Large magnetodielectric coupling in the vicinity of metamagnetic transition in 6H−perovskite Ba3GdRu2O9

The 6H-perovskites Ba3RRu2O9 (R = rare earth element) demonstrate the magnetodielectric (MD) coupling as a manifestation of 4d - 4f magnetic interactions. Here, we have reported a detailed study of the structural, magnetic, heat capacity, and MD properties of the 6H-perovskite Ba3GdRu2O9. The signature of long-range antiferromagnetic (AFM) ordering at ~14.8 K (TN) is evident from the magnetization and heat capacity studies. The TN shifts towards the lower temperature side, apart from splitting in two with the application of the magnetic field. Field-dependent magnetization at 2 K shows three metamagnetic transitions with the opening of small hysteresis in different regions. A new transition at T1 emerges after the onset of the first metamagnetic transition. Complex magnetic behavior is observed in different magnetic field regions whereas these field regions themselves vary with the temperature. Dielectric response recorded at zero and 80 kOe field exhibits the development of MD coupling well above TN. The MD coupling (~ 4.5 % at 10 K) is enhanced by 25 % as compared to the Dy counterpart. Effect of complex magnetic behavior is also conveyed in the MD results where the maximum value of MD coupling is observed in the vicinity of 10 K (onset of T1) and near the second metamagnetic transition. Our investigation suggests that both Gd and Ru moments align simultaneously at TN. Short-range magnetic correlations are possibly responsible for MD coupling above TN.

Epitaxial growth and room-temperature ferromagnetism of quasi-2D layered Cr4Te5thin film

Large-scale growth of two-dimensional (2D) ferromagnetic thin films will provide an ideal platform for studying 2D magnetism and active spintronic devices. However, controllable growth of 2D ferromagnets over large areas faces tremendous challenges. Herein, we report a large-area growth of 2D ferromagnetic single-crystal thin films Cr4Te5 on Al2O3 (0001) substrates using pulsed laser deposition. X-ray diffraction patterns and atomic force microscopy detection confirm that all thin films are high quality epitaxy together with atom-level smooth. Magnetic measurements show the persistence of ferromagnetic ordering state up to above room temperature, with a Curie temperature 320 K, atomic magnetic moment 0.307µB/Cr, and the easy-magnetization axis in film plane. Comparing bulk Cr4Te5 single-crystal, the critical exponent β=0.491 indicates that the magnetic interactions of thin film obey mean-field model rather than 3D Heisenberg model. This work will open a avenue for growing large-scale 2D ferromagnet and developing room temperature 2D magnet-based nanodevices.

Phase-transforming metamaterial with magnetic interactions

Solid–solid phase transformations can affect energy transduction and change material properties (e.g., superelasticity in shape memory alloys and soft elasticity in liquid crystal elastomers). Traditionally, phase-transforming materials are based on atomic- or molecular-level thermodynamic and kinetic mechanisms. Here, we develop elasto-magnetic metamaterials that display phase transformation behaviors due to nonlinear interactions between internal elastic structures and embedded, macroscale magnetic domains. These phase transitions, similar to those in shape memory alloys and liquid crystal elastomers, have beneficial changes in strain state and mechanical properties that can drive actuations and manage overall energy transduction. The constitutive response of the elasto-magnetic metamaterial changes as the phase transitions occur, resulting in a nonmonotonic stress–strain relation that can be harnessed to enhance or mitigate energy storage and release under high–strain-rate events, such as impulsive recoil and impact. Using a Landau free energy–based predictive model, we develop a quantitative phase map that relates the geometry and magnetic interactions to the phase transformation. Our work demonstrates how controllable phase transitions in metamaterials offer performance capabilities in energy management and programmable material properties for high-rate applications.

Conceptual Fields and Magnetic Field: a theoretical model for epistemological classification of tasks in magnetostatics

This work presents a theoretical model for epistemological classification of tasks in magnetostatics aimed at High School and Higher Education. The approach is based on the theory of conceptual fields and includes classification in terms of thought operations necessary to solve the tasks and in these situations’ parameters. Four primary classes of situations are proposed, namely, description of magnetic interactions, analogic symbolization of magnetic fields, non-analogic symbolization of magnetic fields and calculation of magnetic fields. These classes cannot be reduced one to another, however they can occur simultaneously in the same task. Each one was subdivided in secondary classes of situations based on parameters they can assume and ordered by epistemological complexity. As contributions for physics teaching research this work offers a theoretical-methodological model for analyzing students’ progression in the conceptual field of magnetostatics, a conceptual structure for building situations based on predicative and operational competences for understanding the concept of magnetic field, and a practical example of epistemological classification of situations that can be adapted for other areas of Science like Quantum Mechanics, for example.

Investigation of field-controlled magnetocaloric switching and magnetodielectric phenomena in spin-chain compound Er2BaNiO5

The Haldane spin-chain compound Er2BaNiO5 has been known to possess magnetoelectric coupling below the magnetic ordering temperature. Here we report various low-temperature magnetic and magnetocaloric properties, and magnetodielectric effect above magnetic ordering temperature in this compound. The present compound displays a coexistence of conventional and inverse magnetocaloric effects with a large entropy change of 5.9 and −2.5 J/kg K, respectively. Further, it exhibits a remarkable switching between them, which can be tuned with temperature and magnetic field. In addition, evolution of two magnetic field-dependent metamagnetic transitions at 19.7 and 27.7 kOe, and their correlation with magnetocaloric switching effect, make this compound effective for potential applications. On the other hand, demonstration of intrinsic magnetodielectric effect (1.9%) near and above antiferromagnetic ordering temperature, through a moderate coupling between electric dipoles and magnetic spins, establishes this compound as a useful candidate for future research. A detailed analysis of these findings, in a framework of different magnetic interactions and magnetocrystalline anisotropies, is discussed here. Overall, these results may provide a future pathway to tune the magnetic, magnetodielectric, and magnetocaloric properties in this compound toward better application potential.

Electromagnetic Torque Ripple in Multiple Three-Phase Brushless DC Motors for Electric Vehicles

This paper investigated an electromagnetic torque ripple level of BLDC drives with multiple three-phase (TP) permanent magnet (PM) motors for electric vehicles. For this purpose, mathematical models of PM machines of different armature winding sets-single (STP), dual (DTP), triple (TTP), and quadruple (QTP) ones of asymmetrical configuration and optimal angular displacement between winding sets were developed and corresponding computer models in the Matlab/Simulink environment were created. In conducted simulation, the influence of various factors on the electromagnetic torque ripple of the multiple-TP BLDC drives was investigated—degree of modularity, magnetic coupling between armature winding sets, and drive operation in open and closed-loop control systems. Studies have shown an increase of the electromagnetic torque ripple generated by one module in the multiple TP BLDC drives with magnetically coupled winding sets, due to additional current pulsations caused by magnetic interactions between the machine modules. However, the total electromagnetic torque ripples are much lower than in similar drives with magnetically insulated winding sets. Compared with the STP BLDC drive, the multiple TP BLDC drives with the same output parameters showed a reduction of the electromagnetic torque ripple by 27.6% for the DTP, 32.3% for the TTP, and 34.0% for the QTP BLDC drive.