|MadSci Network: Physics|
The solution: Generally speaking, elements and even compounds are divided into three categories: 1-Paramagnetic 2-Diamagnetic 3-Ferromagnetic Before going into details, there is a theory in chemistry called quantum numbers. This theory explains that the electrons are not at rest, but they are rotating and spinning in their atomic orbitals. This spin causes a magnetic field. This magnetic field is manifested only if the electron is not paired. (It is well known that the old theory that claimed that the electrons rotate in circular paths is no longer valid. The new theories says that the electrons exist in so called orbitals, which is a space that can contain up to 2 electrons. If the one electron exists, the magnetic properties will be manifested.) Returning back to our questions, the first category is for the elements or compounds that show some magnetic properties under certain conditions. These materials have unbalanced (unpaired) electron(s) in their orbitals. These unpaired electrons spin, and their spinning creates magnetic fields. Each molecule, hence, forms a magnet. Thus if a magnetic field is applied to these molecular magnets, they will arrange themselves and align to increase this effect. This type of magnetism is far weaker than the one due to Iron and some other compounds. Experimentally, paramagnetic property was found to directly proportional to the applied magnetic field, and inversely proportional to the temperature (Curie's law). There is a famous example in nearly all Physics and Chemistry textbooks showing liquid oxygen being poured between magnetic poles; oxygen is seen being attracted to the poles. The other type is diamagnetism. These are materials that have their electrons paired in their orbitals, thus their magnetic effect cancels out. However, if a magnetic field is applied to such a material, the fields in the atom will be disturbed causing a weak magnetic field to appear, which is far weaker than the one due to paramagnets. The last type is ferromagnetism. Iron, Cobalt, gadolinium, dysprosium, and Nickel show ferromagnetic properties. These are the materials used to fabricate permanent magnets. In addition to the unpaired electrons, these materials have other magnetic properties described by the Domain theory. This theory proposes that these materials contain microscopic regions called domains, within which the magnetic fields due to atoms are aligned. Their volumes is about 10E-12 to 10E-8 cubic meters. Under normal conditions, domains are randomly oriented, and they have no magnetic effect. However, when they are put in a magnetic field, they tend to perfectly arrange themselves. So maximum magnetic property is achieved. In order to magnetize one of these elements, we use a magnet and we move it on the ferromagnetic metal in one direction; so that domains can be arranged. Or this is done using the magnetic field created from a solenoid, and using it to arrange the domains in one direction. Returning back to your questions. Why is it that only Iron (and it's products, e.g. Steel) is magnetic? Could Titanium (for example) become ionized to the point of being magnetic? Does this happen in nature, or via man-made methods which I just don't know about? What are all metals that can become magnets? Why or why not? I guess you can now attribute the answer of every question to a part in my discussion. However, I would like to point out that the magnetic property is because of the electrons and their pairing, because, as I said, oxygen for example may show magnetic properties. So, if you want to know the magnetism of an element or a compound, look at its electron configuration and you will know how to categorize it. ========================================================================== References: Abbott, A.F. Ordinary Level Physics. Heinemann Educational Books, London. Fourth edition 1984. Blume, Martin. Magnetism. Encyclopaedia Encarta 1997. Microsoft Corporation. Petrucci, Ralph H and Harwood, William. General Chemistry: principles and modern applications. Prentice Hall International, INC, USA. Seventh edition 1997. Serway, Raymond. Physics for Scientists and Engineers. Saunders Collage publishing, USA. Third updated edition 1990. Looking forward to your reply, Moataz Attallah The American University in Cairo firstname.lastname@example.org ========================================================================= P.S.: This is a very good article from Microsoft Encyclopeadia Encarta 97about Magnetism Contributed by: Martin Blume Magnetism, an aspect of electromagnetism, one of the fundamental forces of nature. Magnetic forces are produced by the motion of charged particles such as electrons, indicating the close relationship between electricity and magnetism. The unifying frame for these two forces is called electromagnetic theory . The most familiar evidence of magnetism is the attractive or repulsive force observed to act between magnetic materials such as iron. More subtle effects of magnetism, however, are found in all matter. In recent times these effects have provided important clues to the atomic structure of matter. History of Study The phenomenon of magnetism has been known of since ancient times. The mineral lodestone (see Magnetite), an oxide of iron that has the property of attracting iron objects, was known to the Greeks, Romans, and Chinese. When a piece of iron is stroked with lodestone, the iron itself acquires the same ability to attract other pieces of iron. The magnets thus produced are polarized-that is, each has two sides or ends called north-seeking and south-seeking poles. Like poles repel one another, and unlike poles attract. The compass was first used for navigation in the West some time after AD 1200. In the 13th century, important investigations of magnets were made by the French scholar Petrus Peregrinus. His discoveries stood for nearly 300 years, until the English physicist and physician William Gilbert published his book Of Magnets, Magnetic Bodies, and the Great Magnet of the Earth in 1600. Gilbert applied scientific methods to the study of electricity and magnetism. He pointed out that the earth itself behaves like a giant magnet, and through a series of experiments, he investigated and disproved several incorrect notions about magnetism that were accepted as being true at the time. Subsequently, in 1750, the English geologist John Michell invented a balance that he used in the study of magnetic forces. He showed that the attraction and repulsion of magnets decrease as the squares of the distance from the respective poles increase. The French physicist Charles Augustin de Coulomb, who had measured the forces between electric charges, later verified Michell's observation with high precision. Electromagnetic Theory In the late 18th and early 19th centuries, the theories of electricity and magnetism were investigated simultaneously. In 1819 an important discovery was made by the Danish physicist Hans Christian Oersted, who found that a magnetic needle could be deflected by an electric current flowing through a wire. This discovery, which showed a connection between electricity and magnetism, was followed up by the French scientist André Marie Ampère, who studied the forces between wires carrying electric currents, and by the French physicist Dominique François Jean Arago, who magnetized a piece of iron by placing it near a current-carrying wire. In 1831 the English scientist Michael Faraday discovered that moving a magnet near a wire induces an electric current in that wire, the inverse effect to that found by Oersted: Oersted showed that an electric current creates a magnetic field, while Faraday showed that a magnetic field can be used to create an electric current. The full unification of the theories of electricity and magnetism was achieved by the English physicist James Clerk Maxwell, who predicted the existence of electromagnetic waves and identified light as an electromagnetic phenomenon. Subsequent studies of magnetism were increasingly concerned with an understanding of the atomic and molecular origins of the magnetic properties of matter. In 1905 the French physicist Paul Langevin produced a theory regarding the temperature dependence of the magnetic properties of paramagnets (discussed below), which was based on the atomic structure of matter. This theory is an early example of the description of large-scale properties in terms of the properties of electrons and atoms. Langevin's theory was subsequently expanded by the French physicist Pierre Ernst Weiss, who postulated the existence of an internal, "molecular" magnetic field in materials such as iron. This concept, when combined with Langevin's theory, served to explain the properties of strongly magnetic materials such as lodestone. After Weiss's theory, magnetic properties were explored in greater and greater detail. The theory of atomic structure of Danish physicist Niels Bohr, for example, provided an understanding of the periodic table and showed why magnetism occurs in transition elements such as iron and the rare earth elements, or in compounds containing these elements. The American physicists Samuel Abraham Goudsmit and George Eugene Uhlenbeck showed in 1925 that the electron itself has spin and behaves like a small bar magnet. (At the atomic level, magnetism is measured in terms of magnetic moments-a magnetic moment is a vector quantity that depends on the strength and orientation of the magnetic field, and the configuration of the object that produces the magnetic field.) The German physicist Werner Heisenberg gave a detailed explanation for Weiss's molecular field in 1927, on the basis of the newly-developed quantum mechanics (see Quantum Theory). Other scientists then predicted many more complex atomic arrangements of magnetic moments, with diverse magnetic properties. The Magnetic Field Objects such as a bar magnet or a current-carrying wire can influence other magnetic materials without physically contacting them, because magnetic objects produce a magnetic field. Magnetic fields are usually represented by magnetic flux lines. At any point, the direction of the magnetic field is the same as the direction of the flux lines, and the strength of the magnetic field is proportional to the space between the flux lines. For example, in a bar magnet, the flux lines emerge at one end of the magnet, then curve around the other end; the flux lines can be thought of as being closed loops, with part of the loop inside the magnet, and part of the loop outside. At the ends of the magnet, where the flux lines are closest together, the magnetic field is strongest; toward the side of the magnet, where the flux lines are farther apart, the magnetic field is weaker. Depending on their shapes and magnetic strengths, different kinds of magnets produce different patterns of flux lines. The pattern of flux lines created by magnets or any other object that creates a magnetic field can be mapped by using a compass or small iron filings. Magnets tend to align themselves along magnetic flux lines. Thus a compass, which is a small magnet that is free to rotate, will tend to orient itself in the direction of the magnetic flux lines. By noting the direction of the compass needle when the compass is placed at many locations around the source of the magnetic field, the pattern of flux lines can be inferred. Alternatively, when iron filings are placed around an object that creates a magnetic field, the filings will line up along the flux lines, revealing the flux line pattern. Magnetic fields influence magnetic materials, and also influence charged particles that move through the magnetic field. Generally, when a charged particle moves through a magnetic field, it feels a force that is at right angles both to the velocity of the charged particle and the magnetic field. Since the force is always perpendicular to the velocity of the charged particle, a charged particle in a magnetic field moves in a curved path. Magnetic fields are used to change the paths of charged particles in devices such as particle accelerators and mass spectrometers. Kinds of Magnetic Materials The magnetic properties of materials are classified in a number of different ways. One classification of magnetic materials-into diamagnetic, paramagnetic, and ferromagnetic-is based on how the material reacts to a magnetic field. Diamagnetic materials, when placed in a magnetic field, have a magnetic moment induced in them that opposes the direction of the magnetic field. This property is now understood to be a result of electric currents that are induced in individual atoms and molecules. These currents, according to Ampere's law, produce magnetic moments in opposition to the applied field. Many materials are diamagnetic; the strongest ones are metallic bismuth and organic molecules, such as benzene, that have a cyclic structure, enabling the easy establishment of electric currents. Paramagnetic behavior results when the applied magnetic field lines up all the existing magnetic moments of the individual atoms or molecules that make up the material. This results in an overall magnetic moment that adds to the magnetic field. Paramagnetic materials usually contain transition metals or rare earth elements that possess unpaired electrons. Paramagnetism in nonmetallic substances is usually characterized by temperature dependence; that is, the size of an induced magnetic moment varies inversely to the temperature. This is a result of the increasing difficulty of ordering the magnetic moments of the individual atoms along the direction of the magnetic field as the temperature is raised. A ferromagnetic substance is one that, like iron, retains a magnetic moment even when the external magnetic field is reduced to zero. This effect is a result of a strong interaction between the magnetic moments of the individual atoms or electrons in the magnetic substance that causes them to line up parallel to one another. In ordinary circumstances these ferromagnetic materials are divided into regions called domains; in each domain, the atomic moments are aligned parallel to one another. Separate domains have total moments that do not necessarily point in the same direction. Thus, although an ordinary piece of iron might not have an overall magnetic moment, magnetization can be induced in it by placing the iron in a magnetic field, thereby aligning the moments of all the individual domains. The energy expended in reorienting the domains from the magnetized back to the demagnetized state manifests itself in a lag in response, known as hysteresis. Ferromagnetic materials, when heated, eventually lose their magnetic properties. This loss becomes complete above the Curie temperature, named after the French physicist Pierre Curie, who discovered it in 1895. (The Curie temperature of metallic iron is about 770° C/1300° F.) Other Magnetic Orderings In recent years, a greater understanding of the atomic origins of magnetic properties has resulted in the discovery of other types of magnetic ordering. Substances are known in which the magnetic moments interact in such a way that it is energetically favorable for them to line up antiparallel; such materials are called antiferromagnets. There is a temperature analogous to the Curie temperature called the Neel temperature, above which antiferromagnetic order disappears. Other, more complex atomic arrangements of magnetic moments have also been found. Ferrimagnetic substances have at least two different kinds of atomic magnetic moments, which are oriented antiparallel to one another. Because the moments are of different size, a net magnetic moment remains, unlike the situation in an antiferromagnet where all the magnetic moments cancel out. Interestingly, lodestone is a ferrimagnet rather than a ferromagnet; two types of iron ions, each with a different magnetic moment, are in the material. Even more complex arrangements have been found in which the magnetic moments are arranged in spirals. Studies of these arrangements have provided much information on the interactions between magnetic moments in solids. Applications Numerous applications of magnetism and of magnetic materials have arisen in the past 100 years. The electromagnet, for example, is the basis of the electric motor and the transformer. In more recent times, the development of new magnetic materials has also been important in the computer revolution. Computer memories can be fabricated using bubble domains. These domains are actually smaller regions of magnetization that are either parallel or antiparallel to the overall magnetization of the material. Depending on this direction, the bubble indicates either a one or a zero, thus serving as the units of the binary number system used in computers. Magnetic materials are also important constituents of tapes and disks on which data are stored. In addition to the atomic-sized magnetic units used in computers, large, powerful magnets are crucial to a variety of modern technologies. Magnetic levitation trains use strong magnets to enable the train to float above the track so that there is no friction between the vehicle and the tracks to slow the train down. Powerful magnetic fields are used in nuclear magnetic resonance imaging, an important diagnostic tool used by doctors. Superconducting magnets are used in today's most powerful particle accelerators to keep the accelerated particles focused and moving in a curved path. ==================================================================== please email me if you need any further help Moataz Attallah
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