United States

A review of soft magnetic amorphous and nanocrystalline alloys currently used in the market along their primary industrial applications will be discussed. The distribution transformer market continues to be the largest volume application of Fe-based amorphous foil with higher efficiency standards globally helping to drive the growth of amorphous-based transformers. High permeability grades of amorphous foil have largely supplanted the convention grades due to the higher induction levels (1.63T) and increased stacking factor (&amp;gt;90%). Magnetic domain refinement of amorphous foil, further reducing the core losses, is now commercially available.&lt;br/&gt;&lt;br/&gt;Amorphous foil has long been envisioned for high efficiency electric motors. The emerging trends with electric vehicles have revitalized the efforts to incorporate amorphous and nanocrystalline foils as the motor lamination materials. There are many approaches to fabricate these motor components and we will discuss the methods that have been industrially adopted. FeCo based amorphous alloys further enhance the induction levels (1.8T) and can be viable in these applications. Nanocrystalline alloys of the FeBSiNbCu composition have now become an industry standard for ultra-low loss, high frequency and high permeability applications. Advanced processing methods have produced higher induction nanocrystalline alloys with higher Fe and lower Nb content. There are also new FeCo and FeNi nanocrystalline alloys being developed specifically suited towards gapless inductor and motor applications that will be discussed.

2022 Joint MMM-INTERMAG

Recent Advances and Remaining Challenges in Manufacturing of Amorphous and Nanocrystalline Alloys

The 15th Joint MMM-INTERMAG Conference (2022 Joint) is sponsored jointly by AIP Publishing and the IEEE Magnetics Society. Members of the international scientific and engineering communities interested in recent developments in fundamental and applied magnetism are invited to attend and contribute to the technical sessions. The technical program will include invited and contributed papers in oral and poster sessions, invited symposia, a plenary session, and an evening session, with about 1500 presentations overall. This Conference provides an outstanding opportunity for worldwide participants to meet their colleagues and collaborators and discuss developments in all areas of magnetism research.

The 2022 Joint Conference will offer both in-person and prerecorded on-demand content.

For tickets to the event, please register at the following link: https://magnetism.org/register

Please register for the Joint MMM-Intermag conference to join the event.

This Conference provides an outstanding opportunity for worldwide participants to meet their colleagues and collaborators and discuss developments in all areas of magnetism research.

A review of soft magnetic amorphous and nanocrystalline alloys currently used in the market along their primary industrial applications will be discussed. The distribution transformer market continues to be the largest volume application of Fe-based amorphous foil with higher efficiency standards globally helping to drive the growth of amorphous-based transformers. High permeability grades of amorphous foil have largely supplanted the convention grades due to the higher induction levels (1.63T) and increased stacking factor (&gt;90%). Magnetic domain refinement of amorphous foil, further reducing the core losses, is now commercially available. Amorphous foil has long been envisioned for high efficiency electric motors. The emerging trends with electric vehicles have revitalized the efforts to incorporate amorphous and nanocrystalline foils as the motor lamination materials. There are many approaches to fabricate these motor components and we will discuss the methods that have been industrially adopted. FeCo based amorphous alloys further enhance the induction levels (1.8T) and can be viable in these applications. Nanocrystalline alloys of the FeBSiNbCu composition have now become an industry standard for ultra-low loss, high frequency and high permeability applications. Advanced processing methods have produced higher induction nanocrystalline alloys with higher Fe and lower Nb content. There are also new FeCo and FeNi nanocrystalline alloys being developed specifically suited towards gapless inductor and motor applications that will be discussed.

symposium

There is a great interest to generate electricity using ambient RF energy. We addressed this using two different approaches. We first use the intrinsic quantum property of the Weyl semimetal to convert the RF energy into electricity [1]. The nonlinear Hall effect (NLHE) can produce a dc transverse voltage in zero magnetic field. However, it requires NLHE to be detected at room temperature. Despite of several studies of NLHE in topological materials and 2D materials, the room-temperature NLHE has not yet been achieved. We find the room-temperature NLHE in a type-II Weyl semimetal TaIrTe4, which hosts a robust NLHE due to broken inversion symmetry and large band overlapping at the Fermi level. The NLHE is present only when the electric field is applied along the axis of the mirror plane (a-axis of the crystal). Based on the observed room-temperature NLHE in TaIrTe4 we demonstrate the wireless RF rectification with zero external bias and magnetic field. An incident electric field along the a-axis (Ea) generates a rectified voltage along the b-axis (Vb), whereas, there is no rectification when the incident electric field is along the b-axis (Eb) in consistent with the symmetry constraints of NLHE. This work opens a door to realizing room temperature rectification applications based on the NLHE in Weyl semimetals. The other approach is to use the spin-torque diode effect of spin-torque oscillators (STOs) [2]. For the application in rectification and energy harvesting, the spin-diode effect is demonstrated by measuring the rectified dc voltage. Due to the canted anisotropy, the free layer of the individual STOs shows a large RF sensitivity as a result of non-linear dynamics. We demonstrate series connections have an advantage for rectification due to the additive effect of the diode voltages from STOs. Using eight oscillators in series, the rectified voltage is enhanced and we have achieved a rectification efficiency of 6% at -20 dBm, which outperforms the Schottky diode capability at sub µW power. By integrating the electrically connected eight STOs with conventional electronics, we demonstrate the battery-free energy-harvesting system by utilizing the wireless RF energy to power electronic devices such as LEDs. We also demonstrate the capability of this energy harvesting system in holding dc power using a time-varying signal, which is useful in harvesting energy from discrete commercial sources such as a WiFi router. Our results highlight the significance of electrical topology (series vs. parallel) while designing an on-chip STOs system.

WiFi Band Energy Harvesting using Spin-Torque Diode and Nonlinear Hall Effects

A key challenge of neuromorphic computing is to build hardware neural networks with dense connectivity between nanoscale synapses and neurons, approaching the brain’s thousands of synapses per neuron (1). In this talk, I will show that spin diodes are microwave nano-synapses that naturally and densely interface with neurons made of spin-torque nano-oscillators (2). I will describe the principle of these novel synapses and explain how their microwave features can be harnessed to achieve the multiply-and-accumulate operations at the core of neural networks, with over 500 synapses/neuron. I will show that they implement all-to-all connections as well as convolutional operations in a fully parallel way with high density and speed. I will describe our experiments highlighting these functionalities (3), and show that they open the path to radio-frequency deep learning.

Radio-Frequency Spintronic Neural Networks

Antiferromagnets are prospective materials for spintronic applications due to their internal ultrafast dynamics, robustness with respect to the external magnetic fields, and high sensitivity to spin-torques of different nature. Moreover, in contrast to ferromagnets, spin-torques can induce steady precession of the Néel vector at THz frequencies whose values can be controlled by the current. Hence, antiferromagnets can be considered as tunable current controlled auto-oscillators, which is the main component of phase-controlling devices. An auto-oscillation regime is supported solely by antidamping torques that compensate the internal energy losses. However, the frequency of the precession, threshold value, the type of dynamics etc can be effectively manipulated by applying the field-like torques. In this presentation we review recent developments in the field of antiferromagnetic spin-torque oscillators and discuss new functionalities stemming from the combining effect of the field-like and antidamping-like torques. To demonstrate the effects of different torques we start from the dynamics of ultrafast switching and discuss various mechanisms including the Néel spin-orbit torques [1], thermomagnetoelastic mechanism [2], and optically-induced spin-transfer torques [3]. We illustrate possible applications of nontrivial antiferromagnetic dynamics for the detection and emission of teraherz radiation in altermagnets CuMnAs and Mn2Au in which electrical current can induce simultaneously the ac Néel spin-orbit torque and dc spin-orbit torque [1]. Using NiO antiferromagnet as an example, we discuss and compare various scenarios of ultrafast dynamics, such as: i) reorientation of the Néel vector due to the field-like torques of magnetoelastic nature and spin-orbit torques due to spin-pumping [4]; ii) fast switching and stable precession induced by the ac spin-transfer torques whose frequency coinsides with the frequency of antiferromagnetic resonance. We also analyse the chaotic regimes of an antiferromagnetic oscillator that appear at certain combination of field-like and damping-like torques (see Fig.1) and and discuss possible applications for neuromorphic computations [5]. As an outline of future development, we discuss influence of the magnetoelastic and thermal effects and combination of different stimulus for the effective control and manipulation of the antiferromagnet-based devices.

![](https://assets.underline.io/uploads/markdown_image/1/image/b59399d9c1fc0e1b590576e4fe529e56.jpg)

Current-induced transition to chaos traced by variation of the largest of three Lyapunov's exponents. Red lines on the spheres show trajectories of the Neel vector. From [5].

Antiferromagnetic Spin-torque Oscillators: Ultrafast Dynamics and Possible Applications

The spin-torque magnetic diode (STMD) effect [1] is a quadratic rectification effect of the input microwave current IRF(t) in a magnetoresistive nano-junction, which is commonly observed in the traditional regime of operation of an STMD, when the magnetization of the “free” layer (FL) lies in-plane, and when the frequency fs of the current IRF(t) is close to the ferromagnetic resonance (FMR) frequency f0 of the junction. In this case, the induced resonance oscillations of the junction resistance R(t) can mix with the oscillations of the input microwave current IRF(t) , and produce an output DC voltage UDC = &lt;IRF(t)R(t)&gt; (where "&lt;&gt;" denotes time averaging) across the junction. It was demonstrated theoretically in [2] that in an STMD, biased by an out-of-plane static magnetic field, a different dynamical regime of the STMD operation characterized by large-angle out-of-plane magnetization precession can be realized. The excitation of the large-angle precession has a threshold character, and is possible only for input microwave currents exceeding a certain frequency-dependent critical value, and sufficiently low frequency. In this regime of the out-of-plane precession the output DC voltage of an STMD increases with the frequency of the input signal, but is virtually independent of its power. An STMD working in the regime of large-amplitude out-of-plane precession functions as a non-resonant threshold detector of low frequency microwave signals, due to the large nonlinear shift of its operating frequency. Therefore, this precession regime is particularly suitable for applications in the microwave energy harvesting. It was demonstrated experimentally in [3] that the out-of-plane magnetization precession regime in an STMD operation predicted in [2] can be realized without any bias magnetic field, if an STMD FL has a perpendicular magnetic anisotropy. In such a regime an STMD has the rectification properties that are independent of the input microwave frequency, and the performance of the STMD-based energy harvesting device is comparable to the performance of the state-of-the-art Schottky diode for low-power rectification. It was further shown in [3] that the developed bias-free STMD provides sufficient dc voltage to power a practical nanodevice − a black phosphorus photosensor. Here we present an analytical and numerical theory explaining the performance of a bias-free STMD with perpendicular magnetic anisotropy [4]. We show that in an STMD, having a magnetic FL with perpendicular magnetic anisotropy of the first and second order, and no external bias magnetic field, the out-of-plane regime of magnetization precession can be excited by sufficiently large (exceeding a certain threshold) RF signals with the frequencies smaller than 250 MHz . We also show that such a device can operate as a broadband energy harvester capable of converting incident RF power into a DC power with a conversion efficiency of ∼5%. The developed analytical theory of the bias-free STMD operation can be used for the optimization of high-efficiency RF detectors and energy harvesters based on STMDs. Our results are paving a way for use of spintronic detectors and harvesters as building blocks for self-powered nano-systems, such as implantable biomedical devices, wireless sensors, and portable electronics.

Signal Detector and RF Energy Harvester Based On A Spintronic Diode With Perpendicular Anisotropy

Experimental methods allowing for the detection of single spins in the solid-state, which were initially developed for quantum information science, open new avenues for the development of highly sensitive quantum sensors [1]. In that context, the electronic spin of a single nitrogen-vacancy (NV) defect in diamond can be used as an atomic-sized magnetometer, providing an unprecedented combination of spatial resolution and magnetic sensitivity under ambient conditions [2]. In this talk, I will illustrate how scanning-NV magnetometry can be used as a powerful tool for exploring condensed-matter physics, focusing on chiral spin textures in antiferromagnetic materials [3-5].

Exploring antiferromagnetic order at the nanoscale with a single spin microscope

Hydrodynamic electron flow, where electrons in a conductor flow collectively - akin to a fluid, is a unique signature of strong electron interactions in a material. This effect has been observed in 2D materials, but observations in bulk materials are intriguing as high-carrier density should screen the interactions. In this talk, I will discuss a recent measurement of hydrodynamic flow in the semimetal WTe2, allowing us to gain insight into the microscopic origin of its electron interactions. We image the spatial profile of the electric current by using a nitrogen-vacancy scanning tip. Using coherent quantum sensing, we obtain magnetic field resolution of ~10nT and spatial resolution of ~100nm. The current pattern we observe differs substantially from the flat profile of a normal metal, and indicates correlated flow through the semimetal. The pattern also shows non-monotonic temperature dependence, with hydrodynamic effects peaking at ~20 K. We compare our results to a model which combines ab initio electron scattering rates and the electronic Boltzmann transport equation. The model shows quantitative agreement with our measurement, allowing us to extract the strength of electron-electron interactions in our material. Furthermore, we conclude that electron interactions are phonon-mediated. This result opens a path for hydrodynamic flow and strong interactions in a variety of new materials.

Imaging hydrodynamic flow in WTe2 with cryogenic quantum magnetometry

The current-induced torque is one of the most important phenomena in spintronics as it provides a way to control magnetic order parameters by electrical means. So far, most studies on the microscopic mechanisms of the current-induced torque have focused on the role of spin current carried by conduction electrons, which exerts spin-transfer torque on the magnetization upon the injection into a ferromagnet. In solids, however, electronic Bloch states originate from the atomic orbitals of the constituent atoms. Thus, while it is natural to expect that such orbital information may be used to control the magnetization because the orbital degree of freedom carries the angular momentum as the spin degree of freedom does, the role of orbitals in the physics of the current-induced torque has been barely investigated. In recent years, we uncovered mechanisms of generating the electronic current carrying finite orbital angular momentum such as the orbital Hall effect (OHE) [1] and proposed to utilize the orbital current for controlling the magnetization [2]. The latter is shortly denoted by “orbital torque” (OT) nowadays. In this talk, I review recent theoretical progress in the mechanisms of the OHE and the OT. In the first part, I will explain that the OHE arises in various metals regardless of their strength of the spin-orbit coupling, whose magnitude is typically an order of magnitude larger than that of the spin Hall effect (SHE) in heavy metals [3]. In fact, the SHE is a concomitant effect of the OHE, whose hierarchical relation will be explained. In the second part, I will discuss the mechanisms of the OT. The main problem is that it is hard to distinguish the orbital contribution and the spin contribution to the torque on the magnetization in most torque measurements. This is one of the main difficulties to quantify the OT. Theoretically, we recently developed a general theoretical formalism that tracks the transfer of the angular momentum in solids between the lattice, the local magnetic moment, and the electron’s spin and orbital, and successfully implemented it within the density functional theory framework [4]. This enables us to understand the microscopic nature of the OT and quantify different competing contributions. Finally, I will also discuss unique qualitative features of the OT mechanisms: significant dependence of the interface orbital transparency on the crystallinity and long-range transport and dephasing in a ferromagnet [5].

Theory of Orbital Hall Effect and Current-Induced Torques by Orbital Current

Circularly polarized light with spin angular momentum is one of the most valuable probes of magnetism. Recently we demonstrated that light beams with orbital angular momentum (OAM), or vortex beams, can also couple to magnetism exhibiting dichroisms in a magnetized medium [1.2]. Terahertz (THz) vortex beams with various combinations of the orbital angular momentum l=±1, ±2, ±3, and ±4 and spin angular momentum s = ±1, or conventional circular polarization, were used for studies of the magnon spectra at the antiferromagnetic resonance conditions in TbFe3(BO3)4 and Ni3TeO6 single crystals. In both materials we observed strong vortex beam dichroism for the magnon doublet, which is split in an external magnetic field applied along the spin ordering direction. The absorption conditions at the magnon frequencies depend on the total angular momentum of light j that is determined by the combination of the spin and orbital angular momenta: j=s+l. For the higher orders of l, the selection rules for AFM resonances dictated by l completely dominate over that for conventional circular polarization. Our results demonstrate the high potential of the vortex beams with OAM as a new spectroscopic probe of magnetism in matter. In addition to the results for AFM materials, we will also present our recent experiments with vortex beam spectroscopy of the Landau level resonances in 2DEG semiconductor heterostructures in high magnetic field. Various parts of this work was performed in collaboration with T. N. Stanislavchuk1, P. Marsik 2, L. Bugnon2, M. Soulier2, C. Bernhard2, V. Kiryukhin3, and S.-W. Cheong3 1 Department of Physics, New Jersey Institute of Technology, Newark, New Jersey 07102, USA 2 Department of Physics, University of Fribourg, CH-1700 Fribourg, Switzerland 3 Rutgers Center for Emergent Materials and Department of Physics and Astronomy, Rutgers University, Piscataway, New Jersey 08854, USA.

Competition between orbital and spin angular momenta of the THz beams at the antiferromagnetic resonances and Landau level transitions

There exist needs for advanced inductors that are (1) power dense, (2) highly efficient, and (3) high temperature stable for a range of power electronics applications which include on-board converters and off-board charging systems for electric vehicles. Nanocrystalline soft magnetic alloys are of great interest for medium frequency and medium to high power applications due to their large saturation flux density relative to ferrites, as well as their improved losses and reduced magnetostriction relative to amorphous alloys. However, state-of-art commercial Fe-based nanocrystalline alloys display inherently large permeabilities and consequently they require gapping for high power inductor applications and suffer from inherent limitations of mechanical brittleness and relatively poor temperature stability (rated at 150C). Recent advances in Co-based nanocrystalline alloys have enabled a new class of highly scalable inductors which overcome the limitations of existing Fe-based nanocrystalline alloys through in-line tension anneal processing to enable a new level of control for large-scale inductor designs not previously possible without the requirement for core gapping. Local permeability control (i.e. permeability engineering) is made possible through real-time controls of applied tension and controlled thermal processing during the in-line processing step, of particular interest for reduced peak temperature rise and highly power dense inductor designs by engineering the distribution of magnetic flux throughout the core. Advanced thermal processing techniques can also be applied during the in-line processing stage to tailor the characteristic spatial length-scale and distribution of the spatially varied permeability profile, and after the in-line processing to tailor domain structure and optimize losses. Temperature stability of magnetic properties are also far superior to traditional Fe-based alloys, with current experiments showing the potential for stability of structure and magnetic properties as high as 400C and even approaching 500C. The presentation will address the latest advances in Co-based nanocrystalline strain annealed gapless inductors for power dense inductor applications. Topics to be addressed will include: 1) Phase identity and magnetic property variation as a function of chemistry in Co-based nanocrystalline alloys; 2) The latest in tension annealing at scale and spatially tuned permeability engineering methods; 3) Demonstrations of engineered permeabilities as well as optimized domain structures for taliored magnetic properties; 4) Development of tailored multi-objective optimization tools specifically for permeability engineered gapless core inductors; 5) Application of advanced lmulti-objective optimization tools for inductor design and benchmarking in both electric vehicle and medium voltage power electronics applications; The presentation will conclude with recent experimental results as well as emerging ideas and future perspectives for highly optimized thermal processing methods and techniques, including spatial optimization of the crystallization process and consequently the magnetic properties through spatially tailored rapid thermal processing with electromagnetic field-assisted methods and techniques.

Power Dense Inductors Based Upon Co-Based Nanocrystalline Alloys

This presentation will focus on the applications of Soft Magnetic Components and Materials for Emerging Power Conversion Applications such as Solid State Transformer [SST] Technology and several power conversion systems at both Medium-Voltage [MV] and Low-Voltage [LV]. The re-evaluation of conventional magnetics solutions has become important and essential due to the emergence and adoption of WBG [Wide-Band Gap] power devices such as SiC and GaN devices. These devices not only enable co-design of MV and higher switching frequency, but also enable higher temperature operations requiring characterization of magnetics for such specifications. This presentation will cover advances in medium frequency magnetics for WBG devices based power converters and especially for high power converters. It will highlight the latest advances in soft magnetic material qualification and characterization under non-sinusoidal waveforms. It will provide an overview of magnetic core loss models and implications for thermal modeling. It will also address novel techniques for understanding leakage inductance and anomalous losses due to leakage flux. The novel concept of strain annealing for permeability engineering and design opportunities for heterogeneously tuned permeability cores in high power converter applications will be addressed.

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