An 'Intermetallic' Molecular Nanomagnet with the Lanthanide Coordinated Only by Transition Metals

The best performing molecular nanomagnets are currently designed by carefully arranging p-element donor atoms (usually carbon, nitrogen and/or oxygen) around the central magnetic ion. Inspired by the structure of the hardest intermetallic magnet SmCo5, we have demonstrated a nanomagnetic molecule where the central lanthanide (Ln) ion Er is coordinated solely by three transition metal (TM) ions in a perfectly trigonal planar fashion. The molecule [Er(ReCp2)3] (ErRe3) constitutes the first example of a molecular nanomagnet (MNM; or single molecule magnet SMM) with unsupported Ln-TM bonds and paves the way towards molecular intermetallics with strong direct magnetic exchange interactions. Such interactions are believed to be crucial for quenching the quantum tunneling of magnetization which limits the application of Ln-SMMs as sub-nanometer magnetic memory units.

Analysis of vibronic coupling in a 4f molecular magnet with FIRMS

<p><b>Vibronic coupling, the interaction between molecular vibrations and electronic states, is a pervasive effect that profoundly affects chemical processes. In the case of molecular magnetic materials, vibronic, or spin-phonon, coupling leads to magnetic relaxation, which equates to loss of magnetic memory and loss of phase coherence in molecular magnets and qubits, respectively. The study of vibronic coupling is challenging, and most experimental evidence is indirect. Here we employ far-infrared magnetospectroscopy to probe vibronic transitions in in [Yb(trensal)] (where H₃trensal = 2,2,2-tris(salicylideneimino)trimethylamine). We find intense signals near electronic states, which we show arise due to an “envelope effect” in the vibronic coupling Hamiltonian, and we calculate the vibronic coupling fully <i>ab initio</i> to simulate the spectra. We subsequently show that vibronic coupling is strongest for vibrational modes that simultaneously distort the first coordination sphere and break the C₃ symmetry of the molecule. With this knowledge, vibrational modes could be identified and engineered to shift their energy towards or away from particular electronic states to alter their impact. Hence, these findings provide new insights towards developing general guidelines for the control of vibronic coupling in molecules.</b></p>

Tunable asymmetric spin wave excitation and propagation in a magnetic system with two rectangular blocks

Asymmetric spin wave excitation and propagation are key properties to develop spin-based electronics, such as magnetic memory, spin information and logic devices. To date, such nonreciprocal effects cannot be manipulated in a system because of the geometrical magnetic configuration, while large values of asymmetry ratio are achieved. In this study, we suggest a new magnetic system with two blocks, in which the asymmetric intensity ratio can be changed between 0.276 and 1.43 by adjusting the excitation frequency between 7.8 GHz and 9.4 GHz. Because the two blocks have different widths, they have their own spin wave excitation frequency ranges. Indeed, the spin wave intensities in the two blocks, detected by the Brillouin light scattering spectrum, were observed to be frequency-dependent, yielding tuneable asymmetry ratio. Thus, this study provides a new path to enhance the application of spin waves in spin-based electronics.

Magnetic particles and strings in iron langasite

Magnetic topological defects can store and carry information. Replacement of extended defects, such as domain walls and Skyrmion tubes, by compact magnetic particles that can propagate in all three spatial directions may open an extra dimension in the design of magnetic memory and data processing devices. We show that such objects can be found in iron langasite, which exhibits a hierarchy of non-collinear antiferromagnetic spin structures at very different length scales. We derive an effective model describing long-distance magnetic modulations in this chiral magnet and find unusual two- and three-dimensional topological defects. The order parameter space of our model is similar to that of superfluid 3He-A, and the particle-like magnetic defect is closely related to the Shankar monopole and hedgehog soliton in the Skyrme model of baryons. Mobile magnetic particles stabilized in non-collinear antiferromagnets can play an important role in antiferromagnetic spintronics.

Flaw detection of ship equipment parts

The need for non-destructive testing is regulated by the rules of the Russian River Register, which can determine the choice of the method of non-destructive testing and the procedure for its implementation. Non-destructive testing methods used in naval mechanical engineering are: visual and measuring control, ultrasonic control, radiographic control, capillary control, magnetic control, eddy current control. Each of the methods, due to the difference in the implemented physical principles, has its own advantages and disadvantages, which impose restrictions on the flaw detection of parts. The analysis of the sculpted defects of ship equipment and machines, depending on the manufacturing method and operating conditions, was carried out. The limitations on the use of non-destructive testing methods are shown. Examples of non-flaw detective parts are given, the control of which is difficult, as well as flaw detective parts that can be controlled with a guaranteed condition for detecting defects. The advantage of the method of magnetic memory of metal is indicated, relative to other methods of non-destructive testing. Using the example of a piston pin of a marine diesel engine NVD 36, a comparative analysis of the applicability of ultrasonic testing methods, the magnetic memory method and the penetrating solutions method for detecting fatigue cracks was performed. The results of the control show that the applied methods confidently identify fatigue cracks in the controlled parts, machines and mechanisms of ship equipment.

Observation of giant exchange bias effect in Ni-Mn-Ti all-d-metal Heusler alloy

We report a giant exchange bias (EB) field of about 3.68 KOe during field cooled process in all-d-metal Ni40(FeCo)4Mn36Ti20 Heusler alloy. The study of magnetic memory effect and isothermal magnetic relaxation processes suggest that the giant EB field arises due to the possible coexistence of antiferromagnetic (AFM) and ferromagnetic (FM) phase exchange interaction in the studied system at temperatures below 35 K. Furthermore, the temperature and cooling field dependence of EB effect are analyzed which are related to the change in unidirectional anisotropy at FM/AFM interface. The study of a well-established training effect confirms the intrinsic nature of the observed EB behavior. This result will open up a new way towards the development of EB materials considering all-d-metal Heusler alloy systems.

Mobile robot with failure inspection system for ferromagnetic structures using magnetic memory method

Flaws or cracks are one of the major failures in oil and gas pipeline networks. The early detection of these failures is very important for the safety of the industry, and this last requires of analysis for non-destructive testing (NDT), which is reliable, inexpensive and easy to implement. In this paper, we propose the development of an embedded prototype mounted on a mobile robot for the inspection of defects in ferromagnetic plates. This prototype has two embedded systems (control and data acquisition), which are based on a microcontroller of 8 and 32 bits, respectively. On the one hand, the first system for control has the logic to govern the sensors and motors that will allow to the robot moves with autonomous way during 45 min. While, the second system presents an algorithm for storing, processing and sending the data obtained from the sensors, being able to measure variations in the magnetic field in the order of 0.1 µT. Magnetic-field reading tests have been carried out on control ASTM A-27 ferromagnetic plates, obtaining experimental response in the 3 axes of the magnetic domains, which is very close to the expected results by the magnetic-flux density model that is calculated from the fields E and B derived from the equations of a Hertz dipole, and developed in the high-level Python programming language. The prototype proposed for NDT can detect geometric defects in the range of millimeters, producing changes in the density of the magnetic field in the order of thousands of µT.

Magnetic memory driven by topological insulators

Giant spin-orbit torque (SOT) from topological insulators (TIs) provides an energy efficient writing method for magnetic memory, which, however, is still premature for practical applications due to the challenge of the integration with magnetic tunnel junctions (MTJs). Here, we demonstrate a functional TI-MTJ device that could become the core element of the future energy-efficient spintronic devices, such as SOT-based magnetic random-access memory (SOT-MRAM). The state-of-the-art tunneling magnetoresistance (TMR) ratio of 102% and the ultralow switching current density of 1.2 × 105 A cm−2 have been simultaneously achieved in the TI-MTJ device at room temperature, laying down the foundation for TI-driven SOT-MRAM. The charge-spin conversion efficiency θSH in TIs is quantified by both the SOT-induced shift of the magnetic switching field (θSH = 1.59) and the SOT-induced ferromagnetic resonance (ST-FMR) (θSH = 1.02), which is one order of magnitude larger than that in conventional heavy metals. These results inspire a revolution of SOT-MRAM from classical to quantum materials, with great potential to further reduce the energy consumption.

Writing of strain-controlled multiferroic ribbons into MnWO4

Local and low-dimensional structures, such as interfaces, domain walls and structural defects, may exhibit physical properties different from the bulk. Therein, a wide variety of local phases were discovered including conductive interfaces, sheet superconductivity, and magnetoelectric domain walls. The confinement of combined magnetic and electric orders to spatially selected regions may be particularly relevant for future technological applications because it may serve as basis of electrically controllable magnetic memory devices. However, direct observation of magnetoelectric low-dimensional structures cannot readily be done partly because of the lack of experimental techniques locally probing their physical nature. Here, we report an observation of multiferroic ribbon-like domains in a non-multiferroic environment in MnWO4. Using optical second harmonic generation imaging, we reveal that a multiferroic phase is stabilized by locally generated strain while the bulk magnetic structure is non-multiferroic. We further find that the confined multiferroic state retains domains with different directions of electric polarization and we demonstrate deterministic writing of a multiferroic state embedded in a non-multiferroic environment.