Magnetic History Research Articles

Magnetic-Electrical Synergetic Control of Non-Volatile States in Bilayer Graphene-CrOCl Heterostructures.

Anti-ferromagnetic insulator chromium oxychloride (CrOCl) has shown peculiar charge transfer and correlation-enhanced emerging properties when interfaced with other van der Waals conductive channels. However, the influence of its spin states to the channel material remains largely unknown. Here, this issue is addressed by directly measuring the density of states in bilayer graphene (BLG) interfaced with CrOCl via a high-precision capacitance measurement technique and a surprising hysteretic behavior in the charging states of the heterostructure is observed. Such hysteretic behavior depends only on the history of magnetization, but not on the history of electrical gating; it can also be turned off electrically, providing a synergetic control of these non-volatile states. First-principles calculations attribute this observation to magnetic field-controlled charge transfer between BLG and CrOCl during the phase transition of CrOCl from antiferromagnetic (AFM) to ferrimagnetic-like (FiM) states. This magnetic-electrical synergetic control mechanism broadens the scope of proximity effects and opens new possibilities for the design of advanced 2D heterostructures and devices.

The Correlation of Vessel Wall Macrophage Infiltration With Hemosiderin in Arteriovenous Malformations

Endothelial dysfunction, induced by high shear stress from increased nidal blood flow, may promote a cycle of inflammation, possibly leading to instability and cerebral arteriovenous malformations (AVMs) rupture. Macrophages, identified with CD68, are key inflammatory components in AVM pathology. We aim to evaluate the relationship of inflammation with AVM flow and hemosiderin. This is a retrospective study of archived tissue. Adult patients (2002-2022) with baseline quantitative magnetic resonance angiography (QMRA) imaging, no embolization, and history of microsurgical resection (n=17), with both ruptured (n=9) and unruptured cases (n=8). Brain AVM sections were stained with CD68 to quantify vessel wall macrophage infiltration and hematoxylin and eosin stain as a control and to quantify hemosiderin. QMRA with noninvasive optimal vessel analysis (NOVA) was reviewed, and AVM flow was calculated. Statistical analyses were performed. There were no significant differences between macrophage infiltration and patient demographics, Spetzler-Martin grade, eloquence, venous stenosis, nidus compactness, volume, and AVM flow. Vessel wall macrophage infiltration positively correlated with patients who presented with confirmed AVM rupture (163.8 +/- 46.7 vs. 101.3 +/- 49.4, p=0.017). Increases in vessel wall macrophage infiltration were found to positively correlate with higher grades of hemosiderin (p=0.023), except for grade 4 hemosiderin. Venous anomaly showed a negative association with macrophage infiltration (p=0.035). These findings suggest a relationship between AVM vessel wall inflammation, hemosiderin, and hemorrhage presentation. Further investigations with larger sample sizes are warranted to understand the role of altered hemodynamics, hemosiderin deposition and inflammation in AVM vessel walls.

Weak magnetism of Martian impact basins may reflect cooling in a reversing dynamo

Understanding the longevity of Mars’s dynamo is key to interpreting the planet’s atmospheric loss history and the properties of its deep interior. Satellite data showing magnetic lows above many large impact basins formed 4.1-3.7 billion years ago (Ga) have been interpreted as evidence that Mars’s dynamo terminated before 4.1 Ga—at least 0.4 Gy before intense late Noachian/early Hesperian hydrological activity. However, evidence for a longer-lived, reversing dynamo from young volcanics and the Martian meteorite ALH 84001 supports an alternative interpretation of Mars’s apparently demagnetized basins. To understand how a reversing dynamo would affect basin fields, here we model the cooling and magnetization of 200-2200 km diameter impact basins under a range of Earth-like reversal frequencies. We find that magnetic reversals efficiently reduce field strengths above large basins. In particular, if the magnetic properties of the Martian mantle are similar to most Martian meteorites and late remagnetization of the near surface is widespread, >90% of large ( > 800 km diameter) basins would appear demagnetized at spacecraft altitudes. This ultimately implies that Mars’s apparently demagnetized basins do not require an early dynamo cessation. A long-lived and reversing dynamo, unlike alternative scenarios, satisfies all available constraints on Mars’s magnetic history.

Spin switching in Er1-xSmxFeO3 (x = 0, 0.2) single crystals

We investigated spin-switching transitions in Er1-xSmxFeO3 (x = 0, 0.2) single crystals and variations in spin configurations with the applied field. The crystals were grown using the optical floating zone technique, and the magnetic properties were measured under field-cooled cooling (FCC) and field-cooled warming (FCW) protocols. The crystals exhibit field-dependent variation in the spin-switching temperature. In FCC, spin switching temperature increases with a magnetic field. However, in FCW, the spin-switching temperature (TSSW) rises initially with an increasing magnetic field, reaches a maximum value and later decreases when field strengths are high. We observe that spin switching depends not only on the magnitude of the externally applied magnetic field but also on the starting temperature of FCC. The magnetic and thermal history of the sample has a critical role in this phenomenon. A phase diagram (magnetic field-TSSW) constructed using the FCC and FCW data helps to illustrate various magnetic configurations. The FCC and FCW measurements in the a-direction of ErFeO3 at high fields (2T, 3T) suggest that spin switching, which involves the reversal of spins, does not occur. Instead, there is a change in the magnitude of the weak ferromagnetic moment, and rare earth spins below the compensation temperature (Tcomp).

Femtosecond Laser-Induced Transient Magnetization Enhancement and Ultrafast Demagnetization Mediated by Domain Wall Origami.

Femtosecond laser-induced ultrafast magnetization dynamics are all-optically probed for different remanent magnetic domain states of a [Co/Pt]22 multilayer sample, thus revealing the tunability of the direct transport of spin angular momentum across domain walls. A variety of different magnetic domain configurations (domain wall origami) at remanence achieved by applying different magnetic field histories are investigated by time-resolved magneto-optical Kerr effect magnetometry to probe the ultrafast magnetization dynamics. Depending on the underlying domain landscape, the spin-transport-driven magnetization dynamics show a transition from typical ultrafast demagnetization to being fully dominated by an anomalous transient magnetization enhancement (TME) via a state in which both TME and demagnetization coexist in the system. Thereby, the study reveals an extrinsic channel for the modulation of spin transport, which introduces a route for the development of magnetic spin-texture-driven ultrafast spintronic devices.

Edge dislocation with [001] [formula omitted] induced positive magnetoresistance in BaTiO3/La0.66Sr0.33MnO3 heterostructure

The magnetoresistance (MR) effect holds immense potential for applications in various fields, including but not limited to storage and sensing. Manganese oxide has garnered significant attention due to its colossal magnetoresistance characteristics. Investigating the effects of the complex magnetic interactions on the magnetism and transport enables a better understanding of magnetic materials. La0.66Sr0.33MnO3 (LSMO) manganese oxides typically exhibiting negative MR as a result of magnetic field-induced spin order, while positive MR typically occurs in systems with spin-orbit coupling (SOC) or P-N junctions. In this work, the magnetic and transport properties of BaTiO3 (BTO)/LSMO heterostructure were studied. By introducing edge dislocation with [001] b→ (burgers vector) in BTO, the c-axis lattice constant is increased, resulting in positive MR in LSMO, which could be modulated by the magnetic field history and the annealing temperature. The nonlinear magnetic order induced by antiferromagnetism at the interface is proposed to cause the positive MR. Finally, the influence of ferroelectric layer on MR could be controlled by the ferroelectric BTO film. The increase in the large lattice constant and the observed variations in MR under magnetic field and annealing temperature provide valuable insights for further studies on the complex oxide.

Unidirectional multipulse helicity-independent all-optical switching in [Ni/Pt] based synthetic ferrimagnets

Nickel-platinum-based synthetic ferrimagnets (SFi's) are highly tunable and rare-earth-free materials that allow ultrafast all optical control of magnetism to be explored. This study considers a SFi composed of a ferromagnetic [Ni/Pt] multilayer and a ferromagnetic Co layer, separated by an Ir layer that mediates an antiferromagnetic coupling. Helicity-independent all optical switching (HI-AOS) between two antiparallel magnetization states is observed. AOS may be realized at increased temperature through reduction of the thickness of the Pt layers. Switching is unidirectional and has a strong dependence on the applied magnetic field history, which suggests the possible presence of a nanoscale magnetic texture that may be important in controlling AOS in SFi systems. Published by the American Physical Society 2024

Contrasting Recording Efficiency of Chemical Versus Depositional Remanent Magnetization in Sediments

AbstractHow and when sedimentary rocks record Earth's magnetic field is complex. Most studies assume a time‐progressive lock‐in mechanism during sediment deposition called depositional remanent magnetization (DRM). However, magnetic minerals can also form in situ, recording a chemical remanent magnetization (CRM) that is discontinuous in time. Disentangling the two mechanisms represents a major hurdle, and differences in their recording efficiencies remain unexplored. Here, our theoretical solutions demonstrate that CRM intensities exceed DRM by a factor of six when acquired in the same magnetic field. Novel experiments growing greigite (Fe3S4) in sediments and subsequent redeposition under identical magnetic field conditions confirm the predicted difference in recording efficiency. Thus, if left unrecognized, CRM leads to overestimated paleointensity and deserves more attention when interpreting Earth's magnetic history from sedimentary records. Recognition of fundamental differences between CRM and DRM characteristics provide a way forward to distinguish the recording mechanisms through routine laboratory protocols.

Investigation of magnetic hysteresis in biased Ta/Pt/Co/FeMn/Ta antidots: Influence of structural dimensions

There exists a controversy in the literature concerning the values of coercive and bias fields in antidots magnetic structures formed by a hexagonal network of nanoholes. The coercive fields (HC) and the exchange bias fields (∣HEXC∣) for antidots (deposited on ultrathin anodic aluminum oxide, namely, AAO) are either increased or diminished by comparison with the same magnetic nanostructures grown on continuous substrates (namely, CML). We propose to elucidate these debates by showing the importance of the easy axis of the magnetization, the direction of the applied magnetic field, the thicknesses of the layers, and the 3D-topology of nanoholes, as well as the magnetic and thermal history of the magnetic measurements. Here, biased Ta(5 nm)/Pt(5 nm)/Co(0.6 nm)/Fe50Mn50(X)/Ta(5 nm) antidots are investigated by extraordinary Hall effect measurements at 5 K, where X varies in the (0–5.5) nm range. The substrate consists in a hexagonal array of holes, described by the pair of (p,d) values, respectively, the period as the distance from center to center of two consecutive holes and the hole diameter. The dimensions of antidots are (p≈100 and d≈40 nm) for X=(2–5.5) nm, (p≈150 and d≈60 nm) for X=3.5 nm, and (p≈100 and d≈60 nm) for X=0. A continuous stack using Si/SiO2(100 nm) is used for comparison. HC and ∣HEXC∣ gradually increase when X is enhanced for both substrates, with nevertheless a weak decrease at high X for the continuous system. Perpendicular magnetic anisotropy is only observed for both unbiased samples, the X=2 nm continuous sample, and both X=5 nm samples that have undergone field cooling treatment from 500 to 5 K under −2 T. Usually, HC(AAO)>HC(CML), ∣HEXC(AAO)∣>∣HEXC(CML)∣, and ∣HA(AAO)∣<∣HA(CML)∣ (HA designating the anisotropy field). However, for certain conditions, as, for instance, for FC-procedures starting from high temperatures and/or strong magnetic field, other situations might be observed. A discussion pertaining to the amplitudes of HC, ∣HEXC∣ and the anisotropy field (∣HA∣) of continuous and discontinuous samples is given for our experimental results as well as for published data in the literature, in the light of structural characteristics (wedge-to-wedge distance, porosity, or coverage ratio). Such biased perpendicular antidots might be particularly used in specific nanomaterials devoted to spintronics.

Experimental study of the effects of a magnetic field/magnetic field-ferromagnetic nanocomposite pour point depressant on wax deposition.

A magnetic field and pour point depressant, as a new avenue for improving the submarine pipeline flow of waxy oils, has attracted increasing attention along with the development of efficient wax mitigation techniques. Although advances have been made recently in understanding the rheological behavior and crystallization properties of waxy oils, the effect of magnetic field and pour point depressants on wax deposition remains an open question. In this work, a ferromagnetic nanocomposite pour point depressant (FNPPD) was prepared. The variations in wax deposition mass and component under the effect of different magnetic treatments and magnetic field-FNPPDs were investigated using cold fingers and high-temperature gas chromatography. It was evident that both the high-intensity and high-frequency magnetic fields generated by the magnet and magnetic coil can effectively reduce the deposition mass and have a long-term magnetic history effect. The synergistic effect of magnetic fields and FNPPDs concurrently reduced the thickness/mass and wax content in the deposition layer, as compared to the individual use of magnetic fields or FNPPDs. The wax precipitation properties and wax crystal morphology of waxy oils under the action of the magnetic field were characterized by differential scanning calorimetry, focused beam reflectance measurement and polarizing microscopy experiments, and the mechanism of the magnetic field was elaborated from the perspective of crystallization kinetics by combining the fitting analysis of Avrami and size-independent growth model.

Field‐Free and Energy‐Efficient Switching of a Ferrimagnetic Insulator Through Orbital Currents of Copper

AbstractElectrically manipulating the magnetization of insulators presents exciting opportunities for fast and energy‐efficient spintronic devices. However, the existing approaches, which rely on spin‐orbit torque (SOT), invariably require an auxiliary field. Here field‐free current‐induced magnetization switching in perpendicularly magnetized Tm3Fe5O12 films is demonstrated. This is achieved through a magnetic hybrid structure, Tm3Fe5O12/Co40Fe40B20/Cu/SiO2, where the Cu layer acts as the source of orbital current, and the in‐plane magnetized Co40Fe40B20 layer functions as the converter of orbital‐to‐spin current. The interplay between the insulating and metallic magnetic layers not only yields a significant anomalous Hall signal for monitoring the Tm3Fe5O12 magnetization states, but also enables field‐free switching that is immune to the magnetic history of the structure. It also observes similar Tm3Fe5O12 switching in stacks with different spin/orbital current sources, with the SOT‐driven switching consuming substantially more power. This work establishes a pathway for achieving energetically efficient all‐electrical manipulation of insulator spins through orbital currents.

Hysteresis of magnetization statics and dynamics in [Pt/Co] multilayer

The magnetic multilayer of Co separated by thin spacer layer of Pt was deposited by DC-magnetron sputtering. From the longitudinal magneto-optical Kerr effect based magnetometry and microscopy as well as magnetic force microscopy, the hybrid magnetization structure was deduced: the large size, micrometer scale magnetic domains with in-plane “core magnetization” patterned by nanometer scale domains with out-of-plane components. The hysteresis as a function of in-plane applied magnetic field of both: (i) magnetization curve measured by Superconducting Quantum Interference Device and (ii) dynamic responses measured by broadband Vector Network Analyzer spectroscopy were observed. The experimental results are well described by micromagnetic simulations. These magnetic history dependent effects were explained by magnetization cores, with in plane component, switching.

Vacancy-driven magnetism of GdMnO[formula omitted] multiferroic compound

The impact of the preparation atmosphere (air, Ar, or O2) on the magnetic properties of the multiferroic GdMnO3+δ compound is presented. It was found that the preparation atmosphere has only minor effect on TN, which can be found at temperatures 41.6 – 42.10 K. The transition connected with Tlock is strongly dependent on the preparation atmosphere and can be observed in temperature interval 18.7(1) – 23.4(1) K and can be hysteretic (sample prepared in air and O2 atmosphere), or non-hysteretic (sample prepared in Ar atmosphere). TGd can be found in temperature range 6.4(1) – 12.7(1) K, depending on the preparation route and the magnetic history of the sample. The mechanism hidden behind these effects is the oxygen off-stoichiometry of the prepared samples. The butterfly-type → ferromagnetic/ferrimagnetic → butterfly-type → antiferromagnetic sequence of the hysteresis loops with temperature increasing from 2 K to TN suggests the rich magnetic phase diagram of this compound.

Nonvolatile magnetization switching in a single-layer magnetic topological insulator

Magnetization in a ferromagnetic layer could be manipulated by the spin-orbit torque whose generation commonly relies on the spin-orbit coupling from the adjacent heavy-metal layer within the bilayer. The fact that the magnetic topological insulator possesses both the ferromagnetic order with perpendicular anisotropy and inherent spin-orbit coupling inspires to realize such a torque-induced magnetization switching without forming any heterostructure with other materials. Here, only using a single layer of magnetically-doped topological insulator Cr:(Bi,Sb)2Te3, we realize a magnetization switching only by applying a large dc current. Assisted by the magnetic history, such a switching behaves nonvolatile under zero field but becomes volatile otherwise, as consistently shown by magnetoelectric transports and magneto-optical Kerr effect measurements. Static and quasistatic current are found to be equivalent for the switching. We propose that this switching may associate with the torque resulted from the spin-orbit coupling and the compositional asymmetry in the Cr-profile of the single layer.

Tunable contact angle hysteresis on compliant magnetoactive elastomers

It is shown that the advancing (ACA) and receding (RCA) contact angles of water on extremely soft (shear modulus of the order of 10kPa) magnetoactive elastomer (MAE) films significantly depend on the applied magnetic field. The difference between these angles, known as the contact angle hysteresis, is examined. The roles of the filler concentration and material softness are elaborated. The highest change in the contact angle hysteresis (CAH) from 34∘ in the absence of magnetic field to 76∘ in a magnetic field of 0.4T is achieved for the softest sample with the lowest mass fraction of iron particles (70wt%). The dependence of the CAH on magnetization history (“magnetic hysteresis”) is observed. This magnetic hysteresis is clearly pronounced for the ACA and has little effect on the RCA. Magnetic field-induced changes of the surface roughness exhibit qualitatively the same hysteresis behavior with regard to the external magnetic field as the ACA. The results are promising for the development of smart surfaces for applications where the dynamic wetting has to be controlled.

A Long-lived Lunar Magnetic Field Powered by Convection in the Core and a Basal Magma Ocean

An internally generated magnetic field once existed on the Moon. This field reached high intensities (∼10–100 μT, perhaps intermittently) from ∼4.3 to 3.6 Gyr ago and then weakened to ≲5 μT before dissipating by ∼1.9–0.8 Gyr ago. While the Moon’s metallic core could have generated a magnetic field via a dynamo powered by vigorous convection, models of a core dynamo often fail to explain the observed characteristics of the lunar magnetic field. In particular, the core alone may not contain sufficient thermal, chemical, or radiogenic energy to sustain the high-intensity fields for >100 Myr. A recent study by Scheinberg et al. suggested that a dynamo hosted in electrically conductive, molten silicates in a basal magma ocean (BMO) may have produced a strong early field. However, that study did not fully explore the BMO’s coupled evolution with the core. Here we show that a coupled BMO–core dynamo driven primarily by inner core growth can explain the timing and staged decline of the lunar magnetic field. We compute the thermochemical evolution of the lunar core with a 1D parameterized model tied to extant simulations of mantle evolution and BMO solidification. Our models are most sensitive to four parameters: the abundances of sulfur and potassium in the core, the core’s thermal conductivity, and the present-day heat flow across the core–mantle boundary. Our models best match the Moon’s magnetic history if the bulk core contains ∼6.5–8.5 wt% sulfur, in agreement with seismic structure models.

Evolution of switching fields caused by reorientation of GdFeCo/Ir/GdFeCo synthetic ferrimagnet in magnetic field

Anomalous Hall effect (AHE) in GdFeCo/Ir/GdFeCo multilayered structures attracts great interest because all optical switching, spin-torque, and other effects promise effective application for ultrafast memory element creation. Since AHE is controlled by GdFeCo magnetization, domain dynamics has importance for practical applications. In our work, magnetization reversal in perpendicular GdFeCo/Ir/GdFeCo synthetic ferrimagnets is characterized by AHE measurements. The AHE hysteresis loop obtained with the field applied perpendicular to the sample plane is composed of three sub-loops, and two of them are symmetrically biased with respect to the third one. Switching magnetic fields for two of the three transitions are found to be dependent on magnetic history. In particular, exposure of the sample in the in-plane field leads to reduction of the out-of-plane switching fields in side sub-loops. A multiple series of perpendicular hysteresis loops recorded after exposure under high in-plane field reveals gradual (within 30 min) relaxation of the out-of-plane switching fields to their initial values observed in a non-magnetized sample. Domain wall mobility, limiting switching of the bilayer devices, is complicated due to the coupling between partial domains in each single layer. Unusual dynamics of double domain walls results in unexpected new phenomena affecting electrical processes in bilayer structures.

A Hybrid Magneto‐Optic Capacitive Memory with Picosecond Writing Time

AbstractThe long‐term future of information storage requires the use of sustainable nanomaterials in architectures operating at high frequencies. Interfaces can play a key role in this pursuit via emergent functionalities that break out from conventional operation methods. Here, spin‐filtering effects and photocurrents are combined at metal‐molecular‐oxide junctions in a hybrid magneto‐capacitive memory. Light exposure of metal‐fullerene‐metal oxide devices results in spin‐polarized charge trapping and the formation of a magnetic interface. Because the magnetism is generated by a photocurrent, the writing time is determined by exciton formation and splitting, electron hopping, and spin‐dependent trapping. Transient absorption spectroscopy measurements show changes in the electronic states as a function of the magnetic history of the device within picoseconds of the optical pumping. The stored information is read using time‐resolved scanning magneto optic Kerr effect measurements during microwave irradiation. The emergence of a magnetic interface in the picosecond timescale opens new paths of research to design hybrid magneto‐optic structures operating at high frequencies for sensing, computing, and information storage.

Magnetoelastic coupling behaviour of nanocrystalline ε-Fe2O3

Preparation of a ceramic sample which preserved the nanoscale grain sizes of ∼10–30 nm has allowed elastic and anelastic properties of ε-Fe2O3 to be investigated as functions of temperature and magnetic field strength by Resonant Ultrasound Spectroscopy in the frequency range ∼0.1–1 MHz. Formal analysis of spontaneous strains, e, from previously obtained high resolution lattice parameter data confirmed that magnetic ordering below ∼500 K is accompanied by strains of up to ∼±0.002 due to coupling with the order parameter, m, according to λem2. However, this coupling does not result in elastic softening that would be expected if the order parameter relaxed in response to an induced strain on the timescale of the acoustic resonances. Stiffening or softening during heating through ∼450–480 K of the initial as prepared material, which acquired a distinct magnetisation parallel to the stress applied during Spark Plasma Sintering, is attributed to changes in magnetic domain configurations involving preferred local alignments of individual moments of monodomain crystals. The crystallographic space group, Pna21, and magnetic space group at room temperature, Pna'21', allow ε-Fe2O3 to be both piezoelectric and piezomagnetic. It is postulated that changes in the effective coefficients of these properties for bulk samples are responsible for the observed variations in acoustic resonance frequencies according to the magnetic domain structure present. No elastic or anelastic anomalies were observed at the commensurate-incommensurate transition near 110 K. Instead, acoustic resonance frequencies changed in response to an applied magnetic field, consistent with viscous motion of magnetic domain walls and the effect of poling on piezo coefficients. Ceramic samples of ε-Fe2O3 could have potentially functional piezoelectric and/or piezomagnetic properties that are tunable by choice of magnetic and thermal history.

Pinning potential in highly performant CaKFe4As4 superconductor from DC magnetic relaxation and AC multi-frequency susceptibility studies

We have investigated the pinning potential of high-quality single crystals of superconducting material CaKFe4As4 having high critical current density and very high upper critical field using both magnetization relaxation measurements and frequency-dependent AC susceptibility. Preliminary studies of the superconducting transition and of the isothermal magnetization loops confirmed the high quality of the samples, while temperature dependence of the AC susceptibility in high magnetic fields show absolutely no dependence on the cooling conditions, hence, no magnetic history. From magnetization relaxation measurements were extracted the values of the normalized pinning potential U*, which reveals a clear crossover between elastic creep and plastic creep. The extremely high values of U*, up to 1200 K around the temperature of 20 K lead to a nearly zero value of the probability of thermally-activated flux jumps at temperatures of interest for high-field applications. The values of the creep exponents in the two creep regimes resulted from the analysis of the magnetization relaxation data are in complete agreement with theoretical models. Pinning potentials were also estimated, near the critical temperature, from AC susceptibility measurements, their values being close to those resulted (at the same temperature and DC field) from the magnetization relaxation data.