Crystal fields induced compensation temperatures in a decorated square lattice

A two-sublattice decorated Blume-Capel ferrimagnet has been investigated using the mean field theory. Interesting behaviors of long-range order are obtained depending on particular magnitudes of magnetocrystalline anisotropies for both sublattices sites. Distinguishable features have been discovered in two-dimensional decorated lattice consisting of spin-5/2 and decorating spin-7/2 ions on the bonds. It is found the present system shows two ferrimagnetic compensation temperatures. However, one compensation temperature for different or fixed values of decorated magnetic anisotropies with the values of J1=-0.5 , J2=-1.0 , or with J1=-1.0 , J2=-0.5, has been induced, respectively. The magnetization behavior in the (M,DB/IJ2I) space has not already been considered showing the crystalline anisotropy dependence of total magnetization remanences. Besides, the variations of net magnetizations versus the decorated crystal fields, i.e., in the(M,DA/IJ2I) space, have been done, with J1=-0.5, J2=-1.0 , for various values of T=2.0, 2.5,3.0 , respectively.

Control of the Induced Handedness of Helical Nanofilaments Employing Cholesteric Liquid Crystal Fields

In this paper, a simple and powerful method to control the induced handedness of helical nanofilaments (HNFs) is presented. The nanofilaments are formed by achiral bent-core liquid crystal molecules employing a cholesteric liquid crystal field obtained by doping a rod-like nematogen with a chiral dopant. Homochiral helical nanofilaments are formed in the nanophase-separated helical nanofilament/cholesteric phase from a mixture with a cholesteric phase. This cholesteric phase forms at a temperature higher than the temperature at which the helical nanofilament in a bent-core molecule appears. Under such conditions, the cholesteric liquid crystal field acts as a driving force in the nucleation of HNFs, realizing a perfectly homochiral domain consisting of identical helical nanofilament handedness.

Magnetic properties and phase diagrams of the mixed spin-(1 2, 3 2) Ising–Heisenberg model in the mean field approximation

In this paper, the effects of the longitudinal [Formula: see text] and the transverse [Formula: see text] crystal fields on the mixed spin-[Formula: see text] Ising–Heisenberg model have been studied. The thermodynamic properties of the model are obtained by using a new approach of the mean field approximation (MFA). The thermal variations of the order-parameters and the total magnetic susceptibility of the model are carefully investigated to obtain the phase diagrams on the [Formula: see text] planes for [Formula: see text] and on the [Formula: see text] planes for [Formula: see text] and 6. The existence of compensation temperatures between the sublattice magnetizations, [Formula: see text], and the two components of the quadrupole moments, [Formula: see text], are observed. Our results are compared with other existing works in the literature and reliable agreements are found.

Learning crystal field parameters using convolutional neural networks

We present a deep machine learning algorithm to extract crystal field (CF) Stevens parameters from thermodynamic data of rare-earth magnetic materials. The algorithm employs a two-dimensional convolutional neural network (CNN) that is trained on magnetization, magnetic susceptibility and specific heat data that is calculated theoretically within the single-ion approximation and further processed using a standard wavelet transformation. We apply the method to crystal fields of cubic, hexagonal and tetragonal symmetry and for both integer and half-integer total angular momentum values JJ of the ground state multiplet. We evaluate its performance on both theoretically generated synthetic and previously published experimental data on CeAgSb_22, PrAgSb_22 and PrMg_22Cu_99, and find that it can reliably and accurately extract the CF parameters for all site symmetries and values of JJ considered. This demonstrates that CNNs provide an unbiased approach to extracting CF parameters that avoids tedious multi-parameter fitting procedures.

Paramagnetic Transitions Ions as Structural Modifiers in Ferroelectrics

The science of ferroelectric materials has long known that transition metal atom and/or rear earth atom substitution in the composition of a ferroelectric material can produce substantial structural and electric dipole changes and ferroelectric behavior. The focus is on first neighbor changes, symmetry, very tiny atomic displacements, hence magnitudes of electric polarization, charge changes, and mechanical-tensile change of parameters. The transition atom used for the substitution can, or, cannot be paramagnetic. When it is paramagnetic as is the case with Cr3+, Mn2+ and so forth, there emerges an advantage for its experimental characterization at atomic level. Electron Paramagnetic Resonance (EPR) allows the identification of its location within the structure and the number and nature of its neighbors. The presence of crystal fields, symmetry and distortions of the first coordination sphere can also be determined. Here, we describe how a set of EPR spectra is analyzed to extract such atomic information.

SURFACE PHASE DIAGRAMS OF SEMI-INFINITE FERRIMAGNETIC SYSTEM

The three-dimensional semi-infinite mixed spin-1/2 and spin-3/2 ferrimagnetic Ising system with crystal field is investigated using the mean-field approximation and the Monte Carlo simulation. According to the ratio [Formula: see text] of bulk and surface exchange interactions and the ratio [Formula: see text] of bulk and surface crystal fields, we have classified four qualitative types of phase diagrams characterized by the presence or absence of ordinary, extraordinary, surface and special phase transitions. The critical behavior of the surface and bulk magnetizations has also been highlighted in the vicinity of these different transitions. At low temperatures, two critical end-points appear in the bulk and on the surface in the ordered region limiting two successive first-order phase transitions. Furthermore, we have made a comparison with other works on similar models in pure or mixed versions.

Decoupling the metal insulator transition and crystal field effects of VO2

VO2 is a highly correlated electron system which has a metal-to-insulator transition (MIT) with a dramatic change of conductivity accompanied by a first-order structural phase transition (SPT) near room temperature. The origin of the MIT is still controversial and there is ongoing debate over whether an SPT induces the MIT and whether the Tc can be engineered using artificial parameters. We examined the electrical and local structural properties of Cr- and Co-ion implanted VO2 (Cr-VO2 and Co-VO2) films using temperature-dependent resistance and X-ray absorption fine structure (XAFS) measurements at the V K edge. The temperature-dependent electrical resistance measurements of both Cr-VO2 and Co-VO2 films showed sharp MIT features. The Tc values of the Cr-VO2 and Co-VO2 films first decreased and then increased relative to that of pristine VO2 as the ion flux was increased. The pre-edge peak of the V K edge from the Cr-VO2 films with a Cr ion flux ≥ 1013 ions/cm2 showed no temperature-dependent behavior, implying no changes in the local density of states of V 3d t2g and eg orbitals during MIT. Extended XAFS (EXAFS) revealed that implanted Cr and Co ions and their tracks caused a substantial amount of structural disorder and distortion at both vanadium and oxygen sites. The resistance and XAFS measurements revealed that VO2 experiences a sharp MIT when the distance of V–V pairs undergoes an SPT without any transitions in either the VO6 octahedrons or the V 3d t2g and eg states. This indicates that the MIT of VO2 occurs with no changes of the crystal fields.

A remarkable energy barrier for spin reversal in a field induced dinuclear ytterbium single molecule magnet

Strong equatorial and weak axial crystal fields enhance the energy barrier for slow relaxation of magnetization in Yb-based single molecule magnets.