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A uniform magnetic field is required to establish and preserve the spin-polarized state in noble gases with non-zero nuclear spins. Such spin-polarized noble gases, e.g. 3He and 129Xe, exhibit unique properties that are interesting in scientific and medical imaging applications. The balance of field uniformity, spatial accessibility, size and feasibility of construction is vital in the design and optimization of such magnet systems. magcoilcalc is an open-source Python library that enables users to efficiently model, simulate and optimize magnets consisting of axisymmetric circular current loops, such as solenoid coils and Helmholtz coils and their variants.

Orthoferrite solid solution HoFe1−xCrxO3 (x=0, 0.2,…,1.0) was synthesized via solid state reaction methods. The crystal structure, magnetism and spin reorientation properties of this system were investigated by X-ray diffraction, neutron powder diffraction and magnetic measurements. For compositions of x≤0.6, the system exhibits similar magnetic properties to HoFeO3. With increasing Cr-doping, the system adopts a Γ4(GxAyFz) magnetic configuration with a decreased Neel temperature from 640 K to 360 K. A Γ42 spin reorientation of Fe(Cr)3+ was also observed in this system with an increase in transition temperature from 56 K to about 200 K due to competition between the Fe(Cr)–Fe(Cr) and Ho–Fe(Cr) interactions. For the x≥0.8, the system behaves more like HoCrO3 which adopts a Γ2(FxCyGz) configuration with no spin reorientation below the Neel temperature TN. Throughout the whole substitution range, we found that the saturated moment of Fe(Cr) was less than the ideal value for a free ion, which implies the existence of spin fluctuation in this system. A systematic magnetic structure variation with Cr-substitution is revealed by Rietveld refinement. A phase diagram combining the results of the magnetic measurements and neutron powder diffraction results was obtained.

Graphical abstract: Oxygen atmosphere played an important role in inhibiting electrons hopping between Fe{sup 2+} and Fe{sup 3+} and reducing both of magnetic and dielectric losses of Ba{sub 3}Co{sub 2}Fe{sub 24}O{sub 41}, which is favorable in view of antenna substrate applications. - Highlights: • Co{sub 2}Z-type hexaferrites were sintered in different atmospheres. • The losses of the sample sintered in O{sub 2} were reduced effectively without additive. • A 3RC equivalent circuit model was put forward in the impedance analysis. - Abstract: Co{sub 2}Z-type hexaferrites with stoichiometric composition of Ba{sub 3}Co{sub 2}Fe{sub 24}O{sub 41} were fabricated by using a conventional solid–state reaction method. The influence of sintering atmosphere, namely air, O{sub 2} and N{sub 2}, on magnetic and electrical properties of the hexaferrites was systematically investigated. This work reveals that O{sub 2} played an important role in inhibiting the formation of Fe{sup 2+} and thus reducing magnetic and dielectric losses. The Co{sub 2}Z specimen sintered at 1300 °C in O{sub 2} atmosphere showed promising magneto-dielectric properties. Specifically, the magnetic and dielectric losses were less than 0.05 and 0.005 in the frequency range of 30–300 MHz, respectively. Impedance spectra were performed to reveal the underlying mechanisms for the different electrical propertiesmore » of the Co{sub 2}Z ceramics sintered in different atmospheres.« less

M-type barium ferrite (BaM) film is a promising candidate for magnetic recording media and the next-generation high-frequency microwave material. BaM films were fabricated using a chemical solution spin-coating deposition method on (001) plane sapphire. The effect of ethylene glycol (EG) on precursor solution and annealing temperature on microstructure and magnetic properties were investigated. X-ray diffraction showed that strong out-of-plane (001) texture in BaM films can be achieved with adequate EG addition. Films fabricated without EG addition or annealed at lower temperatures showed partial hematite secondary phase. The epitaxial formation of hematite secondary phase on sapphire substrate was confirmed by the X-ray diffraction φ-scan technique. Magnetic measurements showed out-of-plane anisotropy in BaM films. The crystallographic texture and magnetic anisotropy of the films are related to the film microstructure.

Quasi-epitaxial barium hexaferrite thin films (BaM) with crystallographic c -axis parallel to film normal were prepared through a topotactic reactive diffusion process using two-step solution deposition on c -plane sapphire. The two-step spin coating process involves preparing an epitaxial hematite film, coating the film with barium precursor solution and thermal annealing. The crystal orientation and magnetic anisotropy of BaM thin films were investigated by X-ray diffraction analysis, SEM observation and magnetic measurements. Hysteresis loops showed good magnetic anisotropy and high remanence ratio (RR) Mr/Ms = 0.97. The films fabricated by two-step spin coating process displayed wider rocking curve width but better magnetic anisotropy than one-step spin coating. The possible mechanism of this discrepancy is discussed in this paper.

In-plane c-axis oriented M-type barium hexaferrite (BaM) films were grown on a-plane sapphire (1120) substrates by radio frequency magnetron sputtering with ex-situ annealing. Oxygen in sputtering atmosphere played a critical role in the c-axis orientation growth of BaM films. With incorporation of 10% O2 during sputtering, in-plane c-axis highly oriented BaM films with high hysteresis loop squareness (Mr/Ms∼0.94) along in-plane easy axis and low Mr/Ms∼0.08 along in-plane hard axis was achieved. In contrast, films sputtered without O2 incorporation showed poor magnetic anisotropy and low hysteresis loop squareness along both directions. The oxygen induced formation of oriented hematite intermediate phase was found, which was supposed to be responsible for the in-plane orientation growth of BaM grains.