Ferromagnetic Transition Metals Research Articles

Spin-fluctuation theory of temperature-driven spin reorientations in ferromagnetic transition metal thin films

Spin-fluctuation theory of temperature-driven spin reorientations in ferromagnetic transition metal thin films

FenB2+2n (n = 1, 2), an intrinsic room temperature ferromagnetic MBene with significant magnetic performance enhancement achievable by carbon substitution

From spintronics to data storage technology, two-dimensional (2D) ferromagnetic materials show great promise for various applications. This work reports a series of stable ferromagnetic transition metal boride FenB2+2n (n = 1, 2), where robust long-range ferromagnetic exchange coupling and large perpendicular magnetic anisotropy energy (MAE) allow the ferromagnetic transition temperature (Tc) of the FenB2+2n monolayer to reach above room temperature. The metallic FenB2+2n exhibits n- and p-type Dirac transport in both spin channels with a high Fermi velocity. Furthermore, the application of biaxial compressive strain and electron doping can greatly increase the ferromagnetic coupling and MAE of FeB4 monolayers. On this basis, the FeB2C2 alloy with a high concentration of carbon substitution has been designed, which allows the nonvolatile integration of in-plane compressive strain and electron doping. As expected, this substitution doping resulted in a significant increase in the Tc and MAE of the system. Our findings provide perspectives for the study of 2D magnetic materials.

First-principles study of stability, order and disorder based on an entropy descriptor in noble and ferromagnetic transition metal alloys

Binary alloys AB composed of ferromagnetic metals A (Fe, Co, Ni) and the late 4d−5d noble metals B (Rh, Pd, Ag, Ir, Pt, Au) have been investigated using density functional theory with the generalized gradient approximation to understand the role of magnetism in the stability and the order–disorder transition which has an impact on their physicochemical properties, their applications and their possible implementation as precursors of high-entropy alloys. The enthalpy of formation related to the stability demonstrates that all the alloys are more stable in the ferromagnetic phase than in the nonmagnetic phase. The transition from ordered to disordered phases is quantified using a descriptor which is the standard deviation of the energy spectrum of a set of small nanoalloys with random atomic configurations. The study highlights the fact that the entropy-related descriptor, which is a quantity in determining the formation of a disordered phase as a solid solution or an ordered phase is highly dependent on the atomic environment. Despite the fact that the overall variation of this descriptor is supposed to be unpredictable, there is a noticeable trend showing that the environment-dependent ferromagnetism contributes to a chemical order in alloys and nanoalloys and that this order depends on the atomic radius of the species considered. The results indicate that species with small atomic radii, such as nickel, rhodium or iridium are more likely to form solid solutions than species with larger atomic radii and with more delocalized orbitals.

Study on the texture evolution and mechanical properties of selective laser melting pure nickel

As a ductile and ferromagnetic transition metal, nickel possesses exgrainent metallurgical compatibility, corrosion resistance, high electrical conductivity and high temperature stability. This study investigates the influence of energy density on the microstructure and properties of laser powder bed fusion pure nickel. The research results demonstrate that: during the formation process of Ni, with the increase in energy density, the grain texture exhibits anisotropy. The surfaces parallel and perpendicular to the building direction demonstrate strong {111} and {220} textures respectively. Primary and secondary recrystallization leads to increase in texture strength, subsequently affecting the decrease in dislocation density. The {111} texture yields preferentially, while the {220} single-crystal-like microstructure (SCM) requires higher energy density to complete primary recrystallization and trigger the recovery and enhancement of {111} texture. The enhancement in tensile properties is mainly attributed to the improvement of unmelted defects and texture. With the loading of stress, the failure of the structure leads to a decrease in the strength of the optimal texture component. The {220} texture strengthens the bond between different cladding layers along the building direction, resulting in numerous epitaxial grains parallel to the building direction on the fracture surface, significantly increasing the elongation of the specimen.

Proximity effects induced exchange bias and perpendicular net moment in SrIrO3

The magnetic proximity effect enables the incorporation of magnetic properties into non-magnetic materials, thereby achieving high-performance electronic devices. The 5d perovskite-oxide iridates provide a versatile platform for investigating competing electronic states due to their strong spin–orbit coupling. By proximity to conventional 3d transition-metal oxide ferromagnets, originally paramagnetic SrIrO3 is expected to exhibit exotic magnetic phenomena. In this study, we report the emergence of perpendicular net moment and an unprecedented exchange bias effect in SrIrO3 sandwiched between two ferromagnetic LaMnO3 layers. The magnetization measurements clearly demonstrate antiferromagnetic coupling in the heterostructures, resulting in a shift of the magnetic hysteresis loops. Furthermore, magneto-transport measurements provide evidence for the induction of a net moment along the perpendicular direction of the SrIrO3 film plane due to proximity effects. Both the magnetic pinning effect and perpendicular magnetization can be controlled by an external magnetic field. These findings expand the potential applications of iridate-related heterostructures in modern information storage fields such as skyrmions, spin–orbit torques, and antiferromagnet-based spintronics.

Influence of platinum content (X) in the LaNi5PtX catalyst and reaction conditions on the properties of ferromagnetic Ni-filled CNTs

This research highlights the synthesis of carbon nanostructures using the catalytic chemical vapor deposition (CCVD) method, a hybrid process combining chemical vapor deposition (CVD) and Gas-Solid Heterogeneous Catalysis (GSHC). Intermetallic catalysts, LaNi5Ptx (x = 0, 0.05, 0.5, 1.0), were fabricated through an arc melting procedure to serve as templates for the catalytic conversion of carbon precursors into solid materials. These catalysts, featuring the ferromagnetic transition metal Ni, tend to aggregate into larger particles, reducing the rate of hydrocarbon cracking at the catalyst surface. Rare earth metals like Lanthanum were introduced to form an alloy with a higher melting point to prevent thermal aggregation. Additionally, Pt was incorporated to modify the catalytic properties of the alloy. The study primarily explores the impact of catalyst composition on carbon nanotube (CNT) production. The introduction of platinum content to the catalyst influences the rate at which Ni is filled. The research aimed to alter the catalyst's composition by varying platinum doping in the Pauli paramagnetic lanthanum nickel alloy (LaNi5) to understand the growth mechanism and morphological variations of Ni-filled CNTs. Platinum and lanthanum oxides significantly influence nickel filling in CNTs, resulting in an increased filling rate as the catalyst's Pt content varies from 0 to 1.0. However, higher Pt doping content disrupts the CNT structure with spontaneous nickel encapsulation.

Strong ultrafast demagnetization due to the intraband transitions

Demagnetization in ferromagnetic transition metals driven by a femtosecond laser pulse is a fundamental problem in solid state physics, and its understanding is essential to the development of spintronic devices. Ab initio calculation of time-dependent magnetic moment in the velocity gauge so far has not been successful in reproducing the large amount of demagnetization observed in experiments. In this work, we propose a method to incorporate intraband transitions within the velocity gauge through a convective derivative in the crystal momentum space. Our results for transition-element bulk crystals (bcc Fe, hcp Co and fcc Ni) based on the time-dependent quantum Liouville equation show a dramatic enhancement in the amount of demagnetization after the inclusion of an intraband term, in agreement with experiments. We also find that the effect of intraband transitions on each ferromagnetic material is distinctly different because of their band structure and spin property differences. Our finding has a far-reaching impact on understanding of ultrafast demagnetization.

Promising cathode material MnO2/CoO2 heterostructure for the Li and Na ion battery: A computational study

Although two-dimensional (2D) transition metal oxide monolayers have shown potential for applications in metal-ion batteries, the heterostructures of this family are yet to be studied in details for energy storage applications. In this work, we have made the heterostructure by taking half-metallic ferromagnetic 2D transition metal oxide CoO2 and semiconducting MnO2 monolayers and demonstrated its potential application as a cathode material in lithium and sodium-ion batteries by performing first-principles calculations using density functional theory approach. We have systematically studied the electronic structure and stability of the MnO2/CoO2 heterostructure. We have carefully examined the adsorption and diffusion behavior of metal ions (lithium and sodium). Our structure has offered a maximum adsorption energy of −3.84 eV, which is greater than the adsorption energy of individual monolayers. We found that the lowest diffusion barrier is 0.4 eV for lithium ion and 0.32 eV for sodium ion. Also, our system has shown a maximum open circuit voltage of 2.18 V for lithium ion battery and 0.32 V for Na-ion battery. The specific capacity is found to be 584 mAh g−1 for lithium ion and 529 mAh g−1 for sodium ion battery. These findings can serve as a proof that the MnO2/CoO2 heterostructure should be considered as a potential cathode for lithium- and sodium-ion batteries.

Spin- and valley-resolved tunneling magnetoresistance in a ferromagnetic transition metal dichalcogenide planar heterojunction modulated by polarized light

Spin- and valley-resolved tunneling magnetoresistance in a ferromagnetic transition metal dichalcogenide planar heterojunction modulated by polarized light

Synthetic route to low damping in ferromagnetic thin-films

Previous theory indicated that the individual monolayers within transition metal ferromagnet thin-films contribute different magnitudes to the total ferromagnetic damping. Here, the aim was to investigate if the thin-film damping could be reduced by electronic engineering of the higher damping regions via localized doping. We present new theoretical analysis and experimental results for sputtered Co thin-films in which the upper and lower surface regions were locally doped with Cr. Theory indicates that local doping does reduce the damping and the experiments show a comparable reduction of the damping with increasing local doping up to 30% Cr, while the measured damping falls further with higher local doping, which may be attributed to changes in the film structure. This work opens a route to create low-damping magnetic thin-films.

Extrinsic anomalous Hall effect in van der Waals ferromagnet Fe5GeTe2

We investigate the anomalous Hall effect in a van der Waals material Fe5GeTe2. We find a distinct difference in the temperature dependence of the anomalous Hall effect associated with the evolution of magnetic states in Fe5GeTe2 films. In the low-temperature region, the anomalous Hall conductivity changes with the longitudinal conductivity, which highlights the substantial contribution from the extrinsic mechanism. The extracted skew scattering coefficient in the Fe5GeTe2 films is an order of magnitude larger than that in transition metal ferromagnets. This result sheds light on the role of the extrinsic mechanism in the anomalous Hall effect in van der Waals magnets.

First-principles calculation of anomalous Hall and Nernst conductivity by local Berry phase

In this study, we implemented a finite-difference algorithm for computing anomalous Hall and Nernst conductivity. Based on the expression to evaluate the Berry curvature in an insulating system [J. Phys. Soc. Jpn. 74 1674(2005)], we extended the methods to a metallic system. We calculated anomalous Hall conductivity and Nernst conductivity in a two-dimensional ferromagnetic material FeCl$_2$ and three-dimensional ferromagnetic transition metals bcc-Fe, hcp-Co, and fcc-Ni. Our results are comparable to previously reported results computed by Kubo-formula or Wannier representation. To evaluate anomalous Nernst coefficients, the detailed Fermi-energy dependence of the anomalous Hall conductivity is required. Nonetheless, previous methods based on Wannier representation or Kubo-formula have numerical instability due to the ${\boldsymbol k}$-space Dirac monopole. The present method will open an efficient thermoelectric material design based on the high-throughput first-principles screening.

Toward Sabatier Optimal for Ammonia Synthesis with Paramagnetic Phase of Ferromagnetic Transition Metal Catalysts.

The Sabatier principle defines the essential criteria for being an ideal catalyst in heterogeneous catalysis, while approaching the Sabatier optimal is a major pursuit in catalyst design. The Haber-Bosch (H-B) process, converting nitrogen (N2) and hydrogen (H2) to ammonia (NH3), is a holy grail reaction for humans and also a great model reaction for fundamental research, where the established volcano plot between ammonia synthesis activity and nitrogen binding energy among metals has successfully guided new catalyst design. However, reaching the top of the activity volcano is still very challenging. Herein, we identify an elegant strategy to promote the ferromagnetic (FM) catalysts to be the Sabatier optimal of ammonia synthesis via a second-order ferromagnetic-paramagnetic phase transition, which represents an ideal and novel interdisciplinary of the aforementioned century-old classic principle, reaction, and theory in chemistry, physics, and material science. The paramagnetic (PM) Co and Ni metals could have 2-4 orders of magnitude higher ammonia synthesis activity than their ferromagnetic counterparts, holding the potential to achieve a near-ambient H-B process. We believe that our discovery will open a novel avenue for revisiting the catalytic performances of paramagnetic phases of ferromagnetic materials in heterogeneous catalysis.

High-Efficiency Magnon-Mediated Magnetization Switching in All-Oxide Heterostructures with Perpendicular Magnetic Anisotropy.

The search for efficient approaches to realize local switching of magnetic moments in spintronic devices has attracted extensive attention. One of the most promising approaches is the electrical manipulation of magnetization through electron-mediated spin torque. However, the Joule heat generated via electron motion unavoidably causes substantial energy dissipation and potential damage to spintronic devices. Here, all-oxide heterostructures of SrRuO3 /NiO/SrIrO3 are epitaxially grown on SrTiO3 single-crystal substrates following the order of the ferromagnetic transition metal oxide SrRuO3 with perpendicular magnetic anisotropy, insulating and antiferromagnetic NiO, and metallic transition metal oxide SrIrO3 with strong spin-orbit coupling. It is demonstrated that instead of the electron spin torques, the magnon torques present in the antiferromagnetic NiO layer can directly manipulate the perpendicular magnetization of the ferromagnetic layer. This magnon mechanism may significantly reduce the electron motion-related energy dissipation from electron-mediated spin currents. Interestingly, the threshold current density to generate a sufficient magnon current to manipulate the magnetization is one order of magnitude smaller than that in conventional metallic systems. These findings suggest a route for developing highly efficient all-oxide spintronic devices operated by magnon current.

Spin-polarized hybrid states in epitaxially-aligned and rotated graphene on cobalt

The strong interaction between graphene and elemental ferromagnetic transition metals results in considerable shifts of the graphene π band away from the Fermi level. At the same time, a weakly-dispersing single-spin conical band feature is found in the proximity of the Fermi level at the K̄ point in the surface Brillouin zone of epitaxially-aligned graphene/Co(0001). Here, the robustness of this electronic state against twisting angles at the interface is experimentally and theoretically demonstrated by showing the presence of similar band features also in the case of rotated graphene domains on Co(0001). Spin-resolved reciprocal space maps show that the band feature in rotated graphene has similar Fermi velocity and spin polarization as its counterpart in epitaxially-aligned graphene. Density functional theory simulations carried out for the experimentally observed graphene orientations, reproduce the highly spin-polarized conical band feature at the graphene K̄ point, characterized by a hybrid π-d orbital character. The presence of the conical features in the rotated domains is attributed to the unfolding of the superstructure K̄ point states exclusively to the K̄ point of the graphene primitive cell. The similarities found in the electronic character for different graphene orientations are crucial in understanding the magnetic properties of realistic graphene/Co interfaces, facilitating their implementation in spintronics applications.

Spin Swapping Effect of Band Structure Origin in Centrosymmetric Ferromagnets.

We theoretically demonstrate the spin swapping effect of band structure origin in centrosymmetric ferromagnets. It is mediated by an orbital degree of freedom but does not require inversion asymmetry or impurity spin-orbit scattering. Analytic and tight-binding models reveal that it originates mainly from k points where bands with different spins and different orbitals are nearly degenerate, and thus it has no counterpart in normal metals. First-principle calculations for centrosymmetric 3d transition-metal ferromagnets show that the spin swapping conductivity of band structure origin can be comparable in magnitude to the intrinsic spin Hall conductivity of Pt. Our theory generalizes transverse spin currents generated by ferromagnets and emphasizes the important role of the orbital degree of freedom in describing spin-orbit-coupled transport in centrosymmetric materials.

Quantum ferromagnetism in transition metals doped II-VI semiconductors for spintronic applications: A merging technology

The spintronic is a merging field of advanced technology in which fuctionality of quantum devices controlled by spin of electrons. Therefore, the electronic, magnetic and thermoelectric characteristics of 6.25% and 25% V, Cr, Mn, and Fe doepd SrS are addressed comprehensively. The comparison of ferromagnetic and the antiferromagnetic states favour the stability of ferromagnetic state. The formation energy and Curie temperature (Tc) are analysed for thermodynamic stability and room temperature ferromagnetism. The ferrmagnetic semiconductors (V, Mn), and Half metallic ferromagneitsm (Cr, Fe) are ensured through band structures, and density of states. The nature of ferroamgnetism and spin polarization density are computed by exchange energies (Δx(d), Δx(pd), crystal field energies (ΔCF), exchange constants (N0α and N0β), and integer magnetic moments. Furthermore, the effect of thermoelectric paramters are addressed by Seebeck coefficient, thermal conductivity, power factor, and electrical conductivity.

Effect of stacking faults on magnetic properties and magnetization reversal in Co nanowires

Ferromagnetic 3d transition metal nanowires based on the assembly of shape anisotropy seem apt candidates to replace materials based on rare-earth elements in current permanent magnets. Recently, great efforts have been devoted into enhancing the coercivity of Co nanowires, through accurate control of shape and morphology. Nevertheless, stacking faults can be formed relatively easily in close-packed metals like Co, and its effect on the magnetic properties was usually obscured by the geometrical effect and being ignored. In this work, the Co nanowires with different aspect ratios were synthesized by solvothermal chemistry processes. The effect of aspect ratio on the magnetic properties of Co nanowires was investigated, and a high magnetic property with a coercivity of 9 kOe was obtained in the Co nanowires with an aspect ratio of 10. The stacking faults were observed in the Co nanowires with an aspect ratio beyond 10, which may be a contributing factor to the lower coercivity than expected. The micromagnetic simulation was employed to reveal the effect of stacking faults on the magnetization reversal mechanism, based on which the coercivity degradation mechanism was discussed. This work is instructive for developing high-performance magnetic nanowires.

Temperature dependence of the Gilbert damping of La0.7Sr0.3MnO3 thin films

Due to its half metallic nature, ${\mathrm{La}}_{0.7}{\mathrm{Sr}}_{0.3}{\mathrm{MnO}}_{3}$ is an attractive highly correlated electronic system to obtain ultralow magnetic damping. In this paper we analyze the temperature and thickness dependence of the damping of the magnetization dynamic of epitaxial thin ${\mathrm{La}}_{0.7}{\mathrm{Sr}}_{0.3}{\mathrm{MnO}}_{3}$ films. Our analysis reveals that the damping encompasses resistivelike and conductivelike contributions, as in transition metal ferromagnets. The data also show a large increase of the ferromagnetic resonance linewidth at low temperature, a feature that we ascribe to the presence of a dead layer, insulating and magnetically active, that behaves like a spin sink. The associated spin-pumping term shows a strong temperature dependence, linked to that of the spin mixing conductance. By clarifying some unexplored aspects of spin dynamics in half-metallic manganites, our results contribute to the progress in the burgeoning field of oxide spin orbitronics.

Iron oxide-Palladium core-shell nanospheres for ferromagnetic resonance-based hydrogen gas sensing

Interfaces of ferromagnetic transition metals such as Iron, Cobalt, and Nickel with non-magnetic palladium are of interest due to their unique magnetic and spintronic properties. These interfaces enable ferromagnetic resonance (FMR) based sensing of hydrogen gas. In the present work, we synthesized Fe3O4–Pd core-shell nanospheres via a one-pot synthesis method using the thermal decomposition of Fe3+ acetylacetonate in the presence of a reducing agent to produce the Fe3O4 core, followed by the reduction of a Pd2+ precursor to form the pure Pd shell. We found that our in-situ synthesized core-shell nanostructure is magnetically active and shows excellent H2 gas sensing properties. The effect of reversible hydrogen gas absorption on the magnetism of Fe3O4–Pd core-shell nanospheres was investigated. The hydrogen-induced ferromagnetic-resonance (FMR) peak shift amounted to 30% of the peak linewidth for the virgin state of the sample. In addition, in the presence of hydrogen gas, we observed a fully reversible decrease in the FMR peak linewidth by about two times. This was accompanied by a nearly doubling of the FMR peak height. Response and recovery times of about 2 and 50 s, respectively, were extracted from the measurements. All the data was collected using a mix of just 3% hydrogen in a nitrogen carrier gas.