Ferromagnetism
Ferromagnetism is a physical phenomenon exhibited by certain materials, such as iron and cobalt, that leads to magnetization below a specific temperature known as the Curie temperature. It is recognized as the strongest form of magnetism, enabling significant magnetic forces that can be felt in interactions between magnets. Ferromagnetic materials can retain their magnetic properties even after an external magnetic field is removed, a feature known as spontaneous magnetization. This phenomenon occurs at a molecular level, influenced by the arrangement of atoms and unpaired electrons within the material.
Historically, ferromagnetism was first identified with naturally occurring lodestones, which are magnetite rocks that align themselves with Earth's magnetic field. The term "ferromagnetic" emerged in the mid-19th century, highlighting iron's prominent role in this phenomenon. The understanding of ferromagnetism has evolved, with key contributions from scientists like Pierre Curie and Aleksandr Stoletov, who studied magnetic behavior and introduced concepts like the Stoletov Curve.
Ferromagnetic materials have a wide range of applications in modern technology, including the creation of permanent magnets, magnetic recording media, and medical devices such as MRI machines. The principles of ferromagnetism are foundational to numerous everyday technologies, illustrating the importance of this physical property in various fields.
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Ferromagnetism
Ferromagnetism is a phenomenon demonstrated by certain materials, including iron and cobalt, that causes magnetization below a specific temperature. Magnetism occurs on a molecular level, specifically the arrangement of a material's atoms and their electrons. Ferromagnetism is the strongest type of magnetism, creating a force that is strong enough to be felt—for example, the attraction or repulsion between two magnets. It is the process by which permanent magnets are created by these materials and through which they become attracted to magnets. Common interactions with magnets, including refrigerator magnets, electromagnets, and credit card strips, is due to ferromagnetism.
Ferromagnetism occurs in both hard and soft materials, which refers to the ease with which a material magnetizes. Although iron is the most common example, it is also possible to create a measurable ferromagnetic field in alloys whose parts are themselves not necessarily magnetic. Ferromagnetic materials may also serve as conductors, insulators, or semiconductors. An important aspect of ferromagnetism is the presence of spontaneous magnetization, which is when an object or substance retains magnetic characteristics after it is removed from the magnetic field.
Brief History
Magnets have been a tool of humankind since ancient times, despite early humans' lack of understanding of its mechanics. Some scholars argue that magnetism was the first natural force to be discovered and utilized by humans. Ancient Greeks, Chinese, Arabs, and South Americans recognized that specific types of rock attracted iron and other rocks of the same material. These rocks, known as lodestone, would always point in a north-south direction when placed in water or on a hard, flat surface. Lodestone is made of magnetite and is one of the iron oxides, which are chemical compounds composed of iron and oxygen. It is naturally magnetic because of its response to Earth's magnetic field. Chinese mariners used pieces of lodestone to create primitive compasses, which they perfected over many centuries.
Lodestones were used to magnetize specific objects, such as iron needles, which were used in compasses. During his historic voyage in the fifteenth century, Christopher Columbus carried a large lodestone along with a supply of iron needles on his ship. The needles were rubbed along the lodestone, creating spontaneous magnetization. The needles could then be used in navigating across the Atlantic Ocean.
The term ferromagnetic was first used in the mid-nineteenth century. It combines the word ferro (from the Latin ferrum), meaning "iron," as it was the most common example of this phenomena, and magnetic, which also has roots in Latin and Greek. Russian physicist Aleksandr Stoletov studied magnetism, mathematics, and physics extensively both in Russian university and abroad. He completed his doctoral dissertation in 1871 – 1872 on his research regarding the magnetic properties of iron and the behavior of magnetic fields. His work demonstrated that the magnetism of a ferromagnet increased proportionally to the applied magnetizing field, eventually reaching a maximum before decreasing. This behavior is demonstrated by the Stoletov Curve, which measures the permeability of ferromagnetics.
Overview
Lodestone, and thus magnetite, is a type of iron oxide, the chemical compound of iron and oxygen. Lodestone forms in bands and is naturally magnetic because of its response to Earth's magnetic field.
William Gilbert, an English astronomer and physicist, first theorized the existence of a magnetic field within the planet in 1600. Gilbert offered this conclusion after extensive studies seeking to understand how compasses and lodestones worked. Earth's magnetism is thought to be related to the current within the liquid core of the planet. The poles of a magnet work in correlation to the geographic poles of Earth because the north pole of a magnet is attracted to Earth's magnetic field. The motion within the molecular structure of the magnet creates a magnetic field, which is a space where a magnetic force is exerted. All magnets have static magnetic fields, as well as two poles: north and south. Like poles repel each other. In ferromagnetic materials, this repulsion can be felt if one attempts to touch two north or two south poles together. The north pole of a compass magnet is thus attracted to the south pole of Earth's magnetic field, which is Earth's geographic North Pole.
Ferromagnetic materials include cobalt, iron, nickel, and some rare earth and actinide elements. Ferromagnetism occurs due to two specific quantum mechanical effects: the Pauli Exclusion Principle and spin. Both concepts refer to the motion and structure of subatomic electrons. The Pauli Exclusion Principle states that no two electrons in an atom can have the same quantum numbers at the same time. At the subatomic level, atoms are composed of three types of small particles: protons and neutrons within the center, and electrons that spin in orbit around the atom. These electrons carry a charge, If the electrons are not paired with other electrons, they spin. This creates ferromagnetism when they are drawn into alignment with other unpaired electrons within a magnetic force.
The Curie temperature (or Curie point), discovered in the late nineteenth century by Pierre Curie, is a specific temperature at which ferromagnetic substances are no longer ferromagnetic. For example, iron has a lower Curie temperature than cobalt. Upon being heated to the Curie temperature, magnetization weakens and permanent magnetization disappears. This is due to the heat's disruption of the ions at the atomic level of the material. Magnets are created when the poles of individual atoms within the ferromagnetic material become aligned with the lines of a magnetic field. Once the material's temperature drops below its Curie temperature, it may regain its magnetism if placed in a strong magnetic field.
The field of ferromagnetism was furthered by the Weiss theory, proposed in 1907, which focuses on the existence of domains within ferromagnetic materials. These domains are usually only between 0.01 and 0.1 cm wide and are spontaneously magnetized when a strong internal magnetic interaction aligns at an atomic level within the domain. Ultimately, ferromagnetism and its materials led to the development of technology that has become commonplace and important in the twenty-first century.
The ability of a ferromagnet to remember its magnetic history is called hysteresis. This has allowed researchers to develop many useful applications for magnetized materials. Maintaining magnetism after the driving magnetic force has been applied has led to the ability to create magnetic recording media, which is used in telephones, computer hard disks, audio cassettes, and many other applications. It has also made possible the development of electromagnets, a tool in which magnets are used to interrupt or engage an electric circuit. Medical science has benefited from ferromagnetic developments, such as the magnetic resonance imaging (MRI) machine.
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