Ruderman-Kittel-Kasuya-Yoshida Interaction Research Articles

Monte Carlo study of magnetic behavior of a Phenanthrene-like biplane with RKKY interactions

Magnetic properties of a Phenanthrene-like biplane with Ruderman-Kittel-Kasuya-Yoshida (RKKY) interactions are examined using Monte Carlo simulations. We investigate the blocking temperature and hysteresis loops behaviors under the influence of non-magnetic planes, coupling interactions, temperature and the crystalline field. The seven hysteresis loops identified in this study could be useful in multi-state memory storage and nanotechnology.

Dielectric Properties of Ovalene-Like Nanostructure with RKKY Interactions: Monte Carlo Study

In this study, we investigated the dielectric properties of ovalene-like nanostructure with RKKY (Ruderman–Kittel–Kasuya–Yoshida) interactions, using Monte Carlo simulations. Nanosystem consists of an ovalene-like nanostructure with mixed spins [Formula: see text]-7/2 and S-1, separated by non-electric layers (NEL). We investigated the effect of the non-electric layers, external longitudinal electric field and ferrielectric exchange coupling on polarization and dielectric susceptibility of the nanostructure. We find that the transition temperature is affected by an increase in the number of non-electrical layers. These results can enrich the dielectric properties of ovalene-like nanostructure for future nanotechnology applications.

Blume-Capel model of a borophene layers structure with RKKY interactions: Monte Carlo simulations

In this paper, we study the magnetic properties of a bi-layer borophene structure with RKKY (Ruderman-Kittel-Kasuya-Yoshida) interactions. The system is composed by two magnetic layers with mixed spins σ = ±3/2, ±1/2 and S = 0, ±1, separated by (L) non-magnetic planes. Firstly, for zero temperature, the ground state phase diagrams are reported and discussed. Secondly, we use the Monte Carlo simulations to explore the RKKY interactions effect on the magnetic properties of the system. The transition temperature increases when decreasing the number (L) of nonmagnetic layers. Also, the effect of the exchange coupling interactions on the transition temperature behavior is studied. Finally, we report the effect of different physical parameters on the magnetic hysteresis cycles.

Blume-Capel model of a nano-Stanene like structure with RKKY interactions: Monte Carlo simulations

ABSTRACTIn this paper, the magnetic properties of a bi-layer nano-stanene like structure with RKKY (Ruderman-Kittel-Kasuya-Yoshida) interactions have been studied using Monte Carlo simulations. The considered system is composed of two magnetic planes with mixed spins σ = 7/2 and S = 1, separated by the non-magnetic planes (L). Firstly, the ground state phase diagrams for zero temperature are reported and discussed. Secondly, for non-zero temperature, we examine the effect of the RKKY interactions on the magnetic properties of our system. It is found that the value of the blocking temperature increases when decreasing the number of the non-magnetic layers. Furthermore, the effect of the exchange coupling interactions on the blocking temperature behavior are investigated. Finally, the effect of several physical parameters on the hysteresis cycles have been determined.

Magnetic properties of naphthalene-like nano-structure with RKKY interactions: Monte Carlo simulations

In this paper, we have studied the magnetic properties of a bi-layer naphthalene-like nano-structure with RKKY (Ruderman-Kittel-Kasuya-Yoshida) interactions, using Monte Carlo simulations. The system consists of two naphthalene-like magnetic planes, with mixed spins σ = 7/2 and S = 1, separated by L non-magnetic layers. In the first part of this study, the ground state phase diagrams for zero temperature are reported and discussed. In the second part, we investigate the effect of the RKKY interactions on the magnetizations and susceptibilities of the system, for non-zero temperature values. It is found that the value of the blocking temperature decreases when increasing the number of non-magnetic layers. Furthermore, the effect of the ferrimagnetic parameter (JSσ) on the blocking temperature behavior has been investigated. Finally, the effect of different physical parameters, namely the number of non-magnetic layers, the ferrimagnetic parameter, the crystal field and the temperature, on the magnetic hysteresis cycles are illustrated.

Tuning the electronic structure and magnetic coupling in armchair B2S nanoribbons using strain and staggered sublattice potential

Magnetically-doped two dimensional honeycomb lattices are potential candidates for application in future spintronic devices. Monolayer B2S has been recently unveiled as a desirable honeycomb monolayer with an anisotropic Dirac cone. Here, we investigate the carrier-mediated exchange coupling, known as Ruderman-Kittel-Kasuya-Yoshida (RKKY) interaction, between two magnetic impurity moments in armchair-terminated B2S nanoribbons in the presence of strain and staggered sublattice potential. By using an accurate tight-binding model for the band structure of B2S nanoribbons near the main energy gap, we firstly study the electronic properties of all infinite-length armchair B2S nanoribbons (ABSNRs), with different edges, in the presence of both strain and staggered potential.It is found that the ABSNRs show different electronic and magnetic behaviors due to different edge morphologies. The band gap energy of ABSNRs depends strongly upon the applied staggered potential Δ and thus one can engineer the electronic properties of the ABSNRs via tuning the external staggered potential. A complete and fully reversible semiconductor (or insulator) to metal transition has been observed via tuning the external staggered potential, which can be easily realized experimentally. A prominent feature is the presence of a quasiflat edge mode, isolated from the bulk modes in the ABSNRs belong to the family M=6p, with M the width of the ABSNR and p an integer number. As a key feature, the position of the quasi-flatbands in the energy diagram of ABSNRs can be shifted by applying the in-plane strains εx and εy. At a critical staggered potential (Δc∼0.5 eV), for nanoribbons of arbitrary width, the quasi-flatband changes to a perfect flatband.The RKKY interaction has an oscillating behavior in terms of the applied staggered potentials, such that for two magnetic adatoms randomly distributed on the surface of an ABSNR the staggered potential can reverse the RKKY from antiferromagnetism to ferromagnetism and vice versa. The RKKY in terms of the width of the ribbon has also an oscillatory behavior. It is shown that the magnetic interactions between adsorbed magnetic impurities in ABSNRs can be manipulated by careful engineering of external staggered potential. Our findings pave the way for applications in spintronics and pseudospin electronics devices based on ABSNRs.

Blume-Capel model of a bi-layer graphyne structure with RKKY Interactions: Monte Carlo simulations

Abstract In this paper, we study the magnetic properties of a bi-layer graphyne structure with RKKY (Ruderman-Kittel-Kasuya-Yoshida) interaction. The system is composed by two magnetic layers with mixed spins σ = 3/2 and S = 1, separated by (L) non-magnetic ones. Firstly, the ground state phase diagrams are reported and discussed. Then we use the Monte Carlo simulations in order to determine the effect of the RKKY interaction on the system magnetic properties. We find that the transition temperature increases when decreasing the number of non-magnetic layers. This result is confirmed by the displacement of the peak of susceptibility towards the high temperatures. Furthermore, the variation of the total magnetization versus the crystal field remains independent of the parameter L when this one is greater than or equal to three. Besides, the hysteresis loop stays invariable for L ≥ 2.

RKKY interaction in Mn-doped 4 × 4 Luttinger systems

We consider Mn-doped bulk zinc-blende semiconductors described by the 4 × 4 Luttinger Hamiltonian. In these semiconductors, the Mn atom acts as an acceptor providing the system a mobile hole and also acts like a magnetic impurity of spin S=5/2. We obtain exact analytical expressions of the hole mediated Ruderman-Kittel-Kasuya-Yoshida (RKKY) exchange interaction between two Mn2+ ions. The RKKY interaction of the Luttinger system consists of collinear Heisenberg-like and Ising-like interactions. The characteristic beating patterns appear in the range functions of the RKKY interaction owing to the presence of multiple Fermi wave-vectors of the underlying j=3/2 states. As an application of the analytical form of the range function, from the finite temperature evaluation of the correlation functions, we calculate the contribution of RKKY interaction to the Curie-Weiss temperatures of a particular dilute magnetic semiconductor ZnMnTe where the 4 × 4 Luttinger Hamiltonian is valid.

Towards microscopic control of the magnetic exchange coupling at the surface of a topological insulator

Magnetically doped topological insulators may produce novel states of electronic matter, where for instance the quantum anomalous Hall effect state can be realized. Pivotal to this goal is a microscopic control over the magnetic state, defined by the local electronic structure of the dopants and their interactions. We report on the magnetic coupling among Mn or Co atoms adsorbed on the surface of the topological insulator Bi2Te3. Our findings uncover the mechanisms of the exchange coupling between magnetic atoms coupled to the topological surface state in strong topological insulators. The combination of x-ray magnetic circular dichroism and ab initio calculations reveals that the sign of the magnetic coupling at short adatom–adatom distances is opposite for Mn with respect to Co. For both elements, the magnetic exchange reverses its sign at a critical distance between magnetic adatoms, as a result of the interplay between superexchange, double exchange and Ruderman–Kittel–Kasuya–Yoshida interactions.

Metamagnetic transition and observation of spin-fluctuations in the antiferromagnetic Heusler compound Pd2MnIn

We report detailed investigations on the structural, magnetic, magneto-transport and calorimetric aspects of a partially ordered Heusler compound Pd2MnIn. The sample shows antiferomagnetic (AFM) state below around 120 K, though positive paramagnetic Curie temperature signifies a complex magnetic ground state with the presence of both ferromagnetic (FM) and AFM correlations. A clear spin-flop type metamagnetic transition is observed as evident from the magnetization and resistivity data. However, non-saturation of magnetization even at 145 kOe of applied field implies that the high field state may be a spin canted state, originating from the enhanced FM correlations by field induced conduction electron spin polarization. The sample shows a profound quadratic temperature dependence of resistivity below about 20–25 K indicating a spin-fluctuation dominated low temperature region. Previous electronic structure calculations show the existence of a subtle balance between superexchange mediated AFM state and an RKKY (Ruderman–Kittel–Kasuya–Yoshida) interaction mediated FM state in Pd2MnIn. Such competing AFM-FM correlations can be accounted for the observed spin fluctuations.

Magnetic structure in Mn1−xCoxGe compounds

The magnetic system of the pseudobinary compound Mn$_{1-x}$Co$_{x}$Ge has been studied using small-angle neutron scattering and SQUID-measurements. It is found that Mn$_{1-x}$Co$_{x}$Ge orders magnetically at low temperatures in the whole concentration range of $x \in [0 \div 0.9]$. Three different states of the magnetic structure have been found: a short-periodic helical state at $x \leq 0.45$, a long-periodic helical state at $0.45 < x \leq 0.8$, and a ferromagnetic state at $x \sim 0.9$. Taking into account that the relatively large helical wavevector $k \gg 1$ nm$^{-1}$ is characteristic for systems with mainly Ruderman-Kittel-Kasuya-Yoshida (RKKY) interaction, we suggest that the short-periodic helical structure at $x \leq 0.45$ is based on an effective RKKY interaction. Also the decay of $k$ with increasing $x$ is ascribed to a reduction of the interaction between second nearest neighbors and, therefore, to an increase of the influence of the Dzyaloshinskiy-Moriya interaction (DMI). As a result of the competition between these two interactions the quantum phase transition from a long-range ordered (LRO) to a short-range ordered (SRO) helical structure has been observed upon increase of the Co-concentration at $x_{c1} \sim 0.25$. Further increase of $x$ leads to the appearance of a double peak in the scattering profile at $0.45 < x < 0.7$. The transition from a helical structure to a ferromagnetic state found at $x = 0.9$ is caused by the weakening of DMI as compared to the cubic anisotropy. In summary, the evolution of the magnetic structure of Mn$_{1-x}$Co$_{x}$Ge with increasing $x$ is an example of a continuous transition from a helical structure based on the effective RKKY interaction to a ferromagnetic structure passing through a helical structure based on DMI.

Magnetic properties of a bi-fullerene-like structure, X60-Y60, with RKKY interactions in the Blume–Capel model

In this paper, we study the influence of the physical parameters on the thermal and magnetic properties of a nano-particle of bi-fullerene-like structure X[Formula: see text]-Y[Formula: see text] separated by nonmagnetic spherical surfaces, using the Metropolis Monte Carlo (MC) simulations. The coupling between the two spheres containing the spins [Formula: see text] = 3/2 and the spins S = 7/2 belongs to the core and shell, respectively. This study is based on the RKKY (Ruderman–Kittel–Kasuya–Yoshida) interaction type. To complete this work, we carry out the hysteresis cycles of the studied system for different nonmagnetic surface (NMS) numbers.

Kondo effect in double quantum dots with ferromagnetic RKKY interaction

We study Kondo effect in parallel-coupled double quantum dots with ferromagnetic Ruderman–Kittel–Kasuya–Yoshida (RKKY) interaction, by using the exact and nonperturbative hierarchical equations of motion approach. We construct the phase diagram in the parameter plane of the inter-dot coupling t and the ferromagnetic exchange interaction J (J − 4t2/U plane). Three different ground states, the Kondo singlet, spin singlet and S = 1 Kondo, are determined in the diagram. We find the ferromagnetic coupling will raise the Kondo peak in the area of finite hopping t which is called ‘J-enhanced Kondo effect’. Another enhancement of the Kondo effect by t (‘t-enhanced Kondo effect’) at J = 0 is also presented. By checking the electron–electron interaction self-energy and magnetic susceptibility, we verify the ground state at large J is an under-screening Kondo state composed of a Fermi liquid with a residual spin 1/2, which is consistent with the ‘singular Fermi liquid state’ in the literature.

RKKY interaction in disordered graphene

We investigate the effects of nonmagnetic disorder on the Ruderman-Kittel-Kasuya-Yoshida (RKKY) interaction in graphene by studying numerically the Anderson model with on-site and hopping disorder on a honeycomb lattice at half filling. We evaluate the strength of the interaction as a function of the distance $R$ between two magnetic ions, as well as their lattice positions and orientations. In the clean limit, we find that the strength of the interaction decays as $1/{R}^{3}$, with its sign and oscillation amplitude showing strong anisotropy. With increasing on-site disorder, the mean amplitude decreases exponentially at distances exceeding the elastic mean free path. At smaller distances, however, the oscillation amplitude increases strongly and its sign changes on the same sublattice for all directions but the armchair direction. For random hopping disorder, no sign change is observed. No significant changes to the geometrical average values of the RKKY interaction are found at small distances, while exponential suppression is observed at distances exceeding the localization length.

Effect of antiferromagnetic RKKY interaction and magnetic field in a two-impurity Kondo system

We explore the magnetic field dependence of the single-particle excitation spectra (SPES) of a magnetic dimer on a conducting surface using the numerical renormalization-group technique. When the antiferromagnetic Ruderman-Kittel-Kasuya-Yoshida (RKKY) interaction is dominant, a dip structure is observed near the Fermi level in the SPES. However, upon application of a certain external magnetic field, a peak structure appears near the Fermi level. Our results show that this peak structure originates in two reasons; (1) combination of the parity splitting and the Zeeman splitting, (2) enhancement of the formation of the Yosida-Kondo singlet in the ground state caused by the cancellation of the antiferromagnetic RKKY interaction.

Two-impurity Kondo model with spin-orbit interactions

We study the two-impurity Kondo model (TIKM) in two dimensions with spin-orbit coupled conduction electrons. In the first part of the paper we analyze how spin-orbit interactions of Rashba as well as Dresselhaus type influence the Kondo and Ruderman-Kittel-Kasuya-Yoshida (RKKY) interactions in the TIKM, generalizing results obtained by H. Imamura et al. [Phys. Rev. B 69, 121303(R) (2004)] and J. Malecki [J. Stat. Phys. 129, 741 (2007)]. Using our findings we then explore the effect from spin-orbit interactions on the non-Fermi-liquid quantum critical transition between the RKKY-singlet and Kondo-screened RKKY-triplet states. We argue that spin-orbit interactions under certain conditions produce a line of critical points exhibiting the same leading scaling behavior as that of the ordinary TIKM. In the second part of the paper we shift focus and turn to the question of how spin-orbit interactions affect the entanglement between two localized RKKY-coupled spins in the parameter regime where the competition from the direct Kondo interaction can be neglected. Using data for a device with two spinful quantum dots patterned in a gated InAs heterostructure we show that a gate-controlled spin-orbit interaction may drive a maximally entangled state to one with vanishing entanglement or vice versa (as measured by the concurrence). This has important implications for proposals using RKKY interactions for nonlocal control of qubit entanglement in semiconductor heterostructures.

Two-stage Kondo effect in side-coupled quantum dots: Renormalized perturbative scaling theory and numerical renormalization group analysis

We study numerically and analytically the dynamical (ac) conductance through a two-dot system, where only one of the dots is coupled to the leads but it is also side coupled to the other dot through an antiferromagnetic exchange Ruderman-Kittel-Kasuya-Yoshida (RKKY) interaction. In this case, the RKKY interaction gives rise to a ``two-stage Kondo effect'' where the two spins are screened by two consecutive Kondo effects. We formulate a renormalized scaling theory that captures remarkably well the crossover from the strongly conductive correlated regime to the low temperature, low conductance state. Our analytical formulas agree well with our numerical renormalization group results. The frequency-dependent current noise spectrum is also discussed.

Experimental study of the competition between Kondo and RKKY interactions for Mn spins in a model alloy system

The quasicrystal Al-Pd-Mn is a model system for an experimental study of the competition between Ruderman-Kittel-Kasuya-Yoshida (RKKY) and Kondo interactions. First, specific of such alloys, only a few Mn atoms carry an effective spin and their concentration x is tunable over several orders of magnitude, even though the Mn amount is almost constant. Second, the characteristic energy scales for the interactions lie in the Kelvin range. Hence we could study the magnetization on both side of these energy scales, covering a range of temperatures [0.1-100 K] and magnetic fields (mu_B H/k_B= 0 to 5 K) for 22 samples and x varying over 2 decades. Using very general Kondo physics arguments, and thus carrying out the data analysis with no preconceived model, we found a very robust and simple result: The magnetization is a sum of a pure Kondo (T_K=3.35K) and a pure RKKY contributions, whatever the moment concentration is and this surprisingly up to the concentration where the RKKY couplings dominate fully and thus cannot be considered as a perturbation.

Temperature dependence of high-resolution resonant photoemission spectra of CeSi

High-resolution Ce 4d–4f resonant photoemission spectra near the Fermi level of CeSi with the Néel temperature of 5.9 K have been measured at temperatures from 5.6 to 200 K, in order to investigate the competition between the Ruderman–Kittel–Kasuya–Yoshida (RKKY) interaction and the Kondo effect. As temperature is decreasing down to 30 K, the intensity due to the Ce 4 f 5 / 2 1 final state increases because of the evolution of the heavy Fermion behaviour caused by the Kondo effect. The intensity, however, decreases gradually from 30 to 5.6 K. This indicates that the heavy Fermion behaviour is strongly suppressed by the anti-ferromagnetic ordering due to the RKKY interaction.

Combination of Dense Kondo Effect and RKKY Interaction in CeCuSb2, Investigated by NMR

A combination of the dense Kondo effect and Ruderman–Kittel–Kasuya–Yoshida interaction exhibited by an antiferromagnetic (AF) heavy-Fermion compound CeCuSb 2 ( T N =8 K) was investigated with the magnetic susceptibility χ and 63 Cu magnetic resonance measurements in the temperature range between 1.4 and 210 K. For temperatures above ∼25 K, characteristics of the localized 4 f spins are observed in the Curie–Weiss-type behavior of the Knight shift K and the strongly enhanced relaxation rate T 1 -1 . For the temperature below ∼25 K, the χ data tend toward a constant value, which is an indication of the onset of the heavy-Fermion state. The slope of the Knight shift versus susceptibility ( K -χ) plots decreases below ∼100 K, which is ascribed to the difference in the anisotropic hyperfine coupling to the crystal-field-split Γ 7 (ground state) and Γ 8 (excited state) wave functions of the Ce ions. The K -χ plots below ∼25 K exhibit another deviation from the linearity in opposite direction. We speculate that ...