Chromium based tantalum disulfide properties

Study was done on Cr₁/₃TaS₂ (Cr atoms are inserted into a layered compound TaS₂ (tantalum disulfide)). The Raman Scattering method was used here.

Pressure changes bond lengths and angles and, at the same time, systematically reduces the van der Waals distance and modifies the structural c/a ratio.


Cr₁/₃TaS₂ has a smaller van der Waals gap, making it less change to structural distortions than Fe based material.


When pressure increases Cr₁/₃TaS₂ magnetic properties remain stable but Fe₁/₃TaS₂ magnetic property decreases drastically.


source:

https://link.springer.com/article/10.1038/s41535-025-00734-x


Study of Cesium lead bromide- local polarization

Material CsPbBr₃ (cesium lead bromide) was studied here. It is widely used in solar cells, LEDs.

At high temperatures (>100K), transport shifts to a band-like motion, where charge carriers move smoothly.


At low temperatures (<100K), charge carriers move by hopping transport (jumping between localized spots). spontaneous grain boundaries form inside the material. 


These grain boundaries create regions of local polarization meaning certain parts of the material develop an electric dipole moment. Here Displacement of Pb Ions occurs. This shift causes an imbalance in charge distribution, leading to localized electric fields.


GB⊥ have been observed here. It means the crystal tilts in a direction that is perpendicular to the boundary. Twinning boundaries have lower energy( more stable) when the in-phase octahedral tilting axis is rotated perpendicularly rather than twisted.


Low temperature (<100K) transport can be explained by the Mott’s variable range hopping (VRH) equation. Its conductivity is given by,

P is Local polarization, V is volume, d is displacement of ion


Source: https://arxiv.org/html/2502.20261v1


Study of Isotropic superconductivity of Nickelate La4Ni3O10


Nickelate La4Ni3O10-δ was studied here at pressure 50.2 GPa and a magnetic field up to 34T for both out-of-plane (H⊥ab) and in-plane (H//ab) direction.


The upper critical magnetic field(𝝁𝟎𝑯𝐜𝟐 ) of La4Ni3O10-δ is nearly isotropic, with the anisotropic parameter γ monotonically decrease from 1.4 near Tc to 1 at lower temperatures.


By analyzing the upper critical magnetic field using the two-band model, researchers found that the anisotropic diffusivity of the bands, primarily originated from 𝒅𝐳𝟐 and 𝒅𝐱𝟐−𝐲𝟐 orbitals resulting in an unusually isotropic superconducting state.


Interlayer coupling between Ni 3dz2 orbitals and apical oxygen p orbitals at high pressures leads to partially occupied 3𝑑x2−y2 orbitals, which has the precise roles of the 𝑑z2 and 𝑑x2−y2 orbitals in the electron pairing mechanism.


As the field strength increases, superconductivity is gradually suppressed, and the transition shifts to a lower temperature.


https://arxiv.org/pdf/2502.14410



Key Points of article related to Sn-based perovskite solar cells

 

(The electron barrier is an energy barrier that prevents or slows down the movement of electrons across an interface between two materials. It occurs due to a difference in energy levels when two materials come into contact.


Different materials have different Fermi levels. To balance out, electrons move from the higher-energy side to the lower-energy side. This movement bends the bands and creates an electric field that can help guide charges in a solar cell.)


Hole diffusion  occurs from the perovskite layer((BA0.5PEA0.5)2FA3Sn4I13) to the PEDOT:PSS layer under illumination and resulting electron barrier reduction.


Under illumination, the electrons are injected from perovskite to PEDOT:PSS which recombine with bipolarons and form localized polarons near the interface, which results in an increased Nspin and enhanced electron barrier and improves Voc and better performance of solar cell (Here bipolaron is  formed when two similar charges bind together within a material. In PEDOT:PSS, bipolarons are created when two holes pair up in the polymer chain).


To measure change of charge states under illumination, researchers analyzed ESR spectra using a least-squares method. Here Lorentzian and Gaussian formulas are used to describe the ESR spectra of semiconductor materials.


https://www.nature.com/articles/s41528-024-00376-2

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Conclusion of Article related to Polarization-based Chirality

 

Here in the experiment, the width of the rectangular waveguide is changed. It influences the effective path of light, refractive index for both Transverse Electric and Transverse Magnetic polarizations at the same time.


TE and TM polarizations are mainly distributed in the central and right regions of the waveguide, respectively.


The detuning of TE and TM polarizations is proportional to the difference in their respective effective refractive indices. The evolution direction for the Hamiltonian parameters is determined by the detuning of double-coupled waveguides.


The hamiltonian can be written as 

Hamiltonian describes the dynamic behavior of light as it propagates through the double-coupled waveguide system. It characterizes the system's energy and the interactions between modes within the waveguides, including factors like polarization, loss, and coupling strength.


https://www.nature.com/articles/s41377-025-01762-9#Sec3


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



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.


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


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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