Search Results (10)

In Fukuroi City Japan, greenhouses are usually used for crown musk melon (CMM) cultivation. When the temperature inside the greenhouse is lower than 25 °C, the CMM quality deteriorates. Hence, from late autumn until the middle of spring, oil is used to supply hot water to greenhouses from a boiler through a heat exchanger . However, since oil prices have recently soared, fuel expenses have drastically increased which heavily pressures the CMM business. In addition, with the promotion of the carbon-neutral policy, environmentally friendly heat sources are emphasized instead of fossil fuels. The TSK corporation has produced a new inducing heating (IH) source where heat is generated by rotating a plate on which a couple of permanent magnets are mounted using a motor. Since the rotation speed is easily controlled, the IH heat source capacity can be freely adjusted. To apply the IH source to the greenhouse, an experimental system was created in this study. During the experiment, water inside a vessel (maximum volume of 90 L) was heated to 70 °C by the IH system. Then, the heated water was circulated for heat dissipation through a heat exchanger by a pump. When the temperature of the water was lower than the target temperature, the IH system restarted to heat the water back up to 70 °C. Under several experimental conditions, the heating time, reheating time, and electric power were measured and evaluated. It was confirmed that the new IH heat source could possibly be applied to greenhouses. Full article

Superlattices (SLs) comprising layers of a soft ferromagnetic metal La_2/3Sr_1/3MnO₃ (LSMO) with in-plane (IP) magnetic easy axis and a hard ferromagnetic insulator La₂MnCoO₆ (LMCO, out-of-plane anisotropy) were grown on SrTiO₃ (100)(STO) substrates by a metalorganic aerosol deposition technique. Exchange spring magnetic (ESM) behavior between LSMO and LMCO, manifested by a spin reorientation transition of the LSMO layers towards perpendicular magnetic anisotropy below T_SR = 260 K, was observed. Further, 3ω measurements of the [(LMCO)₉/(LSMO)₉]₁₁/STO(100) superlattices revealed extremely low values of the cross-plane thermal conductivity κ(300 K) = 0.32 Wm⁻¹K⁻¹. Additionally, the thermal conductivity shows a peculiar dependence on the applied IP magnetic field, either decreasing or increasing in accordance with the magnetic disorder induced by ESM. Furthermore, both positive and negative magnetoresistance were observed in the SL in the respective temperature regions due to the formation of 90°-Néel domain walls within the ESM, when applying IP magnetic fields. The results are discussed in the framework of electronic contribution to thermal conductivity originating from the LSMO layers. Full article

Iron-based compounds with a ThMn₁₂-type structure have the potential to bridge the gap between ferrites and high performance Nd₂Fe₁₄B magnets. From the point of view of possible applications, the main advantage is their composition, with about 10 wt.% less rare earth elements in comparison with the 2:14:1 phase. On the other hand, the main issue delaying the development of Fe-rich alloys with a ThMn₁₂-type structure is their structural stability. Therefore, various synthesis methods and stabilizing elements have been proposed to stabilize the structure. In this work, the influence of increasing Nd substitution on the phase constitution of Zr_0.4−xNd_xCe_0.6Fe₁₀Si₂ (0 ≤ x ≤ 0.3) alloys was analyzed. X-ray diffraction and ⁵⁷Fe Mössbauer spectrometry were used as the main methods to derive the stability range and destabilization routes of the 1:12 structure. For the arc-melted samples, an increase in the lattice parameters of the ThMn₁₂-type structure was observed with the simultaneous growth of bcc-(Fe,Si) content with increasing Nd substitution. After isothermal annealing, the ThMn₁₂-type structure (and the coexisting bcc-(Fe,Si)) were stable over the whole composition range. While the formation of a 1:12 phase was totally suppressed in the as-cast state for x = 0.3, further heat treatment resulted in the growth of about 45% of the ThMn₁₂-type phase. The results confirmed that the stability range of ThMn₁₂-type structure in the Nd-containing alloys was well improved by other substitutions and the heat treatment, which in turn, is also needed to homogenize the ThMn₁₂-type phase. After further characterization of the magnetic properties and optimization of microstructure, such hard/soft magnetic composites can show their potential by exploiting the exchange spring mechanism. Full article

In this work, we demonstrate the possibility of using a soluble ceramic material, 5 wt% CaO, as an additive for an SmCo₅/20wt%Fe exchange-coupled nanocomposite obtained by mechanical milling in order to inhibit the grain growth of the soft magnetic phase during annealing, which results in a more stable microstructure and an implicit improvement in the hard–soft interphase exchange coupling. Moreover, we show that the additive improves the phase stability of the composite material, reducing the amount of Sm₂Co₁₇-type phases formed during the synthesis process, an important aspect because Sm₂Co₁₇ is detrimental to the magnetic performance of the SmCo₅/20%Fe nanocomposite. These effects are reflected in a nearly 13% increase in the coercive field (H_c) and a 20% increase in the energy product, (BH)_max, for the powders produced using CaO as compared to pure SmCo₅/20%Fe nanocomposites processed in the same manner. Full article

The paper refers to the spring-exchange magnetic systems containing magnetically soft and hard phases. This work consists of two parts. The first part is a brief review of hard magnetic materials, with special attention paid to ultra-high coercive compounds, as well as selected spring-exchange systems. The second part is a theoretical discussion based on the Monte Carlo micromagnetic simulations about the possible enhancement of the hard magnetic properties of systems composed of magnetically soft, as well as high and ultra-high coercive, phases. As shown, the analyzed systems reveal the potential for improving the |BH|_max parameter, filling the gap between conventional and Nd-based permanent magnets. Moreover, the carried-out simulations indicate the advantages and limitations of the spring-exchange composites, which could lead to a reduction in rare earth elements in permanent magnet applications. Full article

Magnetization reversal processes in the NiFe/FeMn exchange biased structures with various antiferromagnetic layer thicknesses (0–50 nm) and glass substrate temperatures (17–600 °C) during deposition were investigated in detail. Magnetic measurements were performed in the temperature range from 80 K up to 300 K. Hysteresis loop asymmetry was found at temperatures lower than 150 K for the samples with an antiferromagnetic layer thickness of more than 10 nm. The average grain size of FeMn was found to increase with the AFM layer increase, and to decrease with the substrate temperature increase. Hysteresis loop asymmetry was explained in terms of the exchange spring model in the antiferromagnetic layer. Full article

Core–shell structured magnetic nanoparticles combine hard and soft phases to improve energy efficiency. The mutual interaction of the two phases can lead to the exchange spring effect, leading to higher magnetic energy. In this regard, synthesis of Nd₂Fe₁₄B-based core–shell-structured powders have proven to be elusive, due to the relatively reactive nature of this phase. In this study, a process has been established for successfully coating the surface of Nd₂Fe₁₄B powders with a FeCo layer using the galvanic displacement method. Initially, a binary phase magnetic powder was synthesized containing Nd₂Fe₁₄B and Nd₂Fe₁₇ phase. Subsequently, the powders were coated using a Co precursor at 303 K. During coating, the metastable Nd₂Fe₁₇ phase was dissolved, and the Fe ions were released into the solution. Subsequently, the Fe ions deposited together with the Co ions on the surface of Nd₂Fe₁₄B powder to form a FeCo shell. The deposited layer thickness and composition was confirmed using TEM analysis. Full article

Magnetic properties of ferromagnetic nanostructures were studied by atomistic simulations following Monte Carlo and Landau–Lifshitz–Gilbert approaches. First, we investigated the influence of particle size and shape on the temperature dependence of magnetization for single cobalt and gadolinium nanoparticles and also in bi-magnetic Co@Gd core–shell nanoparticles with different sizes. The Landau–Lifshitz–Gilbert approach was subsequently applied for inspecting the magnetic hysteresis behavior of 2 and 4 nm Co@Gd core–shell nanoparticles with negative, positive, and zero values of interfacial magnetic exchange. We were able to demonstrate the influence of finite-size effect on the dependence of the Curie temperature of Co and Gd nanoparticles. In the Co@Gd core–shell framework, it was possible to handle the critical temperature of the hybrid system by adjusting the Co core size. In addition, we found an improvement in the coercive field values for a negative interfacial exchange energy and for a different core size, suggesting an exchange spring behavior, while positive and zero values of interfacial exchange constant showed no strong influence on the hysteresis behavior. Full article

High-pressure torsion (HPT), a technique of severe plastic deformation (SPD), is shown as a promising processing method for exchange-spring magnetic materials in bulk form. Powder mixtures of Fe and SmCo₅ are consolidated and deformed by HPT exhibiting sample dimensions of several millimetres, being essential for bulky magnetic applications. The structural evolution during HPT deformation of Fe-SmCo₅ compounds at room- and elevated- temperatures of chemical compositions consisting of 87, 47, 24 and 10 wt.% Fe is studied and microstructurally analysed. Electron microscopy and synchrotron X-ray diffraction reveal a dual-phase nanostructured composite for the as-deformed samples with grain refinement after HPT deformation. SQUID magnetometry measurements show hysteresis curves of an exchange coupled nanocomposite at room temperature, while for low temperatures a decoupling of Fe and SmCo₅ is observed. Furthermore, exchange interactions between the hard- and soft-magnetic phase can explain a shift of the hysteresis curve. Strong emphasis is devoted to the correlation between the magnetic properties and the evolving nano-structure during HPT deformation, which is conducted for a 1:1 composition ratio of Fe to SmCo₅. SQUID magnetometry measurements show an increasing saturation magnetisation for increasing strain $\gamma$ and a maximum of the coercive field strength at a shear strain of $\gamma$ = 75. Full article

In this study, magnetostrictive powders of CoFe₂O₄ (CFO) and Zn-substituted CoFe₂O₄ (CZFO, Zn = 0.1, 0.2) were synthesized in order to decrease the optimal dc magnetic field (H_opt.), which is required to obtain a reliable magnetoelectric (ME) voltage in a 3-0 type particulate composite system. The CFO powders were prepared as a reference via a typical solid solution process. In particular, two types of heterogeneous CZFO powders were prepared via a stepwise solid solution process. Porous-CFO and dense-CFO powders were synthesized by calcination in a box furnace without and with pelletizing, respectively. Then, heterogeneous structures of pCZFO and dCZFO powders were prepared by Zn-substitution on calcined powders of porous-CFO and dense-CFO, respectively. Compared to the CFO powders, the heterogeneous pCZFO and dCZFO powders exhibited maximal magnetic susceptibilities (χ_max) at lower H_dc values below ±50 Oe and ±10 Oe, respectively. The Zn substitution effect on the H_dc shift was more dominant in dCZFO than in pCZFO. This might be because the Zn ion could not diffuse into the dense-CFO powder, resulting in a more heterogeneous structure inducing an effective exchange-spring effect. As a result, ME composites consisting of 0.948Na_0.5K_0.5NbO₃–0.052LiSbO₃ (NKNLS) with CFO, pCZFO, and dCZFO were found to exhibit H_opt. = 966 Oe (NKNLS-CFO), H_opt. = 689–828 Oe (NKNLS-pCZFO), and H_opt. = 458–481 Oe (NKNLS-dCZFO), respectively. The low values of H_opt. below 500 Oe indicate that the structure of magnetostrictive materials should be considered in order to obtain a minimal H_opt. for high feasibility of ME composites. Full article