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B. Saha

Publications and source records attributed to B. Saha.

16 recordsLinked to original sources
arXiv2025

Multiscale Magnetic Correlations in La2Mn2-xNixO6: Role of Crystal Structure in Double Perovskites

The magnetic correlations in double perovskites La2Mn2-xNixO6 (x = 0.5, 0.75, 1.0, 1.25 and 1.5) have been systematically investigated across macroscopic, mesoscopic, and microscopic length scales using temperature-dependent bulk DC magnetization, neutron depolarization, and neutron powder diffraction measurements, respectivitly. The magnetic properties evolve from a long-range ferromagnetic (FM) order to a cluster ferromagnetic or spin-glass (FM or SG) behavior as the Ni concentration increases. This evolution is directly linked to changes in the crystal structure, transitioning from pure orthorhombic (x=0.5) to mixed orthorhombic and monoclinic (x=0.75-1.0), and eventually to mixed trigonal and monoclinic symmetries (x=1.25-1.5). Ni substitution enhances the magnetic ordering temperature from 170 K (x=0.5) to 280 K (x=1.0), but this is accompanied by a reduction in both magnetization and ordered magnetic moment. Beyond x=1.0, any long-range magnetic ordering is absent. Additionally, all compositions exhibit a reentrant spin-glass-like phase at low temperatures (below about 50 K). Neutron diffraction analysis confirms that long-range FM order occurs only in the orthorhombic phase, while the monoclinic and trigonal phases lack such magnetic ordering. The temperature-dependent magnetic correlations are closely connected to variations in crystal structural parameters, including lattice constants and unit cell volume. The electrical conductivity behavior, following the variable range hopping (VRH) model, highlights the role of multivalence Mn and Ni ions on the electrical properties. This study elucidates the microscopic mechanisms behind the tunable magnetic and electrical properties of La2Mn2-xNixO6, offering valuable insights for the design of advanced materials for spintronic applications.

cond-mat.mtrl-sci↗
arXiv2023

Two-dimensional short-range spin-spin correlations in the layered spin-3/2 maple leaf lattice antiferromagnet Na2Mn3O7 with crystal stacking disorder

We report the nature of magnetic structure, microscopic spin-spin correlations and their dependence on the underlying crystal structure of the geometrically frustrated layered spin-3/2 maple-leaf-lattice (MLL) antiferromagnet Na2Mn3O7 by a comprehensive neutron diffraction study. Crystal structural studies by x-ray and neutron diffractions reveal that the MLL layers (constituted by Mn3O72- units) are well separated by non-magnetic Na layers. The studies also conclude the presence of stacking faults (in-plane sliding of magnetic MLL layers) as well as a distortion in the MLL of Mn4+. Temperature dependent magnetic susceptibility, heat capacity, and neutron diffraction data yield a short-range antiferromagnetic (AFM) ordering below ~ 100 K without a long-range magnetic ordering down to 1.5 K. The analysis of the diffuse magnetic neutron scattering patterns by reverse Monte Carlo method reveals 2D spin-spin correlations within the MLL layers. Additionally, we establish a relation between the correlation length of the short-range magnetic ordering with the stacking faults through a varying synthesis condition. The present study, therefore, explores a microscopic picture of the crystal- and spin-structures, as well as their correlation, hence, provides an experimental insight of the magnetic ordering in a MLL AFM. Further, we have outlined the formation of several 2D frustrated lattice geometry having triangular plaquettes, including the MLL, by crystal engineering of the triangular lattice and their role on the stabilization of multiple novel chiral spin states which opens up a door for study of novel chiral spin states.

cond-mat.str-el↗
arXiv1998

Solitons of Induced Scalar Field and Their Stability

Exact particle-like static, spherically and/or cylindrically symmetric solutions to the equations of interacting scalar and electromagnetic field system have been obtained. We considered Freedman-Robertson-Walker (FRW) space-time as an external homogenous and isotropic gravitational field whereas the homogeneous and anisotropic Universe is given by the G$\ddot o$del model. Beside the usual solitonian solutions some special regular solutions know as droplets, anti-droplets and bags (confined in finite interval and having trivial value beyond it) have been obtained. It has been shown that in FRW space-time equations with different interaction terms may have stable solutions while within the scope of G$\ddot o$del model only the droplet-like and the hat-like configurations may be stable, if they are located in the region where $g^{00}>0$.

gr-qc↗
arXiv1998

Soliton Model of Hydrogen Atom: Resonance Effects

Some first principles that, we believe, could serve as foundation for quantum theory of extended particles are formulated. It is also shown that in the point-like particles limit the non-relativistic quantum mechanics can be restored. As an illustration the soliton model of hydrogen atom is considered.

physics.atom-ph↗
arXiv1998

Electrodymanics of Moving Continuous Media with Toroid Polarization

With regard to the toroid contributions, a modified system of equations of electrodynamics moving continuous media has been obtained. Alternative formalisms to introduce the toroid moment contributions in the equations of electromagnetism has been worked out. The two four-potential formalism has been developed for the electromagnetic continous media subjected to Lorentz transformations.

cond-mat↗
arXiv1998

Electrodymanics with Toroid Polarization

A modified system of equations of electrodynamics has been obtained. Beside the Lagrangian one an alternative gauge-like formalism has been developed to introduce the toroid moment contributions in the equations obtained. The two potential formalism that was worked out by us earlier has been developed further where along with the two vector potentials we introduce two scalar potentials thus taking into account all the four equations of electromagnetism.

cond-mat↗
arXiv1998

Scalar Field with Induced Nonlinearity: Regular Solutions and their Stability

Exact particle-like static, spherically and/or cylindrically symmetric solutions to the equations of interacting scalar and electromagnetic field system have been obtained within the scope of general relativity. In particular, we considered Freedman-Robertson-Walker (FRW) space-time as an external homogenous and isotropic gravitational field whereas the inhomogenous and isotropic Universe is given by the G$\ddot o$del model. The solutions obtained have been thoroughly studied for different types of interaction term. It has been shown that in FRW space-time equations with different interaction terms may have stable solutions while within the scope of G$\ddot o$del model only the droplet-like configurations may be stable, if they are located in the region where $g^{00}>0$.

gr-qc↗
arXiv1996

Exact Self-consistent Particle-like Solutions to the Equations of Nonlinear Scalar Electrodynamics in General Relativity

Exact self-consistent particle-like solutions with spherical and/or cylindrical symmetry to the equations governing the interacting system of scalar, electromagnetic and gravitational fields have been obtained. As a particular case it is shown that the equations of motion admit a special kind of solutions with sharp boundary known as droplets. For these solutions, the physical fields vanish and the space-time is flat outside of the critical sphere or cylinder. Therefore, the mass and the electric charge of these configurations are zero.

gr-qc↗
arXiv1996

Nonlinear Spinor Field in Bianchi type-I Universe filled with Perfect Fluid: Exact Self-consistent Solutions

Self-consistent solutions to nonlinear spinor field equations in General Relativity have been studied for the case of Bianchi type-I space-time filled with perfect fluid. The initial and the asymptotic behavior of the field functions and the metric one has been thoroughly studied. It should be emphasized the absence of initial singularity for some types of solutions and also the isotropic mode of space-time expansion in some special cases.

gr-qc↗
arXiv1996

Multipolar Representation of Maxwell and Schroedinger Equations: Lagrangian and Hamiltonian Formalisms: Examples

Development of quantum engineering put forward new theoretical problems. Behavior of a single mesoscopic cell (device) we may usually describe by equations of quantum mechanics. However if experimentators gather hundreds of thousands of similar cells there arises some artificial medium that one already needs to describe by means of new electromagnetic equations. The same problem arises when we try to describe e.g. a sublattice structure of such complex substances like perovskites. It is demonstrated that the inherent primacy of vector potential in quantum systems leads to a generalization of the equations of electromagnetism by introducing in them toroid polarizations. To derive the equations of motion the Lagrangian and the Hamiltonian formalisms are used. Some examples where electromagnetic properties of molecules are described by the toroid moment are pointed out.

cond-mat↗
arXiv1996

Droplets in General Relativity: Exact Self-Consistent Solutions to the Interacting Scalar and Electromagnetic Field Equations

It is shown, for the self-consistent system of scalar, electro-magnetic and gravitational fields in general relativity, that the equations of motion admit a special kind of solutions with spherical or cylindrical symmetry. For these solutions, the physical fields vanish and the space-time is flat outside of the critical sphere or cylinder. Therefore, the mass and the electric charge of these configurations are zero. The principal difference between droplet-like solutions with spherical symmetry and those with cylindrical one has been established. In the first case there exists a possibility of continuous transformation of droplet-like configuration into the solitonian one, when for the second case there is no such a possibility.

gr-qc↗
arXiv1996

Interaction of Charged 3D Soliton with Coulomb Center

The Einstein - de Broglie particle-soliton concept is applied to simulate stationary states of an electron in a hydrogen atom. According to this concept, the electron is described by the localized regular solutions to some nonlinear equations. In the framework of Synge model for interacting scalar and electromagnetic fields a system of integral equations has been obtained, which describes the interaction between charged 3D soliton and Coulomb center. The asymptotic expressions for physical fields, describing soliton moving around the fixed Coulomb center, have been obtained with the help of integral equations. It is shown that the electron-soliton center travels along some stationary orbit around the Coulomb center. The electromagnetic radiation is absent as the Poynting vector has non-wave asymptote $O(r^{-3})$ after averaging over angles, i.e. the existence of spherical surface corresponding to null Poynting vector stream, has been proved. Vector lines for Poynting vector are constructed in asymptotical area.

atom-ph↗