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Phase transitions

In chemistry, thermodynamics, and other related fields, a phase transition (or phase change) is the physical process of transition between one state of a medium and another. Commonly the term is used to refer to changes among the basic states of matter: solid, liquid, and gas, and in rare cases, plasma. A phase of a thermodynamic system and the states of matter have uniform physical properties. During a phase transition of a given medium, certain properties of the medium change as a result of the change of external conditions, such as temperature or pressure. This can be a discontinuous change; for example, a liquid may become gas upon heating to its boiling point, resulting in an abrupt change in volume. The identification of the external conditions at which a transformation occurs defines the phase transition point. vapor pressure and phase diagram Phase transitions commonly refer to when a substance transforms between one of the four states of matter to another. At the phase transition point for a substance, for instance the boiling point, the two phases involved - liquid and vapor, have identical free energies and therefore are equally likely to exist. Below the boiling point, the liquid is the more stable state of the two, whereas above the boiling point the gaseous form is the more stable. Common transitions between the solid, liquid, and gaseous phases of a single component, due to the effects of temperature and/or pressure are identified in the following table: For a single component, the most stable phase at different temperatures and pressures can be shown on a phase diagram. Such a diagram usually depicts states in equilibrium. A phase transition usually occurs when the pressure or temperature changes and the system crosses from one region to another, like water turning from liquid to solid as soon as the temperature drops below the freezing point. In exception to the usual case, it is sometimes possible to change the state of a system diabatically (as opposed to adiabatically) in such a way that it can be brought past a phase transition point without undergoing a phase transition.

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High-temperature superconductivity

High-temperature superconductors (abbreviated high-Tc or HTS) are defined as materials with critical temperature (the temperature below which the material behaves as a superconductor) above , the boiling point of liquid nitrogen. They are only "high-temperature" relative to previously known superconductors, which function at even colder temperatures, close to absolute zero. The "high temperatures" are still far below ambient (room temperature), and therefore require cooling.

Evaporation

Evaporation is a type of vaporization that occurs on the surface of a liquid as it changes into the gas phase. High concentration of the evaporating substance in the surrounding gas significantly slows down evaporation, such as when humidity affects rate of evaporation of water. When the molecules of the liquid collide, they transfer energy to each other based on how they collide. When a molecule near the surface absorbs enough energy to overcome the vapor pressure, it will escape and enter the surrounding air as a gas.

Lever rule

In chemistry, the lever rule is a formula used to determine the mole fraction (xi) or the mass fraction (wi) of each phase of a binary equilibrium phase diagram. It can be used to determine the fraction of liquid and solid phases for a given binary composition and temperature that is between the liquidus and solidus line. In an alloy or a mixture with two phases, α and β, which themselves contain two elements, A and B, the lever rule states that the mass fraction of the α phase is where is the mass fraction of element B in the α phase is the mass fraction of element B in the β phase is the mass fraction of element B in the entire alloy or mixture all at some fixed temperature or pressure.

MSE-432: Introduction to magnetic materials in modern technologies

Interactive course addressing bulk and thin-film magnetic materials that provide application-specific functionalities in different modern technologies such as e.g. wind energy harvesting, electric art

MSE-101(a): Materials:from chemistry to properties

Ce cours permet l'acquisition des notions essentielles relatives à la structure de la matière, aux équilibres et à la réactivité chimique en liaison avec les propriétés mécaniques, thermiques, électri

PHYS-201(d): General physics: electromagnetism

The topics covered by the course are concepts of fluid mechanics, waves, and electromagnetism.

Thermodynamics

Ce cours complète le MOOC « Thermodynamique : fondements » qui vous permettra de mettre en application les concepts fondamentaux de la thermodynamique. Pour atteindre cet objectif, le Professeur J.-P

Thermodynamics

Ce cours vous apportera une compréhension des concepts fondamentaux de la thermodynamique du point de vue de la physique, de la chimie et de l’ingénierie. Il est scindé un deux MOOCs. Première partie:

Magnetism and metal-organic self-assembly of rare-earth atoms on decoupling layers

Sébastien Reynaud

This thesis presents investigations of magnetic and structural properties of two dimensional metal-organic frameworks and of single atoms, both adsorbed on decoupling layers grown on metal surfaces, with focus on rare earth elements.We first report on a series of attempts at realizing self-assembled metal-organic networks on different decoupling layers, probed by scanning tunneling microscopy. The aim is to produce regular structures with high surface filling factors such that the magnetic properties of the rare earth atoms in the metal-organic networks can be investigated by X-ray ensemble measurements. The combinations of three molecular ligands (QDC, BDA, ZnTPyP) on three insulating layers (MgO, NaCl, graphene) with Tb as rare earth are reported. Of the three decoupling layers, only graphene is found to allow the synthesis of metal-organic structures. We successfully synthesized large islands of a rare earth-QDC coordination complex, with a majority of fivefold coordination of the rare earth atoms. The same structure is reproduced with Dy and Er.X-ray absorption spectroscopy, X-ray magnetic circular and linear dichroism measurements are then carried out on the Dy- and Er-QDC/gr/Ir(111) networks. Compared to single atoms on gr/Ir(111), both Dy and Er change their

4f

occupancy from 4

f^n

4f^{n-1}

and change their easy axis of magnetization. Both species are paramagnetic when incorporated into the metal-organic structure. The last part of the thesis is devoted to the study of Dy, Ho, and Gd on NaCl thin films. All three atoms display

4f

occupancy of the gas phase. The top-Cl adsorption site is determined with scanning tunneling microscopy. The magnetic properties are probed with X-ray absorption spectroscopy, X-ray magnetic circular and linear dichroism. Ho and Gd are paramagnetic. Dy has out-of-plane anisotropy with open hysteresis at non zero magnetic field. However, thermally assisted quantum tunneling of the magnetization prevents remanence at zero field.

EPFL2022

Canted antiferromagnetic phases in the candidate layered Weyl material EuMnSb2

Xiao Wang

EuMnSb2 is a candidate topological material which can be tuned towards a Weyl semimetal, but there are differing reports for its antiferromagnetic (AFM) phases. The coupling of bands dominated by pure Sb layers hosting topological fermions to Mn and Eu magnetic states provides a potential path to tune the topological properties. Here we present single-crystal neutron diffraction, magnetization, and heat-capacity data as well as polycrystalline 151Eu M??ssbauer data which show that three AFM phases exist as a function of temperature, and we present a detailed analysis of the magnetic structure in each phase. The Mn magnetic sublattice orders into a C-type AFM structure below TNMn = 323(1) K with the ordered Mn magnetic moment ??Mn lying perpendicular to the layers. AFM ordering of the Eu sublattice occurs below TNEu1 = 23(1) K with the ordered Eu magnetic moment ??Eu canted away from the layer normal and ??Mn retaining its higher temperature order. ??Eu is ferromagnetically aligned within each Eu layer but exhibits a complicated AFM layer stacking. Both of these higher-temperature phases are described by magnetic space group (MSG) Pn'm'a' with the chemical and magnetic unit cells having the same dimensions. Cooling below TNEu2= 9(1) K reveals a third AFM phase where ??Mn remains unchanged but ??Eu develops an additional substantial in-plane canting. This phase a' . We also find some evidence of short-range magnetic correlations associated with the Eu between 12 K ??? T ??? 30 K. Using the determined magnetic structures, we postulate the signs of nearest-neighbor intralayer and interlayer exchange constants and the magnetic anisotropy within a general Heisenberg model. We then discuss implications of the various AFM states in EuMnSb2 and their potential for tuning topological properties.

AMER PHYSICAL SOC2022

Magnetic structure of the topological semimetal Co3Sn2S2

Henrik Moodysson Rønnow, Ivica Zivkovic, Jian Rui Soh

Co3Sn2S2 has recently been predicted to be a Weyl semimetal in which magnetic order is key to its behavior as a topological material. Here, we report unpolarized neutron diffraction and spherical neutron polarimetry measurements, supported by magnetization and transport data, which probe the magnetic order in Co3Sn2S2 below TC = 177 K. The results are fully consistent with ferromagnetic order in which the spins on the Co atoms point along the crystal c axis, although we cannot rule out some canting of the spins. We find no evidence for a type of long-ranged (k = 0) in-plane 120?? antiferromagnetic order which had previously been considered as a secondary phase present at temperatures between -90 K and TC. A discontinuous change in bulk properties and neutron polarization observed at T = 125 K when samples are cooled in a field and measured on warming is found to be due to a sudden reduction in ferromagnetic domain size. Our results lend support to the theoretical predictions that Co3Sn2S2 is a magnetic Weyl semimetal.

AMER PHYSICAL SOC2022

Chemical substances

A chemical substance is a form of matter having constant chemical composition and characteristic properties. Chemical substances can be simple substances (substances consisting of a single chemical element), chemical compounds, or alloys. Chemical substances that cannot be separated into their simpler constituent elements by physical means are said to be 'pure'; this notion intended to set them apart from mixtures.

Organometallic chemistry

Organometallic chemistry is the study of organometallic compounds, chemical compounds containing at least one chemical bond between a carbon atom of an organic molecule and a metal, including alkali, alkaline earth, and transition metals, and sometimes broadened to include metalloids like boron, silicon, and selenium, as well. Aside from bonds to organyl fragments or molecules, bonds to 'inorganic' carbon, like carbon monoxide (metal carbonyls), cyanide, or carbide, are generally considered to be organometallic as well.

Electrodynamics

In physics, electromagnetism is an interaction that occurs between particles with electric charge via electromagnetic fields. The electromagnetic force is one of the four fundamental forces of nature. It is the dominant force in the interactions of atoms and molecules. Electromagnetism can be thought of as a combination of electrostatics and magnetism, two distinct but closely intertwined phenomena.

Materials Science of Magnetic Materials MSE-670: Advanced Microscopy for Magnetic Materials

Covers the materials science of magnetic materials, focusing on properties, concepts, and optimization for functional applications.

Magnetic Interactions: Ferromagnetism & Exchange PHYS-310: Solid state physics II

Covers ferromagnetism, antiferromagnetism, and paramagnetism, explaining exchange interactions and magnetic domains.

Nanomagnetism: Magnetic Fields and Domains

Explores magnetism, magnetic sources, fields, domains, hysteresis, energy contributions, types of magnetism, and nanoscale magnetic structure investigation.