Ferromagnetic Domain Structure Research Articles

Harnessing ferroic ordering in thin film devices for analog memory and neuromorphic computing applications down to deep cryogenic temperatures

The future computing beyond von Neumann era relies heavily on emerging devices that can extensively harness material and device physics to bring novel functionalities and can perform power-efficient and real time computing for artificial intelligence (AI) tasks. Additionally, brain-like computing demands large scale integration of synapses and neurons in practical circuits that requires the nanotechnology to support this hardware development, and all these should come at an affordable process complexity and cost to bring the solutions close to market rather soon. For bringing AI closer to quantum computing and space technologies, additional requirements are operation at cryogenic temperatures and radiation hardening. Considering all these requirements, nanoelectronic devices utilizing ferroic ordering has emerged as one promising alternative. The current review discusses the basic architectures of spintronic and ferroelectric devices for their integration in neuromorphic and analog memory applications, ferromagnetic and ferroelectric domain structures and control of their dynamics for reliable multibit memory operation, synaptic and neuronal leaky-integrate-and-fire (LIF) functions, concluding with their large-scale integration possibilities, challenges and future research directions.

Out-of-plane polarization reversal and changes in in-plane ferroelectric and ferromagnetic domains of multiferroic BiFe0.9Co0.1O3 thin films by water printing

BiFe0.9Co0.1O3 is a promising material for an ultra-low-power-consumption nonvolatile magnetic memory device because local magnetization reversal is possible through application of an electric field. Here, changes in ferroelectric and ferromagnetic domain structures in a multiferroic BiFe0.9Co0.1O3 thin film induced by “water printing”, which is a polarization reversal method involving chemical bonding and charge accumulation at the interface between the liquid and the film, was investigated. Water printing using pure water with pH = 6.2 resulted in an out-of-plane polarization reversal from upward to downward. The in-plane domain structure remained unchanged after the water printing process, indicating that 71° switching was achieved in 88.4% of the observation area. However, magnetization reversal was observed in only 50.1% of the area, indicating a loss of correlation between the ferroelectric and magnetic domains because of the slow polarization reversal due to nucleation growth.

Film size-dependent bias voltage regulated resistance switching behavior for ultra-thin Fe65Co35 films on Pb(Mg1/3Nb2/3)O3–PbTiO3 piezoelectric substrates

We report the film size dependent bias voltage modulated resistance switching behavior for a novel memory cell, constructed with ultra-thin Fe65Co35 (FeCo) thin films grown on Pb(Mg1/3Nb2/3)O3–PbTiO3 (PMN-PT) single crystal piezoelectric substrates. Measurement results show that the PMN-PT exhibits good ferroelectric properties and excellent piezoelectric performance. The saturation polarization intensity and piezoelectric displacement are 35.5 μC/cm2 and 80 Å, respectively. The PMN-PT/FeCo heterostructure shows a clear magnetic hysteresis loop with a coercive field of 114 Oe and FeCo films possess ferromagnetic domain structures. By applying a bias voltage in the thickness direction of the heterostructure, the current-voltage (I–V) characteristics of the FeCo films on the PMN-PT could be adjusted, and multiple resistance states are generated. The FeCo film size dependence of resistance switching behaviors was investigated by analyzing the resistance change of the samples, a maximum resistance change of 61.5% was obtained for the heterostructure with 100 μm × 100 μm FeCo films, at a bias voltage of 30 V. It is revealed that the resistance switching behaviors of the heterostructures has been enhanced by using small lateral size FeCo films. The memory device can directly write information and data by using an electric field, and read information by using the change of resistance.

Enhanced Reversible Magnetic-Field-Induced Strain in Ni-Mn-Ga Alloy

A phase-field model was developed to simulate the ferromagnetic domain structure and martensite variant microstructure of Ni-Mn-Ga shape-memory alloy. The evolution of reversible magnetic-field-induced strain (MFIS) and associated magnetic domain/martensite variant structure were modeled under an external magnetic field. It was found that MFIS increased significantly from 0.2% to 0.28% as the temperature increased from 265 K to 285 K. In addition, compressive pre-stress efficiently enhanced the MFIS of the alloy, while tensile stress reduced MFIS. Furthermore, it was proved that there was possibility of achieving similar enhancement of MFIS by replacing compressive stress with perpendicular biaxial tensile stress. The results revealed that the residual variant induced by stress plays an important role in the reversible MFIS effect.

Stabilization of correlated ferroelectric and ferromagnetic domain structures in BiFe0.9Co0.1O3 films

Co-substituted bismuth ferrite, BiFe0.9Co0.1O3, thin film is a promising candidate material for low-power-consumption nonvolatile magnetic memory devices because magnetization reversal by an electric field has been directly observed at room temperature. However, this phenomenon takes place in a limited region where the ferroelectric domain is composed of two polarization variants forming stripe patterns. We demonstrate the extension of the stripe domain structure to the entire electrically poled region by utilizing an effective in-plane electric field called a trailing field. A one-to-one correlation between ferroelectric and ferromagnetic domains was also demonstrated.

Magnetic contributions in multiferroic gadolinium modified bismuth ferrite ceramics

Bi0.88Gd0.12FeO3 multiferroics are of interest for next-generation electronics and are shown with a remnant magnetization 0.2 emu·g−1, coercive field 8 kOe, Curie temperature 370 °C and magnetization of 0.7 emu·g−1 at magnetic fields 30 kOe. Scanning probe microscopy confirmed the intrinsic multiferroicity in the perovskite phase with coexistence of ferroelectric/ferroelastic and ferromagnetic domain structures. Strong magnetic hysteresis was produced by thermal cycling to 1000 °C due to degeneration of the perovskite phase into iron oxide inclusions, highlighting the importance of processing, thermal history and thermodynamic stability for minimizing the amount of parasitic magnetic secondary phases.

Contribution of Ukrainian Scientists to the Development of Electrodynamics

The aim of the paper is to prove the importance of the works performed by Ukrainian scientists for the development of electrodynamics. Some examples of achievements made by Ukrainian scientists in this scientific area include physical theories in such directions as the electrical conductivity, domain structure of ferromagnets, photoelectromotive force in semiconductors, microscopic theory of superconductivity, Shubnikov–de Haas effect, magneto-acoustic resonance, invention of an electric tram, live broadcast of the moving-image signal, distant control of objects by means of radio signals, and arc welding of metals. Most Ukrainian scientists have founded their own scientific schools, which works are recognized throughout the world. They were not only engaged in the scientific and lecturing activities, but also in the popularization of science, reformation of the education system, and social activity.

A Two-Dimensional Manganese Gallium Nitride Surface Structure Showing Ferromagnetism at Room Temperature

Practical applications of semiconductor spintronic devices necessitate ferromagnetic behavior at or above room temperature. In this paper, we demonstrate a two-dimensional manganese gallium nitride surface structure (MnGaN-2D) which is atomically thin and shows ferromagnetic domain structure at room temperature as measured by spin-resolved scanning tunneling microscopy and spectroscopy. Application of small magnetic fields proves that the observed magnetic domains follow a hysteretic behavior. Two initially oppositely oriented MnGaN-2D domains are rotated into alignment with only 120 mT and remain mostly in alignment at remanence. The measurements are further supported by first-principles theoretical calculations which reveal highly spin-polarized and spin-split surface states with spin polarization of up to 95% for manganese local density of states.

Vortex ferromagnetic domain structures of ferromagnetic CoFe2O4 nanodisks formed by local crystallization using a heated atomic force microscope tip

Magnetic domain structures of CoFe2O4 nanodisks were investigated by magnetic force microscopy (MFM). A CoFe2O4 thin film was deposited on a Pt/TiO2/SiO2/Si substrate using a spin coating process. Locally crystallized CoFe2O4 nanodisks were formed by local annealing with a heated atomic force microscopy tip at a fixed temperature of 700 °C. By controlling the local heating time, the diameters of the CoFe2O4 nanodisks with ferromagnetic domains were systematically adjusted over the range from 150 to 300 nm. MFM observations showed that the 150 nm CoFe2O4 nanodisks had magnetic domains with a vortex shape along the in-plane direction, with the magnetic spin oriented along the out-of-plane direction at the center of the nanodisk.

Giant room temperature multiferroicity and domain structures in hot-press sintered Bi0.85Sm0.15Fe0.97Sc0.03O3 ceramics

Abstract In this work, Bi 0.85 Sm 0.15 Fe 0.97 Sc 0.03 O 3 ceramics were prepared by rapid hot pressing. Their crystal structures, dielectric and multiferroic properties were studied with an emphasis on microscopic ferroelectric and ferromagnetic domains characterizations. X-ray diffraction data revealed a diphase structure consisting of rhombohedra R 3 C and orthorhombic Pbnm . The ferroelectric polarization and magnetization measurements showed the ceramics， possessing simultaneously a giant remanent polarization of 42.36 μC/cm 2 and a high remanent magnetization of 0.134 emu/g at room temperature. Moreover, the regularly striped ferroelectric and ferromagnetic domain structures have been identified and analyzed by combining transmission electron microscopy and piezoresponse/magnetic force microscopy.

Changes in magnetic domain structure during twin boundary motion in single crystal Ni-Mn-Ga exhibiting magnetic shape memory effect

The complexity of Ni-Mn-Ga single crystal originates from the interplay between ferromagnetic domain structure and ferroelastic twinned microstructure. Magnetic domain structure in the vicinity of single twin boundary was studied using magneto-optical indicator film and magnetic force microscopy technique. The single twin boundary of Type I was formed mechanically and an initial magnetization state in both variants were restored by local application of magnetic field (≈40 kA/m). The differently oriented variants exhibited either stripe or labyrinth magnetic domain pattern in agreement with the uniaxial magnetocrystalline anisotropy of the martensite. The twin boundary was then moved by compressive or tensile stress. The passage of the boundary resulted in the formation of granular or rake domains, respectively. Additionally, the specific magnetic domains pattern projected by twin boundary gradually vanished during twin boundary motion.

Irreversible magnetization switching at the onset of superconductivity in a superconductor ferromagnet hybrid

We demonstrate that the magnetic state of a superconducting spin valve, that is normally controlled with an external magnetic field, can also be manipulated by varying the temperature which increases the functionality and flexibility of such structures as switching elements. In this case, switching is driven by changes in the magnetostatic energy due to spontaneous Meissner screening currents forming in the superconductor below the critical temperature. Our scanning Hall probe measurements also reveal vortex-mediated pinning of the ferromagnetic domain structure due to the pinning of quantized stray fields in the adjacent superconductor. The ability to use temperature as well as magnetic field to control the local magnetisation structure raises the prospect of potential applications in magnetic memory devices.

Piezo-Barkhausen Emission as an Indicator of the Fatigue Limit of Steel

The fatigue properties of two variants of AISI 1018 steel samples were measured in a series of 33 experiments using new kinds of magnetic diagnostics. An MTS-810 servohydraulic test machine applied sinusoidal fully reversed (R = −1) loads under strain (Є) control in the range of 0.0008 ≤ (Є)≤ 0.0020. In 28 experiments, the number of cycles to fatigue failure Nf varied between 36,000 < Nf < 3,661,000. By contrast, in five runs extending over 107 cycles, the specimens showed no detectable signs of weakening or damage. The corresponding “S-N” or classical Wöhler plots indicated that the transitions from fatigue failure to nominally infinite life (i.e., the fatigue limit) occurred at strains of about Є = 0.0009 and Є = 0.0010, respectively, for the two types of steel. Every loading cycle of each test was instrumented to record continual values of stress and strain. Flux gate magnetometers measured the variations of the piezomagnetic fields near the specimens. A 1000-turn coil surrounding the test pieces detected the piezo-Barkhausen pulses generated by abrupt rearrangements of their internal ferromagnetic domain structures. Analyses of the magnetic data yielded four independent indices each of which located the fatigue limits in complete agreement with the values derived from the Wöhler curves.

Temperature and field dependence of magnetic domains inLa1.2Sr1.8Mn2O7

Colossal magnetoresistance and field-induced ferromagnetism are well documented in manganite compounds. Since domain wall resistance contributes to magnetoresistance, data on the temperature and magnetic field dependence of the ferromagnetic domain structure are required for a full understanding of the magnetoresistive effect. Here we show, using cryogenic magnetic force microscopy, domain structures for the layered manganite ${\mathrm{La}}_{1.2}{\mathrm{Sr}}_{1.8}{\mathrm{Mn}}_{2}{\mathrm{O}}_{7}$ as a function of temperature and magnetic field. Domain walls are suppressed close to the Curie temperature ${T}_{C}$, and appear either via the application of a $c$-axis magnetic field, or by decreasing the temperature further. At temperatures well below ${T}_{C}$, new domain walls, stable at zero field, can be formed by the application of a $c$-axis field. Magnetic structures are seen also at temperatures above ${T}_{C}$: these features are attributed to inclusions of additional Ruddleston-Popper manganite phases. Low-temperature domain walls are nucleated by these ferromagnetic inclusions.

Insight into spin transport in oxide heterostructures from interface-resolved magnetic mapping.

At interfaces between complex oxides, electronic, orbital and magnetic reconstructions may produce states of matter absent from the materials involved, offering novel possibilities for electronic and spintronic devices. Here we show that magnetic reconstruction has a strong influence on the interfacial spin selectivity, a key parameter controlling spin transport in magnetic tunnel junctions. In epitaxial heterostructures combining layers of antiferromagnetic LaFeO(3) (LFO) and ferromagnetic La(0.7)Sr(0.3)MnO(3) (LSMO), we find that a net magnetic moment is induced in the first few unit planes of LFO near the interface with LSMO. Using X-ray photoemission electron microscopy, we show that the ferromagnetic domain structure of the manganite electrodes is imprinted into the antiferromagnetic tunnel barrier, endowing it with spin selectivity. Finally, we find that the spin arrangement resulting from coexisting ferromagnetic and antiferromagnetic interactions strongly influences the tunnel magnetoresistance of LSMO/LFO/LSMO junctions through competing spin-polarization and spin-filtering effects.

AC driven magnetic domain quantification with 5 nm resolution.

As the magnetic storage density increases in commercial products, e.g. the hard disc drives, a full understanding of dynamic magnetism in nanometer resolution underpins the development of next-generation products. Magnetic force microscopy (MFM) is well suited to exploring ferromagnetic domain structures. However, atomic resolution cannot be achieved because data acquisition involves the sensing of long-range magnetostatic forces between tip and sample. Moreover, the dynamic magnetism cannot be characterized because MFM is only sensitive to the static magnetic fields. Here, we develop a side-band magnetic force microscopy (MFM) to locally observe the alternating magnetic fields in nanometer length scales at an operating distance of 1 nm. Variations in alternating magnetic fields and their relating time-variable magnetic domain reversals have been demonstrated by the side-band MFM. The magnetic domain wall motions, relating to the periodical rotation of sample magnetization, are quantified via micromagnetics. Based on the side-band MFM, the magnetic moment can be determined locally in a volume as small as 5 nanometers. The present technique can be applied to investigate the microscopic magnetic domain structures in a variety of magnetic materials, and allows a wide range of future applications, for example, in data storage and biomedicine.

Simultaneous imaging of the ferromagnetic and ferroelectric structure in multiferroic heterostructures

By measuring the spin polarization of secondary electrons and the intensity of backscattered electrons generated in a scanning electron microscope, we are able to simultaneously image the ferromagnetic domain structure of a ferromagnetic thin film and the ferroelectric domain structure of the underlying ferroelectric substrate upon which it is grown. Simultaneous imaging allows straightforward, quantitative measurements of the correlations in these complex multiferroic systems. We have successfully imaged domains in CoFe/BFO and Fe/BTO, two systems with very different ferromagnet/ferroelectric coupling mechanisms, demonstrating how this technique provides a new local probe of magneto electric/strictive effects in multiferroic heterostructures.

Direct observation of temperature dependent magnetic domain structure of the multiferroic La0.66Sr0.34MnO3/BiFeO3 bilayer system by x-ray linear dichroism- and x-ray magnetic circular dichroism-photoemission electron microscopy

Low-thickness La0.66Sr0.34MnO3 (LSMO)/BiFeO3 (BFO) thin film samples deposited on SrTiO3 were imaged by high resolution x-ray microscopy at different temperatures. The ultra-thin thickness of the top layer allows to image both the ferromagnetic domain structure of LSMO and the multiferroic domain structure of the buried BFO layer, opening a path to a direct observation of coupling at the interface on a microscopic level. By comparing the domain size and structure of the BFO and LSMO, we observed that, in contrast to LSMO single layers, LSMO/BFO multilayers show a strong temperature dependence of the ferromagnetic domain structure of the LSMO. Particularly, at 40 K, a similar domain size for BFO and LSMO is observed. This indicates a persistence of exchange coupling on the microscopic scale at a temperature, where the exchange bias as determined by magnetometer measurements is vanishing.

A device for the recording of the dynamic domain structure of ferromagnets in rotating magnetic fields

The principle of operation of a device for the observation and recording of the type of domain structure (DS) of ferromagnets that are remagnetized in rotating magnetic fields is described. This makes it possible to reliably fix the type of the domain structure of a ferromagnet under single cycles of magnetization reversal in the frequency range of 20–400 Hz and in the induction interval of 0.25–2.0 T. The observed features of the rearrangement of the DS in the samples of anisotropic electrotechnical steel allowed us to find a method for reducing the level of its magnetic losses in rotating magnetic fields and thus to improve its performance characteristics significantly.

Microwave electromagnetic and absorption properties of magnetite hollow nanostructures

Two types of magnetite (Fe3O4) hollow nanostructures, namely, nanoring (NR) and nanotube (NT), were fabricated by chemical method. The NR and NT exhibit a vortex and ferromagnetic domain structure, respectively, as revealed by 3D micromagnetic simulation. The measurement on microwave electromagnetic properties suggests that the NT exhibits obviously higher permittivity than that of the NR. In comparison, their initial permeability is close to each other. In addition, a broad nature resonance peak of the NR and NT is observed at 3.5 and 4.5 GHz, respectively. The calculated microwave absorption property indicates that the NT composite exhibits a broad band effective absorption (<−10 dB), which is superior to the NR. It suggests that the NT could serve as a promising candidate for microwave absorption.