After this reading this section you will be able to do the following:
Perform an experiment to detect what materials are magnetic and explain why you think they are magnetic.
Just like when the Greeks of the old times discovered the first naturally occurring magnetic stones, or natural magnets, you have been observing a property of matter called magnetism. Magnetism is the force of attraction or repulsion in and around a material. Magnetism is present is all materials, but in some materials it is at such low levels that it is not easily detected. Certain materials such as magnetite, iron, steel, nickel, cobalt and alloys of rare earth elements
, exhibit magnetism at levels that are easily detectable.
Magnets are very common items in the workplace and household. Uses of magnets range from holding pictures on the refrigerator to causing torque in electric motors. A magnet is any piece of material that has the property of attracting iron (or steel). Magnetite, also known as lodestone, is a naturally occurring rock that is a magnet. This natural magnet was first discovered in a region known as magnesia and was named after the area in which it was discovered. Magnetism may be naturally present in a material or the material may be artificially magnetized by various methods. Magnets may be permanent or temporary. After being magnetized, a permanent magnet will retain the properties of magnetism indefinitely. A temporary magnet is a magnet made of soft iron, that is usually easy to magnetize; however, temporary magnets lose most of their magnetic properties when the magnetizing cause is discontinued. Permanent magnets are usually more difficult to magnetize, but they remain magnetized. Materials which can be magnetized are called ferromagnetic materials. We will talk more about making a magnet later on.
The applet below demonstrates magnetism in action: a magnet moves over various objects and magnetism attacts some of them to the magnet.
What Happens when you cut a magnet?
A magnet can be cut into smaller and smaller pieces indefinitely, and each piece will still act as a small magnet. Thus, the cause of magnetism must be from a property of the smallest particles of the material, the atoms. So what is it about the atoms of magnets, or objects that can be magnetized (ferromagnetic materials), that is different from the atoms of other material? For example, why is it that copper keys or aluminum soda cans cannot be magnetized? These questions will be explored in the upcoming pages.
Magnetic behavior refers to the properties and interactions exhibited by materials in the presence of a magnetic field. It is a fundamental aspect of physics and has numerous applications in various fields, including technology, medicine, and industry. Understanding magnetic behavior is crucial for developing magnetic materials, designing electronic devices, and studying the behavior of particles at the atomic and subatomic levels.
At its core, magnetism arises from the movement of charged particles, such as electrons, within a material. These charged particles generate magnetic fields, which can interact with other magnetic fields or with external magnetic fields. The behavior of a material in a magnetic field depends on its composition, structure, and temperature.
There are three main types of magnetic behavior observed in materials: diamagnetism, paramagnetism, and ferromagnetism. Additionally, there are other less common types such as antiferromagnetism and ferrimagnetism.
Diamagnetism is the weakest form of magnetism and is exhibited by all materials to some extent. Diamagnetic materials have no permanent magnetic moment and are weakly repelled by a magnetic field. When placed in a magnetic field, the orbital motion of electrons within the atoms generates an opposing magnetic field that causes the material to be repelled. This effect is typically very small and easily overshadowed by other forms of magnetism.
Paramagnetism is observed in materials that have unpaired electrons. These materials are weakly attracted to a magnetic field due to the alignment of their electron spins with the external field. However, paramagnetic materials do not retain any magnetization once the external field is removed. The strength of paramagnetism depends on factors such as the number of unpaired electrons and their mobility within the material.
Ferromagnetism is the strongest form of magnetism and is exhibited by certain materials such as iron, nickel, and cobalt. In ferromagnetic materials, groups of atoms called domains align their magnetic moments parallel to each other, resulting in a macroscopic magnetization. This alignment can be induced by an external magnetic field or occur spontaneously below a certain temperature called the Curie temperature. Ferromagnetic materials retain their magnetization even after the external field is removed, making them useful for applications such as permanent magnets.
Antiferromagnetism is a type of magnetic behavior observed in certain materials where adjacent atomic magnetic moments align in opposite directions, canceling each other out. As a result, antiferromagnetic materials do not exhibit any net magnetization. Ferrimagnetism is similar to ferromagnetism but with unequal magnetic moments in adjacent atomic groups, resulting in a net magnetization.
The study of magnetic behavior has led to the development of various theories and models to explain and predict magnetic properties. One such model is the Weiss theory, which describes ferromagnetism as arising from the interaction between atomic magnetic moments within a material. The Ising model is another important theoretical framework used to study magnetism, particularly in systems with discrete spins.
Understanding and controlling magnetic behavior have numerous practical applications. In technology, magnets are used in motors, generators, transformers, and magnetic storage devices such as hard drives. Magnetic resonance imaging (MRI) is a medical imaging technique that utilizes the behavior of atomic nuclei in a magnetic field to generate detailed images of the human body. Magnetic materials also find applications in data storage, sensors, actuators, and magnetic levitation systems.
In conclusion, magnetic behavior encompasses the properties and interactions exhibited by materials in the presence of a magnetic field. Diamagnetism, paramagnetism, and ferromagnetism are the three main types of magnetic behavior observed in materials. Understanding these behaviors is crucial for various technological advancements and scientific research.