Magnetizing a material without applying an external magnetic field is suggested by researchers at São Paulo State University (UNESP), Brazil, in an article published in the journal Scientific reportswhere they describe the experimental approach used to achieve this goal.
The study was part of the Ph.D. Research by Lucas Squillante under the direction of Mariano de Souza, professor at the Department of Physics at UNESP in Rio Claro. Contributions were also made by Isys Mello, another Ph.D. the candidate supervised by Souza and Antonio Seridonio, Professor at the Department of Physics and Chemistry at UNESP in Ilha Solteira. The group was supported by FAPESP.
“In short, magnetization occurs when a salt is adiabatically compressed without exchanging heat with the outside environment,” Souza said. “The compression increases the temperature of the salt and at the same time rearranges the spins of its particles. As a result, the total entropy of the system remains constant and the system remains magnetized at the end of the process. “
To understand the phenomenon, it is worth remembering the basics of spin and entropy.
Spin is a quantum property that elementary particles (quarks, electrons, photons, etc.), composite particles (protons, neutrons, mesons, etc.) spin down – when exposed to a magnetic field.
“Paramagnetic materials like aluminum, which is a metal, are only magnetized when an external magnetic field is applied. Ferromagnetic materials, including iron, can have finite magnetization even without an applied magnetic field because they have magnetic domains,” explained Souza.
Entropy is basically a measure of accessible configurations or states of the system. The greater the number of accessible states, the greater the entropy. The Austrian physicist Ludwig Boltzmann (1844-1906) used a statistical approach to combine the entropy of a system, which is a macroscopic quantity, with the number of possible microscopic configurations that make up its macrostate. “In the case of a paramagnetic material, the entropy embodies a probability distribution that describes the number of upward spins or downward spins in the particles it contains,” said Souza.
In the recently published study, a paramagnetic salt was compressed in one direction. “The uniaxial loading reduces the salt volume. Since the process takes place without heat exchange with the environment, the compression leads to an adiabatic increase in temperature of the material. An increase in temperature means an increase in entropy As a result, the spins tend to align, which leads to magnetization of the system, “Souza said.
The total entropy of the system remains constant and the adiabatic compression leads to magnetization. “Experimentally, adiabatic compression is achieved when the sample is compressed for less time than is required for thermal relaxation – the typical time it takes for the system to exchange heat with the environment,” said Souza.
The researchers also suggest that the adiabatic rise in temperature could be used to study other interacting systems, such as Bose-Einstein condensates in magnetic isolators and dipolar spin-ice systems.
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Lucas Squillante et al., Elastocaloric Effect-Induced Adiabatic Magnetization in Paramagnetic Salts Due to Mutual Interactions, Scientific reports (2021). DOI: 10.1038 / s41598-021-88778-4
citation: Researchers propose a method for magnetizing a material without the application of an external magnetic field (2021, July 29), accessed on July 29, 2021 from https://phys.org/news/2021-07-method-magnetizing-material- external-magnetic. html
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