INFLUENCE OF THE REMNANT MAGNETIZATION OF THE CURRENT TRANSFORMER CORES UPON THE COMPLIANCE OF THEIR TECHNICAL CHARACTERISTICS WITH THE REQUIREMENTS FOR MICROPROCESSOR TYPE PROTECTIVE RELAYS

Work objective is finding rational technical and economic solutions for examining current transformers for techspecs compliance satisfying the requirements of reinstalled microprocessor type protective relays and automation devices manufactured by NP EKRA LLC, taking into account DC component. Research methods: analytical methods for calculating the time of remnant magnetization in the core of a current transformer. Research results and novelty: it is understood that the saturation time of current transformers of the basic and backup protections, according to the results of the analytical method, was more than 25 ms, and for current transformers of differential bus bar protection was more than 5 ms. The obtained saturation time values for all types of current transformers built into oil circuit-breaker bushings (HV line) of 110 kV and bus bar coupling connector (BCC) of 110 kV (main protection, backup protection, differential bus protection), both in the absence and in the presence of remanent induction magnetic in CT cores with three-phase and single-phase short circuits, satisfy completely technical requirements either of microprocessor type protective relays or CT differential bus bar protection. Conclusion: built into CT BCC circuit-breaker bushings of 110 kV and oil circuit-breaker bushings (HV line) of 110 kV Foundry substations do not necessitate a mandatory replacement in case of non-complex redesign of microprocessor type protective relays and automation devices. When replacing oil circuit breakers with gas-insulated ones, it is recommended to use CT with similar characteristics.

Synthesis and Characterization of Ni-Ti Partially Substituted Hexaferrites for High-Density Magnetic Recording Applications

M-type hexaferrite (AFe12O19; A = Ba2+, Sr2+, Pb2+) is an important magnetic oxide exhibiting magnetic properties suitable for a wide range of technological and industrial applications. The magnetic properties of M-type hexaferrite can be tuned for a specific application by adopting suitable synthesis routes and/or using special cationic substitutions for either Fe3+ or A2+ cations. In particular, coercive fields in the range of ~ 1 – 3 kOe and remnant magnetization > 20 emu/g are required for data storage media in high-density magnetic recording applications. Partial substitution of Fe3+ ions by Co2+-Ti4+ ions in BaM (BaFe12O19) or SrM (SrFe12O19) hexaferrite was long recognized as an effective procedure for reducing the coercivity to values appropriate for high- density magnetic recording, without decreasing the remnant magnetization appreciably. Also, the effects of other substitutions were extensively investigated. However, the M-type hexaferrite with Ni2+-Ti4+ substitution was generally ignored, especially when compared with the extensively investigated Co2+-Ti4+ substituted system. This work was motivated by the potential of Ni-Ti substitution to reduce the coercivity of SrM hexaferrite to appropriate levels and maintain the remnant magnetization high enough for high-density magnetic recording applications. A set of SrFe12–2xNixTixO19 hexaferrites was prepared by mixing and ball milling stoichiometric ratios of high-purity starting powders, pelletizing in the form of 4 cm-diameter disks and sintering in air at 1100 C for 2 hours. Rietveld analysis of the X-ray diffraction (XRD) patterns (Fig. 1) revealed that all samples examined in this work (0.0 ≤ x ≤ 0.8) consisted of a single SrFe12O19 (SrM) hexaferrite phase (standard pattern ICDD file: 00-033-1340), with no secondary phases. The refined lattice parameters decreased slightly (≤ 0.1%), but monotonically with the increase of x. Further, the crystallite size in all samples fluctuated in the range of 60 – 70 nm, without any systematic behavior. M-type hexaferrite (AFe12O19; A = Ba2+, Sr2+, Pb2+) is an important magnetic oxide exhibiting magnetic properties suitable for a wide range of technological and industrial applications. The magnetic properties of M-type hexaferrite can be tuned for a specific application by adopting suitable synthesis routes and/or using special cationic substitutions for either Fe3+ or A2+ cations. In particular, coercive fields in the range of ~ 1 – 3 kOe and remnant magnetization > 20 emu/g are required for data storage media in high-density magnetic recording applications. Partial substitution of Fe3+ ions by Co2+-Ti4+ ions in BaM (BaFe12O19) or SrM (SrFe12O19) hexaferrite was long recognized as an effective procedure for reducing the coercivity to values appropriate for high- density magnetic recording, without decreasing the remnant magnetization appreciably. Also, the effects of other substitutions were extensively investigated. However, the M-type hexaferrite with Ni2+-Ti4+ substitution was generally ignored, especially when compared with the extensively investigated Co2+-Ti4+ substituted system. This work was motivated by the potential of Ni-Ti substitution to reduce the coercivity of SrM hexaferrite to appropriate levels and maintain the remnant magnetization high enough for high-density magnetic recording applications. A set of SrFe12–2xNixTixO19 hexaferrites was prepared by mixing and ball milling stoichiometric ratios of high-purity starting powders, pelletizing in the form of 4 cm-diameter disks and sintering in air at 1100 C for 2 hours. Rietveld analysis of the X-ray diffraction (XRD) patterns (Fig. 1) revealed that all samples examined in this work (0.0 ≤ x ≤ 0.8) consisted of a single SrFe12O19 (SrM) hexaferrite phase (standard pattern ICDD file: 00-033-1340), with no secondary phases. The refined lattice parameters decreased slightly (≤ 0.1%), but monotonically with the increase of x. Further, the crystallite size in all samples fluctuated in the range of 60 – 70 nm, without any systematic behavior. Analysis of the magnetic data revealed a slow decrease of the saturation magnetization (from 67.6 emu/g at x = 0.0 to 65.3 emu/g at x = 0.8) and remnant magnetization (from 38.8 emu/g at x = 0.0 to 30.4 emu/g at x = 0.8) with the increase of x. These values, however, remained relatively high for practical applications. The coercivity, on the other hand, exhibited a significant reduction with the increase of x (from 4386 Oe at x = 0.0 to 1150 Oe at x = 0.8)). The remnant magnetization of ~ 30 – 36 emu/g and intermediate coercivity of ~ 1.2 – 3 kOe for the samples with 0.4 ≤ x ≤ 0.8 render these materials suitable for high-density magnetic recording media. The effectiveness of Ni-Ti substitution in reducing the coercivity without appreciably influencing the remnant magnetization is comparable with the reported effectiveness of Co-Ti substitution, thus providing a cheaper alternative by avoiding the use of Co. The switching field distribution (SFD) revealed a progressive reduction of the mean magnetic anisotropy field, Ha, from 10 kOe at x = 0.0 to 2.8 kOe at x = 0.8. Fig. 3 shows representative curves of the reduced isothermal remnant magnetization (mr) and their derivatives representing the SFD, from which the mean anisotropy field was evaluated. The behavior of the SFD and Ha is the main mechanism responsible for the monotonic decrease of the coercivity with the increase of x. The magnetization induced by an applied field of 100 Oe was measured versus temperature for all samples. The results indicated that the Ni-Ti substitution did not lead to a significant reduction of the Curie temperature, rendering the substituted hexaferrites suitable for high-density magnetic recording at relatively high operating temperatures. Keywords: Hexaferrites, Partial substitution, Nickel, Titanium, High-density magnetic recording.

Magnetic nanoparticles for the measurement of cell mechanics using force-induced remnant magnetization spectroscopy

Interactions of magnetic nanoparticles with cells were investigated from a cell mechanics perspective, and magnetic nanoparticle-based force spectroscopy was developed as a novel method to measure the adhesion force among various cancer cell lines.

Modulating the magnetic properties of BiFeO3 by addition of Ba5TbTi3V7O30

xBiFeO3-(1-x)Ba5TbTi3V7O30 (xBFO-BTTV) ceramic composites with different x values were prepared by high temperature solid state reaction technique and sintering at 1073K. The formation of composite structure consisting of BFO and BTTV phases was confirmed by XRD study. Surface morphology was studied by scanning electron microscope (SEM) and shows that structure with high density was obtained in the composite 0.3BFOBTTV whereas the average grain size increases by increasing x, i.e. by increasing amount of BiFeO3 in the system. Magnetic measurements were done in a wide temperature range, i.e. from 10 to 350K, by vibrating sample magnetometer (VSM) and showed that the magnetization changes by changing the value of x in the composite. BiFeO3 is antiferromagnetic in nature with weak ferromagnetism. Addition of Ba5TbTi3V7O30 enhances magnetic properties of the composite and maximal coercivity and remnant magnetization are obtained in the composite 0.7BFO-BTTV.

Ferromagnetic excess moments and apparent exchange bias in FeF2 single crystals

The anisotropic antiferromagnet FeF2 has been extensively used as an antiferromagnetic layer to induce exchange bias effects in ferromagnetic/antiferromagnetic bilayers and heterostructures. In this work, an apparent exchange bias occurring in the low temperature hysteresis loops of FeF2 single crystals is investigated. A detailed investigation of the hysteresis and remnant magnetization indicates that the observation of an apparent exchange bias in FeF2 stems from an intrinsic excess moment associated with a distortion of the antiferromagnetic structure of piezomagnetic origin.

Instabilities of the Vortex Lattice and the Peak Effect in Single Crystal YBa2Cu4O8

We report on the measurements of the remnant magnetization, and hence critical current, in a single crystal of YBa2Cu4O8. A peak in the temperature dependence of the critical current is observed when the external magnetic field is tilted away from the a–b planes. The observed behavior is attributed to a thermally activated instability-driven vortex-lattice splitting or vortex chain formation. The nature of the peak and the possibility of a thermally-activated dimensional crossover have been discussed.

Magnetic response of bovine spleen

Bovine spleen has been used as a sample for deep magnetochemical investigation. Temperature dependence of the magnetic susceptibility and field dependence of the magnetization reveal a paramagnetic behaviour that violates the Curie law. The zero-field cooled magnetization and field cooled magnetization experiments show the bifurcation point at ca TC = 20 K and the blocking temperature TB = 10 K confirming a dominating portion of ferritin along with the organic tissue. There is a remnant magnetization at temperature below 20 K and the search for the magnetic hysteresis was positive.

The structure and magnetic properties of Eu-doped BiFeO3 prepared by a solid-phase sintering method

In this work, [Formula: see text] and Eu-doped [Formula: see text] samples were prepared by a simple solid-phase sintering method and the structure and magnetic properties were studied. The results of X-ray diffraction show that [Formula: see text] sample maintains the same rhombohedral R3c structure as [Formula: see text] sample but with a slight lattice distortion due to the Eu substitution for Bi. Compared with [Formula: see text], the [Formula: see text] sample exhibits a larger remnant magnetization and a higher Curie–Weiss temperature. These results indicate that appropriate doping with Eu is effective in improving the magnetic properties of [Formula: see text] and the solid-phase sintering method used in this study is a simple and good solid-phase sintering method to prepare [Formula: see text].