Types of Magnetism and Magnetic Domains

Transcription

1 Types of Magnetism and Magnetic Domains

2 Magnets or objects with a Magnetic Moment A magnet is an object or material that attracts certain metals, such as iron, nickel and cobalt. It can also attract or repel another magnet. All magnets have North-seeking (N) and South-seeking (S) poles. When magnets are placed near each other, opposite poles attract and like poles repel each other.

3 Types of magnets (The Boad View) Permanent magnets: a magnet that will creates and maintains its own magnetic field over a long period of time. Examples: Lodestone (a version of Magnetite)-probably created by lightening striking magnetite Alloys- magnets created with a combination or alloy of iron, nickel and cobalt. Temporary magnets:a magnet that will lose its magnetism. Example: soft iron Electromagnet: A magnet can be created by wrapping a wire around an iron or steel core and running an electrical current through the wire.

4 Recall that magnetic fields result from the motion of a electron. If you spin a ball of electric charge, the electric charge goes around in a circle. You effectively have a tiny current going around, and when you have a current like that you have a magnetic field the electron becomes a tiny magnet. The presence of that magnetic effect is pictured as the electric charge spinning around. If the electron was still, it wouldn t have this magnetic effect.

5 Recall: 1. Magnetic flux is the result of the vector sum of all the individual magnetic fields. 2. Electrons will tend towards the lowest energy state 3. Paired electrons have the lowest energy state. Magnetic properties come about because of the interactions of unpaired electrons.

6 Types of Magnetism at an Atomic Level Diamagnetism Diamagnetism is the property of an object or material that causes it to create a magnetic field in opposition to an externally applied field. It is not the result of unpaired electrons, but is found in all materials. The electrons in a diamagnetic material rearrange their orbits slightly to create small persistent currents that oppose or repel the external field.

7 Diamagnetism (Con't) Materials called diamagnetic are those that non-physicists generally think of as non-magnetic. and include water, wood, most organic compounds, some plastics and metals with many core electrons such as mercury, gold and bismuth. Superconductor can be considered perfect diamagnet as they expel all fields. In September 2009, NASA announced that they were able to levitate a mouse using a superconducting magnet Check here for a brief explanation of how and why you can levitate a frog using its diamagnetic properties diamagnetism.html

8 Paramagnetism (Temporary Magnet) (con't) There will be only a small induced magnetism because only a small percentage of all of the electron spins (magnetic moments) will orient with the field. Paramagnetic properties are commonly found in transitionals elements, lanthanides and their compounds as a result of unpaired electrons in the d and f orbitals.

9 Paramagnetism (Temporary Magnet) Materials in which the unpaired electrons are randomly arranged.(ie. Aluminum, Manganese, Oxygen gas, Platinum) Only becomes magnetic when in the presence of an externally applied magnetic field. Paramagnets will not retain any magnetization in the absence of the externally applied field because thermal motion randomizes the electrons spin orientation

10 Ferromangetism Materials in which the unpaired electron spins are all aligned These materials have an overall magnetic moment A few elements are ferromagnetic at room temperature (iron, cobalt, nickel) The electric energy within these atoms is found to be lower if the electron spins (magnetic moment) of the valence electrons are aligned.

11 Every ferromagnetic material has its own individual temperature, called the Curie Temperature or the Curie Point, above which it loses its ferromagnetic properties. (This is because the thermal tendency to disorder overwhelms the energy lowering due to ferromagnetic order.)

12 Antiferromagnetic A material in which the unpaired electrons line up in opposite directions to one another Materials include hematite, chromium, iron Manganese and oxides such as nickel oxide. Antiferromagnetic material have a net magnetic moment of zero

13 Types of magnetism: (A) paramagnetism (B) ferromagnetism (C) antiferromagnetism (D) ferrimagnetism (E) enforced ferromagnetism. Credit and : Sigma- Aldrich

14 Magnetic Domains and Domain Theory A magnetic domain is a region within a magnetic material which has uniform magnetization. Magnetic moments (electron spin) in real ferromagnets are not perfectly aligned. They do have perfectly aligned regions within the material, called magnetic domains Each domain has its own magnetization directions.

15 Magnetic Domains and Domain Theory (con't) Domains form as molten material cools into a solid. During solidification, a trillion or more atom moments are aligned parallel so that the magnetic force within the domain is strong in one direction Domains tend to be small because this is more energy efficient.

16 Ferromagnetic materials become magnetized when the magnetic domains within the material are aligned. This can be done by placing the material in a strong external magnetic field or by passing electrical current through the material. Some or all of the domains can become aligned. The more domains that are aligned, the stronger the magnetic field in the material.

17 Magnetic Saturation When all of the domains are aligned, the material is said to be magnetically saturated. When a material is magnetically saturated, no additional amount of external magnetization force will cause an increase in its internal level of magnetization.

18 The connection between electric current and magnetic field was first observed when the presence of a current in a wire near a magnetic compass affected the direction of the compass needle. We now know that current gives rise to magnetic fields, just as electric charge gave rise to electric fields.

19 Magnetic field lines of a permanent magnet, cylindrical coil, iron-core electromagnet, straight current-carrying wire, and a circular current-carrying loop.

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