Summary of Article related to magneto ferroelectricity effect


Ferroelectricity: It is a characteristic of certain materials that have a spontaneous electric polarization that can be reversed by the application of an external electric field.


Magneto Ferroelectricity:

Magnetic spins interact with the lattice structure, leading to a coupling between magnetic and ferroelectric properties. Here the applied magnetic field causes the structural deformation of the material by changing the bond lengths and bond angles, which inevitably leads to the change of internal dipoles.


The magnetic interactions of transition metal ions with unpaired d electrons are generally sensitive to the deformation of bond lengths and angles.


(TMCM)[FeCl4] was studied here.

A second harmonic generation was conducted.  It indicates change of noncentrosymmetric structure to a centrosymmetric. SHG signal changes sharply around 320K.


The local ferroelectric domains within (TMCM)[FeCl4] were calculated by piezoelectric force microscopy (PFM). Magnetostriction was measured by Atomic Force Microscopy. (Magnetostriction is the ability of a material to undergo mechanical strain in response to a magnetic field.)


The external magnetic field strongly affects the ferroelectric loops, leading to changes in their symmetry, amplitude, and coercive fields( Coercive field is the strength of a magnetic or electric field that's required to demagnetize or depolarize a material). 

As per study, polarization along the a-axis is suppressed by the magnetic field,which corresponds to the stretching of the halogen Cl‧‧‧Cl bonds and the shrinking volume occupancy of [FeCl4]− anions.


The density functional theory (DFT) calculations were performed with projector-augmented wave pseudopotentials-a technique used in electronic structure calculations.


polarization was calculated using the standard Berry phase method. This helps to calculate valence electronic and ionic contribution.


source:

https://www.nature.com/articles/s41467-024-49053-y#:~:text=Magnetostriction%20loops%20are%20observed%20in,the%20results%20of%20AFM%20measurements.


article about ferromagnetic coupling in CrI3 - In Brief


Methods Used: Projector augmented wave (PAW) method is a numerical algorithm that is used to perform efficient density functional theory (DFT) calculations. The generalized gradient approximation (GGA) is a method that improves the description of nonuniform electron distributions in molecules, solids, and atoms.


The bilayer CrI3 has interlayer antiferromagnetic coupling. For introduction of dopants O, P, S, As, and Se substitution at the I1(I2) site leads to interlayer ferromagnetism. For C or N doped cases, interlayer antiferromagnetism occurs.


As per study, there is no correlation between the strength of ferromagnetic coupling and the interlayer distance. The interlayer magnetism of vdW materials is closely related to different 3d electron occupation between different layers.

As-doping leads to obvious change of charge distribution inside the interlayer space.


Interlayer ferromagnetic coupling in doped bilayer CrI3 occurs due to formation of localized spin-polarized state. It is a small region where the electron spins are aligned, creating a tiny magnetic area due to something unusual (like a dopant) in the material. This tiny magnetic area can have a big effect on the material’s overall magnetic behavior.


Source: https://link.springer.com/article/10.1007/s11467-024-1435-2#:~:text=Further%20analysis%20shows%20that%20the,can%20realize%20interlayer%20ferromagnetic%20coupling.



Brief Summary of article related to radiation by carbon-ion beam

Microdosimetry is a technique used to measure the stochastic(process that evolves in a random way) distribution of energy deposited by radiation at microscopic sites. It can help determine how energy is transferred inside cancer cells. 


In study, three sensitive volumes (SVs) of different thicknesses have been used.

Lineal energy is the amount of energy deposited in a given volume of matter by a single energy-deposition event, divided by the mean chord length of that volume.

lineal energy dose distribution d(y): It describes the probability density of the energy deposited in a volume by ionizing radiation.

f(y) is the lineal energy probability density function and ¯y(F) its expectation value, called frequency-mean lineal energy.

The microdosimeter measures current pulses proportional to the energy deposited by a single-event.


Double linearinsed method

alin is the linearised signal amplitude, ach is the signal amplitude in acquisition-channels units and mA,mB and q are the three linearisation coefficients. aT is a free parameter.


The final calibration in lineal energy was then obtained according to the carbon-edge method. The carbon-edge method is calculated from the stopping power values of carbon ions. Stopping power in medical physics is the average amount of energy a material absorbs from a charged particle as it moves through the material.

The calibrated data obtained are eventually organised in the form of a histogram with logarithmic lineal energy.

By calculating first order approximation of taylor series, Final uncertainty was measured by

water-equivalent depth uncertainty was measured in study.

The thickness of the sensitive volumes (SVs) in microdosimetry significantly influences the radiation quality measurements.

Thinner detectors are more sensitive to high-energy events but are affected by noise and lower energy thresholds. Thicker detectors can better capture a broader spectrum of radiation, especially in regions dominated by secondary particles.


Source: https://iopscience.iop.org/article/10.1088/1361-6560/ad965e


Key Points of article about new hydrogen-deficient white star


Scientists found 3 pre-white dwarfs (WDs) with helium-dominated atmospheres.

They calculated the effective temperature and surface gravity by comparing the He II line profiles of different stars.


Tübingen Model-Atmosphere Package tool was used for spectral analysis and to compute nonlocal thermodynamic equilibrium, plane-parallel, line-blanketed atmosphere models in radiative and hydrostatic equilibrium. It is based on the Accelerated Lambda Iteration method.



Kiel (Teff– log(g)) diagram was used to analyse the stars. The masses of stars were determined via comparison with evolutionary tracks using linear interpolation or Extrapolation and use of very late thermal pulse (VLTP)- a stage of evolution that occurs when a star re-ignites helium after leaving the Asymptotic Giant Branch (AGB) and still has a hydrogen-burning shell. By using these parameters, stellar radii was calculated by,

Luminosity was calculated by,

Gaia parallax distances can be used to derive masses, radii, and luminosities.

They used a spectral energy distribution (SED) graph that shows how much energy a star emits at different wavelengths. It's usually represented as luminosity per unit wavelength or frequency.


Source:

https://arxiv.org/html/2412.15984v1


Summary of Article: Study of High‑entropy alloys in nuclear applications


ZrNbVTiAl alloy was studied here.


Nb, V, Zr, Ta, Hf, Mo and W, commonly referred to as refractory high entropy alloy (RHEA) has been recently emphasized as promising materials for the next-generation high temperature reactors. These RHEAs exhibit better high-temperature performance due to the high melting points of constituent elements and superior radiation resistance due to their BCC-type structures which are resistant to irradiation swelling.


Nb, Zr and Al have low neutron absorption cross sections, which is necessary for an alloying element to be used in nuclear structural materials.

The atomic radius of Al (143 pm) is similar to V, Ti and Nb which satisfies one of the major criteria of formation of solid solutions in the HEA.


The induction levitation melting (ILM) was done. It is a non-radioactive technology that uses an electromagnetic field to melt and levitate electrically conductive materials. Here Lorentz force created by the field stirs the molten metal, producing a uniform temperature distribution.


In certain cases, Due to irradiation of BCC-based low-activation HEAs results in the segregation(uneven distribution of constituent elements within the alloy's microstructure). The constituent elements like Cr and V atoms migrate at the grain boundaries. 


The displacement per atom was calculated to measure radiation damage in materials. The relative stability of the BCC phase was observed higher in comparison to the intermetallic phases.


 In high-entropy alloys, diffusivity of constituent elements is low due to multiple sizes of atoms causing lattice distortion and slow diffusion.Thus, the effect of diffusion led growth is expected to be less prominent in high-entropy alloys, aggravating the chances of instability under irradiation.


The high yield strength (1.045 GPa) of alloy at room temperature and dynamic recrystallization during high-temperature deformation was observed.

When alloys are exposed to radiation, the intermetallic phases (secondary phases) decrease, causing the material's structure to become a single BCC phase. This is better at resisting void swelling.


Source:

https://link.springer.com/article/10.1007/s10853-024-10511-z


Key Points: atmosphere of exoplanets and its magnetic field

 

Ohmic heating: The variations of the time varying magnetic field can induce currents in the upper atmosphere of some exoplanets, which dissipate and locally heat it up; it is called ohmic heating.


Equation for Induction and heating within a planet (which is described from ohm’s law, Ampere law, Faraday’s law) is:

where

 

Ap(x) is the steady magnetic field, the conductivity tensor σα depends on the magnetic field, and time.


Parallel conductivity is for the direction parallel to the magnetic field line.  

Pedersen conductivity is for the direction vertical to the magnetic field and parallel to the electric field. It is denoted as σp.

Hall conductivity is for the direction vertical to both the magnetic and electric fields. It is denoted as σH. In the ionosphere this conductivity is due to the drift motion of the electron (ExB drift).

Heating Rate,

Skin depth δ is defined as the depth where the current density is 1/e (about 37%) of the value at the surface; It depends on the oscillation frequency Ω  of the time-varying field and on the Pedersen conductivity in the atmosphere σp.

For constant σP, we see the maximum heating rate decreases with increasing orbital period.


Here In study, Trappist 1b and πMenc exoplanets are observed.

The differences in the electron number density lead to significant differences in the parallel, Hall and Pedersen conductivities of the upper atmospheres of the Earth, Trappist-1 b and π Men c.

Electron density of planets: Earth <Trappist 1b< πMenc.


The Pedersen conductivity is determined by the ions and electrons mixture in the atmosphere and planetary Magnetic Field.

The Pedersen conductivity of Trappist-1 b is dominated by the contribution from H2O+ and O+2 , whereas in π men c it is dominated by H+ , C+ and O+.


Due to the different XUV flux the planets receive and the π Men c atmosphere presents more electrons than Trappist-1 b, π Men c  have much stronger upper atmosphere conductivities than Trappist-1 b. therefore more efficient Ohmic heating.


Ohmic heating is expected to be important for the atmosphere only on a range of intermediate magnetic Bp values. For Trappist-1 b it matters if Bp ∈ [0.08, 0.2]G, and in the case of π Men c if BP ∈ [0.03, 0.1]G.


Source: https://arxiv.org/abs/2412.14072#:~:text=Indeed%2C%20close%2Din%20exoplanets%20are,it%20up%20through%20Ohmic%20heating.


Overview: Study of magnetization temperature in ferromagnetic crystals


EuO and EuS Materials are used in study. As per Weiss mean field approximation (MFA), below certain critical temperature(Tc) ferromagnetic materials have spontaneous magnetization — i.e., a sizable macroscopic magnetic moment even in the absence of an external magnetic field. The effective field acting on a magnet in a ferromagnetic medium is H+gM(T), term gM(T) is called self-consistent molecular field.

Magnetization M is given by,

 

Langevin function describes the average alignment of magnetic moments with an applied magnetic field at a given temperature.

x=uB/kT

For very large T, x becomes small and Langevin function becomes

For H = 0 and T slightly below TC , The equation  becomes

Brillouin function is a quantum mechanical function that describes the magnetization of a system of spins in response to an applied magnetic field at a given temperature.

The study shows that M(T) exhibits anomalous scaling near Tc, with a scaling index β≈1/3, consistent with experimental data for EuO and EuS.

This result differs from the classical MFA prediction of β=1/2


The Weiss-Heisenberg MFA value of the Curie Temperature Tc wh ≈ 86.6K in EuO was observed.(about 20 % larger than its experimental value Tc exp≈ 69.8 K). spin-wave included  MFA equations match with experimental data across all temperature ranges. 


Source: https://arxiv.org/abs/2412.10124







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