Recently Yuce and coworkers reported high barocaloric effect in the well know giant magnetocaloric material Gd5Si2Ge2 around the first order magnetic phase transition. In this paper, we propose a theoretical microscopic model to discuss the barocaloric and magnetocaloric effects in the Gd5Si2Ge2 compound. For this purpose, our model Hamiltonian contains three interactions: Zeeman, magnetoelastic and exchange interactions. Also, magnetic field dependence of phonons entropy was included in our model. Using this model the combined magnetocaloric and barocaloric effects were calculated in Gd5Si2Ge2 compound showing satisfactory agreement with the experimental data. Besides, simulating the applied pressure simultaneously with the variation of the applied magnetic field in Gd5Si2Ge2, high isothermal entropy change was predicted.
INTRODUCTION
The magnetocaloric effect (MCE) was discovered by P. Weiss and A. Piccard in 1917 by observing a sizable and reversible temperature change in nickel near its Curie temperature [1]. The order parameter (magnetization), and consequently, the total entropy of magnetic materials can be modified by the magnetic field, pressure, and impurities [2-7]. The change in total entropy implies the transfer of heat between the compound and the environment. Therefore, a magnetic material can heat or cool upon cyclically applying and removing a magnetic field, so the MCE can be used for magnetic refrigeration as an ecological alternative to gas compression - expansion refrigeration technique. Similarly, a material can change its temperature upon application of an external pressure, barocaloric effect (BCE) [2, 7]. This effect is usually investigated by two processes: the isothermal entropy change (∆S_T...
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...field and 3) both pressure and magnetic field are changed simultaneously. All these three processes were simulated increasing and decreasing temperature, showing the existence of thermal hysteresis which was ascribed to the magnetoelastic interaction. Our microscopic model includes in the Hamiltonian: 1) the magnetoelastic interaction which is responsible for the onset of the magnetic first order phase transition and the hysteresis; 2) the exchange interaction and 3) the Zeeman interaction. Besides, the influence of magnetic deformation was included in the phonons and magnetic entropies. Our results are in good agreement with the recent experimental data reported by Yuce et.al. [19] and Jun-Ding [20] and we predicted that by varying the applied pressure simultaneously with the variation of the applied magnetic field leads to a significant increase in 〖ΔS〗_T-peak.
Whereby, instead of using a separate material as a regenerator to recuperate the heat from the magnetic material, the AMR concept made use of the refrigerant itself as the regenerator [6], thus, making it an active part of the refrigeration cycle. This is possible due to the high heat capacities of common magnetocaloric materials near their Curie temperatures [25].
2. Liang Chi Shen and Jin Au Kong, Applied Electromagnetism, 3rd ed. PWS Publishing Company, 1995.
For most of history, ice and snow, packed into cellars insulated with wood or straw, were used for refrigeration. It wasn’t until 1755 that the first artificial refrigeration system was established by William Cullen (Koelet, 1992). Throughout the 1800s, many mechanical refrigeration systems were designed and developed, and the vapour compression cycle most commonly used today dates back to this time.
The MRI works by using hydrogen atoms’ magnetic properties within the human body to produce high quality images. These protons of the hydrogen atoms can be look upon as bar magnets, in normal situations, they will flow inside...
...gnetic. This new magnetic state stems from the fact that the spins are interacting by the double exchange interaction. Subsequently the insulating state changes to semiconductor. Furthermore, the general concept is that ferromagnetic materials favours metalicity.
From this project I learned many things from the internet. I learned that magnets were first called “Lodestones” that were used in compasses used by the sailors to lead them home. I also learned that magnetic pull is strongest on the north and south poles, incredibly, where the planets temperature is the coldest. But most importantly, I learned the abilities of magnets, under different temperatures.
Magnets are one of the fundamental items in physics. This page is designed in order to provide a general overview of magnets and their uses as well as an in depth look into certain aspects of magnetism.
Magnetism is very useful in our daily life. A magnetic field is a mathematical description of the magnetic influence of electric currents and magnetic materials. In addition, magnetic field is a region which a magnetic material experiences a force as the result of the presence of a magnet or a current carrying conductor. Current carrying conductors also known as wire. As we know there have north pole and south pole of a magnet. If same pole of magnet approaches each other, there will repel each other. In contrast, if different pole of magnet approaches each other, they will attract. These are same with the electric charge, if same charge it will repel, different charge it will attract. Although magnets and magnetism were known much earlier, the study of magnetic fields began in 1269 when French scholar Petrus Peregrinus de Maricourt mapped out the magnetic field on the surface of a spherical magnet using iron needles [search from Wikipedia]. Noting that the resulting field lines crossed at two points he named those points 'poles' in analogy to Earth's poles. Each magnet has its own magnetic field which experiences a force as the result of the presence of a magnet and magnetic field has made up of magnetic field lines. The properties of magnetic field lines is it begin at the north pole and end at the south pole. The north pole always flow out while south pole always flow in. The closer the magnetic field lines, the strength of magnetic field increases. Furthermore, these line cannot cross each other. Ferromagnetism is the basic mechanism by which certain materials (such as iron) form permanent magnets, or are attracted to magnets. Ferromagnetic materials...
A magnetar is a kind of neutron star with one of the strongest magnetic fields detected in the Universe. Many stars have magnetic fields, but that by itself does not distinguish as magnetar from other stars. The distinguishing characteristic of magnetars is their extraordinarily intense magnetic fields that range between ~1014 and ~1015 Gauss (G) making them hundreds to thousands of times stronger than pulsars and among the strongest magnetic fields ever observed (Tiengo & Schartel, 2013). Explained another way ~1015 is equal to ~1011 tesla; or a magnetic field so strong that if the Moon possessed that magnetic field, the magnetic stripe on all credit cards would be stripped clean (Tate, 2010). That still might be challenging to comprehend. However, the strongest permanent magnet on Earth is approximately 1 Tesla compared to a magnetar with at least 100 billion times that strength (Tate, 2010).
This paper is about the calculation of standard thermodynamic properties of the four solid solutions in the phase diagram of Ag2S – Ag2Se. They calculated these properties using the model of regular and subregular solutions. The four solid solutions are: a restricted fcc solid solution (γ- Ag2S-Ag2S1-xSe (x<0.3)), a complete bcc solid solution (β- Ag2S – Ag2Se), monoclinic solid solution (α) from Ag2S to Ag2S0.4Se0.6, and a orthorhombic solid solution (α) from Ag2S0.3Se0.7 to Ag2Se. There is also a miscibility gap between Ag2S0.4Se0.6 and Ag2S0.3Se0.7. In this region Gmix and Smix have been calculated using subregular model for asymmetric solutions.
Temperature has a large effect on particles. Heat makes particles energized causing them to spread out and bounce around. Inversely the cold causes particles to clump together and become denser. These changes greatly F magnetic the state of substances and can also influence the strength of magnetic fields. This is because it can alter the flow of electrons through the magnet.
Cengel, Y. A., & Boles, M. A. (2011). Thermodynamics: An engineering approach (7th ed.). New York, NY: McGraw-Hill.¬¬¬¬
Have any of you wondered about the magic that occurs within a hot hand? The hot hand is a small pouch that contains mysterious elements that combines to start a reaction that produces heat. There is a specific field of chemistry that studies the heat associated with reactions, and today we begin our journey learning about this form of chemistry called thermochemistry! Thermochemistry is a fascinating field of chemistry that contains new terms and ideas that need to be understood in order to proceed into the mathematical applications of thermochemistry. We are going to create “I wonder…” statements to help with learning about these new terms while we read the
The development of superconductors has been a working progress for many years and some superconductors are already in use, but there is always room for improvement. In 1911, Dutch physicist Heike Kamerlingh Onnes first discovered superconductivity when he cooled mercury to 4 degrees K (-452.47º F / -269.15º C). At this temperature, mercury’s resistance to electricity seemed to disappear. Hence, it was necessary for Onnes to come within 4 degrees of the coldest temperature that is theoretically attainable to witness the phenomenon of superconductivity. Later, in 1933 Walter Meissner and Robert Ochsenfeld discovered that a superconducting material will repel a magnetic field. A magnet moving by a conductor induces currents in the conductor, which is the principle upon which the electric generator operates. However, in a superconductor the induced currents exactly mirror the field that would have otherwise penetrated the superconducting material - causing the magnet to be repulsed- known today as the “Meissner effect.” The Meissner effect is so strong that a magnet can actually be levitated over a superconductive material, which increases the use of superconductors. After many other superconducting elements, compounds, and theories related to superconductivity were developed or discovered a great breakthrough was made. In 1986, Alex Muller and Georg Bednorz invented a ceramic substance which superconducted at the highest temperature then known: 30 K (-243.15º C). This discovery was remarkable because ceramics are normally insulators – they do not conduct electricity well. Since their discovery the highest temperature for superconductivity to occur is 138 K (-130.15º C).
Mann, M., 2013. Mind Action Series Physical Sciences 12 Textbook and Workbook. Sanlamhof: Allcopy Publishers.