Magnetochemistry, Volume 8, Issue 6 (June 2022) – 7 articles

FeCoB (25 nm)/Hf($t_{\mathrm{Hf}}$)/FeCoB (25 nm) sandwich films with different hafnium thicknesses $t_{\mathrm{Hf}}$ were fabricated using a modified compositional gradient sputtering method to obtain self-biased high-frequency performances. The effects of $t_{\mathrm{Hf}}$ on the interlayer coupling and FMR frequency were investigated. It is revealed that interlayer coupling enhanced the resonance frequency by 48%, and a ferromagnetic coupling between the FeCoB films occurred for the trilayers with $t_{\mathrm{Hf}}$ < 3.0 nm, likely due to the interface roughness and pinhole effect. In this case, only acoustic mode resonance was observed with the same high-frequency performance as the corresponding FeCoB single layer. In contrast, a $t_{\mathrm{Hf}}$-dependent antiferromagnetic interlayer coupling appeared at $t_{\mathrm{Hf}}$ > 3.0 nm. The coupling coefficient J₁ was antiferromagnetic, and a biquadratic coupling J₂ appeared at t_Hf > 3.5 nm. The coupling mechanism was simulated and verified by Layadi’s rigid model, and the simulation was consistent with the experimental results. Full article

Realizing the high molecular orientation and structurally ordered microstructure of organic semiconductor polymer thin films is beneficial for enhancing the charge transport of conjugated polymers and achieving high-performance organic electronic devices. In this work, we successfully developed large-area highly aligned films of a thiophene-based polymer, namely poly(2,5-bis(3-alkylthiophen-2-yl) thieno [3,2-b] thiophene) (PBTTT), using the magnetic alignment method at a low magnetic field (0.12 T), which was assisted by superparamagnetic nanoparticles Fe₃O₄@C. The aligned microstructure of the composite films is confirmed by systematic analysis that includes polarized optical microscopy, polarized UV–visible absorption spectroscopy, and an atomic force microscope. Organic field effect transistors based on magnetic aligned composite film exhibit a 2.8-fold improvement in carrier mobility compared with the unaligned films. We hold a formation mechanism that the rapid magnetically induced self-assembly property of Fe₃O₄@C and its intermolecular interaction with polymer chains are key to the new method of preparing oriented thin films. Full article

The magnetic nanoparticles (MNPs) with decreasing heating efficiency (characterized by specific loss power, SLP) with temperature increase, especially around the Curie temperature (T_C), are expected to realize the self-regulated temperature hyperthermia of the tumor. However, the actual decrease of the SLP is gradual, resulting in the deviation of self-regulated temperatures from the measured T_C. So far, no method is available for evaluating the heating performances of those MNPs. Here, by simulating the temperature-dependent SLP, the heating performances of MNPs are evaluated from three clinically concerning aspects: the capacity for effective heating, the temperature uniformity in the tumor, and the temperature stability under environmental changes such as MNP loss or tumor progression. The developed methods were applied to ZnCoCrFeO, Fe₃O₄, and γ-Fe₂O₃ MNPs. It was found that the uniform temperature distribution relies on lowering the heating power in the inner regions of the tumor, and the stable control of temperature depends on the dynamic adaptation of the heating power to the tumor temperature change. The proposed method may be used to predict the heating ability of MNPs and help the selection of MNPs for hyperthermia. Full article

Calcium phosphate coatings were formed on a Ti6Al4V substrate by electrodeposition under a high magnetic field up to 16 T. The magnetic field was parallelly applied to the vertical surface electrode. Changes in crystal morphology of calcium phosphates were investigated as a function of the magnetic field amplitude, and the results are discussed in terms of magnetic field effects. Magnetohydrodynamic convection due to the Lorentz force could considerably reduce the formation of volcano-like structures and generate more uniform deposits without changing Ca/P ratios. Full article

The major aim of the current investigations is to study the magnetohydrodynamic effects on heat and mass transfer phenomena in third-grade fluid past an inclined exponentially stretching sheet fixed in a porous medium with Darcy–Forchheimer law influence. The constitutive equations compatible for heat and mass transportation in third-grade fluid in terms of partial differential equations are modeled. These partial differential equations are then converted to ordinary differential equations by using suitable similarity variables formulation. The transformed flow model is solved by using MATLAB built-in numerical solver bvp4c. Effects of pertinent parameters on physical properties that are velocity field, temperature field and mass concentration along with skin friction coefficient, Nusselt number and Sherwood number are demonstrated in graphs and tables. The impact of dimensionless numbers on the physical properties is analyzed and discussed with a physical view point at angle $\alpha =\pi /6$ (inclined sheet). It is seen that as the third-grade fluid parameter $\left(0.1\le \beta \le 11\right)$ is increased, the velocity profile increases, but the temperature field and mass concentration are decreased. It is observed that as the permeability parameter $(1\le K^{*}\le 11)$ is raised, the velocity distribution decreases and mass concentration increases. It is concluded from the results that owing to an increase in the local inertial coefficient $\left(0.1\le Fr\le 5\right)$, the velocity profile reduces but an increment in mass concentration is noted. It is concluded that by increasing values of magnetic field parameter $\left(0.1\le M\le 10\right)$ the velocity field is delineated and temperature field is elevated exactly according to the physics of magnetic field parameters. The present results are compared with already published results and it is observed that there is good agreement between them. This good agreement ensures the validation of accuracy of the results. Full article

We review the basic phenomenology of magnetic losses from DC to 1 GHz in commercial and laboratory-prepared soft ferrites considering recent concepts regarding their physical interpretation. This is based, on the one hand, on the identification of the contributions to the magnetization process provided by spin rotations and domain walls and, on the other hand, the concept of loss separation. It additionally contemplates a distinction between the involved microscopic dissipation mechanisms: spin damping and eddy currents. Selected experimental results on the broadband behavior of complex permeability and losses in Mn-Zn ferrites provide significant examples of their dependence on sintering methods, solute elements, and working temperature. We also highlight the peculiar frequency and temperature response of Ni-Zn ferrites, which can be heavily affected by magnetic aftereffects. The physical modeling of the losses brings to light the role of the magnetic anisotropy and the way its magnitude distribution, affected by the internal demagnetizing fields, acts upon the magnetization process and its dependence on temperature and frequency. It is shown that the effective anisotropy governs the interplay of domain wall and rotational processes and their distinctive dissipation mechanisms, whose contributions are recognized in terms of different loss components. Full article

The pressure–temperature phase diagram of the multiferroic TbFe${}_{2.46}$Ga${}_{0.54}$(BO${}_3$)${}_4$ was studied for hydrostatic pressures up to 7 GPa and simultaneously with temperatures up to 400 K by the Raman spectroscopy technique. The structural phase transition from the $R32$ phase to the $P{3}_{1}21$ phase was determined by observing the condensation of soft modes and the appearance of new lines. An increase in pressure leads to an increase in the temperature of the structural phase transition. These phases are stable over the entire investigated temperature and pressure range. No other phases have been found. Full article