Ruderman-Kittel-Kasuya-Yoshida Research Articles

Transition from an incommensurate spin density wave to a commensurate magnetic order in a triangular lattice compound Ho2PdAl6Ge4

Rare-earth (RE) intermetallics on a triangular lattice are promising candidates for generating interesting magnetic phases due to the complex interplay between Ruderman-Kittel-Kasuya-Yoshida (RKKY) interaction and geometrical frustration. Here we report the exotic magnetic structure of a layered compound Ho2PdAl6Ge4 with triangular lanthanide nets. Magnetization and heat capacity measurements in zero magnetic field reveal two magnetic phase transitions at TN1 = 10.8 K and TN2 = 6.0 K. Neutron powder diffraction demonstrates a commensurate antiferromagnetic phase with k1 = (0, 0, 1.5) below TN2. With increasing temperature, another incommensurate vector appears and therefore, the magnetic structure of the intermediate state is identified as an unusual incommensurate spin density wave with two propagation vectors k1 = (0, 0, 1.5) and k2 = (0.0492, 0.0492, 1.5). The magnetic moments in the intermediate state rotate continuously and form an unusual S-shaped wave arrangement in the ab plane, sharing similarities with typical cycloid and helix magnetic orders. These results identify Ho2PdAl6Ge4 as a candidate for exploring field-induced topological magnetic phases such as skyrmions, opening the way for further investigations on the family of RE2PdAl6Ge4 materials.

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.

RKKY-type in-plane ferromagnetism in layered Mn1/4NbS2 single crystals

Placing the layers of the $3d$ magnetic elements in the van der Waals gap pulls the Nb/Ta-based transition metal dichalcogenides family from a nonmagnetic to a magnetic zone. However, the magnetic spectrum is strongly sensitive to the specific combination of host lattice and type of intercalated magnetic element and thus each combination needs a proper explicit study. In this context, we systematically investigate the magnetization of the Mn-intercalated layered ferromagnet ${\mathrm{Mn}}_{1/4}{\mathrm{NbS}}_{2}$ single crystal. Magnetization measurement revealed paramagnetic to ferromagnetic phase transition at around 105 K and an easy in-plane ($H\ensuremath{\perp}c$) significantly high magnetic anisotropy. The in-plane magnetic anisotropic energy (MAE) evaluated via the noncollinear first-principle approach is $\ensuremath{\sim}\ensuremath{-}600 \ensuremath{\mu}\mathrm{eV}$ per unit cell. The position of the Fermi level in between the spin-up and spin-down Mn states suppresses the positive contribution in the overall MAE, which lifts the overall MAE negative (in plane) with a larger size in ${\mathrm{Mn}}_{1/4}{\mathrm{NbS}}_{2}$. The comprehensive analysis of magnetization isotherms measured in the vicinity of ${T}_{c}$ with magnetic field $H$ applied parallel to the $ab$ plane ($H\ensuremath{\perp}c$) yields the asymptotic critical exponents $\ensuremath{\beta}=0.3251(2)$ and $\ensuremath{\gamma}=1.2(1)$, and $\ensuremath{\delta}=4.691(1)$. These critical exponents fulfill the scaling relation and scaling equation of the magnetic state predicted by the scaling theory. The determined critical exponents agree well with those obtained from the results of the renormalization group theory approach for a three-dimensional Ising system coupled with a long-range interaction between spins decaying as $J(r)\ensuremath{\approx}{r}^{\ensuremath{-}(d+\ensuremath{\sigma})}$ with $\ensuremath{\sigma}$ = 1.84. The Ising-type spin state in ${\mathrm{Mn}}_{1/4}{\mathrm{NbS}}_{2}$ is attributed to the higher size of MAE. Our theoretical analysis shows that indirect exchange interaction between Mn-Mn along the $c$ axis, mediated via spins' polarized conduction electrons of Nb atoms, a Ruderman-Kittel-Kasuya-Yoshida (RKKY) type ferromagnetic interaction, dominates over the direct in-plane Mn-Mn exchange interaction (less favorable due to large ${d}_{\text{Mn-Mn}}\ensuremath{\sim}6.67\phantom{\rule{4pt}{0ex}}\stackrel{\ifmmode \mathring{}\else \r{}\fi{}}{\mathrm{A}}$) and is thus responsible for the macroscopic magnetization in ${\mathrm{Mn}}_{1/4}{\mathrm{NbS}}_{2}$. The RKKY-type ferromagnetic interaction in ${\mathrm{Mn}}_{1/4}{\mathrm{NbS}}_{2}$ arises due to the large spin polarization of the conduction electrons associated with the Nb atoms at the Fermi energy and existence of unoccupied Mn $3d$ states well above the Fermi level.

Magnetic properties of bilayer nano-stanene-like structure with Ruderman–Kittel–Kasuya–Yoshida coupling

A bilayer nano-stanene-like structure with Ruderman–Kittel–Kasuya–Yoshida (RKKY) coupling described by the Ising model is proposed. The magnetic and thermodynamic properties are studied using the effective-field theory with correlations. The exchange coupling, longitudinal magnetic field, number of non-magnetic layers, and anisotropies had major influences on the magnetization, specific heat, and internal energy. Different saturation magnetizations are observed on the magnetization curve. The variation in the system blocking temperature is studied. The results provide theoretical guidance for the magnetic investigation of nanomaterials with RKKY coupling.

First-principles study of magnetic properties of the cobalt doped silver copper sulfide

First principles calculations in the framework of density functional theory have been carried out to study the electronic and magnetic properties of cobalt (Co) doped silver copper sulfide (AgCuS) system. Cobalt doped at Cu site can induces a significant amount of magnetism in AgCuS. The total and partial density of states reveal that 3d orbital electron of the Co atom is the primary source of magnetism and the rest of magnetic moment comes from the 3d orbital electron of Cu atoms. Spin-spin interaction study suggests a ferromagnetic ordering with Ruderman-Kittel-Kasuya-Yoshida (RKKY) type of exchange interaction. The spin polarized density of states calculation suggest the presence of polarized density of states at the Fermi level which makes the system more interesting as a half-metallic ferromagnetic system.

Magnetoresistance anisotropy in ErB12 antiferromagnetic metal: The evidence for dynamic charge stripes

The nature of charge transport and magnetization anisotropy was investigated in the ErB12 antiferromagnetic metal with both cooperative Jahn-Teller distortions of the fcc crystal structure and electronic instability (dynamic charge stripes). A butterfly pattern of the H-φ magnetic phase diagram in the (1 1 0) plane was reconstructed, including a large number of different magnetic phases separated from each other by radial and circular boundaries. It is argued that fluctuations of electron density are responsible for the suppression of the indirect Ruderman-Kittel-Kasuya-Yoshida (RKKY) exchange between the nearest neighbored Er3+ ions located along the 〈110〉 directions producing the magnetic phase diversity in ErB12.

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.

Observation of flat band, RKKY plateau, and magnetization jump in quasi-one-dimensional triangular kagome lattice model

Inspired by the research interest on the realization of flatbands and magnetization plateaus in kagome lattices, herein we study the electronic properties and exchange magnetic interactions in quasi-one-dimensional boron triangular kagome lattice (1D-BTKL) models by using the real-space Green’s function approach in a tight-binding model. First, we study the electronic properties of 1D-BTKLs in the presence of staggered sublattice potential, and then, by analyzing the Ruderman–Kittel–Kasuya–Yoshida (RKKY) interaction in these lattice structures, the magnetic ground states of 1D-BTKLs in the presence of two magnetic adatoms are evaluated. It is found that the 1D channels of BTKL show different electronic and magnetic behaviors due to different values of the hopping integrals and spin–orbit couplings. Two important salient features of 1D-BTKLs are the presence of flatbands in their band structures as well as the emergence of the RKKY plateau vs the Fermi energy. To the best of our knowledge, it is the first time that the RKKY plateau is systematically reported and as we will see this idea has been advocated forcefully. It was shown that both the width and location of the magnetization plateaus could be controlled through variation of the staggered potential and the Fermi energy as well as the spatial configuration of the magnetic impurities, enabling a variety of electromagnetic devices to be produced. The other fascinating feature of the present study is the magnetic susceptibility discontinuity, named as magnetization jump, which accompanies with the discontinuity in the magnetization curves. We believe that our results provide significant insights into designing further experiments to search for the realization of the flatbands and magnetization plateau phases in spintronics and pseudospin electronic devices based on TKLs.

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.

RKKY coupling in Weyl semimetal thin films

We consider the effective coupling between impurity spins on surfaces of a thin-film Weyl semimetal within Ruderman-Kittel-Kasuya-Yoshida (RKKY) theory. If the spins are on the same surface, their coupling reflects the anisotropy and the spin-momentum locking of the Fermi arcs. By contrast when the spins are on opposite surfaces, their coupling is mediated by the Fermi arcs as well as by bulk states. In this case the coupling is both surprisingly strong and strongly thickness dependent, with a maximum at an optimum thickness. We demonstrate our results using analytical solutions of states in the thin-film geometry, as well using a two-surface recursive Green's function analysis of the tight-binding model.

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.

Systematic Study of Ferromagnetism in CrxSb2\u2212xTe3 Topological Insulator Thin Films using Electrical and Optical Techniques

Ferromagnetic ordering in a topological insulator can break time-reversal symmetry, realizing dissipationless electronic states in the absence of a magnetic field. The control of the magnetic state is of great importance for future device applications. We provide a detailed systematic study of the magnetic state in highly doped CrxSb2−xTe3 thin films using electrical transport, magneto-optic Kerr effect measurements and terahertz time domain spectroscopy, and also report an efficient electric gating of ferromagnetic order using the electrolyte ionic liquid [DEME][TFSI]. Upon increasing the Cr concentration from x = 0.15 to 0.76, the Curie temperature (Tc) was observed to increase by ~5 times to 176 K. In addition, it was possible to modify the magnetic moment by up to 50% with a gate bias variation of just ±3 V, which corresponds to an increase in carrier density by 50%. Further analysis on a sample with x = 0.76 exhibits a clear insulator-metal transition at Tc, indicating the consistency between the electrical and optical measurements. The direct correlation obtained between the carrier density and ferromagnetism - in both electrostatic and chemical doping - using optical and electrical means strongly suggests a carrier-mediated Ruderman-Kittel-Kasuya-Yoshida (RKKY) coupling scenario. Our low-voltage means of manipulating ferromagnetism, and consistency in optical and electrical measurements provides a way to realize exotic quantum states for spintronic and low energy magneto-electronic device applications.

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.

Effect of Ga substitution on low temperature transport and magnetic response of Ce75Al25 metallic glass

The low temperature transport and magnetic behavior of Ce75Al25-xGax (x=0, 2, 4 and 6 at. %) metallic glasses (MGs) have been investigated. The temperature dependence of the resistance shows that the temperature coefficient of resistance (TCR) changes with Ga content. The significant change in the magnetoresistance (MR) behaviour has been observed for these alloys. The alloys with x=2, 4 and 6 show a magnetic field tuned MR transition from positive to negative values at low temperature. The magnetization (M-H) curves of the MGs at 5 K exhibit no magnetic hysteresis and show paramagnetic characteristics. However, a curious type of hysteretic behaviour for Ce75Al25-xGax alloys in non-zero magnetic field has been observed. The hysteric field range has been found to shift to higher magnetic field with increase in the value of x. It has been suggested that the formation of nano-amorphous domains in the glassy matrix and the delocalization of 4f1 configuration of Ce atoms due to Ga substitution may result in the unusual transport behaviour of Ce-Al (Ga) MGs. These changes in the transport behaviour at low temperature have been discussed in terms of the competition between the Kondo effect and Ruderman–Kittel–Kasuya–Yoshida (RKKY) interaction. The genesis of hysteretic behaviour in M-H curve has been proposed to arise due to Anti-ferromagnetic screening interaction (AFSI) in two kinds of clusters.

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.