Permanent Magnets | SDM Magnetics Co., Ltd.

Ι What are Permanent Magnets?

Magnets are materials that generate their own magnetic fields. The term “magnet” originates from Magnesia, Greece, where lodestone was first mined. Magnets are generally categorized into two types: temporary and permanent. Temporary magnets display magnetic properties only when exposed to an external magnetic field. In contrast, permanent magnets are capable of producing persistent magnetic fields and maintaining their magnetism over extended periods without requiring an external field.

The earliest known application of a permanent magnet was the “south pointer” (compass), a spoon-shaped lodestone device. Today, permanent magnets serve as essential components in a broad array of electromechanical devices, such as motors, generators, loudspeakers, instruments, and sensors, which are integral to products spanning from automobiles and consumer electronics to medical devices and renewable energy systems.

History of Permanent Magnets

Since the 19th century, the theory of magnetism has advanced rapidly, with new magnetic materials being continually discovered. As essential functional materials, they have been widely applied across diverse fields. It can be argued that modern sectors like the power industry, industrial automation, and information technology could not exist without magnetic materials. Permanent magnets, soft magnetic materials, and magnetic recording materials are recognized as the three main categories of magnetic materials. Along with magnetic refrigeration materials, magnetostrictive materials, magnetic absorbing materials, and emerging spin-electronic materials, they comprise the vast family of magnetic materials. Permanent magnetic materials, also known as hard magnetic materials, are the earliest type of magnetic material employed in human history.

Unlike many other fields, magnetism transitioned from practical technology to scientific understanding. The Chinese crafted compasses from lodestone as far back as 300 BC. Yet, while humans have long harnessed the magnetic properties of substances, it was only in the 19th century that the comprehension of magnetism elevated to a theoretical plane, spurring its swift progress.

1820: Danish physicist Hans Christian Ørsted discovered the magnetic effect of electric current, becoming the first to demonstrate the relationship between electricity and magnetism.

1820: French physicist André-Marie Ampère demonstrated that a current-carrying coil can generate a magnetic field and elucidated the interaction forces between current-carrying conductors.

1824: British engineer William Sturgeon invented the electromagnet.

1831: British scientist Michael Faraday discovered electromagnetic induction, revealing the inherent connection between electricity and magnetism and laying the theoretical foundation for the application of electromagnetic technology.

1860s: Scottish scientist James Clerk Maxwell established the unified electromagnetic field theory and formulated Maxwell’s equations. From that point onward, human understanding of magnetic phenomena truly began to advance rapidly.

The development of magnetism theory also spurred accelerated research into the magnetic properties of materials.

1845: Michael Faraday classified magnetism in matter into diamagnetism, paramagnetism, and ferromagnetism based on differences in magnetic susceptibility.

1898: French physicist Pierre Curie investigated the relationship between diamagnetism, paramagnetism, and temperature, leading to the formulation of the renowned Curie’s law.

1905: French physicist Paul Langevin applied classical statistical mechanics to explain the temperature dependence of type I paramagnetism. Subsequently, another French physicist, Léon Brillouin, accounted for the discontinuity of magnetic energy and proposed a semiclassical theory of paramagnetism building upon Langevin’s work.

1907: French physicist Pierre-Ernest Weiss developed the molecular field theory and introduced the concept of magnetic domains, drawing inspiration from the theories of Langevin and Brillouin. This molecular field theory and the idea of magnetic domains are considered the cornerstone of modern ferromagnetic theory, giving rise to two major research areas: spontaneous magnetization theory and technical magnetization theory.

1928: German physicist Werner Heisenberg established the exchange interaction model, elucidating the essence and origin of the molecular field.

1936: Soviet physicist Lev Davidovich Landau completed his seminal work, “Course of Theoretical Physics,” which comprehensively and systematically summarized modern electromagnetism and ferromagnetic theory. Shortly thereafter, French physicist Louis Néel introduced the concepts and theories of antiferromagnetism and ferrimagnetism.

Meanwhile, ferromagnetic theory has played an increasingly significant role in the research and development of permanent magnet.

1917: Japanese inventor Kotaro Honda invented KS steel.

1931: Japanese metallurgist Tokushichi Mishima invented MK steel, which can be regarded as the pioneer of AlNiCo magnets. AlNiCo magnets, also known as the first generation of permanent magnet.

1933: Yogoro Kato and Takeshi Takei co-invented ferrite magnets. Ferrite magnets represent the second generation of permanent magnet and still hold a substantial market share today.

1967: Karl J. Strnat, along with his colleagues, discovered the 1:5 type rare earth cobalt alloy. The magnetic properties of sintered 1:5 type rare earth cobalt magnets are many times superior to those of AlNiCo magnets. This marked the emergence of the first generation of rare earth permanent magnet.

1977: Teruhiko Ojima from TDK Corporation achieved great success in developing 2:17 type sintered Samarium Cobalt magnets, heralding the birth of the second generation of rare earth permanent magnet.

1983: Japanese scientist Masato Sagawa and American scientist John Croat independently invented sintered Neodymium magnets and melt-spun NdFeB powder, respectively. As the third generation of rare earth permanent magnet, the advent of Neodymium magnets significantly advanced related fields.