Magnetic Anisotropy Research Articles

Investigation of magnetic domain interactions and switching mechanism in sputter deposited Fe–Co–Al thin film

To create a high-density data storage system, a thorough understanding of magnetic domain interactions is essential. In this work, we present a systematic study of magnetic domain state interaction and switching mechanism of Fe–Co–Al films across various thicknesses. Structural analysis confirms the formation of an A2-type disorder structure. Magnetic investigation reveals that all films are soft magnetic in nature, exhibiting a predominant in-plane magnetic anisotropy with a low coercive field that increases from 1.9 mT to 3 mT as the film thickness grows from 5 nm to 25 nm. Analysis of first-order reversal curves reveals the formation of multi-domain (MD) states. An enhancement of magnetic domain interactions occurs as the contour graph shifts along the coercive field direction with an increase in film thickness. Switching field distribution (SFD) analysis reveals broader SFD curves, indicating more inter-grain interactions as magnetostatic interactions between magnetic grains intensify with thickness. Further, magnetic force microscopy analysis confirms the presence of MD structures in all films. Magnetization reversal dynamics elucidates domain wall pinning near to zero field and possesses a large out-of-plane switching field. Simulations are performed to corroborate experimental findings. These findings underscore the critical role of domain state configuration and switching mechanisms for designing spintronic devices using soft magnetic thin films.

Enhancement of interlayer exchange coupling via intercalation in 2D magnetic bilayers: towards high Curie temperature.

Two-dimensional magnetic materials are considered as promising candidates for developing next-generation spintronic devices by providing the possibility of scaling down to nanometers. However, a low Curie temperature is a crucial problem for practical applications, being intimately related to weak interlayer exchange coupling. Here, by using density functional theory calculations, we show that interlayer exchange coupling can be enhanced by intercalating 3d transition metals (Sc to Zn) into a bilayer of CrI3 and NiI2. It is found that intercalated Ni and Cr atoms exhibit strong antiferromagnetic coupling with the CrI3 and NiI2 host layers, respectively. This enhances the ferromagnetic interlayer exchange coupling between the host layers by many folds compared to pristine CrI3 and NiI2 bilayers. Moreover, both intercalated compounds show out-of-plane magnetic anisotropy with half metallic nature, which makes them ideal candidates for spintronics applications. Thereby our work provides a rational approach to raise the Curie temperature of non-metallic two-dimensional magnets by intercalation.

Zero Thermal Expansion Behavior in High‐Entropy Anti‐Perovskite Mn3Fe0.2Co0.2Ni0.2Mn0.2Cu0.2N

AbstractThe exploration of the non‐collinear antiferromagnetic (AFM) phase holds promise for the discovery of zero thermal expansion (ZTE) materials, which is of great significance to resist the temperature effect in aerospace and precision engineering fields. Currently, there is still a lack of effective approaches to regulate this special AFM phase. In this work, a non‐collinear AFM phase has been obtained in the anti‐perovskite compound Mn3Fe0.2Co0.2Ni0.2Mn0.2Cu0.2N proposed by high‐entropy engineering. Utilizing neutron powder diffraction (NPD) analysis, the magnetic structure is resolved to be a triangular AFM phase with a k = [0, 0, 0] and a ferromagnetic (FM) component located at the corner of the cubic structure, which belongs to the R‐3 space group. Particularly, it presents ZTE behavior in a wide temperature range from 10 to 180 K. In‐situ NPD analysis reveals that the negative thermal expansion attributed to magnetic evolution almost offsets the normal positive thermal expansion quantified by the Debye formula. Further first principles calculations reveal that the specific AFM phase derives from the AFM‐type nearest neighboring magnetic exchange interactions and the easy‐axis‐type magnetic anisotropy. This demonstration offers an efficient strategy for designing magnetic structures and achieving ZTE over a wide temperature range.

Above-room-temperature intrinsic ferromagnetism in ultrathin van der Waals crystal Fe3+xGaTe2

Two-dimensional (2D) van der Waals (vdW) magnets are crucial for ultra-compact spintronics. However, so far, no vdW crystal has exhibited tunable above-room-temperature intrinsic ferromagnetism in the 2D ultrathin regime. Here, we report the tunable above-room-temperature intrinsic ferromagnetism in ultrathin vdW crystal Fe3+xGaTe2 (x = 0 and 0.3). By increasing the Fe content, the Curie temperature (TC) and room-temperature saturation magnetization of bulk Fe3+xGaTe2 crystals are enhanced from 354 to 376 K and 43.9 to 50.4 emu·g−1, respectively. Remarkably, the robust anomalous Hall effect in 3-nm Fe3.3GaTe2 indicates a record-high TC of 340 K and a large room-temperature perpendicular magnetic anisotropy energy of 6.6 × 105 J m−3, superior to other ultrathin vdW ferromagnets. First-principles calculations reveal the asymmetric density of states and an additional large spin exchange interaction in ultrathin Fe3+xGaTe2 responsible for robust intrinsic ferromagnetism and higher TC. This work opens a window for above-room-temperature ultrathin 2D magnets in vdW-integrated spintronics.

Swift heavy ion irradiation-induced enhancement of spin–orbit torque efficiency in Pt/Co/Ta trilayers

Increasing the efficiency of spin–orbit torque (SOT) is of great interest in applications for magnetic random access memory and logic devices due to decreased energy consumption. Here, we present that the SOT efficiency of Pt/Co/Ta films with perpendicular magnetic anisotropy can be improved by swift high-energy heavy Fe11+ ion irradiation, which is an effective method to alter crystallinity, interface roughness, and defects in ferromagnet/heavy metal heterostructures. Specifically, the Pt/Co/Ta films show an optimal SOT efficiency at ion fluence around 1.0 × 1013 ions/cm2 with the largest spin Hall angles reaching 0.59, which is the largest improvement of spin Hall angle by ion irradiation compared to previous studies using light ions. We demonstrate that the increase in SOT efficiency arises from structural changes in the Pt layer due to ion irradiation-induced damage effects at proper fluence, while the decrease in SOT efficiency is mainly attributed to the restoration of Pt crystallinity induced by beam-heating effects at high fluence. This work demonstrates that an appropriate ion irradiation process could improve the SOT efficiency and the spin Hall angle, thereby providing a way to develop future SOT-based spintronic devices.

Control of chiral damping in magnetic trilayers using He+ ion irradiation

In the forefront of spintronic advancements, structures with strong perpendicular magnetic anisotropy (PMA) such as Pt/Co/Pt are essential for the miniaturization and performance enhancement of high-density magnetic storage technologies. The robust PMA characteristic of these systems facilitates the development of scalable spintronic devices, crucial for next-generation magnetic memory applications. This study investigates the interplay between PMA and the Dzyaloshinskii-Moriya interaction (DMI)—an antisymmetric exchange interaction prevalent in non-centrosymmetric magnetic systems—and its dissipative counterpart, chiral damping. While chiral damping arises from the same broken inversion symmetry as DMI, it typically introduces an additional energy dissipation channel, reducing device efficiency. Our research examines the effects of controlled helium ion (He+) irradiation on a Pt/Co/Pt system. We find that ion beam irradiation enhances interfacial intermixing, which correlates with a decrease in PMA. However, domain wall velocity measurements indicate a concurrent reduction in both DMI and chiral damping, along with enhanced velocities as irradiation fluence increases. These observations suggest that ion beam irradiation can be judiciously applied to achieve a balance between lower DMI, chiral damping, and reasonable PMA, thereby optimizing the system for improved device performance.

Isolation and Electronic Structures of Lanthanide(II) Bis(trimethylsilyl)phosphide Complexes.

While lanthanide (Ln) silylamide chemistry is mature, the corresponding silylphosphide chemistry is underdeveloped, with [Sm{P(SiMe3)2}{μ-P(SiMe3)2}3Sm(THF)3] being the sole example of a structurally authenticated Ln(II) silylphosphide complex. Here, we expand the Ln(II) {P(SiMe3)2} chemistry through the synthesis and characterization of nine complexes. The dinuclear "ate" salt-occluded complexes [{Ln[P(SiMe3)2]3(THF)}2(μ-I)K3(THF)] (1-Ln; Ln = Sm, Eu) and polymeric "ate" complex [KYb{P(SiMe3)2}3{μ-K[P(SiMe3)2]}2]∞ (2-Yb) were prepared by the respective salt metathesis reactions of parent [LnI2(THF)2] (Ln = Sm, Eu, Yb) with 2 or 3 equiv of K{P(SiMe3)2} in diethyl ether. The separate treatment of these complexes with either pyridine or 18-crown-6 led to the formation of the mononuclear solvated adducts trans-[Ln{P(SiMe3)2}2(py)4] (3-Ln; Ln = Sm, Eu, Yb) and [Ln{P(SiMe3)2}2(18-crown-6)] (4-Ln; Ln = Sm, Eu, Yb), with concomitant loss of K{P(SiMe3)2}. The complexes were characterized by a combination of NMR, electron paramagnetic resonance (EPR), attenuated total reflectance infrared (ATR-IR), electronic absorption and emission spectroscopies, elemental analysis, SQUID magnetometry, and single crystal X-ray diffraction. We find that these complexes contrast with those of related Ln(II) bis(silyl)amide complexes due to differences in ligand donor atom hardness and ligand steric requirements from Ln-P bonds being longer than Ln-N bonds. This leads to higher coordination numbers, shorter luminescence lifetimes, and smaller easy-axis magnetic anisotropy parameters.

Osmium(III) Acetylacetonate and Its Missing Polymorph: A Magnetic and Structural Investigation.

Despite the potential for their application, the magnetic behavior of complexes containing 4d and 5d metal ions is underexplored, evidencing the need for benchmark multi-technique studies on simple molecules. We report here a structural and magnetic study on osmium(III) acetylacetonate [Os(acac)3]. X-ray single crystal diffraction did not allow us to determine the structure of the β-polymorph of [Os(acac)3]. The combined magnetic (dc magnetic measurements on powder and cantilever torque magnetometry on single crystal) and spectroscopic (electron paramagnetic resonance, EPR) characterization is here used to provide further evidence that its structure is indeed the one of the orthorhombic "missing polymorph", analogous to the ruthenium(III) derivative. Our study shows that all acetylacetonate complexes of the eighth group of the periodic table show dimorphism and are isomorphic. The EPR characterization allowed the experimental assessment of the easy axis nature of the ground doublet and the determination of the first hyperfine coupling in an osmium complex. Torque magnetometry, applied here for the first time on an osmium-based molecule, determined the orientation of the easy axis along the pseudo C3 axis of the complex. Ac magnetometric measurements revealed in-field slow relaxation of the magnetization further slowed by the suppression of dipolar fields via magnetic dilution in the isostructural gallium(III) analogue.

Magnetic Anisotropy of Cr2Te3: Competition between Surface and Middle Layers

Recently, the orbital coupling in 2D materials has been demonstrated to have a significant impact on the magnetic anisotropy (MA) of CrTe2. The Te atomic layers on the surface layers determine the magnetocrystalline anisotropy (MCA) of the system due to orbital coupling. Herein, is proposed to investigate the surface and middle layers of Te atoms on MA. The MCA of consists of in‐plane and out‐of‐plane components, which are contributed by the surface layer and middle layer, respectively. Due to the lack of Cr–Te–Cr chemical bonds in the z‐axis, the surface layer produces coupling and results in the in‐plane MA. In addition, a tensile strain can enhance the coupling on the middle layer and lead to the out‐of‐plane MCA. At the same time, the out‐of‐plane MCA breaks the vertical mirror symmetry and an anomalous Hall effect has been detected on monolayer (1L) . Based on this result, an anomalous Hall device is designed to record and read information. The opposing contribution of the surface and middle layers provides a completely new way to understand 2D materials.

Role of surface roughness in determining surface energy and magnetic properties of Fe80Ce20 films during thermal processing on Si(100) and glass substrates

In this study, Fe80Ce20 films were deposited on Si(100) and glass substrates using sputtering in a high-vacuum environment and subsequently heat-treated in a vacuum annealing furnace. The films, with thicknesses ranging from 10 nm to 50 nm, were annealed at temperatures of 100 °C, 200 °C, and 300 °C. The objective was to investigate the effects of film thickness and annealing temperature on the structural, surface energy, and magnetic properties of the material. X-ray diffraction (XRD) analysis confirmed the crystalline nature of both Si(100)/Fe80Ce20 and Glass/Fe80Ce20 films. Atomic force microscopy (AFM) revealed a smooth film surface that became rougher after annealing. Contact angle measurements indicated hydrophilic properties, with the highest surface energy observed in the as-deposited films due to a higher density of defects and grain boundaries. The hysteresis loop demonstrated exceptional soft magnetic properties and a high saturation magnetization (Ms) of approximately 2000 emu/cm³. Annealing at 100 °C altered the magnetic domain structure from a striped labyrinthine configuration to an aligned pattern. At higher annealing temperatures, the films exhibited grain growth, increased surface roughness, and new grain formation. Following annealing, the grains in the Fe80Ce20 films became larger, surface roughness increased, and the water contact angle increased, rendering the films more hydrophobic. The as-deposited films displayed the highest surface energy due to the high density of defects and grain boundaries. Increased surface roughness led to more grain boundary defects and irregularities, which served as pinning points for magnetic domain walls, thus increasing coercivity (Hc). Rough surfaces induced local stress fields, increased magnetic anisotropy, and decreased saturation magnetization. Thermal perturbations from higher annealing temperatures further disrupted the alignment of the magnetic moments, leading to a reduction in saturation magnetization.

Enhancing Crystallinity and Magnetic Properties of Cobalt Ferrite Nanoparticles via Thermal Oxidation

AbstractCobalt ferrite (CFO) nanoparticles (NPs) are highly promising for data storage, energy conversion, permanent magnets, and biomedical applications owing to their exceptional magnetic properties. However, the presence of phase impurities (particularly FeO and CoO) can severely degrade their magnetic properties, hindering their practical use. Here, we present a simple post‐synthesis oxidation approach to address this challenge. Our method involves the thermal decomposition of Fe−Co oleate followed by oxidation using trimethylamine N‐oxide. The results reveal the effective elimination of FeO and CoO impurities and the formation of spinel ferrite crystal structures post‐oxidation with no change in morphology or size. Magnetic measurements demonstrate a significant enhancement in magnetic properties (e. g., magnetic saturation, coercivity, and blocking temperature) in oxidized CFO NPs compared to the non‐oxidized counterparts, indicative of the recovered ferrimagnetic structure upon post‐synthesis oxidation. As expected, the restoration of the ferrimagnetic structure, resulting in improved magnetic anisotropy, led to decreased SAR values as the nanoparticles moved away from the optimal anisotropy range. The study underscores the necessity of post‐synthesis oxidation for ensuring phase purity and enhancing the magnetic properties of CFO NPs, irrespective of the synthesis method. This approach offers a promising route for producing highly functional magnetic nanoparticles for practical applications.

Unusual inverse spin Hall effect in Pt/Co/Pt multilayers on single-crystalline YIG

The inverse spin Hall effect (ISHE) is a significant phenomenon that enables the conversion of spin current into charge current, offering promising applications in novel spintronic devices. In conventional ISHE measurements, it is widely recognized that the spin polarization, spin current, and generated charge current are mutually perpendicular. This study systematically investigates the ISHE in Pt/Co/Pt multilayers grown on a single-crystalline yttrium iron garnet (YIG) layer. A non-zero ISHE voltage was obtained along the direction parallel to the external magnetic field within the YIG coercive field range, deviating from the classical ISHE behavior. Our investigation revealed that the in-plane magnetic anisotropy of single-crystalline YIG plays a crucial role, as the easy axis of YIG and the external magnetic field collaboratively determine the polarization direction of the spin current, especially when the external magnetic field is smaller than the YIG coercive force. Furthermore, by tuning the small in-plane magnetization component of the Pt/Co/Pt multilayers, which couples with the YIG magnetization, we were able to control the shape and reversal path of the ISHE voltage loop. These findings deepen our understanding of how magnetic order affects charge current flow in ISHE measurements. The variety of ISHE voltage loop shapes and reversal paths observed suggest potential applications for this device as a magnetic field sensor.

Tailoring microstructure in a soft-magnetic Fe-based amorphous-nanocrystalline alloy for high resistivity according to electrical percolation threshold

Superior soft-magnetic materials are necessary for the development of modern magnetic devices with energy-saving and high-power density requirements. However, improving the magnetism by nanocrystallization always brings about the sacrifice of resistivity, presenting a common trade-off in Fe-based amorphous-nanocrystalline alloys. Here, the comprehensive merits of both superior soft-magnetic properties (high saturation magnetization of 1.81 T and low coercivity of 3.8 A/m) and high resistivity of 117.2 μΩ·cm were obtained by precisely tailoring amorphous-nanocrystalline microstructure close to electrical percolation threshold for a Fe82.5B12P2C1Cu0.5Co2 amorphous alloy. The soft-magnetic properties are attributed to the low magnetic anisotropy stemming from high nuclei number density and ultrafine nanocrystalline grains of 9.2 nm. The high resistivity is associated with the electrical percolation behavior with a nanocrystalline volume threshold of 14.8 % in the composite alloy. The results provide an effective strategy to overcome the trade-off in traditional amorphous-nanocrystalline alloys, significant for applications in high-frequency, high-power, and energy-saving devices.

Magnetic properties of GdFeCo thin films tailored by sputtering conditions

The unique properties of ferrimagnets including easy detection of their dynamic and static states, strong resistance to external disturbances, and rapid dynamic characteristics, have made them attractive in the spintronics community. Our study focuses on the engineering of these magnetic properties of ferrimagnets, particularly employing a GdFeCo alloy, a prominent ferrimagnetic material, by utilizing magnetron sputtering. A series of GdFeCo films are fabricated by altering their thicknesses and working pressure during the sputtering process. Our experimental results reveal that these sputtering parameters significantly influence a Gd composition within the films, which in turn affects critical properties of ferrimagnets such as magnetic anisotropy, and magnetic moment compensation temperature. By precisely controlling these sputtering parameters, we successfully tailored the magnetic properties of the GdFeCo thin films with desired properties, offering new possibilities for the creation of sophisticated magnetic materials tailored to specific technological needs.

Effects of Ta and W insertion on thermal stability in Co2FeAl/HM/Co2FeAl multilayers

In this paper, by inserting a certain thickness of the Ta and W into the Ta (5)/MgO (1)/Co2FeAl (1.5)/HM/Co2FeAl (1.5)/MgO (1)/Ta (2) multilayer films, the thermal stability of the multilayers is regulated. When Ta is inserted, the sample shows perpendicular magnetic anisotropy (PMA) in the as-deposited state, but the thermal stability is only maintained at 250 °C; when Ta is replaced with a W insertion, the thermal stability is increased to 450 °C.The XPS results show that after annealing at 350°C, Ta diffused into the ferromagnetic layer to absorb oxygen atoms, resulting in underxidation of Fe and Co, and PMA disappeared in films with Ta insertion. During the preparation of the film with W insertion, the oxygen in MgO sputtered onto the ferromagnetic layer, resulting in excessive oxidation of Fe and Co in films, so the as-deposited film shows in-plane magnetic anisotropy (IMA). However, after annealing at 350 °C, FeOx and CoOx were reduced, and some oxygen atoms returned to MgO. The oxidation state in the ferromagnetic layer is adjusted to the ideal level. Additionally, the roughness of the CFA/MgO interface of the films with W insertion was reduced, so the films with W insertion after annealing still maintained good PMA.

Synthesis of Low-Symmetric α-Cobalt(II) Hydroxide-Incorporated Cyanuric Acid Layers with High Néel Temperature and Large Coercivity: Structure and Magnetism.

α-Cobalt(II) (CoII) hydroxide (compound 1) incorporating cyanuric acid layers was synthesized via the solvothermal method. 1 exhibited two distinct characteristics, which were different from reported α-CoII hydroxides. (i) The presence of abundant consecutive hydrogen bonds between the adjacent hydroxide layers enhanced the driving force of crystallization along the direction of the c axis. Thus, 1 revealed high crystallinity without the disorder phenomenon. (ii) 1 showed low symmetry. The configuration of CoTd sites did not follow the regular triangular net. The low symmetry favored the magnetic anisotropy. Thus, 1 revealed ferrimagnetic behavior with a high Néel temperature (TN = 56.8 K) and coercivity (Hc = 36 kOe at 2 K). The ferrimagnetic behavior of 1 was validated via the Hubbard U correction density functional theory.

The electronic and magnetic properties modulated by ferroelectric polarization switching in two-dimensional VSeTe/Sc2CO2 van der Waals heterostructures.

Exploring multiferroic materials that combine magnetic and ferroelectric properties is scientifically interesting and has important technical implications for many functions of nanoscale devices. In this work, spintronics and magnetoelectric coupling devices are proposed in two-dimensional (2D) layered ferromagnetic (FM)/ferroelectric (FE) van de Waals (vdW) heterostructures, VSeTe/Sc2CO2, employing density functional theory (DFT) calculations. The results indicate that the VSeTe/Sc2CO2 vdW heterostructure changes from a metal to a semiconductor in Sc2CO2-P↑ and Sc2CO2-P↓ polarization states. At the same time, the charge at the interface of the VSeTe/Sc2CO2 heterostructure will also be redistributed with the transformation of the ferroelectric polarization state, resulting in the change of the distribution of the electronic states near the Fermi level, and thus the change in the magnetic anisotropy energy (EMAE) of the heterostructure. Interestingly, biaxial strain brings reversibility and non-volatile regulation to the heterostructure of semiconductors and metals. The results provide an effective way to fabricate magnetoelectric coupling devices with 2D multiferroic heterostructures.

Magnetic Domain and Structural Defects Size in Ultrathin Films

Herein, a model is proposed for measuring the structural defects size r0 in an ultrathin magnetic layer with perpendicular magnetic anisotropy. Based on the observations of magnetic domains in Ta/Pt/Co/Pt ultrathin films, using polar magneto‐optical Kerr effect microscopy and measurements of their magnetic anisotropies, the correlation between magnetic domains size D and structural defects size r0, as well as the defects concentration parameter αK, which designates the degree of pinning, has been modeled. The average r0 value found is high in the sample with unannealed buffer layers and considerably decreases with annealing. It is 6.17 nm with unannealed Ta/Pt buffer layers, 1.06 nm in sample with Ta/Pt buffer layers annealed at 423 K, and 0.49 nm in that with buffer layers annealed at 573 K. The significant drop of r0 is in good agreement with the high depinning noted with buffer layers annealing in recent work.

Centimeter-scale above room temperature ferromagnetic Fe3GaTe2 thin films by molecular beam epitaxy

Abstract Fe3GaTe2, as a layered ferromagnetic material, has a Curie temperature (T c ) higher than room temperature, making it the key material in the next generation of spintronic devices. To be used in practical devices, large-size and high-quality Fe3GaTe2 thin films need to be prepared. Here, the centimeter-scale thin film samples with high crystal quality and above room temperature ferromagnetism with strong perpendicular magnetic anisotropy (PMA) have been prepared by molecular beam epitaxy technology. Furthermore, the T c of the samples raises as the film thickness increases, and reaches 367 K when the film thickness is 60 nm. This study provides material foundations for the new generation of van der Waals spintronic devices and paves the way for the commercial application of Fe3GaTe2.

Origin of perpendicular magnetic anisotropy in Fe0.6Al0.4/Cr0.8Al0.2 metallic superlattice

Abstract In this study, we investigated a perpendicular magnetic anisotropy (PMA) in a ferromagnet/antiferromagnetic stacking structure without using heavy metal elements. The Fe0.6Al0.4/Cr0.8Al0.2/Fe0.6Al0.4 stacked films exhibited perpendicular magnetization. We discussed the origin of the PMA based on the Cr0.8Al0.2 thickness, t Cr-Al (= 0.6 – 3.0 nm) dependences of the uniaxial anisotropy energy density K u, elastic strain ε 1 – ε 3, and unit cell volume V of the Fe0.6Al0.4 and Cr0.8Al0.2 layers. The K u value was approximately 25 kJ/m3, independent of t Cr-Al. The positive ε 1 – ε 3, i.e., the tensile strain in the Cr0.8Al0.2 layer can promote the PMA. The possible degradation of PMA due to the lattice relaxation with increasing t Cr-Al could be compensated by recovering the Cr magnetic moment. Our analysis suggests that PMA is caused by interfacial exchange coupling between ferromagnetic Fe0.6Al0.4 and antiferromagnetic Cr0.8Al0.2.