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Scientists have discovered that there are many types of magnetic materials. Some are called ferromagnetic, others are paramagnetic. Scientists have found that every material has its own unique magnetic property. Ferromagnetic materials, for example, react strongly to the Earth’s magnetic field and show a marked response in their magnetization to external forces. In contrast, paramagnetic materials do not show any marked response in the magnetization. In this article we will discuss ferromagnetic materials. Heat can have a significant impact on the magnetization of a substance. If a substance is heated above its Curie temperature, its magnetic properties will change. The Curie temperature is the temperature at which a substance’s magnetization starts to disappear due to the heat. When the substance cools back down below the Curie temperature, its magnetic properties will re-appear. It is useful to consider what happens to a simple bar magnet when it is heated up and cooled back down again. When heated above its Curie temperature, the magnet will lose its magnetization. When it cools down again, the magnet will re-appear. Physicists refer to this process as an "exchange" of magnetization between molecules of the material in a process called intermolecular exchange. One of the most important entities in magnetic materials is the domain wall. A boundary in which magnetic field lines split in two or three different directions is known as a domain wall. If there are no domain walls, then the material would be said to be ferromagnetic. If there are many domain walls present, then the material would be said to be paramagnetic. Ferromagnetic materials are able to be magnetized often because the domain walls are constantly moving. The fact that the domain walls move constantly is what makes the material magnetic. Ferromagnetic materials behave in some ways like simple bar magnets. A simple bar magnet acts like a single magnet, while a ferromagnetic material acts like many magnets spread throughout it. The individual domains act like individual magnets which all contribute to the overall effect on the material’s magnetic properties. Ferromagnetic substances are used in instruments such as pacemakers and computer hard drives because of their ability to retain their magnetic properties very strongly when heated up past their Curie temperature. Ferromagnetic materials are able to be magnetized often because the domain walls are constantly moving. The fact that the domain walls move constantly is what makes the material magnetic. These domains move in all different directions which causes them to split apart and start new magnetic lines of force. As they split apart, they cut through others of their kind, creating more domain walls. This movement causes domains to move closer together or further apart depending on how many there are and how strongly-aligned these domain walls are. If there were no domain walls, the material would act like a single magnet; but if there were many, then it would act like many magnets spread throughout it. cfa1e77820
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