Total Magnetic Momentum Research Articles

Hinge-like Co2S3and Co2Te3Nanosheets: Promising Two-Dimensional Optical, Thermoelectric, and Spintronic Materials

In this study, the structural and physical properties of hinge-like Co2S3 and Co2Te3 nanosheets are predicted using spin-polarized density functional theory. Our calculations show that Co2S3 and Co2Te3 nanosheets are ferromagnetic semiconductors and antiferromagnetic metals in the ground state, respectively, and these nanosheets are dynamically and thermodynamically stable. According to the mean-field theory, Co2S3 and Co2Te3 nanosheets have the Néel temperature of 933 K and the Curie temperature of 285 K. Also, Co2Te3 nanosheets have unique properties such as significant total magnetic momentum (5.07 μB) and high magnetic anisotropy energy (2.62 meV). The examination of optical properties shows that Co2S3 and Co2Te3 nanosheets can be used in optoelectronic devices such as strong far- ultraviolet and ultraviolet absorbers, respectively. Calculating thermoelectric properties using Boltzmann’s theory shows that the Co2S3 nanosheet not only has ZT = 1 at 100 K but has significant thermoelectric efficiency at temperatures higher than room temperature (ZT = 0.97 at 700 K). Based on spin-dependent transport calculations, the current passing through Co2S3 (37.55 μA) and Co2Te3 (75 μA) nanosheets is higher than many 2D nanostructures, and the transport properties of these nanosheets are anisotropic. Therefore, Co2S3 and Co2Te3 nanosheets can be promising candidates for the development of nanoscale thermoelectric and spintronic devices.

Tunable electronic, magnetic, and optical properties of carbon-nanomaterial/α-Fe2O3 interface: A first-principles study

Based on first-principles calculations, a series of heterostructures C x /Fe-O 3 -Fe, Li@C x /Fe-O 3 -Fe, in the (0001) plane has been designed. We studied the effects of carbon nanomaterials C x (C x = C 20 , C 24 , and C 26 ) and Li@C x systems adsorbing on the Fe-O 3 -Fe(0001) surface. The stability and density of states, band structure, local potentials, charge densities, magnetic and optical properties are analyzed in detail. The results of the density of states and band structure show that impurity bands (IBs) can be observed. A hetero-structure bearing C x /Fe-O 3 -Fe and Li@C x /Fe-O 3 -Fe impurity bands depends on the type of carbon nanocrystals and interaction sites in the hetero-structure. We conclude from the total magnetic moment of the Fe-O 3 -Fe relaxed slab and heterostructures that the antiferromagnetic ordering is retained in Fe-O 3 -Fe, but the introduction of C x and Li@C x components on top of the Fe-O 3 -Fe surface slab causes some magnetic perturbations. A Li@C x component placed on top of a Fe-O 3 -Fe surface slab increases the total magnetic momentum relative to a C x component. From the optical absorption, in visible and infrared wavelengths, C x /Fe-O 3 -Fe and Li@Cx/Fe-O 3 -Fe heterostructures exhibit enhanced optical absorptions due to the impurity bands.

Electron liquid state in the symmetric Anderson lattice

Using mean field approach, we provide analytical and numerical solution of the symmetric Anderson lattice for arbitrary dimension at half filling. The symmetric Anderson lattice is equivalent to the Kondo lattice, which makes it possible to study the behavior of an electron liquid in the Kondo lattice. We have shown that, due to hybridization (through an effective field due to localized electrons) of electrons with different spins and momenta mathbf{k} and mathbf{k} +overrightarrow{pi }, the gap in the electron spectrum opens at half filling. Such hybridization breaks the conservation of the total magnetic momentum of electrons, the spontaneous symmetry is broken. The state of electron liquid is characterized by a large Fermi surface. A gap in the spectrum is calculated depending on the magnitude of the on-site Coulomb repulsion and value of s–d hybridization for the chain, as well as for square and cubic lattices. Anomalous behavior of the heat capacity at low temperatures in the gapped state, which is realized in the symmetric Anderson lattice, was also found.

Contribution of Iron Clusters to the Magnetic Properties of Pb1 – yFe y Te Alloys

The field dependences of the magnetization (temperatures T = 2.0–70 K, magnetic fields B ≤ 7.5 T) of the samples from a single-crystalline Pb1 – yFe y Te ingot (y = 0.02) grown by the Bridgman method are studied. It is established that the sample magnetization contains several major contributions such as the paramagnetism of iron ions, diamagnetism of the crystal lattice, and the contributions of charge carriers and clusters of iron atoms. The field dependences of the paramagnetic contribution of iron ions and the contribution of clusters of iron atoms are approximated by theoretical dependences based on the Brillouin and Langevin functions, respectively. The average concentrations and magnetic moment of clusters as well as the total magnetic momentum of clusters in the volume unit in the samples upon increasing the impurity concentration along the ingot are determined.

Вклад кластеров железа в магнитные свойства сплавов Pb-=SUB=-1-y-=/SUB=-Fe-=SUB=-y-=/SUB=-Te

AbstractThe field dependences of the magnetization (temperatures T = 2.0–70 K, magnetic fields B ≤ 7.5 T) of the samples from a single-crystalline Pb_1 – y Fe_ y Te ingot ( y = 0.02) grown by the Bridgman method are studied. It is established that the sample magnetization contains several major contributions such as the paramagnetism of iron ions, diamagnetism of the crystal lattice, and the contributions of charge carriers and clusters of iron atoms. The field dependences of the paramagnetic contribution of iron ions and the contribution of clusters of iron atoms are approximated by theoretical dependences based on the Brillouin and Langevin functions, respectively. The average concentrations and magnetic moment of clusters as well as the total magnetic momentum of clusters in the volume unit in the samples upon increasing the impurity concentration along the ingot are determined.

First principles study of structural, electronic, magnetic and elastic properties of Mg0.75TM0.25S (TM=Mn, Fe, Co, Ni)

The objective of this work is to predict the structural, electronic, magnetic and elastic properties of Mg1−xTMxS (TM=Mn, Fe, Co and Ni) compound in the zinc blende Ferromagnetic phase using first principal approach. The structural and elastic properties are performed using the generalized gradient approximation proposed by Wu and Cohen(WC-GGA). However, the electronic and magnetic properties have been performed using modified Becke-Johnson potential combined with the LDA correlation (mBJLDA). The results show that all compounds Mg1−xMnxS, Mg1−xFexS and Mg1−xNixS exhibit a half-metallic ferromagnetic character with 100% spin-polarization at the Fermi level, except Mg1−xCoxS is a metal. For each compounds study here, the total magnetic momentum is an integer equal to magnetic moments of TM atom in their free space charge value. Due to the p–d hybridization, there is a small local magnetic moment on the Mg and S sites; whereas, the local magnetic moments of TM atom reduce from their free space charge value. In addition, we investigate the mechanical behavior of MgS and Mg1−xTMxS; all compounds studied here are mechanically stable and exhibit a strong anisotropic behavior.

First-Principles Study of Structural, Electronic and Magnetic Properties of Cr-Doped MgS

The objective of this work is to predict the structural, electronic and magnetic properties of Mg 1−xCr xS (x = 0, 0.25, 0.50, 0.75 and 1) compound in the zinc blende ferromagnetic phase using the first principal approach. The structural properties are performed using the generalized gradient approximation developed by Perdew–Burk–Ernzerhof (PBE-GGA). However, the electronic and magnetic properties have been performed using the modified Becke–Johnson potential combined with the LDA correlation (mBJLDA) which provides better description of electronic properties than PBE-GGA. The results show that this compound exhibits a half-metallic ferromagnetic character with 100 % spin polarization at the Fermi level. For all Cr concentrations (0.25, 0.50, 0.75 and 1), the total magnetic momentum is equal to 4 μB, and there is a small local magnetic moment on the Mg and S sites. Furthermore the local magnetic moments of Cr atom reduce from their free space charge value.

Synthesis, structure and magnetic properties of L10 alloy (FePt)100−x Zn x nanoparticles

In the present work, alloy (FePt)100−xZnx nanoparticles have been successfully synthesized by simple wet chemical method with the aid of Pt(acac)2, Fe(acac)3 and Zn(acac)2 as the starting reagents. Oleic acid and oleylamine was used as a surfactant agent. The addition of zinc promoted the face-centered cubic to tetragonal phase transition. Reduction in temperature required for this transition compared with FePt nanoparticles with no additives. This reduction in ordering temperature significantly reduces FePt particle coalescence and enhancing chemical ordering, so magnetic measurements show high coercivity up to 6 kOe of the (FePt)82Zn18 nanoparticles with average size <10 nm after annealing at 500 °C for 60 min. The coercivity increases with the content of zinc up to 18 %, and above this percent, the coercivity starts to decrease. In order to calculate magnetic properties for Zn in FePt: Zn structure, we used density functional theory and GGA approximation. The energy of FePt: Zn structure in which Zn atom replaces Fe ones is lower than other possible structures, so forming of this system is more probable. Calculations show than Zn atoms do not have a significant magnetic momentum when replacing Fe atoms. Curie temperature variation as a function of added Zn atoms is derived. Added Zn atoms replace Fe atoms and previous Fe site is occupied with Zn with approximately zero magnetic momentum. Since these sites are randomly occupied, we have random exchange interactions in the system which can be modeled like spin glass system. Zn atoms have a zero magnetic momentum when replacing Fe atoms, so total magnetic momentum and Curie temperature of FePt: Zn structure decrease with increasing Zn percentage.

Structural and magnetic properties of Mn-doped ZnO nanocrystals

Mn-doped ZnO nanocrystals were successfully prepared using a novel sol–gel method followed by drying in autoclave under supercritical conditions. The estimated crystallite size is in the range of 30–50nm, in agreement with TEM analysis. Rietveld refinements confirm the formation of pure Mn-doped ZnO for lower Mn concentration. i.e. less than 5%. The lattice parameters increase with increasing Mn content according to Vegard's law due to the larger ionic radius of Mn2+ compared to that of Zn2+. Magnetic analysis reveals that increasing the doping level of Mn above 2% is not helping the long range ferromagnetic order in the sample but only enhancing the paramagnetic component. The paramagnetic susceptibility is found to increase linearly with increasing Mn concentration which suggests the formation of uncoupled magnetic moment. The estimated values for the magnetic moment per Mn atom are found to be in the range of 2–3.5µB/Mn. Ab-initio calculations also have been performed which showed that doping diamagnetic bulk ZnO with Mn induces ferromagnetic at room temperature, the total magnetic momentum increases with increasing Mn content whereas the magnetic moment of Mn is predicted to be in the range of 3–3.5μB/Mn atom which is consistent with the values obtained from magnetic measurements.

Electrons in a Magnetic Field: Special Spin in de Haas-van Alphen effect

When the magnetic field is applied in a metal, the electrons behave like a harmonic oscillator. When the field is increased these harmonic oscillator type levels cross the Fermi energy at a particular point resulting into the discontinuities in the population of any particular level at that point. For a large orbital magnetic moment, different from L = 0 and both signs of spin in the total magnetic momentum quantum number, j = l ± s, the discontinuities in the population of the electrons in a particular level become double valued resulting into doubling of oscillations in the magnetization. There is a double valued change in the energy of the electrons when they transfer from the harmonic oscillator type level to the Fermi level. The magnetization depends on the value of j = l ± s so that there is a double valued period in the oscillations. The de Haas-van Alphen effect is usually described for the L = 0 electrons. Hence, we see that the de Haas-van Alphen effect is considerably modified in going from L = 0 to j = l ± s, with both signs in the spin.

Quantum-classical phase transition of escape rates in biaxial spin particles

The escape rates of the biaxial single domain spin particles with and without an applied magnetic field are investigated. Using the strict potential field description of spin systems developed by Ulyanov and Zaslavskii we obtain new effective Hamiltonians which are considered to be in exact spin-coordinate correspondence unlike the well studied effective Hamiltonians with the approximate correspondence. The sharp first-order transition is found in both cases. The phase diagram of the transitions depending on the anisotropy constant and the external field is also given.

Nonlinear magnetization dynamics of the classical ferromagnet with two single-ion anisotropies in an external magnetic field

By using a stereographic projection of the unit sphere of magnetization vector onto a complex plane for the equations of motion, the effect of an external magnetic field for integrability of the system is discussed. The properties of the Jost solutions and the scattering data are then investigated through introducing transformations other than the Riemann surface in order to avoid double-valued functions of the usual spectral parameter. The exact multisoliton solutions are investigated by means of the Binet-Cauchy formula. The results showed that under the action of an external magnetic field nonlinear magnetization depends essentially on two parameters: its center moves with a constant velocity, while its shape changes with another constant velocity; its amplitude and width vary periodically with time, while its shape is also dependent on time and is unsymmetric with respect to its center. The orientation of the nonlinear magnetization in the plane orthogonal to the anisotropy axis changes with an external magnetic field. The total magnetic momentum and the integral of the motion coincident with its z component depend on time. The mean number of spins derivated from the ground state in a localized magnetic excitations is dependent on time. The asymptotic behavior of multisoliton solutions, the total displacement of center, and the phase shift of the $j$th peak are also analyzed.

Nonlinear dynamics of a continuum Heisenberg spin chain with an anisotropy and an external magnetic field

By stereographically projecting the spin vector onto a complex plane in the equations of motion for a continuum Heisenberg spin chain with an anisotropy (an easy plane and an easy axis) and an external magnetic field, the effect of the magnetic field for integrability of the system is discussed. Then, introducing an auxiliary parameter, the Lax equations for Darboux matrices are generated recursively. By choosing the constants, the Jost solutions are satisfied the corresponding Lax equations. The exact soliton solutions are investigated, then the total magnetic momentum and its z-component are obtained. These results show that the solitary waves depend essentially on two velocities which describe a spin configuration deviating from a homogeneous magnetization. The depths and widths of solitary waves vary periodically with time. The center of an inhomogeneity moves with a constant velocity, while the shape of soliton also changes with another velocity and this shape is not symmetrical with respect to the center. The total magnetic momentum and its z-component vary with time.

Solitons in a uniaxial anisotropic Heisenberg spin chain with Gilbert damping in an external magnetic field

Using the stereographic projection of the unit sphere of the spin field onto a complex plane for the equations of motion in a uniaxial anisotropic Heisenberg spin chain with Gilbert damping in an external magnetic field, the effect of the magnetic field for the integrability of the system is discussed. The effect of the Gilbert damping is also analyzed. Then, introducing an auxiliary parameter, the Lax equations for the Darboux matrices are generated recursively. The Jost solutions satisfy the corresponding Lax equations if constants are suitably chosen. The exact soliton solutions are then investigated. These results show that the solitary waves depend essentially on two velocities that describe a spin configuration deviated from a homogeneous magnetization, while the depths and widths of surface of solitary waves vary periodically with time. The center of an inhomogeneity moves with a constant velocity, while the shape of a soliton also changes with another constant velocity and it is not symmetrical with respect to the center. The z component of the total magnetic momentum and the total magnetic momentum vary with time. The asymptotic behavior of multisoliton solutions is also given.