Ruderman-Kittle-Kasuya-Yosida Research Articles

RKKY interaction in topological crystalline insulators

We theoretically study the Ruderman–Kittle–Kasuya–Yosida (RKKY) interaction between two magnetic impurities embedded on the (001) surface of a topological crystalline insulator (TCI), using the Green’s function method. The highly anisotropic band structure of TCI, gives rise to a highly anisotropic magnetic exchange coupling. We show that the interaction is oscillatory; the amplitude and wavelength of oscillations have angular dependence arising from the anisotropy of the surface state band structure. The spatial configurations of the magnetic impurities can also dramatically change the quality and quantity of the RKKY interaction. We find a strong anisotropy of the exchange interaction and the magnetic ground state of two magnetic adatoms can be tuned by changing the rotational configuration of impurities. It is found that the three types of interactions contribute to the magnetic exchange coupling in the (001) TCI surfaces: the Heisenberg, Dzyaloshinsky–Moriya, and Ising types. Our results will open up a new route toward spintronics based on TCIs.

Indirect RKKY interaction in doped armchair nanotube due to electron phonon interaction effects

We study the Ruderman-Kittle-Kasuya-Yosida (RKKY) interaction in doped armchair nanotube in the presence of gap parameter. The effects of both next nearest neighbor hopping parameter and electron-Holstein phonon on RKKY interaction have been addressed. RKKY interaction as a function of distance between localized moments have been analyzed. In order to calculate the exchange interaction along arbitrary direction between two magnetic moments, we should obtain the transverse static spin susceptibility of armchair graphene nanoribbon in the presence of electron-phonon coupling and gap parameter. The spin susceptibility components are calculated using Green’s function approach for Holstein model Hamiltonian. The effects of electron doping on dependence of exchange interaction on distance between moments are investigated via calculating correlation function of spin density operators. Our results show the influences of next nearest neighbor hopping parameter on the spatial behavior of RKKY interactions are different in the presence of electron phonon coupling.

RKKY interaction in doped nanotubes: A full band study

We study the Ruderman-Kittle-Kasuya-Yosida (RKKY) interaction in doped both armchair and zigzag nanotubes. The effects of both gap parameter and electron doping on RKKY interaction have been addressed. RKKY interaction for traverse components of localized spins as a function of distance between localized moments has been analyzed. In order to calculate the exchange interaction along arbitrary direction between two magnetic moments, we should obtain transverse static spin susceptibility of graphene like nanotubes in the presence of gap parameter and electron doping. The spin susceptibility components are calculated using the spin dependent Green's function approach for tight binding model Hamiltonian. The effects of tube diameter on the dependence of exchange interaction on distance between moments are investigated via calculating correlation function of spin density operators. Our results show the influences of electron doping on the spatial behavior of transverse RKKY interactions are different for zigzag and armchair types of nanotube.

The effects of electron–phonon interaction on anisotropic RKKY interaction in graphene nanoribbon

We study the Ruderman–Kittle–Kasuya–Yosida (RKKY) interaction in doped armchair graphene nanoribbon. The effects of both external magnetic field and electron-Holstein phonon on RKKY interaction have been addressed. RKKY interaction as a function of distance between localized moments has been analyzed. It has been shown that a magnetic field along the z-axis mediates an anisotropic interaction which corresponds to a XXZ model interaction between two magnetic moments. In order to calculate the exchange interaction along arbitrary direction between two magnetic moments, we should obtain both transverse and longitudinal static spin susceptibilities of armchair graphene nanoribbon in the presence of electron-phonon coupling and magnetic field. The spin susceptibility components are calculated using the spin dependent Green’s function approach for Holstein model Hamiltonian. The effects of spin polarization on the dependence of exchange interaction on distance between moments are investigated via calculating correlation function of spin density operators. Our results show the influences of magnetic field on the spatial behavior of in-plane and longitudinal RKKY interactions are different in the presence of magnetic field.

Staggered potential and spin polarization effects on RKKY interaction in armchair graphene nanoribbon

Indirect exchange interaction between two magnetic external atoms, named by Ruderman–Kittle–Kasuya–Yosida (RKKY) interaction, has been presented in the staggered armchair graphene nanoribbon. We have studied RKKY interaction as a function of distance between localized moments. It has been shown that a magnetic ordering along the z-axis mediates an anisotropic interaction which corresponds to a XXZ model interaction between two magnetic moments. The static spin susceptibility components of armchair graphene nanoribbon have been calculated to find exchange interaction between arbitrary components of magnetic moments. We have exploited Green’s function approach in order to calculate spin susceptibility components of electronic gas in nanoribbon structure in the context of tight binding model Hamiltonian. The effects of parameter and ribbon width on the dependence of exchange interaction on distance between moments are investigated. Our results show the spin polarization along perpendicular to the plane leads to anisotropic behavior for exchange interaction between the two magnetic moments. In other words the spatial behavior of RKKY interaction between longitudinal components of magnetic moments is different from that of transverse components.

RKKY interaction in spin polarized armchair graphene nanoribbon

We present the Ruderman–Kittle–Kasuya–Yosida (RKKY) interaction in the presence of magnetic long range ordered armchair graphene nanoribbon. RKKY interaction as a function of distance between localized moments has been analyzed. It has been shown that a magnetic ordering along the z-axis mediates an anisotropic interaction which corresponds to a XXZ model interaction between two magnetic moments. In order to calculate the exchange interaction along arbitrary direction between two magnetic moments, we should obtain the static spin susceptibilities of armchair graphene nanoribbon. The spin susceptibility components are calculated using Green's function approach for tight binding model Hamiltonian. The effects of spin polarization on the dependence of exchange interaction on distance between moments are investigated via calculating correlation function of spin density operators. Our results show that the chemical potential impacts the spatial behavior of RKKY interaction.

High freezing temperature in SnO2 based diluted magnetic semiconductor

Sn0.95−yMn0.025Co0.025FeyO2 (y=0.0, y=0.01) compounds have been synthesized by the precipitation exchange method. X-ray diffraction revealed that single-phase rutile polycrystalline structure was obtained. Magnetic measurements revealed that this sample exhibits spin glass behaviors for y=0 with a spin-freezing temperature around 150K, while it exhibits ferromagnetism for y=0.01 below Tc=300K. The existences of frustrated moments due to Ruderman–Kittle–Kasuya–Yosida interactions in Sn(Mn, Co)O2 may be responsible for the spin glass state formed in Sn(Mn,Co)O2. With a tri-doping by Fe this magnetic frustration is broken, indicating that the Fe atoms introduces charge carriers responsible for the change of interaction from frustrated behaviors to ferromagnetic interaction.

Anisotropic RKKY interaction in spin-polarized graphene

We study the Ruderman-Kittle-Kasuya-Yosida (RKKY) interaction in the presence of spin polarized two dimensional Dirac fermions. We show that a spin polarization along the z-axis mediates an anisotropic interaction which corresponds to a XXZ model interaction between two magnetic moments. For undoped graphene, while the $x$ part of interaction keeps its constant ferromagnetic sign, its $z$ part oscillates with the distance of magnetic impurities, $R$. A finite doping causes that both parts of the interaction oscillate with $R$. We explore a beating pattern of oscillations of the RKKY interaction along armchair and zigzag lattice directions, which occurs for some certain values of the chemical potential. The two characteristic periods of the beating are determined by inverse of the difference and the sum of the chemical potential and the spin polarization.

Indirect exchange interaction between magnetic adatoms in monolayer MoS2

We study the Ruderman-Kittle-Kasuya-Yosida (RKKY) interaction in a monolayer MoS${}_{2}$. We show that the rotation of the itinerant electron spin due to the spin-orbit coupling causes a twisted interaction between two magnetic adatoms, which consists of different RKKY coupling terms: the Heisenberg, Dzyaloshinsky-Moriya, and Ising interactions. We find that the interaction terms are very sensitive to the Fermi energy values and change dramatically from doped to undoped systems. A finite doping causes all parts of the interaction to oscillate with the distance of two magnetic impurities $R$, and the interaction behaves like ${R}^{\ensuremath{-}2}$ for a long distance between two localized spins. We explore a beating pattern of oscillations of the RKKY interaction that occurs for the doped system.

MFM and Raman studies in PEMBE-grown (Ga,Mn)N thin films showing room-temperature ferromagnetism

We present the room-temperature ferromagnetism in the (Ga,Mn)N films grown on n-type GaN templates by plasma-enhanced molecular beam epitaxy for semiconductor spintronic device applications. Despite of the possible interface effects between the (Ga,Mn)N layers and n-type GaN templates, the (Ga,Mn)N films were found to exhibit the ferromagnetic ordering above room temperature. The magnetic force microscopy identified the magnetic domains with the different magnetic orientations at room temperature, indicating the existence of the ferromagnetic long-range ordering. In Raman spectra, an additional peak at 578 cm −1 was observed, which is attributed to the local vibration of substitutional Mn in the (Ga,Mn)N lattice. Therefore, it is believed that the ferromagnetic ordering in (Ga,Mn)N is due to the carrier-mediated Ruderman–Kittle–Kasuya–Yosida interaction.

Spin-glass behavior with short-range antiferromagnetic order in Nd2AgIn3

We present experimental results of complex susceptibility, static magnetization, magnetic relaxation, specific heat, and electrical resistivity measurements on an intermetallic compound Nd2AgIn3. The results indicated that Nd2AgIn3 undergoes a spin-glass transition at a freezing temperature Tf=12.6 K accompanied with the formation of short-range antiferromagnetic order. The mechanism of formation of spin-glass state in Nd2AgIn3 is different from that in diluted metallic spin-glass or uranium intermetallic compound. The existences of frustrated moments due to the triangles of nearest neighbors in Nd atomic layers and randomly distributed Ruderman–Kittle–Kasuya–Yosida interactions may be responsible for the spin glass state formed in Nd2AgIn3.

Effect of superconductivity on spin dynamics in(Y1−xRx)Rh4B4

An adiabatic---field-cycle method for $^{11}\mathrm{B}$ nuclear magnetic relaxation has been used to study the spin dynamics of rare-earth ions in dilute $({\mathrm{Y}}_{1\ensuremath{-}x}{R}_{x}){\mathrm{Rh}}_{4}{\mathrm{B}}_{4}$. Longitudinal dipolar fluctuations of rare-earth moments are found to be the main source for the spin-lattice relaxation time of $^{11}\mathrm{B}$. The variation of ${T}_{1}$ in the superconducting state is attributed to the reduction of the electronic spin-relaxation time ${\ensuremath{\tau}}_{m}$, which is mainly determined by the Ruderman-Kittle-Kasuya-Yosida (RKKY) interaction mediated by the conduction electrons. The remarkable reduction of the RKKY coupling below ${T}_{c}$ is discussed in connection with the reduction of the conduction-electron spin susceptibility $\ensuremath{\chi}(q)$.