Key Points of Article related to Photon-helicity-induced magnetization in Cobalt-Platinum alloy

 

Photons carry spin angular momentum in circularly-polarized and orbital angular momentum in vortex electromagnetic waves.

The inverse Faraday effect has been observed in which magnetization appears during the dwell time when circularly-polarized light passes through a dielectric medium.

For pure Co "field-like torque" sine wave and for Co35​Pt65​ alloy "damping-like torque" cosine wave were observed. These torques exert on a magnetic moment due to a spin current, a field-like torque acts like an external magnetic field, aligning the magnetization in a specific direction, while a damping-like torque opposes the magnetization's change in direction, similar to friction.

The Landau-Lifshitz equation was used here which describes how the magnetization changes over time due to the influence of applied torques.

γ, µ0, and Heff are the gyromagnetic ratio, vacuum permeability, and effective magnetic field, respectively. 

A reduction of the Kerr effect (when polarized light reflects off a magnetized material and undergoes a change in polarization direction and ellipticity) was observed with an increase in the Pt concentration.

Source:

https://arxiv.org/abs/2405.07405

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Summary of article based on Plastic Strain on Magnetic material

 Magnetic Barkhausen Noise and stress strain curve have been measured here. 

(When the external magnetic field is changed, domains change size by the domain walls moving within the crystal lattice so local abrupt changes of the magnetization occur which are measured as electric signals, it’s called magnetic Barkhausen noise.)

The maximum value of magnetic saturation reached depends on the direction of the anisotropy of the hard boundary.

Coercivity (a material's ability to resist demagnetization in the presence of a magnetic field) depends both on the thickness of the hard boundary and the anisotropy constant (measure of how strongly a material's magnetic properties depend on direction).

(Magnetic anisotropy is defined as the dependency of magnetic properties on a preferred crystallographic direction. It is the required energy to deflect the magnetic moment in a single crystal from the easy to the hard direction of magnetization. 

Exchange energy is a quantum-mechanical effect that determines the alignment of magnetic spins in a material.

Magnetostatic energy is energy required to create the magnetic poles of a body against the internal magnetic field.

Zeeman energy is the potential energy of a magnetized object in an external magnetic field.)

The anisotropy and magnetostatic energy gradually decreases as the applied field decreases from saturation. Zeeman energy increases slightly with the boundary thickness.

The effect of plastic strain( It refers to the permanent deformation of a material that occurs after the material has surpassed its elastic limit) depends on the angle of misalignment between the hard boundary and the soft grain, which affects the demagnetizing and anisotropy energy.

Source:

https://www.mdpi.com/2673-8724/5/1/1#

Definitions are from AI and wikipedia.

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Overview of Article based on BaTiO3

Kerr nonlinear index  is a parameter in nonlinear optics that quantifies the intensity-dependent change in the refractive index of a material.

Pockels coefficient indicates linear change in the refractive index of certain materials when subjected to an external electric field.

Absorption rate

Qabs = ω/κab

Modulation Transfer Spectroscopy was used here. The pump laser modulates the system (through thermal effects, Kerr nonlinearity, or absorption), this modulation transfers to the probe laser which is phase-modulated and tuned near a different resonance frequency to detect the system's response.

At low-frequency, photothermal effect dominates, here heating caused by absorption induces changes in the refractive index and at high-frequency Kerr effect dominates.

BaTiO3 has a higher Kerr nonlinear index and Pockels coefficient r than SiO2, Si3N4, LiNbO3, material absorption-loss Qabs is lower comparative to other materials.

Source:

https://pubs.aip.org/aip/app/article/10/1/016121/3332920/Absorption-loss-and-Kerr-nonlinearity-in-barium

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In Brief - article related to BCC CoMnFe alloy

A magnetic tunnel junction (MTJ) is a device that uses a thin insulating layer to create electrical conduction between two ferromagnetic layers. The resistance of the MTJ depends on the relative alignment of the magnetization in the two magnetic layers.

Most current p-MTJs utilize body-centered cubic (bcc) FeCo(B) alloy magnetic electrodes and an MgO barrier.

Perpendicular Magnetic Anisotropy (PMA) is magnetic property in which the magnetization of a material naturally aligns along the direction perpendicular to the plane of the material, rather than lying in the plane. Here, PMA originates from the tetragonal strain and the value of PMA reaches 1 MJ/m3 with adequate strain.

Magnetic properties were characterized by a vibrating sample magnetometer(vibrating a sample in a magnetic field and measuring the resulting electrical signal) and polar magneto-optical Kerr effect. 

The values for saturation magnetisation Ms tend to decrease with increasing Co concentration.

Magnetic anisotropic energy is given by

The perpendicular magnetic anisotropy (PMA) constant (K) indicates the strength of a material's preference for magnetization along a specific direction. K for the films tend to increase with increasing Co concentration.

Thermal stability is calculated as

Ep is the barrier energy -the energy needed for the magnetization of a material to switch between two stable directions.

Gilbert damping constant  describes how quickly the magnetization in a material stabilizes after being applied magnetic field or spin torque. The threshold of the switching current is proportional to the Gilbert damping constant α. The low Gilbert damping for magnetic free layer is preferable for low power consumption in STT-MRAM(spin-transfer-torque magnetoresistive random access memory).

Source:

https://www.tandfonline.com/doi/full/10.1080/14686996.2024.2421746#abstract

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Key Points of article about Dielectric and spectroscopic property of glass

As per study, Adding Bi2O3 up to 12.5 mol% decreases the thermal stability and increases the crystallization behavior of prepared non-crystalline solids.

Kubelka-Munk function is used to measure the optical band gap of glasses.

where R∞ is the relative remittance (R∞=Rsample / Rstandard) , 

S is the sample’s scattering coefficient, 

K is the absorption coefficient, and 

F(R∞) is the K-M function or the remission function.

Tauc equation has been used to calculate band gap energy.

By increasing the Bi2O3 content, the band gap energy slightly increases.

Here Non-bridging oxygen (Connected to only one P atom, associated with a metal ion (P-O-M)) ions decrease, a development of bridging oxygens occurs and the dense glass structure is created.)

The refractive index decreases with increase in Bi2O3. It was calculated for the glass using the Dimitrov and Sakka equation.

The trivalent cations(Bi3+)  improves the strength of phosphate glass due to the relative ability of the glass matrix which leads to the creation of the M3+–O–P bond.

With the addition of Bi2O3 content in the glasses, Metallization criterion(M) values increased. refractive index and optical band gap of the material

have an impact on  M values.

The replacement of the P2O5 by 2.5 mol% of Bi2O3 leads to a decrease in ac-conductivity values, and then the conductivity rises with more replacement of the P2O5 content to 10 mol%. The main reason for the conduction is the presence of Li+ions.

For an Oxygen/Phosphorus ratio < 3, and in spite of the high concentration of Bi3+ ions, the O–P bond becomes longer, which results in decreasing the polarizability and hence, the conductivity of the glass.

At low frequencies, tangent loss (dissipation of energy) is high and reduces as the frequency goes to high due to the presence of Maxwell-Wagner-Sillars polarization. (It occurs at regions with different electrical properties e.g. conductivity or permittivity. It describes the accumulation of charge at interfaces between different phases or regions when an alternating electric field is applied.)

M'(electric modulus) has low values at low frequency, then increases with rising frequency until it attains a constant value at f > 6 kHz due to the increase in the movement of the charges under a high-frequency electric field.

Source: https://link.springer.com/article/10.1007/s00339-024-08103-4

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Overview of article related to Rotation periods of asteroids

The Yarkovsky effect is a phenomenon that causes force to act on a rotating celestial body, such as an asteroid, due to the way it absorbs and re-emits sunlight as heat. The Yarkovsky effect depends on many physical and surface properties of the body such as diameter, albedo, density, obliquity, and rotation period.

The visual magnitude V of an asteroid is a measure of how bright it appears to an observer.  

Heliocentric distance r is the distance between the object and the sun's center. 

H is the absolute magnitude of the asteroid,

Delta is range to the observer (in au), 

g(t) is a periodic function related to the asteroid shape in rotation, it is used to describe the repeating brightness variations (light curve) of an asteroid over time.

The phase function describes how brightness evolves with the phase angle(the Sun-asteroid-observer angle). The phase function is second-degree polynomial here.

To find g(t), fourier series has been used upto 10 order here.

If the shape of an asteroid is well-described by a tri-axial ellipsoid, the light-curve is expected to display two local maxima and two local minima. local maxima and local minima are the peaks and troughs of the asteroid's brightness variations over time. 

Source: https://arxiv.org/abs/2501.07189 

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Brief Summary of article: Interlayer dislocations in MoS2

The minimal energy density has been found for a dislocation with its axis oriented along the zigzag direction (α = 90◦),

screw dislocation energy density increases logarithmically with the number of layers.

The strongest piezoelectric charge densities are in the layers closest to the dislocation plane.As far a layer is from the dislocation plane, the smaller the charge density.

For a bilayer, the piezoelectric potential (When an external force is applied, the material's internal structure deforms, separating the centers of positive and negative charges) is strong and varies significantly across the dislocation. For tetralayers and hexalayers, the potential weakens in the outer layers, the alternating charges cancel each other.

https://iopscience.iop.org/article/10.1088/2053-1583/ad9f7d

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