RKKY Research Articles

Influence of flat bands on RKKY interaction: Perspective of Fano defects

Influence of flat bands on RKKY interaction: Perspective of Fano defects

Orbital currents in lattice multiorbital systems: Continuity equation, torques, and RKKY interaction

Orbital currents in lattice multiorbital systems: Continuity equation, torques, and RKKY interaction

RKKY interaction in the doped and gapped SnTe(001) surface

In this work, we investigate the complexities (coupling range and magnetic ordering) of the Ruderman–Kittel–Kasuya–Yosida (RKKY) interaction on the (001) surface of SnTe which is a topological crystalline insulator. We aim to enable the transition between ferromagnetic and antiferromagnetic couplings, as well as between collinear and noncollinear magnetic spins by manipulating doping and the gap structure. The gap is achieved through electron–phonon coupling and gate voltage. The spin susceptibility is calculated by Green’s functions in real space. The modulation of RKKY interactions via doping occurs specifically over short (large) impurity separations, with the influence of electron–phonon coupling (gate) only manifesting when the doped Fermi level lies outside the gap. Additionally, electron–phonon coupling leads to weaker adjustments in magnetic orderings, attributed to the renormalized Fermi velocities, while gate voltage induces stronger modifications. This inquiry is of considerable interest due to the potential applications in the realm of spintronics.

Impact of evolution of structural defects on the ferromagnetic and electrical properties of laser deposited Indium-doped SnO2 thin films

Impact of non-magnetic cationic-substitution on the evolution of structural defects and correlated ferromagnetic and electrical properties are investigated in series of pulsed laser deposited Sn1-xInxO2 (0.0 ≤ x ≤ 0.12) thin films. Beyond the nominal doping concentration of 2 at.% (i.e. x > 0.02), Indium (In)-doped SnO2 film switches to exhibit from n-type to p-type electrical conductivity and simultaneously the magnetization (MS) as well as the Curie temperature (TC) of the films increase significantly. Estimated values of ‘MS’ and ‘TC’ are found to achieve as large as 15.21 emu/cm3 and 540 K respectively when In-doping concentration approaches towards x = 0.08 and afterwards tend to decrease abruptly. Various spectroscopic techniques including Positron Annihilation Lifetime Spectroscopy (PALS) have detected the existence of Sn vacancy (VSn) defects within Sn1-xInxO2 films arise as the effect of In-substitution at Sn site (InSn) under O-rich atmosphere. The estimated positron lifetimes and the increase of line-shape S-parameter confirm the rise of VSn defects which serve as the major source of magnetic moments in non-magnetic host SnO2. Besides, InSn defects introduce excess holes within SnO2 lattice and thereby the magnetic spin-spin RKKY interaction between near-by VSn defects are mediated ferromagetically through the localized holes. For x > 0.08, stabilization of various donor-type defects such as Sn interstitial (Sni), indium interstitial (Ini) actually compensates the acceptors that leads to reduce the effective hole density consequently diminishing the strength of ferromagnetism within SnO2. Hence, tuning of such ferromagnetic and semiconducting properties through non-magnetic cationic substitution in transparent conducting oxides can be very promising in the field of next-generation spintronics.

Electron-phonon coupling and magnetic proximity effects on the RKKY interaction in topological crystalline insulators

Understanding the intricacies of magnetism mechanisms on the surface of topological materials, and focusing on the Ruderman-Kittel-Kasuya-Yosida interaction and its modulation, proves to be intriguing for spintronic applications. In this study, we explore switching possibilities between ferromagnetic (FM) and antiferromagnetic (AFM) couplings on the surface of topological crystalline insulator SnTe through electron-phonon coupling (EPC) and magnetic proximity effect (MPE). Our calculations, based on retarded Green's functions in real space, provide insights into the impact of EPC and MPE on FM/AFM couplings at intermediate impurity separations, where significant responses occur. Importantly, both factors induce the switch between FM and AFM in the XYZ-Heisenberg Jx/y/z and in-plane symmetric Jxy components.

Analytical and numerical calculation of the effect of edge states of the Kane-Mele model on the RKKY interaction

In this paper, we investigate the Kane-Mele model and endeavor to demonstrate, through analytical calculations, how the presence of topological edge states influences the RKKY interaction. We illustrate that the effect diminishes as one moves away from the edges. To facilitate our analytical approach, we initially utilize a one-dimensional wire exhibiting linear dispersion for each spin as an approximation to the Kane-Mele model. We examine its impact on the RKKY interaction. Subsequently, we establish a correspondence between the edge states of the Kane-Mele model and a one-dimensional quantum wire model, wherein the coupling strength diminishes with increasing distance from the edges. Finally, we compare the analytical results with numerical findings obtained using the Landauer-Buttiker formulation.

Theoretical study on the effects of Mn ion doping and applied magnetic field in (In,Mn)As

Diluted magnetic semiconductors are a recent research area due to their ability to enhance ferromagnetic properties and facilitate the electrical detection of magnetoresistance and polarization. (In, Mn)As dilute magnetic semiconductor has potential application in the field of spintronic devices, such as spin field-effective transistors, spin laser light-emitted diodes, modern technology, multi-functional devices, green technology, and nanotechnology. For this study, we have considered the RKKY interaction between Mn2+ spins via delocalized carriers. The effect of manganese ion concentration and applied magnetic field on ferromagnetic diluted magnetic semiconductor properties such as dispersion relation, Curie temperature, and reduced magnetization of (In, Mn)As are studied. We have developed a spin-wave model using the Holstein-Primakaff transformation. Based on the developed model, the number of ferromagnetic magnons, dispersion relations, and Curie temperatures were calculated with or without an applied magnetic field. The reduced magnetization is also calculated. The graph of Curie temperature and magnetization of (In,Mn)As versus temperature with applied field up to 6 T and manganese ion concentration from 0.01 to 0.1 are plotted. The graph of spin wave dispersion of (In,Mn)As versus a wave vector with varying manganese ion concentration with and without an applied magnetic field up to 6 T. In this study, an InMnAs Curie temperature of 290.68 K is found without an applied magnetic field with a 0.1 manganese ion concentration, which is near room temperature. Moreover, with an applied magnetic field of 6 T at 0.1 manganese ion concentration, a Curie temperature of 342.466 K is found, which is above room temperature. Hence, these temperatures are suitable for the field of next-generation spintronic new technology.

Compensation temperature and hysteresis behaviors of the ferrimagnetic bilayer zigzag graphyne nanoribbon with RKKY interaction

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.

Anisotropic RKKY interaction in doped monolayer germanene: spin–orbit coupling effects

Anisotropic RKKY interaction in doped monolayer germanene: spin–orbit coupling effects

RKKY interaction in triplet superconductors: Dzyaloshinskii-Moriya-type interaction mediated by spin-polarized Cooper pairs

RKKY interaction in triplet superconductors: Dzyaloshinskii-Moriya-type interaction mediated by spin-polarized Cooper pairs

Metallic local-moment magnetocalorics as a route to cryogenic refrigeration

Commercial adiabatic demagnetisation refrigerators still employ the same hydrated salts that were first introduced over 85 years ago. The inherent limitations of these insulating magnetocalorics – poor thermal conductivity at sub-Kelvin temperatures, low entropy density, corrosiveness – can be overcome by a new generation of rare-earth based metallic magnetocalorics. Here, we present the metallic magnetocaloric YbNi1.6Sn as an attractive alternative to conventional refrigerants. YbNi1.6Sn retains high entropy into the 100 mK regime and avoids the noble metal constituents of alternative refrigerants. Demagnetisation tests demonstrate that YbNi1.6Sn enables economical and durable alternatives to traditional cooling devices for temperatures reaching below 120 mK. We find that the magnetocaloric properties of this material are facilitated by unusually small Kondo and RKKY interactions, which position YbNi1.6Sn in the extreme local moment limit on the generalised Kondo lattice phase diagram.

RKKY interaction in helical higher-order topological insulators

Abstract We theoretically investigate the RKKY interaction in helical higher-order topological insulators (HOTIs), revealing distinct behaviors mediated by hinge and Dirac-type bulk carriers. Our findings show that hinge-mediated interactions consist of Heisenberg, Ising, and Dzyaloshinskii-Moriya (DM) terms, exhibiting a decay with impurity spacing $z$ and oscillations with Fermi energy $\varepsilon_F$. These interactions demonstrate ferromagnetic behaviors for the Heisenberg and Ising terms and alternating behavior for the DM term. In contrast, bulk-mediated interactions include Heisenberg, twisted Ising, and DM terms, with a conventional cubic oscillating decay. This study highlights the nuanced interplay between hinge and bulk RKKY interactions in HOTIs, offering insights into the design of next-generation quantum devices based on the HOTIs.

A Spin Valve-Based Rhombus-Shaped Micro-Object Implementing a Full Wheatstone Bridge.

Spin valves with a synthetic antiferromagnet were fabricated via magnetron sputtering. It was shown that the fabricated spin valve layers had a perfect microstructure and smooth interfaces, and therefore, an RKKY interaction dominated in the coupling of the ferromagnetic layers separated by a copper spacer. Rhombus-shaped micro-objects were fabricated from a single spin valve film. The thermomagnetic treatment procedure was found to form unidirectional anisotropy in the micro-object such that the values of the exchange bias fields in the rhombus' nonparallel sides were opposite in sign. For the CoFeNi/Ru/CoFeNi synthetic antiferromagnet, we determined the differences between the ferromagnetic layer thicknesses at which the thermomagnetic treatment formed the same exchange bias all over each rhombus' side. We also fabricated a sensor element in which each side of the rhombus was the shoulder of a Wheatstone bridge. After the thermomagnetic treatment procedure, each shoulder worked as an active magnetosensitive element, enabling the device to operate as a full Wheatstone bridge. The sensor output exhibited a step shape, high sensitivity to field changes, and significant magnetic hysteresis. Such characteristics are suitable for switching devices.

Ferromagnetism above room temperature in Janus Fe2X (X = S, Se) monolayers

Novel ferromagnetic Janus Fe2X (X = S, Se) monolayers exhibit a high Curie temperature associated with the itinerant-electron-mediated double-exchange and RKKY interaction.

Ion irradiation modulated magnetic properties of materials and its applications

Ion irradiation, a technology in which ion beams are used to irradiate materials, has high manipulation precision, short processing time, and many applications in the fields of material modification, chip manufacturing, biomedicine, energy and chemicals. Especially in magnetic material modification, customized modifications of magnetic materials can be achieved by precisely controlling the energy, dose, and direction of the ion beam. To further enhance the performances of magnetic materials and explore new magnetic devices, this study focuses on how ion irradiation precisely modulates various magnetic interactions and the analysis of its influence on the spin Hall effect and magnetic structural dynamics. Firstly, the latest research achievements are emphasized of ion irradiation regulated magnetic characteristics such as perpendicular magnetic anisotropy, exchange bias, and RKKY interaction. These regulation methods are crucial for understanding and optimizing the microstructure and properties of magnetic materials. Secondly, the significant role played by ion irradiation in regulating spin-orbit torque devices is discussed in detail. These applications demonstrate the potential of ion irradiation technology in designing high-performance magnetic storage and processing devices. Finally, the future applications of ion irradiation technology in the preparation of multifunctional magnetic sensors and magnetic media for information storage are discussed, highlighting its great enormous innovation and application potential in the field of magnetic materials.

Photo-induced reversible modification of the Curie–Weiss temperature in paramagnetic gadolinium compounds

Gadolinium oxyhydride GdHO is a photochromic material that darkens under illumination and bleaches back by thermal relaxation. As an inorganic photochromic material that can be easily deposited by magnetron sputtering, GdHO has very interesting potential applications as a functional material, specially for smart glazing applications. However, the underlying reasons behind the photochromic mechanism – which can be instrumental for the correct optimisation of GdHO for different applications – are not completely understood. In this paper, we rely on the well-established magnetic properties of Gd3+ to shed light on this matter. GdHO thin films present paramagnetic behaviour similar to other Gd3+ compounds such as Gd2O3. Illumination of the films result in a reversible increase of the Curie–Weiss temperature pointing to Ruderman–Kittel–Kasuya–Yosida RKKY interactions, which is consistent with the resistivity decrease observed in the photodarkened films.

Magnetic and magnetocaloric properties of Tb1.4Dy0.6In compound

This work summarizes the magnetic, thermal, magnetocaloric, and electrical transport properties of Tb1.4Dy0.6In and its critical behavior. First, we find that 60% Dy at the 2d (1/3, 2/3, 3/4) lattice sites of Tb2In (hexagonal Ni2In -type (space group- P63/mmc (No. 194))) leads to the formation of Tb1.4Dy0.6In, which undergoes a ferromagnetic transition at 155 K (T1) followed by an antiferromagnetic transition around 75 K (T2). Successive second-order magnetic transitions at T1 and T2 demonstrate a table-like hysteresis-free magnetocaloric effect around natural gas's liquefaction temperature (55–196 K). To understand the efficiency of Tb1.4Dy0.6In as a coolant, various cooling figures of merits such as isothermal entropy change, adiabatic temperature change, relative cooling power, the temperature averaged entropy change, and coefficient of refrigerant performance were determined. Along with the studies of magnetic properties, the critical exponent analysis endorses mean–field model that concord with the indirect long-range RKKY interaction between the rare-earth atoms in Tb1.4Dy0.6In. Furthermore, first-principle calculations indicate that the most hybridized dp states lie below the Fermi energy level and support the second-order magnetic nature of the transition. Overall, this study provides insights into the magnetocaloric properties of Dy-doped Tb2In and highlights its potential as an efficient coolant.

The PointGroupNRG code for numerical renormalization group calculations with discrete point-group symmetries

The numerical renormalization group (NRG) has been widely used as a magnetic impurity solver since the pioneering works by Wilson. Over the past decades, a significant attention has been focused on the application of symmetries in order to reduce the computational cost of the calculations and to improve their accuracy. In particular, a notable progress has been made in implementing continuous symmetries such as SO(3), useful for studying impurities in an isotropic medium, or SU(N), which is applicable to a wide range of systems. In this work, we focus on the application of discrete point group symmetries, which are particularly relevant for impurity systems in metals where crystal field effects are important. With this aim, we have developed an original NRG code written in the Julia language, PointGroupNRG, where we have implemented crystal point-group symmetries for the Anderson impurity model, as well as the continuous spin and charge symmetries. Among other results, we demonstrate the advantage of our procedure by applying the code to a two-impurity model with RKKY interaction and an impurity system with two orbitals of Eg symmetry and two channels. We also provide benchmarks to show the performance improvements obtained by exploiting the orbital symmetries.

RKKY Interactions and Magneto-Caloric Properties of a Nano-Graphene Structure: Monte Carlo study

RKKY Interactions and Magneto-Caloric Properties of a Nano-Graphene Structure: Monte Carlo study

RKKY interaction in one-dimensional flat-band lattices

RKKY interaction in one-dimensional flat-band lattices