Showing papers on "Exchange interaction published in 2010"
01 Jan 2010
TL;DR: The basic results of sp-d and d-d interactions in DMS are discussed in this article. But they do not consider the effect of spin and energy transfer between carriers, Magnetic Ions, and Lattice.
Abstract: Basic Consequences of sp-d and d-d Interactions in DMS.- Optical Spectroscopy of Wide-Gap Diluted Magnetic Semiconductors.- Exchange Interaction Between Carriers and Magnetic Ions in Quantum Size Heterostructures.- Band-Offset Engineering in Magnetic/Non-Magnetic Semiconductor Quantum Structures.- Diluted Magnetic Quantum Dots.- Magnetic Ion-Carrier Interactions in Quantum Dots.- Magnetic Polarons.- Spin and Energy Transfer Between Carriers, Magnetic Ions, and Lattice.- Coherent Spin Dynamics of Carriers and Magnetic Ions in Diluted Magnetic Semiconductors.- Spectroscopy of Spin-Polarized 2D Carrier Gas, Spin-Resolved Interactions.- Quantum Transport in Diluted Magnetic Semiconductors.- Neutron Scattering Studies of Interlayer Magnetic Coupling.
128 citations
TL;DR: Due to the direct Mn-Mn exchange interaction in Mn(2)CoZ, the Curie temperature decreases, although the total moment increases when the valence electron number Z is increased, which follows from the decreasing magnetic moments.
Abstract: The generalized Heusler compounds Mn2CoZ (Z = Al, Ga, In, Si, Ge, Sn, Sb) with the Hg2CuTi structure are of large interest due to their half-metallic ferrimagnetism. The complex magnetic interactions between the constituents are studied by first principles calculations of the Heisenberg exchange coupling parameters, and Curie temperatures are calculated from those. Due to the direct Mn-Mn exchange interaction in Mn2CoZ, the Curie temperature decreases, while the total moment increases when changing Z from one group to another. The exchange interactions are dominated by a strong direct exchange between Co and its nearest neighbor Mn on the B site, which is nearly constant. The coupling between the nearest-neighbor Mn atoms scales with the magnetic moment of the Mn atom on the C site. Calculations with different lattice parameters suggest a negative pressure dependence of the Curie temperature, which follows from decreasing magnetic moments. Curie temperatures of more than 800 K are predicted for Mn2CoAl (890 K), Mn2CoGa (886 K), and Mn2CoIn (845 K).
81 citations
TL;DR: In this paper, a single crystal of the magnetoelectric compound Cu2OSeO3 was studied and the temperature dependence of the local electronic moments extracted from the NMR data was fully consistent with a magnetic phase transition from the high-T paramagnetic phase to a low-T ferrimagnetic state with 3/4 of the Cu2+ ions aligned parallel and 1/4 aligned antiparallel to the applied field of 14.09 T.
Abstract: We present a thorough Se-77 nuclear-magnetic-resonance (NMR) study of a single crystal of the magnetoelectric compound Cu2OSeO3. The temperature dependence of the local electronic moments extracted from the NMR data is fully consistent with a magnetic phase transition from the high-T paramagnetic phase to a low-T ferrimagnetic state with 3/4 of the Cu2+ ions aligned parallel and 1/4 aligned antiparallel to the applied field of 14.09 T. The transition to this 3up-1down magnetic state is not accompanied by any splitting of the NMR lines or any abrupt modification in their broadening, hence there is no observable reduction in the crystal symmetry from its high-T cubic P2(1)3 space group. These results are in agreement with high-resolution x-ray diffraction and magnetization data on powder samples reported previously by Bos et al. [Phys. Rev. B 78, 094416 (2008)]. We also develop a mean-field theory description of the problem based on a microscopic spin Hamiltonian with one antiferromagnetic (J(afm) similar or equal to 68 K) and one ferromagnetic (J(fm) similar or equal to -50 K) nearest-neighbor exchange interaction.
70 citations
TL;DR: In this paper, the origin of antiferromagnetic magnetism of CoO in the rocksalt structure using spin-polarized density functional theory calculations was investigated, and it was shown that the interaction between the occupied and unoccupied eg states plays the dominant role.
Abstract: We have investigated the origin of antiferromagnetism of CoO in the rocksalt structure using spin-polarized density functional theory calculations. We find that in the rocksalt structure, the superexchange interaction between the occupied and unoccupied eg states plays the dominant role, which leads to an antiferromagnetic ground state, but the system also has a strong direct exchange interaction between the partially occupied minority spin t2g states that leads to the unusual situation that the ferromagnetic phase is more stable than most antiferromagnetic configurations.
58 citations
01 Jan 2010
TL;DR: In this article, the spin current across the interface between a normal metal and an insulating ferromagnet in a junction was studied, which is proportional to spin accumulation as well as the population of magnons.
Abstract: We study the spin current across the interface between a normal metal and an insulating ferromagnet in a junction. At the interface, conduction electrons in the normal metal interact with localized moments of the ferromagnet via the sd-type exchange interaction. In the presence of spin accumulation in the normal metal, the spin accumulation decays by spin-flip scattering of conduction electrons at the interface, thereby emitting magnons through the exchange interaction at the interface. Using the linear response theory, we obtain the spin current through the interface, which is proportional to spin accumulation as well as the population of magnons.
58 citations
TL;DR: In this paper, the authors give a systematic and comprehensive description of the exchange interactions in polynuclear systems based on orbitally degenerate metal ions in the context of their relevance to the modern molecular magnetism.
Abstract: This review article is a first attempt to give a systematic and comprehensive description (in the framework of the unified theoretical approach) of the exchange interactions in polynuclear systems based on orbitally degenerate metal ions in the context of their relevance to the modern molecular magnetism. Interest in these systems is related to the fundamental problems of magnetism and at the same time steered by a number of impressive potential applications of molecular magnets, like high-density memory storage units, nanoscale qubits, spintronics and photoswitchable devices. In the presence of orbital degeneracy, the conventional spin Hamiltonian (Heisenberg–Dirac–van Vleck model) becomes inapplicable even as an approximation. The central component of this review article constitutes the concept of orbitally-dependent exchange interaction between metal ions possessing unquenched orbital angular momenta. We present a rigorous procedure of derivation of the kinetic exchange Hamiltonian for a pair of orbita...
54 citations
TL;DR: In this article, a spin-polarized tip was used for scanning tunneling microscopy and spectroscopy using a spin polarization tip. And the authors provided a theory to partition the tunneling conductance into three separate contributions, a background conductance independent of the local spin, a dynamical conductance proportional to the local-spin moment, and a conductance which is proportional to a noise spectrum of local spin interactions.
Abstract: We provide a theory for scanning tunneling microscopy and spectroscopy using a spin-polarized tip. It it shown that the tunneling conductance can be partitioned into three separate contributions, a background conductance which is independent of the local spin, a dynamical conductance which is proportional to the local-spin moment, and a conductance which is proportional to the noise spectrum of the local-spin interactions. The presented theory is applicable to setups with magnetic tip and substrate in noncollinear arrangement, as well as for nonmagnetic situations. The partitioning of the tunneling current suggests a possibility to extract the total spin moment of the local spin from the dynamical conductance. The dynamical conductance suggests a possibility to generate very high-frequency spin-dependent ac currents and/or voltages. We also propose a measurement of the dynamical conductance that can be used to determine the character of the effective exchange interaction between individual spins in clusters. The third contribution to the tunneling current is associated with the spin-spin correlations induced by the exchange interaction between the local-spin moment and the tunneling electrons. We demonstrate how this term can be used in the analysis of spin excitations recorded in conductance measurements. Finally, we propose to use spin-polarized scanning tunneling microscopy for detailed studies of the spin-excitation spectrum.
48 citations
TL;DR: There is strong renormalization of t, a significant role of the superexchange coupling J, and a rich phase diagram of the 0 and π-junction regimes when both the superconductivity and the exchange interaction compete with the Kondo physics.
Abstract: We study the Josephson current through a serial double quantum dot and the associated 0 � � transitions which result from the subtle interplay between the superconductivity, the Kondo physics, and the interdot superexchange interaction. The competition between them is examined by tuning the relative strength � =TK of the superconducting gap and the Kondo temperature, for different strengths of the superexchange coupling determined by the interdot tunneling t relative to the level broadening � . We find strong renormalization of t, a significant role of the superexchange coupling J, and a rich phase diagram of the 0 and � -junction regimes. In particular, when both the superconductivity and the exchange interaction
46 citations
TL;DR: In this paper, weakly bound trimers with energies below and above the continuum of scattering states of a single particle (monomer) and a bound-particle pair (dimer) were obtained from an effective Hamiltonian in the strong coupling regime.
Abstract: We pursue three-body bound states in a one-dimensional tight-binding lattice described by the Bose-Hubbard model with strong on-site interaction. Apart from the simple strongly bound ``trimer'' state corresponding to all three particles occupying the same lattice site, we find two novel kinds of weakly bound trimers with energies below and above the continuum of scattering states of a single-particle (``monomer'') and a bound-particle pair (``dimer''). The corresponding binding mechanism can be inferred from an effective Hamiltonian in the strong-coupling regime which contains an exchange interaction between the monomer and the dimer. In the limit of very strong on-site interaction, the exchange-bound trimers attain a universal value of the binding energy. These phenomena can be observed with cold atoms in optical lattices.
46 citations
TL;DR: In this article, the spin filling pattern in the few electron limit of silicon metal-on-semiconductor based quantum dots (QDs) was reported, and the magnetic field dependence of Coulomb oscillation peaks showed filling of parallel spins for the last few electrons.
Abstract: We report the spin filling pattern in the few electron limit of silicon metal-on-semiconductor based quantum dots (QDs). Magnetic field dependence of Coulomb oscillation peaks showed filling of parallel spins for the last few electrons. This implies the existence of a large spin exchange energy compared with the orbital level spacing, which has been predicted for relatively large silicon QDs. Our excited-state spectroscopy study confirmed a large spin exchange energy, as well as a large valley splitting at zero magnetic field.
45 citations
TL;DR: In this article, the Coulomb interaction on the quantum dot can provide more information from tunnel spectroscopy of the impurity spin, and the frequency-dependent Fano factor can be used to study the nontrivial, coherent dynamics of the spins on the dot due to the interplay between exchange interaction and coupling to external and exchange magnetic fields.
Abstract: We investigate transport through a single-level quantum dot coupled to noncollinearly magnetized ferromagnets in the presence of localized spins in either the tunnel barrier or on the quantum dot. For a large, anisotropic spin embedded in the tunnel barrier, our main focus is on the impurity excitations and the current-induced switching of the impurity that lead to characteristic features in the current. In particular, we show how the Coulomb interaction on the quantum dot can provide more information from tunnel spectroscopy of the impurity spin. In the case of a small spin on the quantum dot, we find that the frequency-dependent Fano factor can be used to study the nontrivial, coherent dynamics of the spins on the dot due to the interplay between exchange interaction and coupling to external and exchange magnetic fields.
TL;DR: Theory of exciton fine structure in semiconductor quantum dots and its dependence on quantum-dot anisotropy and external lateral electric field is presented in this article, where the effective exciton Hamiltonian including long-range electron-hole exchange interaction is derived within the $k\ensuremath{\cdot}p$ effective-mass approximation.
Abstract: Theory of exciton fine structure in semiconductor quantum dots and its dependence on quantum-dot anisotropy and external lateral electric field is presented. The effective exciton Hamiltonian including long-range electron-hole exchange interaction is derived within the $k\ensuremath{\cdot}p$ effective-mass approximation. The exchange matrix elements of the Hamiltonian are expressed explicitly in terms of electron and hole envelope functions. The matrix element responsible for the ``bright'' exciton splitting is identified and analyzed. An excitonic fine structure for a model quantum dot with quasi-two-dimensional anisotropic harmonic oscillator confining potential is analyzed as a function of the shape anisotropy, size, and applied lateral electric field.
TL;DR: In this article, the authors report spin relaxation and coherence times for mobile electrons and natural quantum dots at a 28Si/SiO2 interface and show that confining electrons and cooling increases T1 to 0.3 us at 5 K.
Abstract: While electron spins in silicon heterostructures make attractive qubits, little is known about the coherence of electrons at the Si/SiO2 interface. We report spin relaxation (T1) and coherence (T2) times for mobile electrons and natural quantum dots at a 28Si/SiO2 interface. Mobile electrons have short T1 and T2 of 0.3 us at 5 K. In line with predictions, confining electrons and cooling increases T1 to 0.8 ms at 350 mK. In contrast, T2 for quantum dots is around 10 us at 350 mK, increasing to 30 us when the dot density is reduced by a factor of two. The quantum dot T2 is shorter than T1, indicating that T2 is not controlled by T1 at 350 mK but is instead limited by an extrinsic mechanism. The evidence suggests that this extrinsic mechanism is an exchange interaction between electrons in neighboring dots.
TL;DR: In this paper, the results of the first principles calculations for bcc iron over a wide range of lattice constants using the magnetic force theorem and the one-electron Green's function were discussed.
Abstract: Functional representations of the spin polarization and the exchange interaction in terms of the lattice configuration is necessary to model the dynamics of the coupled spin and lattice subsystems in large-scale atomistic simulation of magnetic materials. Data needed for this purpose have only existed in the regime of small displacements from the equilibrium perfect lattice configurations. In this paper, we report and discuss the results of our first-principles calculations for bcc iron over a wide range of lattice constants using the magnetic force theorem and the one-electron Green's function. Despite the relatively complex functional form of the exchange interaction function for bcc iron our results show that it can be expressed as a superposition of Bethe-Slater-type curves representing interatomic exchange interaction of the $3d$ electrons.
TL;DR: In this article, the polarization properties of an undoped InGaAs quantum well with a Mn delta layer in the GaAs barrier have been studied in a wide range of temperatures and magnetic fields.
Abstract: The polarization properties of the luminescence of an undoped InGaAs quantum well in InGaAs/GaAs het-erojunctions with a Mn delta layer in the GaAs barrier have been studied in a wide range of temperatures and magnetic fields. It has been found that the s, p-d exchange interaction of carriers in the quantum well with Mn ions in the δ layer leads to the ferromagnetic behavior of both the Zeeman splitting and spin polarization of the carriers with a Curie temperature typical of the Mn delta layer in the GaAs barrier. The saturation of the spin polarization of holes associated with their Fermi degeneracy has been observed at low temperatures (T < 20 K).
TL;DR: In this paper, a promising method to investigate dark exciton transitions in quantum dots is presented, where the optical recombination of the dark-exciton is allowed when the exciton state is coupled with an individual magnetic impurity (manganese ion).
Abstract: A promising method to investigate dark exciton transitions in quantum dots is presented. The optical recombination of the dark exciton is allowed when the exciton state is coupled with an individual magnetic impurity (manganese ion). It is shown that the efficient radiative recombination is possible when the exchange interaction with the magnetic ion is accompanied by a mixing of the heavy-light hole states related to an in-plane anisotropy of the quantum dot. It is also shown that the dark exciton recombination is an efficient channel of manganese spin orientation.
TL;DR: Investigations on the temperature dependent Raman spectroscopy provide evidence for such structural characteristics, which affects the exchange interaction of LaMn-O-Co having monoclinic structure with distinct physical properties, and Raman scattering suggests the presence of spin-phonon coupling for both the phases around the T(c).
Abstract: Two distinct ferromagnetic phases of LaMn0.5Co0.5O3 having monoclinic structure with distinct physical properties have been studied. The ferromagnetic ordering temperature Tc is found to be different for both the phases. The origin of such contrasting characteristics is assigned to the changes in the distance(s) and angle(s) between Mn–O–Co resulting from distortions observed from neutron diffraction studies. Investigations on the temperature dependent Raman spectroscopy provide evidence for such structural characteristics, which affects the exchange interaction. The difference in B-site ordering which is evident from the neutron diffraction is also responsible for the difference in Tc. Raman scattering suggests the presence of spin–phonon coupling for both the phases around the Tc. Electrical transport properties of both the phases have been investigated based on the lattice distortion.
TL;DR: In this article, the concept of spin heat accumulation in excited spin valves was studied, more precisely the effective electron temperature that may become spin dependent, both in linear response and far from equilibrium.
Abstract: We study the concept of spin heat accumulation in excited spin valves, more precisely the effective electron temperature that may become spin dependent, both in linear response and far from equilibrium. A temperature or voltage gradient create nonequilibrium energy distributions of the two spin ensembles in the normal-metal spacer, which approach Fermi-Dirac functions through energy relaxation mediated by electron-electron and electron-phonon coupling. Both mechanisms also exchange energy between the spin subsystems. This interspin energy exchange may strongly affect thermoelectric properties of spin valves, leading, e.g., to violations of the Wiedemann-Franz law.
TL;DR: In this paper, the transport properties of a single-molecule magnet (SMM) weakly coupled to one nonmagnetic and one ferromagnetic lead are investigated.
Abstract: We study transport properties of a single-molecule magnet (SMM) weakly coupled to one nonmagnetic and one ferromagnetic lead. Using the diagrammatic technique in real time, we calculate transport in the sequential and cotunneling regimes for both ferromagnetic and antiferromagnetic exchange coupling between the molecule's LUMO level and the core spin. We show that the current flowing through the system is asymmetric with respect to the bias reversal, being strongly suppressed for particular bias polarizations. Thus, the considered system presents a prototype of a SMM spin diode. In addition, we also show that the functionality of such a device can be tuned by changing the position of the molecule's LUMO level and strongly depends on the type of exchange interaction.
TL;DR: In this article, the transport properties of a single-molecule magnet (SMM) weakly coupled to one nonmagnetic and one ferromagnetic lead are investigated.
Abstract: We study transport properties of a single-molecule magnet (SMM) weakly coupled to one nonmagnetic and one ferromagnetic lead. Using the diagrammatic technique in real time, we calculate transport in the sequential and cotunneling regimes for both ferromagnetic and antiferromagnetic exchange coupling between the molecule's LUMO level and the core spin. We show that the current flowing through the system is asymmetric with respect to the bias reversal, being strongly suppressed for particular bias polarizations. Thus, the considered system presents a prototype of a SMM spin diode. In addition, we also show that the functionality of such a device can be tuned by changing the position of the molecule's LUMO level and strongly depends on the type of exchange interaction.
TL;DR: In this paper, it was shown that a complex non-coplanar magnetic order with a quadrupled unit cell is stabilized by itinerant electrons on the pyrochlore lattice.
Abstract: Exchange interaction tends to favor collinear or coplanar magnetic orders in rotationally invariant spin systems. Indeed, such magnetic structures are usually selected by thermal or quantum fluctuations in highly frustrated magnets. Here we show that a complex noncoplanar magnetic order with a quadrupled unit cell is stabilized by itinerant electrons on the pyrochlore lattice. Specifically, we consider a Kondo-lattice model with classical localized moments at quarter filling. The electron Fermi "surface" at this filling factor is topologically equivalent to three intersecting Fermi circles. Perfect nesting of the Fermi lines leads to magnetic ordering with multiple wave vectors and a definite handedness. The chiral order might persist without magnetic order in a chiral spin liquid at finite temperatures.
TL;DR: It is actually shown that both parts of the imvdz ligand simultaneously influence the ferromagnetic behavior which ultimately reaches J(calc)=6.3 cm(-1), in very good agreement with the experimental value.
Abstract: The exchange channels governing the experimentally reported coupling constant (J(expt)=6 cm(-1)) value in the verdazyl-ligand based Cu(II) complex [Cu(hfac)(2)(imvdz)] are inspected using wave function-based difference dedicated configuration interaction calculations. The interaction between the two spin 1/2 holders is summed up in a unique coupling constant J. Nevertheless, by gradually increasing the level of calculation, different mechanisms of interaction are turned on step by step. In the present system, the calculated exchange interaction then appears alternatively ferromagnetic/antiferromagnetic/ferromagnetic. Our analysis demonstrates the tremendously importance of some specific exchange mechanisms. It is actually shown that both parts of the imvdz ligand simultaneously influence the ferromagnetic behavior which ultimately reaches J(calc)=6.3 cm(-1), in very good agreement with the experimental value. In accordance with the alternation of J, it is shown that the nature of the magnetic behavior results from competing channels. First, an antiferromagnetic contribution can be essentially attributed to single excitations involving the pi network localized on the verdazyl part. In contrast, the sigma ligand-to-metal charge transfer (LMCT) involving the imidazole moiety affords a ferromagnetic contribution. The distinct nature sigma/pi of the mechanisms is responsible for the net ferromagnetic behavior. The intuitively innocent part of the verdazyl-based ligands is deeply reconsidered and opens new routes into the rational design of magnetic objects.
TL;DR: In this article, the mean field theory and the probability law of Zn 1− x Mn x Cr 2 O 4 nanoparticles were used to calculate the magnetic exchange energies and the magnetic susceptibility.
TL;DR: In this article, the fine structure of the band-edge biexciton in nanometer-size crystallites of direct semiconductors with a cubic lattice structure or a hexagonal lattice was analyzed within the framework of a quasicubic lattice model.
Abstract: We present a theoretical analyses of the fine structure of the band-edge biexciton in nanometer-size crystallites [nanocrystal (NC) quantum dots] of direct semiconductors with a cubic lattice structure or a hexagonal lattice structure, which can be described within the framework of a quasicubic lattice model. The six ground biexciton states created from the two fourfold degenerate hole states and the two twofold degenerate electron states, according to the Pauli principle, are split into three levels by the crystal-shape asymmetry, the intrinsic crystal field (in hexagonal lattice structure), and the hole-hole exchange interaction. The size-dependent splitting and oscillator transition strength between the biexciton states and the ground exciton states were calculated in NCs with different types of spatial confinement: NCs surrounded by impenetrable barrier and NCs with a soft confinement created by gradually changing along the radius composition of the alloy forming the NC. The results of the calculations were compared with available experimental data on CdSe NCs.
TL;DR: In this paper, a polymer precursor method has been used to synthesize Ni-doped SnO2 nanoparticles, and X-ray diffraction (XRD) data analyses indicate the exclusive formation of nanosized particles with rutile-type phase (tetragonal SnO 2) for Ni contents below 10−mol%.
Abstract: A polymer precursor method has been used to synthesize Ni-doped SnO2 nanoparticles. X-ray diffraction (XRD) data analyses indicate the exclusive formation of nanosized particles with rutile-type phase (tetragonal SnO2) for Ni contents below 10 mol%. In this concentration range, the particle sizes decrease with increasing Ni content and a bulk solid solution limit was determined at ~ 1 mol%. Ni surface enrichment is present at concentrations higher than the solution limit. Only above 10 mol% Ni, the formation of a second NiO-related phase has been determined. Magnetization measurements suggest the occurrence of ferromagnetism for samples in the solid solution regime (below ~ 1 mol%). This ferromagnetism is associated with the exchange interaction between electron spins trapped on oxygen vacancies, and is enhanced as the amount of Ni2+ substituting at Sn4+ sites increases. Above the solid solution limit, ferromagnetism is destroyed by the Ni surface enrichment and the system behaves as a paramagnet.
TL;DR: Structural analysis with synchrotron powderX-ray diffraction data and the Mn L-edges X-ray absorption spectrum revealed that the A-site-ordered perovskite YMn(3)Al(4)O(12) was prepared by high-pressure synthesis with a chemical composition Y(3+)Mn (3+)(3+)Al(3++)(4) O(2-)(12).
Abstract: The A-site-ordered perovskite YMn3Al4O12 was prepared by high-pressure synthesis. Structural analysis with synchrotron powder X-ray diffraction data and the Mn L-edges X-ray absorption spectrum revealed that the compound has a chemical composition Y3+Mn3+3Al3+4O2−12 with magnetic Mn3+ at the A′ site and non-magnetic Al3+ at the B site. An antiferromagnetic interaction between the A′-site Mn3+ spins is induced by the nearest neighboring Mn−Mn direct exchange interaction and causes an antiferromagnetic transition at 34.3 K.
SIDI1
TL;DR: In this article, the magnetic properties of the spinels systems Zn1−xCdxCr2Se4 and Hg1+xCdCr2S4 have been studied by mean-field theory and high-temperature series expansions in the range 0.
TL;DR: In this article, the authors consider a resonant-tunneling model where the electron spin in a quantum dot or molecule is coupled to an additional local, anisotropic spin via exchange interaction and find that the characteristic fine structure in the differential conductance persists even if the hybridization energy exceeds thermal energies.
Abstract: Transport through molecular magnets is studied in the regime of strong coupling to the leads We consider a resonant-tunneling model where the electron spin in a quantum dot or molecule is coupled to an additional local, anisotropic spin via exchange interaction The two opposite regimes dominated by resonant tunneling and by Kondo transport, respectively, are considered In the resonant-tunneling regime, the stationary state of the impurity spin is calculated for arbitrarily strong molecule-lead coupling using a master-equation approach, which treats the exchange interaction perturbatively We find that the characteristic fine structure in the differential conductance persists even if the hybridization energy exceeds thermal energies Transport in the Kondo regime is studied within a diagrammatic approach We show that magnetic anisotropy gives rise to the appearance of two Kondo peaks at nonzero bias voltages
TL;DR: In this article, the first thiooxoverdazyl metal complex (Cu(hfac) 2 (Svdpy) was synthesized and the fit of the thermal variations of the magnetic susceptibility reveal a ferromagnetic intramolecular exchange interaction.
Abstract: The synthesis, structure and magnetic properties of the first thiooxoverdazyl metal complex (Cu(hfac) 2 (Svdpy)] [hfac = (1,1,1,5,5,5)-hexafluoroacetylacetonate; Svdpy = 1,5-dimethyl-3-(2-pyridyl)-6-thiooxoverdazyl] is described. The organic radical acts as a bidentate ligand leading to a six-coordinate metal complex. The fit of the thermal variations of the magnetic susceptibility reveal a ferromagnetic intramolecular exchange interaction. This finding is confirmed and analysed by using wavefunction-based methods which indicate that the exchange interaction is governed by the substituent of the radical rather than by its heteroatom.
TL;DR: In this paper, a biaxial anisotropy (5% of the dominant exchange interaction) was detected for the spin-ladder material C5H12N2CuBr4 [BPCB] in high-resolution multi-frequency electron spin resonance (ESR) spectroscopy.
Abstract: Magnetic excitations in the spin-ladder material (C5H12N)2CuBr4 [BPCB] are probed by highresolution multi-frequency electron spin resonance (ESR) spectroscopy. Our experiments provide a direct evidence for a biaxial anisotropy (� 5% of the dominant exchange interaction), that is in contrast to a fully isotropic spin-ladder model employed for this system previously. It is argued that this anisotropy in BPCB is caused by spin-orbit coupling, which appears to be important for describing magnetic properties of this compound. The zero-field zone-center gap in the excitation spectrum of BPCB, �0/kB = 16.5 K, is detected directly. Furthermore, an ESR signature of the inter-ladder exchange interactions is obtained. The detailed characterization of the anisotropy in BPCB completes the determination of the full spin hamiltonian of this exceptional spin-ladder material and shows ways to study anisotropy effects in spin ladders.