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The exchange coupling between two ferromagnetic thin films, one with magnetically hard and the other with soft phases, separated by a thin non-magnetic layer, is studied. Nd-Fe-B/Ti/Fe thin film heterostructures were fabricated using DC magnetron sputtering on Si substrates, which were heated in situ at 650 °C using a house-built vacuum-compatible heater. The effect of the thickness of the Ti buffer layer and the annealing temperature on the formation of various phases of Nd-Fe-B was investigated. The effect of the thickness of the non-magnetic Ti spacer layer on the exchange coupling strength between the hard phase Nd-Fe-B ferromagnetic thin layer and the soft phase transition metal Fe layer was experimentally investigated. Hysteresis loops of multilayer thin films indicate an antiferromagnetic coupling was observed when the thickness of the spacer layer was 2 nm. This is within the range of an antiferromagnetic coupling calculation based on RKKY theory predictions. [ABSTRACT FROM AUTHOR]

The rapid development of 2D magnetic materials has opened new possibilities in the field of spintronics. CrTe2, a 2D material with perpendicular magnetic anisotropy (PMA) and ferromagnetic transient temperature near room temperature, holds promise for various applications. However, the underlying mechanism responsible for its global magnetism remains unclear. This work focuses on investigating the magneto‐transport properties of ultra‐thin CrTe2 Field Effect Transistor (FET) under the influence of top gate biases. The application of gate voltage ranging from 25 to −15 V tunes its coercivity (HC) and Curie temperature (TC) (from 152 to 191 K). Notably, a linear correlation is observed between the TC and the hole concentration (np1/3$n_{\mathrm{p}}^{1/3}$) in the CrTe2 film, indicating the involvement of the Ruderman–Kittel–Kasuya–Yosida interaction. This experimental analysis sheds light on the mechanism of the CrTe2's ferromagnetism and paves the way for future advancements and applications in this material. [ABSTRACT FROM AUTHOR]

Abstract The rapid development of 2D magnetic materials has opened new possibilities in the field of spintronics. CrTe2, a 2D material with perpendicular magnetic anisotropy (PMA) and ferromagnetic transient temperature near room temperature, holds promise for various applications. However, the underlying mechanism responsible for its global magnetism remains unclear. This work focuses on investigating the magneto‐transport properties of ultra‐thin CrTe2 Field Effect Transistor (FET) under the influence of top gate biases. The application of gate voltage ranging from 25 to −15 V tunes its coercivity (HC) and Curie temperature (TC) (from 152 to 191 K). Notably, a linear correlation is observed between the TC and the hole concentration (np1/3) in the CrTe2 film, indicating the involvement of the Ruderman–Kittel–Kasuya–Yosida interaction. This experimental analysis sheds light on the mechanism of the CrTe2’s ferromagnetism and paves the way for future advancements and applications in this material.

[Display omitted] Presence of the Dzyaloshinskii-Moriya (DM) interaction in limited noncentrosymmetric materials leads to novel spin textures and exotic chiral physics. The emergence of DM interaction in centrosymmetric crystals could greatly enrich material realization. Here we show that an itinerant centrosymmetric crystal respecting a nonsymmorphic space group is a new platform for the DM interaction. Taking the P 4 / nmm space group as an example, we demonstrate that the Ruderman-Kittel-Kasuya-Yosida (RKKY) interaction induces the DM interactions, in addition to the Heisenberg exchange and the Kaplan-Shekhtman-Entin-wohlman-Aharony (KSEA) interaction. The direction of DM vector depends on the positions of magnetic atoms in the real space, and the amplitude depends on the location of the Fermi surface in the reciprocal space. The diversity stems from the position-dependent site groups and the momentum-dependent electronic structures guaranteed by the nonsymmorphic symmetries. Our study unveils the role of the nonsymmorphic symmetries in affecting magnetism, and suggests that the nonsymmorphic crystals can be promising platforms to design magnetic interactions. [ABSTRACT FROM AUTHOR]

The exchange coupling between two ferromagnetic thin films, one with magnetically hard and the other with soft phases, separated by a thin non-magnetic layer, is studied. Nd-Fe-B/Ti/Fe thin film heterostructures were fabricated using DC magnetron sputtering on Si substrates, which were heated in situ at 650 °C using a house-built vacuum-compatible heater. The effect of the thickness of the Ti buffer layer and the annealing temperature on the formation of various phases of Nd-Fe-B was investigated. The effect of the thickness of the non-magnetic Ti spacer layer on the exchange coupling strength between the hard phase Nd-Fe-B ferromagnetic thin layer and the soft phase transition metal Fe layer was experimentally investigated. Hysteresis loops of multilayer thin films indicate an antiferromagnetic coupling was observed when the thickness of the spacer layer was 2 nm. This is within the range of an antiferromagnetic coupling calculation based on RKKY theory predictions.

By using a Monte Carlo simulation, we have studied the effects on the multilayer transition and magnetic properties of the crystal field D ∕ J 2 , the four-spin coupling J 4 ∕ J 2 and RKKY interaction in the spin-1 Ashkin–Teller (AT) model of a system composed of two magnetic multi-layer materials, of various thicknesses, separated by a nonmagnetic spacer of thickness M. By varying the strength of J 4 ∕ J 2 , we have obtained a new partially ordered phase 〈 σ S 〉 , for different values of D ∕ J 2 . We have established a rich phase diagram with first and second-order phase transitions with tricritical points. It is shown that the transition temperature of both magnetic blocks depends strongly on the thickness of the magnetic layers N , as well as J 4 ∕ J 2 and D ∕ J 2 . There exists a critical thickness of the magnetic layers N L above which the multilayer blocks undergo a transition separately at different temperatures, for a high value of J 4 ∕ J 2 and D ∕ J 2 . Besides, the critical exponents are computed. [ABSTRACT FROM AUTHOR]

The topological insulators Bi2-xFexSe3–xSx have been investigated by the dc-magnetization, magneto-transport and angle resolved photoemission spectroscopy (ARPES) techniques. With doping of Fe and S, a negative giant magneto-resistance (MR) is observed for parallel electric and magnetic fields (H||E). The MR behavior at lower magnetic field can be explained with the semi-classical theory whereas the MR behavior at higher field has been attributed to the axial anomaly. Interestingly, the system reached to the quantum limit at low magnetic field (∼ 4.5T). The magnetic ordering can be explained with the presence of both the RKKY (surface) and van-Vleck (bulk) interaction. The ARPES study reveals that a surface gap is suppressed when the magnetic ordering changes from ferromagnetic to anti-ferromagnetic ordering. The ARPES study and the appearance of quantum oscillations (SdH) in the resistivity pattern reveal that the topological surface property is preserved with the co-doping of Fe and S.

The effect of strains on electronic structures, elastic properties, magnetic properties and Curie temperature of Pd 2 FeCu are calculated by GGA + U method. The impact of strains on the magnetism of Pd 2 FeCu is evaluated. The magnetism without and with spin-orbit coupling (SOC) effect under diverse strain are examined. The results show that Pd 2 FeCu is a ferromagnetic metal with good ductility and mechanical stability. The SOC effect has a negligible impact on the atomic magnetic moment of Pd 2 FeCu. When the compressive and tensile strains are imposed, the ferromagnetic metal properties still keep, and the Curie temperature of Pd 2 FeCu is higher than room temperature. The ferromagnetism for Pd 2 FeCu is very robust with respect to the variation of the strain. And the Ruderman-Kittel-Kasuya-Yoshida (RKKY) type ferromagnetic interaction play a crucial role to determine the ferromagnetism. We expect this work could stimulate experimental study. • Pd 2 FeCu is a ferromagnetic metal with good ductility and mechanical stability. • Spin-orbit coupling effect has a negligible impact on the magnetism. • Compressive and tensile strains are imposed, the ferromagnetic metal still be kept. • The Curie temperature of Pd 2 FeCu is higher than room temperature. • RKKY interaction play a crucial role to determine the ferromagnetism. [ABSTRACT FROM AUTHOR]

• Use of Monte Carlo simulations to study the influence of physical parameters on the magnetic properties of a cylindrical core/shell structure. • The structure consists of two cylinders separated by nonmagnetic cylindrical surfaces. • Coupling between the two cylinders involves spins σ=3/2 for the core and S = 2 for the shell. • The study is based on the RKKY (Ruderman-Kittel-Kasuya-Yoshida) type of interaction. • Conducting hysteresis cycles of the system for different numbers of nonmagnetic surfaces to complete the study. In this paper, we use Monte Carlo simulations to study the influence of physical parameters on the magnetic properties of a cylindrical core/shell structure separated by nonmagnetic cylindrical surfaces. The coupling between the two cylinders includes the spins σ=3/2 and S = 2 belonging to the core and shell, respectively. This study is based on the RKKY (Ruderman-Kittel-Kasuya-Yoshida) type of interaction. In order to complete this study, we carry out the hysteresis cycles of the system under study for a different number of non-magnetic surfaces. [ABSTRACT FROM AUTHOR]

Using dilute silver erbium alloys as a paramagnetic temperature sensor in metallic magnetic calorimeters (MMCs) has the advantage of the host material not having a nuclear quadrupole moment, in contrast to the alternative of using gold erbium alloys. We present numerical calculations of the specific heat and magnetization of Ag:Er, which are necessary for designing and optimizing MMCs using this type of alloy as sensor material. The parameter ranges we consider are temperatures between 1 mK and 1 K , external magnetic fields of up to 20 mT , and erbium concentrations of up to 2000 ppm . The system is dominated by an interplay of crystal field effects, Zeeman splitting, and the RKKY interaction between erbium ions, with certain specific constellations of erbium ions having noticeable effects on the specific heat. Increasing the external magnetic field or assuming a decreased strength of the RKKY interaction leads to a higher magnetization and a narrowing of the main Schottky peak, while changes in the erbium concentration can be well described by parameter scaling. [ABSTRACT FROM AUTHOR]

We study a model of Ising spins in which direct exchange interactions compete with the Ruderman-Kittel-Kasuya-Yosida (RKKY) coupling, which may arise effectively from itinerant electrons. We consider the model in the two-dimensional square lattice and focus on values of the RKKY coupling constant (JRKKY) and the Fermi momentum (kF) that induce strong frustration. We study the low-temperature magnetic field phase diagram using Monte Carlo simulations, considering several nearest neighbors in the RKKY interaction. Magnetic frustration yields a rich phase diagram with a variety of exotic phases. We compute the structure factors and define appropriate order parameters to describe the transitions. We also discuss the validity of the approximation made for long-range couplings and analytically demonstrate the change in the coexistence lines in the phase diagram by including up to the tenth nearest neighbors., (© 2024 IOP Publishing Ltd. All rights, including for text and data mining, AI training, and similar technologies, are reserved.)

In this study, a bilayer zigzag graphyne nanoribbon with RKKY interaction is described using a ferrimagnetic mixed-spin (2, 5/2) Ising model. The compensation behaviors and hysteresis characteristics of the system generated by various physical parameters, such as crystal fields of sublattices, interlayer exchange coupling and the intralayer exchange coupling are explored using Monte Carlo simulation. In the research results, we found that among the 30 possible spin configurations that may occur in the ground state of the system, only 21 spin configurations are stable. At the same time, under certain parameters, the system exhibit interesting behaviors such as compensation phenomena and multi-loop hysteresis. This can provide a theoretical reference for multi-state magnetic recording. • Ising model and Monte Carlo method were used to study the bilayer zigzag graphyne nanoribbon. • The effect of RKKY interaction on the magnetic properties of the graphyne was investigated. • The ground-state phase diagram, magnetization, magnetic susceptibility were obtained. • Phase diagrams and hysteresis loop of the system were presented. • Interesting behaviors of compensation temperatures and multi-loop hysteresis were found under certain parameters. [ABSTRACT FROM AUTHOR]

We report the physical properties of EuPtIn4 single crystalline platelets grown by the In-flux technique. This compound crystallizes in the orthorhombic Cmcm structure with lattice parameters a=4.542(1)A., b=16.955(2)A. and c=7.389(1)A. Measurements of magnetic susceptibility, heat capacity, electrical resistivity, and electron spin resonance (ESR) reveal that EuPtIn4 is a metallic Curie-Weiss paramagnet at high temperatures with an effective moment of μeff≈7.8(1)μB due to divalent Eu ions. At low temperatures, antiferromagnetic (AFM) ordering is observed at TN=13.3K followed by a successive anomaly at T=12.6K. In addition, within the magnetic state, a spin-flop transition is observed with Hc~2.5T at T=1.8 K when the magnetic field is applied along the ac-plane. In the paramagnetic state, a single divalent Eu2+ Dysonian ESR line with a Korringa relaxation rate of b=4.1(2)Oe/K is observed. Interestingly, even at high temperatures, both ESR linewidth and electrical resistivity reveal a similar anisotropy. We discuss a possible common microscopic origin for the observed anisotropy in these physical quantities likely associated with an anisotropic magnetic interaction between Eu2+ 4f electrons mediated by conduction electrons. © 2014 Elsevier B.V.

We theoretically investigate the effect of the nonmagnetic and magnetic impurities to the 2D parabolic Dirac system. The induced charge density by the charged impurity is obtained by the linear response theory within the random phase approximation. We also calculate in-detail, the Ruderman–Kittel–Kasuya–Yosida (RKKY) interaction between two magnetic impurities placed within the 2D sheet of the Dirac materials with isotropic and anisotropic dispersion. For the anisotropic dispersion, the RKKY interaction is also anisotropic and related to the lattice parameters which can be obtained through the DFT calculation or the experiments. The features of the RKKY interaction also can be treated as a signature of the topological phase transition as well as the change of Berry curvature. Our results are also illuminating to the study of the static screening and the RKKY interaction of the isotropic or anisotropic 3D Dirac/Weyl semimetals or the 2D transition metal dichalcogenide family. [ABSTRACT FROM AUTHOR]

The Ruderman–Kittel–Kasuya–Yosida (RKKY) interaction has been extensively explored in isotropic Dirac systems with linear dispersion, which typically follows an exponent decaying rate with the impurity distance R , i.e., J ∝ 1/ R ^d (1/ R ^2 ^d ^−1 ) in d -dimensional systems at finite (zero) Fermi energy. This fast decay makes it rather difficult to be detected and limits its application in spintronics. Here, we theoretically investigate the influence of anisotropic dispersion on the RKKY interaction, and find that the introduction of non-relativistic dispersion in semi-Dirac semimetals (S-DSMs) can significantly prolong the decay of the RKKY interaction and can remarkably enhance the Dzyaloshinskii–Moriya interaction around the relativistic direction. The underlying physics is attributed to the highly increased density of states in the linear-momentum direction as a result of the interplay of relativistic and non-relativistic electrons. Furthermore, we propose a general formula to determine the decaying rate of the RKKY interaction, extending the typical formula for isotropic DSMs. Our results suggest that the S-DSM materials are a powerful platform to detect and control the magnetic exchange interaction, superior to extensively adopted isotropic Dirac systems.

Highlights • The DOS and Landau levels of parabolic system under weak magnetic field are calculated and compared to linear system. • In lowest-order Born approximation, the relaxation rate is related to the imaginary part of the disorder-induced self-energy. • The RKKY range function for the parabolic Dirac system is calculated at finite temperature. Abstract We investigate the electronic properties of the parabolic Dirac system. In the presence of magnetic field, we discuss the thermodynamical potential and the anomalous diamagnetism due to the Dirac cone, and compared to the results of linear dispersion system. We found the local density of state peaks and the Landau levels are equidistant unlike the case of linear dispersion. The integer Hall conductivity and the intrinsic Hall conductivity induced by the Berry curvature are also investigated. Considering the disorder-induced self-energy in self-consistent Born approximation, the Ruderman-Kittel-Kasuya-Yosida (RKKY) interaction (temperature-dependent), long-range scattering rate and the spectral function are also calculated, which are distinct to these in the linear dispersion systems or the clean case (without impurity). In the presence of impurity scattering, the long-range scattering rate is not simply the inverse of quasiparticle lifetime, but the inverse of transport relaxation time which related also to the scattering angle θ (where the forward scattering θ = 0 is forbiddened due to the leading-order corrections to the current vertex). For the temperature-dependent RKKY indirect exchange interaction, its oscillation and power-law decay are shown and we found that its fluctuation amplitude decreases with the increasing temperature for itinerant electrons with parabolic dispersion. [ABSTRACT FROM AUTHOR]

Abstract Localized charge injection by formation of vacancies provides an attractive platform for the development of multifunctional nanomaterials with direct implications in spintronics. However, further progress in spintronics critically depends on a deeper understanding of polaronic interactions between the localized charge states. This report is focused on TiN metallic system, which exhibits Pauli paramagnetism due to the absence of unpaired localized spin states. Here, nitrogen vacancies (V N) are used as a variable to tune the magnetic properties of epitaxial TiN thin films by thermal annealing in high-vacuum and N 2 environment. Systematic introduction of V N generates robust magnetic ordering in vacuum-annealed TiN 1-x films, with Curie temperature (T C) ∼700 K, and saturation magnetization (M s) at absolute zero of 13.6 emu g−1. The signature spin-glass behavior below the irreversibility temperature (T ir ∼40 K) indicates the Ruderman-Kittel-Kasuya-Yosida (RKKY) coupling interactions between the unpaired localized spin-states. Through spatially resolved electron energy-loss spectroscopy, we have determined the generation of unpaired localized spins at Ti+2 polarons with ∼12 ± 2 at.% V N in TiN 1-x films. Such a large concentration of V N results in increased spin stiffness and high T C. These findings open a definitive pathway for tuning the magnetic nature of metallic materials for spintronic applications. Graphical abstract Image 1 [ABSTRACT FROM AUTHOR]

Abstract We theoretically investigate the current–current correlation of the two-dimensional (2D) parabolic Dirac system in hexogonal lattice. The analytical expressions of the random phase approximation (RPA) susceptibility, Ruderman–Kittel–Kasuya–Yosida (RKKY) Hamiltonian, and the diamagnetic orbital susceptibility in noninteracting case base on the density–density or current–current correlation function are derived and quantitatively analyzed. In noninteracting case, the dynamical polarization within RPA, and spin transverse susceptibility as well as the RKKY interaction (when close to the half-filling) are related to the current–current response in the 2D parabolic Dirac systems. Both the cases of anisotropic dispersion and isotropic dispersion are discussed. Highlights • Analytical expressions of the current–current correlation-related quantities are analytically derived and quantitatively discussed. • Orbital diamagnetic susceptibility is derived and compared to the result obtained by the approximated result of spin susceptibility in real space. • The isotropic and anisotropic cases are compared for parabolic 2D Dirac system. [ABSTRACT FROM AUTHOR]

The spectrum of the electron paramagnetic resonance of the Er3+ ion in the matrix of metallic copper has been studied at 9.8 GHz in the temperature range from 1.7 to 4.2 K. The spectrum corresponds to the crystal field of cubic symmetry at g = 6.805 ± 0.01; this value agrees with the expected value for the doublet Γ7. The residual width of the EPR line (T = 0 K) for the even isotopes of erbium was only 4.5 Oe. The temperature and concentration changes in the width of the line indicate the existence of an RKKY interaction between erbium ions. The hyperfine structure (HFS) of the EPR line for the 167Er isotope has been identified. The positions of separate HFS lines are described with an accuracy of 1.5 Oe by a constant A = 74.25 ± 0.1 Oe. The increase in the accuracy of the determination of the hyperfine splitting of lines of the Er3+ ions made it possible to reveal a weak exchange narrowing of the HFS upon an increase of the erbium concentration in these alloys. [ABSTRACT FROM AUTHOR]

α-Fe 2 O 3 /g-C 3 N 4 composites were synthesized by loading different amounts of g-C 3 N 4 on ordered α-Fe 2 O 3 nanowires. The samples were characterized by XRD, SEM, TEM, EDS and N 2 adsorption-desorption isotherms to study the composition, microstructure and morphology. It showed that g-C 3 N 4 was uniformly dispersed around the α-Fe 2 O 3 nanowires to form α-Fe 2 O 3 /g-C 3 N 4 composites. The magnetic properties of samples were obtained by the ZFC-FC and hysteresis loops measurement. The enhancement of exchange bias field in α-Fe 2 O 3 /g-C 3 N 4 composites was discovered. FCN-5 exhibited a higher H EB of 794 Oe at 10 K, which exceeded that of pure α-Fe 2 O 3 of 720 Oe. The influence factors of exchange bias in α-Fe 2 O 3 /g-C 3 N 4 composites were analyzed by FORC method. The results showed that the enhancement of H EB in α-Fe 2 O 3 /g-C 3 N 4 composites was due to the RKKY interaction replacing the original coupling between the initial surface spin-disordered shell layer and the core in α-Fe 2 O 3. [Display omitted] • α-Fe 2 O 3 /g-C 3 N 4 composites were synthesized with adding different amounts of g-C 3 N 4. • The enhancement of H EB in α-Fe 2 O 3 /g-C 3 N 4 composites was discovered. • The influence factors of H EB in α-Fe 2 O 3 /g-C 3 N 4 composites were analyzed by FORC method. • The excitation of H EB at low temperatures was proven to be mainly influenced by RKKY interactions. [ABSTRACT FROM AUTHOR]

In this study, high uniformity AlN thin films with varying Sc doping concentration levels were deposited on Ti (120 nm)/Si substrates. The impact of Sc doping ratio and annealing temperature on the magnetic properties of Al 1−x Sc x N were studied. This work suggests that the origin of ferromagnetism of Al 1−x Sc x N is the Al vacancies introduced by Sc ions. The amount of Al vacancies grew as the Sc doping ratio increased. According to the results of spin-polarized density of states (DOS), it is hypothesized that when the concentration of Al vacancies in Al 1−x Sc x N grows, polarized itinerant electrons exist and result a magnetic phase change. • High uniformity AlN thin films composed of nano columns with different Sc doping concentrations were deposited on Ti (120 nm) /Si substrates in this work. The room-temperature ferromagnetism of the deposited Al1-xScxN films can be observed. • Combining the magnetization hysteresis loops and X-ray photoelectron spectroscopy (XPS) of the doped AlN samples with different Sc doping concentration, this work suggests that the ferromagnetism is originated from Al vacancies which are induced by Sc ions. • According to the spin-polarized density of states (DOS), the Al1-xScxN with a high concentration of Al vacancies exhibit semi-metallic characteristics. These results suggest that the interaction between the magnetic moments belonging to neighboring ions changes from bound magnetic polaron to RKKY interaction when the concentration of Al vacancies in Al1-xScxN increases. [ABSTRACT FROM AUTHOR]

In this study, a bilayer Kagome lattice with RKKY interaction is described using a ferrimagnetic mixed spin-3/2 and spin-2 Ising model. Interesting compensation temperature and hysteresis loops of the system generated by various physical parameters, such as the crystal fields of sublattices (D a , D b), the interlayer exchange coupling (J R) and the intralayer exchange coupling (J b) are explored using Monte Carlo simulation. The results demonstrate that the compensation temperature (T comp), weaker D a and J b , and stronger D b , are favourable for the emergence of the compensation temperatures. Besides, under certain physical parameters, the system may exhibit triple-loop hysteresis behavior and multiple magnetization plateaus. • A ferrimagnetic mixed-spin (3/2, 2) Ising model on the bilayer Kagome lattice with RKKY interaction was proposed. • The effects of the crystal field, exchange coupling and non-magnetic layer were studied. • Magnetization, partial magnetization, and susceptibility were discussed. • Phase diagrams of the critical and compensation temperatures were obtained. • Interesting multi-loop hysteresis characteristics and magnetization plateaus were found. [ABSTRACT FROM AUTHOR]

The classical Monte Carlo method is used to examine effects of electron and hole doping on the magnetocaloric effect in the generalized 2D Ising model with the long-range RKKY interaction on the Shastry–Sutherland lattice. The electron and hole doping in this model is controlled by deviations of the Fermi wave vector k F from the initial value k F = 2 π / 1. 24 which models the most realistically situation in the undoped metallic Shastry–Sutherland rare-earth tetraboride TmB 4. For the undoped case we have found a heating hill (the entropy change Δ S > 0) occurring in the vicinity of metamagnetic transitions and a cooling depression in the paramagnetic phase which is in a very good qualitative agreement with experimental measurements in TmB 4. In the case of small electron doping ( k F = 2 π / 1. 26), a significant decrease of the maximum of − Δ S is observed, while in the strongly hole (electron) doped case k F = 2 π / 1. 17 ( k F = 2 π / 1. 43) the maximum of − Δ S is considerably enhanced against the undoped system, which points to the fact that some of doped systems could have better cooling properties than the undoped one. This is confirmed independently by calculations of relative cooling power for a wide range of parameter k F , where we have found two intervals k F ∈ 〈 2 π / 1. 15 , 2 π / 1. 21 〉 and k F ∈ 〈 2 π / 1. 39 , 2 π / 1. 5 〉 with much larger relative cooling power in comparison to the undoped case. • Effects of electron and hole doping on MCE in the Ising model with RKKY interaction is studied. • Small electron doping decreases the maximum of negative entropy change and relative cooling power. • Strong electron/hole doped cases enhance the magnetocaloric effect in comparison to the undoped one. [ABSTRACT FROM AUTHOR]

We present a simple model for a description of magnetization processes in metallic rare-earth tetraborides. It is based on the two-dimensional Ising model, in which two spins on the Shastry-Sutherland lattice interact via the long-range RKKY interaction mediated by conduction electrons. The model is solved by a combination of the standard Metropolis algorithm and the parallel tempering method and it yields the rich spectrum of magnetic solutions (magnetization plateaus), depending on the value of the Fermi momentum kF and the external magnetic field h. In particular, we have found the following set of individual magnetization plateaus with fractional magnetization m=ms = 1/12, 1/6, 1/4, 1/3, 3/8, 5/12, 1/2, 7/12, 2/3, which for different values of kF, form various sequences of plateaus, changing from very complex ones, appearing near the points kF = 2π=1:243 to very simple ones appearing away from this point. The importance of these results for a description of real rare-earth tetraborides is discussed. [ABSTRACT FROM AUTHOR]

Traditional current-driven spintronics is limited by localized heating issues and large energy consumption, restricting their data storage density and operation speed. Meanwhile, voltage-driven spintronics with much lower energy dissipation also suffers from charge-induced interfacial corrosion. Thereby finding a novel way of tuning ferromagnetism is crucial for spintronics with energy-saving and good reliability. Here, a visible light tuning of interfacial exchange interaction via photoelectron doping into synthetic antiferromagnetic heterostructure of CoFeB/Cu/CoFeB/PN Si substrate is demonstrated. Then, a complete, reversible magnetism switching between antiferromagnetic (AFM) and ferromagnetic (FM) states with visible light on and off is realized. Moreover, a visible light control of 180° deterministic magnetization switching with a tiny magnetic bias field is achieved. The magnetic optical Kerr effect results further reveal the magnetic domain switching pathway between AFM and FM domains. The first-principle calculations conclude that the photoelectrons fill in the unoccupied band and raise the Fermi energy, which increases the exchange interaction. Lastly, a prototype device with visible light control of two states switching with a 0.35% giant magnetoresistance ratio change (maximal 0.4%), paving the way toward fast, compact, and energy-efficient solar-driven memories is fabricated., (© 2023 Wiley-VCH GmbH.)

Using the Hubbard model in the framework of the tight-binding formulation, we studied the effects of the electron–electron (e–e) interaction on the indirect magnetic exchange coupling between the magnetic impurities embedded in triangular graphene nanoflakes. The results show that the magnitude of the coupling enhances in the presence of the e–e interaction and Rashba spin–orbit interaction (RSOI). The RKKY coupling magnitude depends on the impurity positions in nanoflake and the size of the system, as well. [ABSTRACT FROM AUTHOR]

The magnetic properties of magnetic bilayers of Kekulene structure separate by a nonmagnetic layer with Ruderman-Kittel-Kasuya-Yosida (RKKY) exchange interactions with Ising spin model have been studied using Monte Carlo simulations. The RKKY interaction between the bilayers of Kekulene is considered for different distances. The transition temperature has been deduced from the magnetizations and magnetic susceptibilities partial for a fixed value of nonmagnetic layer. The reduced transition temperatures are also deduced from the total magnetization and total magnetic susceptibilities with different values of L. The magnetic hysteresis cycles of systems have been determined. [ABSTRACT FROM AUTHOR]

Motivated by the growing interest in solving the obstacles of spintronics applications, we study the Ruderman-Kittel-Kasuya-Yosida (RKKY) effective pairwise interaction between magnetic impurities interacting through the π -electrons embedded in both electronically doped-semiconducting and metallic armchair graphene nanoribbons. In terms of the Green’s function formalism, treated in a tight-binding approximation with hopping beyond Dirac cone approximation, the RKKY coupling is an attraction or a repulsion depending on the magnetic impurities distances. Our results show that the RKKY coupling in semiconducting nanoribbons is much more affected by doping than metallic ones. Furthermore, we found that the RKKY coupling increases with ribbon width, while there exist some critical electronic concentrations in RKKY interaction oscillations. On the other hand, we find an unusual incoming wave-vector direction for electrons which describes more clearly the ferro- and antiferromagnetic spin configurations in such system. Also, the RKKY coupling at low and high-temperature regions has been addressed for both ferro- and antiferromagnetic spin arrangements. [ABSTRACT FROM AUTHOR]

Thermodynamic description of a model system with magnetoelastic coupling is presented. The elastic, vibrational, electronic and magnetic energy contributions are taken into account. The long-range RKKY interaction is considered together with the nearest-neighbour direct exchange. The generalized Gibbs potential and the set of equations of state are derived, from which all thermodynamic functions are self-consistently obtained. Thermodynamic properties are calculated numerically for FCC structure for arbitrary external pressure, magnetic field and temperature, and widely discussed. In particular, for some parameters of interaction potential and electron concentration corresponding to antiferromagnetic phase, the existence of negative thermal expansion coefficient is predicted. [ABSTRACT FROM AUTHOR]

α-Fe2O3 and α-Fe2O3/graphene oxide (GO) nanocomposites are synthesized by solvothermal method in acetonitrile medium at 200 °C. XRD studies reveals the formation of α-Fe2O3 and α-Fe2O3/GO nanocomposites. Raman studies indicate that GO in α-Fe2O3/GO system was more disordered than GO. The enhanced low temperature magnetic saturation and coercivity in α-Fe2O3 and α-Fe2O3/GO are related to frozen canted spins. Blocking temperature of α-Fe2O3/GO is 348 K, which also shows higher coercivity of the order of about 3064 Oe at 5 K. The α-Fe2O3/GO composite exhibits thermal hysteresis at Morin transition ( ΔTM = 11 K). [ABSTRACT FROM AUTHOR]

In our publication from eight years ago (Kogan, E. 2011, vol. 84, p. 115119), we calculated Ruderman-Kittel-Kasuya-Yosida (RKKY) interaction between two magnetic impurities adsorbed on graphene at zero temperature. We show in this short paper that the approach based on Matsubara formalism and perturbation theory for the thermodynamic potential in the imaginary time and coordinate representation which was used then, can be easily generalized, and calculate RKKY interaction between the magnetic impurities at finite temperature.