Magnetizing and Unmagnetizing

Background

A magnet is a material with poles and a magnetic field created by the configuration of its electrons. It must contain one of the three naturally magnetic metals, iron, nickel, and cobalt. All magnets have magnetic fields around them, and it is this magnetic field, and the poles of the magnet, that allow magnets to attract and repel. When two opposite poles are brought together, they will attract. But when the same poles are nearby their fields will repel each other.

There are two groups of magnets. Permanent magnets are magnets with permanent magnetic fields. They cannot be turned off, nor can their fields be increased or decreased easily. These are items that are almost always magnetized. There are a few ways to remove a magnetic field from a permanent magnet. One of these methods requires increasing the temperature of the magnet. This adds heat and energy to the system which will take away the magnetic field. The temperature at which the magnet no longer holds its field is known as the Curie point. Another way to make a magnet lose its magnetic field is by hitting it. The impacts on the magnet will ruin the needed configuration of the electrons and the magnetic field will weaken and possibly be lost.

The other group is called temporary magnets. This category includes items that are magnetic, but do not contain their own magnetic fields. Items in this group include paper clips, scissors, iron rods, staples, and various other items. These items can be magnetized but will not hold their field and are much more likely to lose their magnetic field than are permanent magnets.

Why do this in your classroom?

• To encourage the following process skills for scientific investigation: prediction, observation, developing a hypothesis, and drawing conclusions.
• To help students understand magnets and what creates magnetism.
• To allow students to manipulate materials and explore their own questions.

Materials

• Various permanent magnets of different shapes, sizes, and strengths. These can be purchased from toy stores and hardware stores, as well as online.
• Paper clips

Procedure

1. Show the students a paperclip, and ask them if this is a magnet. Then ask if the paperclip is magnetic. The paperclip is a temporary magnet. Ask the class if they can think of temporary magnets they may have in their home. Some answers include their refrigerator doors, car doors, the metal legs of their chairs and desks.
2. Attach the paperclip to the magnet, and ask the class if you can attach another paperclip to the first one. Since the paperclip has been magnetized, it can attract another paperclip.
3. Ask the students what will happen if you remove the top paperclip (and the one below it) from the magnet. Gently pull the top paperclip, and both of them should still attract to each other. Since the paperclips were magnetized, they will have all the properties of a magnet until something makes them lose their field.
4. Slowly place a permanent magnet near the bottom of the paperclips. The bottom paperclip will either attract or repel since it is still a magnet. Flip over the permanent magnet and you will make the paperclip react the other way.
5. Bring the permanent magnet near the top of the paperclip using the same pole you used to magnetize the paperclips. You should be holding the magnet and the two paperclips in line. Now pull the paperclips away from the magnet, flip over the magnet and bring the new pole near the top of the paperclips. Because this pole is different from the original pole that magnetized the paperclips, the top paperclip will become remagnetized in the opposite direction and the bottom paperclip will be repelled away.
6. Once more bring the permanent magnet near the paperclips to magnetize them. If you’re very gentle, you can separate the two paperclips and bring them back together. They will still attract! But if you drop them on the table, their field will be lost.
7. Magnetize the paperclips again and drop them into someone’s hands. There will still be an impact, but it will be softer and so the paperclips will still be magnetized. Minimizing the hardness of the impact will allow the paperclips to remains magnetized.

What's happening?

When it comes to the creation of magnetic fields, the spin of a material’s unpaired electrons is the crucial element. In most materials, electrons spin randomly. But in magnets the electrons group into magnetic domains, created whenever the spin of a number of electrons line up in the same direction. This happens in iron, nickel, or cobalt. If a majority of magnetic domains match spins, then that material is said to be magnetic. That material then has a north pole, a south pole, and a magnetic field, each determined by the directions of the spins. These domains support each other by pulling more in the same direction, resulting in an overall magnetic field.

Each time the paperclips are placed on the permanent magnet, the paperclips are being magnetized because their unpaired electrons are being organized. As long as they remain organized, the paperclips will act like magnets. But as soon as their order is disrupted, by dropping them or by introducing another magnetic field, the magnetism is lost until something can reorganize the electrons.

For more information contact MagLab educator Carlos Villa.