The low temperature magnetisation jumps have been observed and studied in nano- and microstructured alloys based on the Nd2Fe14B phase. “Barkhausen-like” jumps can be explained in terms of the two-stage trigger/propagation model. Magnetisation jumps cause the internal parts of the sample to heat up to a critical temperature. This is a temperature at which no magnetisation jumps are observed on the remagnetisation curve. Magnetisation jumps can be activated in some samples by their local heating with electric current pulses. When magnetic alloy powder was placed in a nonmagnetic matrix, increasing the average distance between ferromagnetic particles, the number of magnetisation jumps decreased. The remagnetisation mechanism in alloys changes from a two-stage trigger/propagation process, which occurs in the nanostructured samples, to a thermal activation process, which occurs in the microstructured samples. The increase in grain size leads to a decrease in the critical temperature value at which magnetisation jumps can be observed.

This research focuses on the phase transformation of lead hexagonal ferrite (PbFe12O19) to cubic spinel ferrite (CoFe2O4) induced by increasing the substitution ratio of Co2+ ions. Lead cobalt ferrite nanoparticles with varying Co2+ content (Pb1-xCoxFe12O19, where x = 0.0, 0.25, 0.50, 0.75, and 1.0) were synthesized using the sol-gel auto-combustion method. The structural properties of these nanoparticles were investigated through X-ray diffraction (XRD), Fourier transform infrared spectroscopy (FTIR), and high-resolution transmission electron microscopy (HRTEM). Magnetic characteristics were determined using vibration sample magnetometry (VSM). XRD analysis confirmed the formation of PbFe12O19 in a hexagonal phase with the P63/mmc space group. As the Co2+ ion concentration increased, a complete transformation to a cubic spinel structure with the Fd3m space group occurred. HRTEM observations revealed a change in the polycrystalline structure from hexagonal to cubic as the cobalt content increased at the expense of lead. Selected area electron diffraction (SAED) patterns supported the polycrystalline nature of all samples. Magnetic measurements indicated soft ferrite behavior with negligible hysteresis for all nanoparticles. The saturation magnetization (Ms) improved from 1.782 emu/g to 69.676 emu/g up to x = 1.0 of Co2+ ion. Remanence (Mr) increased from 0.269 to 34.726 emu/g as Co2+ ion concentration rose from 0.0 to 1.0. The squareness ratio (Mr/Ms) increased from 0.151 to 0.498 as the Co2+ ion concentration rose to 1.0. The tunable magnetic properties of these lead cobalt ferrite nanoparticles offer promising applications such as microwave devices, magnetic recording media, and electromagnetic wave absorbers.

The influence of mercuric oxide (HgO) on structural, physical, optical, and radiation shielding capacities of newly developed glasses with nominal compositions (55-x)B2O3 center dot 10SrF(2)center dot 25PbO center dot 10Na(2)O center dot xHgO: x = 0, 2, 4, 6, and 8 mol% has been investigated. Hg-glasses were synthesized by the traditional melt quenching technique and coded as Hg0, Hg2, Hg4, Hg6, and Hg8, respectively. The amorphous nature of Hg-glasses was confirmed via XRD measurements. Density of the prepared glasses was measured via Archimedes' method and it was increased from 4.59 g/cm(3) for Hg0 sample to 5.20 g/cm(3) for Hg8 sample. The values of optical band gap (Eg) were reduced with the insertion of HgO in Hg-glass network. The direct (Eg) was changed from 3.52 to 3.21 eV, while the indirect one change from 2.47 to 2.14 eV. Urbach's energy (Eu) was varied from 0.737 to 1.544 eV and refractive index was improved from 2.197 to 4.077 at wavelength lambda=500 nm. The average oscillator strength (S-o) of Hg-glasses was changed from 2.885x10(-5) (nm)(2) to 11.078 x 10(-5) (nm)(2). The Hg8 glass possessed the maximum values of mass attenuation coefficient (MAC)Phy-X/PSD among all Hg-glasses. The values of (MAC)Phy-X/PSD at (0.015 MeV, 15 MeV) were (0.037, 53.675), (0.38, 58.123), (0.039, 62.352), (0.40, 66.376), and (0.40, 70.210) cm(2)/g for Hg0, Hg2, Hg4, Hg6, and Hg8 glasses, respectively. The variation of the effective atomic number (Zeff)Phy-X/PSD of the prepared Hg-glasses has a similar trend of (MAC)Phy-X/PSD. The half value layer (HVL)Phy-X/ PSD for various samples followed the trend; ((HVL)Phy-X/PSD)Hg0 > ((HVL)Phy-X/PSD)Hg2 > ((HVL)Phy-X/PSD)Hg4 > ((HVL)Phy-X/PSD)Hg6 > ((HVL)Phy-X/PSD)Hg8. However, the reduction of (HVL)Phy-X/PSD with increasing HgO concentration in the glassy system increase its ability to shield against the incident photons. The prepared Hg-glasses with improved physical and optical properties can be used in various optical applications and are superior as radiation shielding materials than seven kinds of concrete OC, HSC, ILC, BMC, IC, SSC, SMC, and RS-253-G18 glasses.

ABSTRACT. Linear, nonlinear optical properties, photon buildup factors, and neutron shielding capability of glasses with chemical composition (65-x)B2O3-10Sb2O3-25Li2O-xBi2O3, where x = 0 (BSLB0) – 20 (BSLB20) mol% with steps of 4 mol% were examined. Molar refractivity (Rmolar) and molar polarizability (αmolar) were increased as Bi2O3 content mol% increase in the examined BSLB-glasses. The values of metallization criterion (Mcriterion) confirmed that the BSLB-glasses were non-metallic materials. The static (εstatic) and optical (εoptical) dielectric constants having the same trend of the refractive index (noptical). Values of optical electronegativity (χ*) were reduced from 0.825 for BSLB0 (Bi2O3 = 0 mol%) glasses to 0.758 for BSLB20 (Bi2O3 = 20 mol%) glasses. The linear electric/dielectric susceptibility (χ(1)) increased from 0.370 to 0.397. The nonlinear optical susceptibility (χ3) and nonlinear refractive index n2optical were enhanced by increasing Bi2O3 content in the BSLB-glasses. The BSLB20 glasses presented the least exposure and energy absorption build-up factors (EBF and EABF) at all considered thickness. BSLB20 sample achieved the best fast neutron removal cross section ( ) shield among all glasses. The total stopping powers (TSP) follows the trend (TSP)BSLB0 < (TSP)BSLB4 < (TSP)BSLB8 < (TSP)BSLB12 < (TSP)BSLB16 < (TSP)BSLB20. The electron absorbing and hence shielding capacity of the BSLB-glasses improves as their Bi2O3 content increase. KEY WORDS: Antimony lithium-borate glasses, Optical properties, Buildup factors, Neutron shielding Bull. Chem. Soc. Ethiop. 2022, 36(4), 949-962. DOI: https://dx.doi.org/10.4314/bcse.v36i4.19

Results of theoretical and experimental studies of the magnetic characteristics of the electromagnetic system of a prototype of the Kibble balance are presented. Based on the prototype, the technical solutions that can be used to create a primary standard of a kilogram from fundamental physical constants are examined. The finite element method for calculating the geometrical shapes and sizes of the components of the system is used, for the purpose of deriving the constant value of the conversion coefficient of BL along the system axis. The electromagnetic system is designed and manufactured from the results of the calculations. The equipment, designed for measurement of the topology of the magnetic field in the gap of the magnetic system, was developed based on the National Primary Standard of units of power of magnetic losses and the magnetic flux density of a permanent magnetic field over the range from 0.1 to 2.5 T and magnetic flux over the range from 1·10 –5 to 3·10 –2 Wb, GET 198-2017. Experimental studies of the distribution of magnetic flux density in the gap of an electromagnetic system and outside of this system were conducted. The power characteristics of the electromagnetic system were determined. The effect of an electric current flowing past, on a coil in weighting mode, on the change of magnetic linkage of the coil is recorded. The condition of a coil in weighting mode in which the conversion coefficient of the magnetic system does not depend on the electric current intensity in the coil was determined.

A novel boro-bariofluoride/sodium/calcium/nickel glasses with chemical compositions (40-x)B2O3·30BaF2·15CaO·15Na2O·xNiO, where x = 0.0 (Ni0.0)–1.5 (Ni1.5) in steps of 0.3 mol% were prepared using the conventional melt quenching technique. Physical and optical features as well as ionizing radiation resistance capacities of the synthesized glass have been examined using various characterization techniques. Radiation shielding abilities have been examined via Phy-X/PSD software. Amorphous state of the Ni-glasses was confirmed by XRD data. Addition of NiO increased the density of glasses from 3.53 to 3.80 g/cm3. The direct optical band gap ( $$E_{Direct}^{Optical}$$ ) was reduced from 3.58 to 3.33 eV, while the indirect ( $$E_{Indirect}^{Optical}$$ ) one was reduced from 3.08 to 2.84 eV. Urbach’s edge (EU) was enhanced from 0.4197 to 0.5009 eV as NiO content increased from 0.0 to 1.5 mol%. At a certain wavelength λ = 500 nm, the values of refractive index (n) increased from 1.84 to 2.56. In the photon energy range (0.15–15 MeV), the mass attenuation coefficient (MAC) results had the following trend: (MAC)Ni0.0 < (MAC)Ni0.3 < (MAC)Ni0.6 < (MAC)Ni0.9 < (MAC)Ni1.2 < (MAC)Ni1.5. The linear attenuation coefficient (LAC) showed a similar trend of the MAC. In the same photon energy range, the half value layer (HVL) of Ni-glasses was reduced as NiO level increased, i.e. (HVL)Ni0.0 > (HVL)Ni0.3 > (HVL)Ni0.6 > (HVL)Ni0.9 > (HVL)Ni1.2 > (HVL)Ni1.5. The effective atomic number (Zeff) of the prepared Ni-glasses has the same trend of MAC and LAC shielding parameters. The Ni-glasses can be applied in optical areas and considered as superior light glasses for radiation shielding applications.

Role of Bi2O3 on the structure, physical, linear optical characteristics, and radiation protection capacity of antimony borate–lithium with the form (65 − x)B2O3 + 10Sb2O3 + 25Li2O + xBi2O3 x = 0 (BSLB0), 4 (BSLB4), 8 (BSLB8), 12 (BSLB12), 16 (BSLB16), 20 (BSLB20) mol% glass systems was examined. The density was increased from 2.7125 to 3.9454 g cm−3 for BSLB0 and BSLB20 glass samples, respectively. The indirect optical bandgap decreases from 2.63 to 2.45 eV, while the direct optical bandgap decreases from 3.06 to 2.89 eV. Therefore, values of the refractive index (n) were varied from 2.50 to 2.56. Both optical (σoptical) and electrical (σelectrical) conductivities were enhanced with increasing Bi2O3 content in the investigated glasses. The observed trend of linear attenuation coefficient (LAC) values throughout the energy spectrum was followed the sequence: (LAC)BSLB20 > (LAC)BSLB16 > (LAC)BSLB12 > (LAC)BSLB8 > (LAC)BSLB4 > (LAC)BSLB0 with values in the range of 0.052–14.469, 0.062–28.291, 0.070–42.738, 0.082–61.708, 0.091–79.616, and 0.104–102.154 cm−1 for BSLB0–BSLB20 glasses, respectively. At each energy within the energy spectrum, the mean free path (MFP) and half value layer (HVL) of the BSLB-glasses were decreased in the order of increasing Bi2O3 content in the glasses. The effective atomic number (Zeff) value varies from 6.53 to 15.12, 6.76–16.32, 7.02–17.37, 7.29–18.36, 7.58–19.29, and 7.89–20.16 for BSLB0–BSLB20 glasses, respectively. Therefore, BSLB-glasses possess superior photon protection capacity than ordinary (OC) and barite (BC) concretes for photons.

In this paper the results of magnetic properties study for a series samples of R(Co0.88Fe0.12)(2) type intermetallic compounds with a heavy rare-earth elements (R = Gd, Tb, Dy, Ho, Er) are presented. Such materials having a plateau-like temperature dependences of magnetic entropy change in the temperature range lower Curie point are considered as a promising functional materials for magnetic refrigerators. Their phase composition was controlled by X-ray diffraction analysis with a help of Bruker D8 Advance diffractometer. Magnetic field magnetization dependences - M(H) were measured using a SQUID magnetometer (MPMS-XL-7, Quantum Design) within the temperature range of 5 - 600 K in magnetic fields up to 5600 kA/m. The crystal lattice parameter - a, Curie temperature - T-C, coercivity - H-c and residual magnetization - M-r values are analyzed as a functions of R-element atomic number. For compounds with Tb, Dy, Ho and Er the second picks on the high field susceptibility temperature dependences - chi(hf)(T) were found in the temperature range lower their T-C.

Rapidly increasing demand for high-energy permanent magnets and volatility of the rear-earth market encourage a search of hard magnetic materials that can compete with those based on the Nd2Fe14B phase. Sm-Fe compounds with the ThMn12-type crystal structure are considered as promising candidates for it. However, their synthesis and achievement of theoretically predicted magnetic properties are still challenging tasks that have not been solved yet. This paper addresses this problem. Its aim was to synthesize and to study magnetic properties of the (Sm0.9Zr0.1)Fe11Ti compound with ThMn12-type structure. Initially amorphous alloy was obtained by melt spinning and its subsequent heat treatments were performed. Structural and phase transformations of the (Sm0.9Zr0.1)Fe11Ti alloy with annealing temperatures were studied along with magnetic properties. For the optimally annealed alloy features of magnetization reversal were discussed and temperature dependences of coercivity and maximum energy product were obtained.

In this paper the results of specific magnetization and magnetocaloric effect (MCE) measurements for Gd(Co1-xFex)2 system upon the Co substitution by Fe for the x = 0 ÷ 0.60 range are presented. Phase composition was controlled by X-ray diffraction analysis. MCE has been studied within the temperature range of 300-850 K in magnetic fields up to 17 kOe by the magnetic entropy change calculation (ΔSm). It was found that in contrast to the previously studied R(Co-Fe)2 compounds where R = Dy, Ho, Er, an ordinary symmetrical peak of ΔSm(T) in the vicinity of TC is observed for presented samples. Additionally, the MCE comparison of Gd(Co0.88Fe0.12)2 with that for the isostructural Gd(Ni0.88Fe0.12)2 compound having a plateau-like ΔSm temperature dependence is given. The obtained results are discussed.

The results of thermomagnetic, metallographic and X-ray diffraction phase analysis as well as the measurements of specific magnetization (σs), Curie temperature (TC), coercive force (HC) of (Sm,M)(Fe,M)12-xTix alloys samples, where M = Zr, Hf, Co with the ThMn12 main phase structure (1-12) are presented. The effect of the annealing temperature and the cooling rate on the formation of 1-12 phase and its magnetic properties, including the effect of high-energy milling on the magnetic hysteresis properties and alloys structure are described. It was found that the highest magnetic characteristics such as σs = 112.6 emu/g and TC = 600 ºC are attained in the (Sm0.8Zr0.2)(Fe0.75Co0.25)11.4Ti0.6 alloy after its annealing at 1050 °C and rapid cooling. It is noted that a mechanical milling of the alloy leads to 1-12 phase amorphization which accompanied by an α-(Fe) or metal Co phases impurity formation.

Neutron irradiation allows the materials to transform to a state, in which the properties of material become different from an initial state. This paper presents the results of neutron irradiation of several magnetic materials including intermetallic compounds Nd2Fe14B and Er2Fe14B, multiferroics BiFe0.95Mn0.05O3 and Bi(0.85)La(0.1)5FeO(3), oxides LiMn2O4 and Li0.9FePO4. The fast neutrons (E-eff > 0.1 MeV) have been used in a fluence range from 1 x 10(18) n/cm(2) to 2 x 10(20) n/cm(2) at 340 K Er2Fe14B alloy becomes amorphous under irradiation, that results in the reduction of Curie temperature to about 200 K. Irradiation destroys charge ordering in LiMn2O4 leading to the transformation from an incommensurate antiferromagnetic to a commensurate ferrimagnetic structure. Neutron irradiation of BiFe0.95Mn0.05O3 oxide is accompanied by decreasing the amount of impurity phases. On the contrary, in Bi0.85La0.15FeO3 fast neutrons result in the appearance of impurity phases. Neutron irradiation distinctly affects the lattice parameters of Li0.9FePO4 compound even with the relatively low fluence.

Magnetic hysteresis properties of nanostructured industrially manufactured Nd-Fe-B and Pr-Fe-B alloys on the base of a tetragonal Nd2Fe14B (2-14-1) hard magnetic phase (MQP-B, MQP-B+ and MQP-16-7 brands) have been investigated at 4.2 K in magnetic fields up to 58 T. The chemical composition of the alloys given in the certificates was defined more precisely. The grain sizes of the main 2-14-1 phase were determined. The average grain size is much smaller than a critical single domain diameter. Coercivity, remanence magnetization, saturation magnetization and maximal magnetic energy product were determined at 4.2 K and compared with those obtained at room temperature.

The crystal structure, the temperature and field dependences of the magnetization M and of the magnetic contribution into the entropy Δ S m , the temperature dependences of the high-field susceptibility χ and the heat capacity C p of specimens of polycrystal R (Co 1 – x Fe x ) 2 compounds, where R is Gd, Dy, Ho or Er, are studied. The width of the Δ S m peak at half-height of its maximum (Δ T FWHM ) is estimated. The dependences of Δ T FWHM and of the temperature behavior of Δ S m of the specimens on the magnetic field, on the iron content ( x ) and on the atomic number of the element R are determined. The causes of the broadening of the Δ S m ( T ) peak upon substitution of cobalt with iron in the R (Co 1 – x Fe x ) 2 compounds are considered.

A study is made of the effects of various factors such as time (7 years), temperature, high magnetic field up to 580 kOe and heat treatment (HT) on the morphological structure and magnetic hysteresis properties of a high-coercive nanocrystalline (Nd0.55Ho0.45)2.7(Fe0.8Co0.2)14B1.2 alloy with a low temperature coefficient of remanence. We find a rather weak time effect on (Nd0.55Ho0.45)2.7(Fe0.8Co0.2)14B1.2. After 7 years, the loss in the maximum magnetic energy product (BH)max is no more than 5%. Annealing of the sample at 250 °C for 30 min decreases the amount of amorphous phase from 7.2 to 1.7%, while the grains’ size of the 2-14-1 phase increases from 83 to 109 nm. For the HT alloy, a magnetization jump is observed at H ~500 kOe. It can be attributed to the first-order magnetization process or a spin-flip magnetic transition. Rectangularity of the hysteresis loop degrades after annealing. In case of the short-time heat treatment, losses in (BH)max are ~10%.

In this paper the results of specific magnetization (M), heat capacity (C-p) and magnetocaloric effect (MCE) measurements for Gd(Ni1-xFex)(2) system over the Ni substitution by Fe range of x = 0 divided by 0.16 are presented. Phase composition was controlled by X-ray diffraction analysis. Heat capacity was measured in the temperature range 77 : 320 K. MCE has been studied within the temperature range 5 : 400 K in magnetic fields up to 70 kOe by the entropy magnetic contribution change calculation (Delta S-m) and by direct Delta T-ad measurements at the adiabatic conditions for external magnetic field change Delta H = +/- 17.5 kOe. It was found that the Fe concentration increase causes both the C-p maxima disappearing at Curie temperature point and emergence of magnetic contribution to C-p in a wide temperature range below this point. Moreover, in compounds with iron, a plateau-like temperature dependence of the MCE was observed for both magnetic entropy change (Delta S-m) and direct Delta T-ad data which are independent on Fe concentration. The possible reasons of such behavior are discussed. (C) 2017 Elsevier B.V. All rights reserved.

In this work the results of measurements of heat capacity (CP) and magnetocaloric effect (MCE) in Er(Co1-хFeх)2 system in the concentration range 0.07 ≤ x ≤ 0.80 are presented. Phase composition was controlled by X-ray difraction analysis. Heat capacity was measured in the temperature range 77-320 K. MCE has been studied within the temperature range 5-670 K in magnetic fields up to 70 kOe. It was found that Fe concentration increase caused the table-like (plateau) MCE temperature dependence for both magnetic entropy change date and direct ∆T-effect measurements independently on Fe concentration. The possible reasons of such behavior are discussed.

A study is made of the effect of multistage treatment on the magnetic hysteresis properties at room temperature and below of high coercive (Nd0.55Ho0.45)2.7(Fe0.8Co0.2)14B1.2 alloy including melt spinning (MS), severe plastic deformation (SPD) and heat treatment (HT). It is shown that SPD and HT of MS samples improves the rectangularity of the second quadrant part of the hysteresis loop resulting in a more than 25% increase of the maximal magnetic energy product as compared to ordinary MS processing. The observed changes in the magnetic properties of the samples are discussed and modelled within the framework of Stoner-Wohlfarth theory of magnetization reversal processes in uniaxial ferromagnets.

In this work the results of measurements of high field susceptibility, paraprocess susceptibility and thermal properties of R(Co1−хFeх)2 intermetallic compounds (R=Dy, Ho, Er and x=(0−0.16)) are presented (heat capacity and magnetocaloric effect (MCE)). A magnetic structure of the Ho(Co0.88Fe0.12)2 at 293K and 78K was studied by neutron powder diffraction. Some peculiarities of a high-field susceptibility were revealed at low temperatures and around the Curie point (TC). In temperature range lower than TC by (100–150)K, magnetic contributions to a zero-field heat capacity were found. Studying MCE in wide temperatures range, the large change of the entropy magnetic contribution (∆S) was observed which correlates with ∆T phenomenon. In particular, for the Er(Co0.84Fe0.16)2 compound the ∆S value at low temperatures is six times higher than that at Curie point. The possible reasons of such behavior were discussed.