Among magnetic materials,soft magnetic and hard magnetic materials are the two main types.In this article,we will explore these two materials,analyze their characteristics,and understand how they play an important role in our daily lives and in technology.
1. Soft magnetic materials
Soft magnetic materials are very easily magnetized,but they are also quickly demagnetize after the external magnetic field is removed.They typically have high electrical conductivity and low coercivity,which means they can respond easily to changes in external magnetic fields and readily change their own magnetic state.
①Pure Iron：Pure iron: Pure iron is the simplest soft magnetic material, with very weak magnetic properties. The chemical composition of pure iron is mainly iron, which contains a small amount of carbon and other impurity elements.
The magnetic properties of pure iron can be adjusted through heat treatment, such as annealing, which can change its magnetic properties. In terms of application, pure iron is mainly used to make iron cores for electrical appliances such as motors, transformers, and electromagnets.
However, its eddy current loss is large and is only suitable for DC iron cores.
②Silicon steel：Silicon steel is speciality steel used in the cores of electromagnetic devices such as motors, generators, and transformers because it reduces power loss.
It is an iron alloy with a silicon content of 1.0-4.5% and a carbon content of less than 0.08%.Compared to pure iron, silicon steel has lower power loss and higher magnetic permeability.
But its brittleness makes it difficult to process and easy to damage.
③Soft ferrite: Ferrites contain metals such as nickel, zinc, or manganese, which can lead to low coercivity. This type of ferrite is generally referred to as soft ferrite.Ferrites are mostly semiconductors, with a much higher electrical resistivity than general metal magnetic materials, which results in less eddy current loss.
Because of their comparatively low losses at high frequencies, they are extensively used in the cores of RF transformers and inductors in applications such as switched-mode power supplies and loopstick antennas used in AM radios.
2.Hard magnetic materials
Hard magnetic materials have high remanence and high coercivity. This means that once hard magnetic materials are magnetized, they will remain in this state even after the external magnetic field disappears. Therefore, hard magnetic materials are also known as permanent magnetic materials.
①Hard ferrite:Compared to soft ferrite, hard ferrite has high coercivity and high remanence after magnetization.Iron oxide and barium carbonate or strontium carbonate are used in manufacturing of hard ferrite magnets.
The maximum magnetic field B is about 0.35 tesla and the magnetic field strength H is about 30–160 kiloampere turns per meter (400–2000 oersteds). The density of ferrite magnets is about 5 g/cm3.
Although compared to rare earth permanent magnet materials, the performance of hard ferrite is poor. But the price of hard ferrite is very cheap, which makes it widely used in daily necessities such as refrigerator magnets.
②Iron chromium cobalt (FeCrCo): Iron chromium cobalt is known as the “transformer” in permanent magnet materials. This material has excellent ductility and is easy to metal process, which is a huge advantage compared to other permanent magnet materials. Due to this characteristic, it can be used to make components with a minimum size of approximately 0.05mm. This makes it applicable in various micro devices, such as micro motors, micro relays, etc. It contains 20% to 33% chromium, 3% to 25% cobalt, 3% molybdenum, and 0.7% to 1.0% silicon.
Its disadvantage is that its magnetic properties are not strong, and the maximum magnetic energy product is only about 6.0 MGOe.
③Samarium cobalt magnet (SmCo): Samarium cobalt magnet is a collective term for the first and second generation rare earth permanent magnets, which have high coercivity and corrosion resistance, and can operate at temperatures up to 250-350 ℃. Samarium cobalt magnets are commonly used in heavy-duty and high-temperature applications, such as marine motors and generators, and train traction motors.
The content of samarium and cobalt in samarium cobalt magnets accounts for 70-80%. The high prices of these two materials have led to higher manufacturing costs. Comparing the prices of samarium cobalt magnets with neodymium magnets of the same size and performance, the price of samarium cobalt magnets is 1.5 to 2 times higher than that of neodymium iron boron.
④Neodymium magnet（NdFeB）:Neodymium magnets, also known as NdFeB, NIB, or Neo magnets.It is a permanent magnet made of alloys of neodymium, iron, and boron to form a Nd2Fe14B tetragonal crystal structure.
Neodymium magnet is the third generation rare earth permanent magnet material and currently the most magnetic magnet. It has the characteristics of high remanence and high magnetic energy product, which makes it widely used in various devices. The maximum magnetic energy product of neodymium magnets is 52MGOe, while that of samarium cobalt magnets is 32MGOe, indicating that the magnetism of neodymium magnets is much higher than that of the previous generation.
Each new energy electric vehicle requires approximately 2.5kg of neodymium magnets, which is mainly used for manufacturing components such as drive motors, ABS, EPS, etc. This material has excellent performance, can significantly improve motor energy efficiency, reduce energy loss, and is currently one of the essential materials for manufacturing top-level motors. In addition, equipment such as speakers and generators that require permanent magnets to generate magnetic fields have significant performance improvements after using neodymium magnets.
Although the performance of neodymium magnets is impressive, their coercivity is relatively low compared to other rare earth permanent magnet materials, with a maximum operating temperature of around 230 ℃. Working in high-temperature environments can lead to performance degradation, leading to a decrease in the operating efficiency of the machine.
Whether they are soft magnetic materials or hard magnetic materials, they are widely used in electric power, communications, motors, computers, aerospace and other industries. They are an indispensable part of modern technology.
Soft magnetic materials and hard magnetic materials are often used in combination. For example, in power transformers, silicon steel sheets are used as soft magnetic materials to make the core of the transformer, while neodymium magnets or other hard magnetic materials are used to provide a stable magnetic field. In electric motors, soft magnetic materials are used to make the stator windings, while hard magnetic materials are used to make the rotor.
In summary, soft magnetic materials and hard magnetic materials are two important categories of magnetic materials. Each has unique properties and applications and plays a key role in a variety of components. By combining soft and hard magnetic materials, we can achieve efficient transmission, conversion and control of energy, providing important support for the energy and industrial development of modern society.
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