abstract
Chapter 16. Magnetic properties
Engineering materials are important in everyday life because of their versatile structural properties. Other than these properties, they do play an important role because of their physical properties. Prime physical properties of materials include: electrical properties; thermal properties; magnetic properties; and optical properties. Magnetic properties play an important role in daily life. Magnetic materials are used in electric motors, generators, transformers. Modern-day devices use data storage technology that is based on magnetic particles. Magnetic materials are used in devices like telephones, televisions, supercomputers, etc. they are also used in medical technology, for example DNA sequencing.
This chapter shall describe magnetic properties like dia-, para-, and ferro-magnetism along with anti-ferro- and ferri- magnetism. It also includes discussion about temperature effects on magnetic behavior, followed by magnetic domains and hysteresis.
Magnetism is a phenomenon by which a material exerts either attractive or repulsive force on another. Basic source of magnetic force is movement of electrically charged particles. Magnetic behavior of a material can be traced to the structure of atoms. Electrons in atoms have a planetary motion in that they go around the nucleus. This orbital motion and its own spin cause separate magnetic moments, which contribute to the magnetic behavior of materials. Thus every material can respond to a magnetic field. However, the manner in which a material responds depend much on its atomic structure, and determines whether a material will be strongly or weakly magnetic.
Magnetic moment due to spin of an electron is known as Bohr magneton,MB, is the most fundamental magnetic moment. 224.10274.94mAXmqhMeB?==?
where q is the charge on the electron, h – Planck’s constant, me – mass of electron. This moment is directed along the axis of electron spin. Magnetic moment resulted from
particles in nucleus is much smaller than that result from spin of electron, so it is ignored. If magnetic moment of electrons could sum up, then the world would be a magnetic place. Fortunately, two reasons are found to explain this phenomenon:- First: according to Pauli exclusion rule, two electrons with same energy level must have opposite spins – thus so are their magnetic moments, which cancel out each other. Second: orbital moments of electrons also cancel out each other – thus no net magnetic moments if there is no unpaired electron(s). Some elements such as transition elements, lanthanides, and actinides have a net magnetic moment since some of their energy levels have an unpaired electron.
المادة المعروضة اعلاه هي مدخل الى المحاضرة المرفوعة بواسطة استاذ(ة) المادة . وقد تبدو لك غير متكاملة . حيث يضع استاذ المادة في بعض الاحيان فقط الجزء الاول من المحاضرة من اجل الاطلاع على ما ستقوم بتحميله لاحقا . في نظام التعليم الالكتروني نوفر هذه الخدمة لكي نبقيك على اطلاع حول محتوى الملف الذي ستقوم بتحميله .
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