattice due to the strong hybridization between the interstitial C and the Mn/Cr atoms. Different phase transitions of the carbides have different response to the external magnetic field. These carbides provide the potential for further research on magneto-transport properties and magnetocaloric effect. Additionally, spin reorientation was observed in SmMn 1.7 Cr 0.3 Si 2 C owing to the competence of magnetocrystalline anisotropy between the Mn/Cr sublattice and the Sm sublattice. [ABSTRACT FROM AUTHOR]

In this work, we report the magnetic and microwave absorption properties of the Sm 1.5 Y 0.5 Fe 17-x Si x (0.0 ≤  x  ≤ 1.5) and their paraffin composites. It was found that the introduction of Si can remarkably tune the intrinsic magnetic properties of the Sm 1.5 Y 0.5 Fe 17-x Si x , making the Sm 1.5 Y 0.5 Fe 17-x Si x -paraffin composites excellent microwave absorption materials. The milled Sm 1.5 Y 0.5 Fe 17-x Si x powders have flake-like shape with length of 5 μm and thickness of 100 nm, consisting of sphere-like crystalline grains with size of about 11 nm. In the tested frequency region, the permeability μ′ of the composites shows, especially at higher frequency, little decrease after introducing the Si, while the permittivity ε′ decreases by about 40% with Si content increasing from x = 0.0 to x = 1.5, which is advantageous to improve the impedance match and enhance the performance of the microwave absorption. The peak frequency ( f p ) of the reflection loss ( RL ) peak with same composite thickness increases with increasing the Si content, in accordance with the variation of the calculated resonance frequency * f r  =  f ( M s , H aθ , H aφ , μ i ). Moreover, the qualified bandwidth (QB, RL  ≤ −10 dB) also increases remarkably with increasing the Si content due to a better impedance match. An extraordinary dielectric microwave absorption peak was also found in the composites, which can further increase the QB in some degree. A maximum RL of −55.1 dB and a QB of 3.7 GHz (12.7–16.4 GHz) are obtained for the Sm 1.5 Y 0.5 Fe 15.5 Si 1.5 -paraffine composite, suppressing many reported microwave absorbing materials. [ABSTRACT FROM AUTHOR]

Using Fe nanoparticles as raw material, we manufactured Fe16N2 nanoparticles by hydrogen reduction and ammonia nitriding process. X-ray diffractometer (XRD) and Mössbauer spectroscopy analyses show that the prepared nanoparticles are composed of Fe16N2 and $\alpha $ -Fe. The proportion of the Fe16N2 phase could reach 75%, and the saturation magnetization of the nanoparticles reaches 197 emu/g. The Fe16N2 nanoparticles are mixed with paraffin, and the microwave absorption properties of the composites are measured. The reflection loss (RL) of the Fe16N2/paraffin composite can reach −18.3 dB at 4.8 GHz, with a thickness of 2.2 mm. The ratios of the magnetic loss and dielectric loss are 40% and 59%, respectively. Only 1% (100%–40%–59%) of the incident microwave energy is reflected, which shows Fe16N2/paraffin composite is a potential candidate for microwave absorbing materials. [ABSTRACT FROM AUTHOR]

In this study alloys with stoichiometry of R 2 Fe 17 and R 10 Fe 90-x Si x (x = 0, 10, 15, 20) (R = Y, Ce, Pr, Nd, Sm, Gd, Tb, Dy, Ho, and Er) have been prepared. Structural transition from the ordered rhombohedral (OR) Th 2 Zn 17 -type structure and the ordered hexagonal (OH) Th 2 Ni 17 -type structure to their disordered structures (DR and DH) has been observed according to the XRD patterns. The lattice parameters were obtained by Rietveld analysis and based on the changing characteristic of the parameters, these samples are divided into two categories: alloys with R = Ce, Pr, Nd, Sm and alloys with R = Y, Gd, Td, Dy, Ho, Er. The lattice parameters of the two categories show different changing behavior. For example, from R 2 Fe 17 to R 10 Fe 90 , the lattice parameters a decrease and c increase for the latter category, whereas for the former the lattice parameters a and c nearly have no change. In addition, increase of the ratio c/a has been found with increasing Fe or Si content, indicating the introduction of extra Fe dumbbells into the crystal cells, forming the DR or DH intermetallic compounds of R 2-y (Fe,Si) 17+2y . The obtained samples with disordered structure have shown better stability than the TbCu 7 -type metastable materials and the higher Fe concentration gives promise of higher magnetization. The mixed-rare-earth effect has also been studied in the (Ce,R) 10 Fe 75 Si 15 alloys and transition between the DR and DH structures has been realized by changing the mixed R-type or adjusting the Ce/R ratio. As for the magnetic properties, the Curie temperatures are increased remarkably by the introduction of Si and the saturation magnetizations of R 10 Fe 90-x Si x are often higher than that of the R 2 Fe 17 alloys. [ABSTRACT FROM AUTHOR]

The preferential site substitution of the Fe by Si, Ga and Zr in the Y(Fe,M) 9.2 and Y(Fe,M) 9.2 C compounds, and the doping effects on the magnetic properties have been studied by the first-principles calculations. It is found that the doping of the Si or Zr can improve the thermodynamic stability of the 1:9 phase, while the substitution of the Fe by Ga makes it unstable. Si atom tends to enter the 3g crystal site and Zr prefers to occupy the 2e site when Y(Fe,M) 9.2 and their carbides are synthesized. Although the substitution of the Fe by Si and Zr will reduce the total magnetic moments of the YFe 9.2 and their carbides, the volumetric and the d-band narrowing effects caused by the doping can still modify the electron density distributions of the Fe near the Fermi level, improving the magnetic ordering temperature of the non-carbonated compound YFe 9.2 . The calculated magnetic ordering temperatures of Y(Fe,M) 9.2 C decrease with the increasing content of the doping elements M due to the stronger hybridization of the d bands in the carbides. For the rare-earth(RE) iron based intermetallics REFe 9.2 with the TbCu 7 -type structure, it is suggested that Zr is able to stabilize the phase and enhance the magnetic ordering temperature, indicating the possible further application in the field of permanent magnets, which has not been reported before. [ABSTRACT FROM AUTHOR]

The compromise between intensity and resolution is the core issue for the powder neutron diffraction techniques. An investigation of the optimum configuration of a neutron instrument is necessary to meet the requirement for both the intensity and resolution before the final construction. In this paper, the performance of the high-intensity powder neutron diffractometer (HIPD) at China Advanced Research Reactor has been studied by Monte Carlo simulation and convolution methods. The virtual detector Monitor-nD with super fine recording elements was used to record the diffraction patterns of the simulated HIPD. In order to introduce the spatial resolution effect of the detector in the diffraction pattern, the convolution method was adopted. The diffraction peaks from the diffraction patterns were then used to calculate the minimum interplanar spacing difference $\Delta d$ that the HIPD can distinguish. It is obtained that the minimum resolution of the HIPD is $2.08 \times 10^{-3}$ ( $\Delta d/d$ ) for the current design. The resolution of the HIPD calculated above is consistent with the resolution actually measured according to the Ni sample diffraction experiment. This indicates that the above simulation method has high reliability. Finally, a movable $20^{\prime }$ Soller collimator and sample cans with 3 and 6 mm diameters are recommended to be used to optimize the ND experiment. After installing the $20^{\prime }$ Soller collimator, the minimum resolution can be $1.88 \times 10^{-3}$ ( $\Delta d/d$ ). The diffraction intensity of the 6-mm-diameter sample will be almost 3 times higher than that of the 3-mm-diameter sample. [ABSTRACT FROM AUTHOR]

The site preference of N atom for R2Fe14BNx (R= Pr, Nd) and the interstitial nitrogen effect on the magnetic properties have been studied by the first-principles method. It was found that the nitrogen is more likely to occupy the 4e site for Pr2Fe14BNx compound, while 4f site for Nd2Fe14BNx. When N atoms entering some specific crystal sites (such as 2a and 4f), the total magnetic moments of these compounds are not reduced, but slightly increased. Although the doping of N may reduce the total magnetic moments of some R2Fe14B compounds in the cases of optimal occupancy, the volumetric effect caused by N doping can still change the electron density distributions of Fe near the Fermi level, improving the magnetic ordering temperature of such compounds. [ABSTRACT FROM AUTHOR]

• The loss of electromagnetic energy in absorbers can be strictly classified into only two types: magnetic and dielectric loss. • The ratios of the two losses with respect to incident microwave intensity can be accurately evaluated. • The dependence of reflection loss on absorber thickness can be well explained with this method. • The proper coordination between dielectric loss and magnetic loss can enhance absorption and widen bandwidth With the increasing demand for high-frequency electronic devices in wide applications, microwave absorption materials of GHz have attracted extensive attention. In this paper, a new method is provided for quantitative analysis of energy dissipation in the microwave absorption materials. The loss of electromagnetic energy in absorbers can be strictly classified into only two types: magnetic and dielectric loss, and the ratios of the two losses with respect to incident microwave intensity can be accurately evaluated. Moreover, different materials were analyzed with the new method. Notably, both magnetic loss and dielectric loss were found to be important in Sm 1.5 Y 0.5 Fe 16.5 Si 0.5 /paraffin composite, which can consume up to 88% and 78% of the incident microwave energy under certain conditions, respectively. The fascinating combination of the magnetic loss and the dielectric loss well explained the peculiar two or three peaks in the reflection loss (RL) curves. This analysis method can be a powerful supplement for current theories to explain the microwave absorption property of materials, thus providing a new perspective for the design of high-performance absorption materials. [ABSTRACT FROM AUTHOR]

Electron beam exposure (EBE) has been implemented to synthesize Nd-Ce-Fe-B-based nanostructured magnetic materials with controllable morphology and tunable magnetic properties. Greatly reduced crystallization time of amorphous ribbons to about 0.1 s is achieved, which is by far the most effective method due to the effect of an extremely high heating rate. The extremely high heating rate gives rise to a huge temperature gradient in the annealed ribbons leading to platelet-like grains due to the oriented nucleation and growth under quasi-static thermal stress. It was found that the size and shape of the grains can be finely controlled by the beam current intensity. A coercivity as high as 12.9 kOe, and a maximum energy product as high as 15.4 MGOe are obtained in pure (Nd 0.8 Ce 0.2) 12.2 Fe 81.6 B 6.2 ribbons exposed to a beam current of 0.4 mA, without doping any other heavy rare earth or coercivity enhancement elements. A single magnetic domain covering many grains was observed by the Lorentz transmission microscope (LTEM). It was found that the improvement of the magnetic performance has a deep correlation with the achievement of a single domain structure. Our results demonstrate that EBE shows great advantages in preparing the high coercivity Ce-substituted Nd 2 Fe 14 B magnets due to higher efficiency and higher controllability than conventional furnace annealing. Image 1 [ABSTRACT FROM AUTHOR]