Wesentliche elektronische Materialien: Teil 7 - Magnetische Werkstoffe

1 Introduction to Magnetic Materials

Magnetic materials are substances that exhibit magnetic properties due to their internal structure, which allows them to generate a magnetic field or be affected by an external magnetic field. These materials can either attract or repel other materials, and their magnetic behavior is fundamental to many modern electronic devices.

Magnetic materials are indispensable in the electronics industry due to their ability to store, transfer, and convert energy. They are used in various applications, from energy-efficient devices to advanced communication technologies. These materials are crucial for components such as motors, transformers, sensors, magnetic storage devices, and antennas, making them essential for industries such as electronics, telecommunications, energy, automotive, and healthcare.

2 Types of Magnetic Materials Used in Electronics

2.1 Hard Magnetic Materials (Permanent Magnets)

‌Hard magnetic materials, also known as permanent magnetic materials, are materials that can maintain their magnetic properties for a long time after magnetization and do not easily lose their magnetic properties. The main characteristics of hard magnetic materials are that they can maintain their original magnetism for a long time after magnetization, have large coercivity (Hc=10^4~10^6 A/m), thicker hysteresis lines, and high maximum magnetic energy product (BH)max and remanent magnetism.

2.1.1 Alnico alloys

Alnico alloys are commonly used permanent magnetic materials with high coercivity and remanent magnetism. The main advantages of Alnico alloys as permanent magnets include high coercivity, high Curie temperature, and good temperature stability. Alnico alloys have high coercivity and can maintain their magnetic properties under the action of a strong external magnetic field and are not easily demagnetized. In addition, its Curie temperature is as high as 860°C, and its maximum operating temperature is 525-550°C, which enables it to maintain good magnetic properties under high-temperature environments. Alnico has a high remanent magnetism and can maintain its magnetic properties in stronger magnetic fields. It has good corrosion resistance and can be used in harsh environments. The demagnetization curve of Alnico alloys varies non-linearly, which means that they exhibit different properties during the demagnetization process.

Fig. 1 Alnico Alloy Magnet

2.1.2 Titanium-cobalt alloy

Titanium-cobalt alloy is one of the more common types of permanent magnets. Titanium-cobalt alloys can maintain high magnetic induction (1.0-1.25 T) and magnetic energy product (2.2×10⁵ erg/cm³) in the range of magnetic field strength up to 8.75-11.94 kA/m. This excellent hysteresis property allows Ti-Co alloys to have low energy loss during magnetic field reversal, which improves energy conversion efficiency and is particularly suitable for motor systems with frequent variable loads. Titanium-cobalt alloys are capable of achieving a magnetic induction of up to 1.25 T in the operating field strength range of 8.75-11.94 kA/m. This high magnetic induction strength enables the production of strong magnetic moments and increased efficiency when operating in high magnetic fields. Titanium-cobalt alloys can maintain their magnetic properties at higher temperatures and do not demagnetize significantly, even in high-temperature environments. This allows them to excel in electric motors and generators operating at high or fluctuating temperatures, ensuring reliable operation. Titanium-cobalt alloys can meet high magnetic properties while maintaining high mechanical strength and high temperature resistance through precisely proportioned chemical compositions (e.g., cobalt, vanadium and other elements). This allows them to excel in a wide range of complex operating conditions.

Fig. 2 Titanium-Cobalt Alloy

2.1.3 Rare earth cobalt permanent magnets

Rare earth cobalt permanent magnets are of two types, RCo5 and R2Co17, where R stands for rare earth elements such as samarium, praseodymium, cerium and lanthanum, etc. The former has a CaCu5 hexagonal crystal structure and the latter has a tripartite crystal structure. The former is CaCu5 type hexagonal crystal system structure, the latter is a tripartite crystal system structure.RCo5 type is characterized by high magnetic crystal anisotropy, R2Co17 type is characterized by high magnetic induction strength and Curie point, by iron, copper and other elements partially replace the cobalt, has been made into a very high-performance material.

Cobalt magnets are characterized by extremely high coercivity and magnetic energy products, are a class of permanent magnets with excellent performance. The preparation process mainly adopts the powder method and casting method, and the powder method adopts the magnetic field molding, hydrostatic pressure and liquid phase sintering and other processes. Mainly used in traveling wave tubes, magnetrons, and other electric vacuum devices and microwave devices such as circulators to provide the magnetic field. It is also widely used in the fields of micro-motors, micro-relays, magnetic bearings, electronic watches, and other small precision instruments and meters.

Fig. 3 Rare Earth Cobalt Permanent Magnets

2.2 Soft Magnetic Materials

Soft magnetic materials refer to when the magnetization occurs at Hc is not greater than 1000A/m, such materials are called soft magnets. Typical soft magnetic materials can achieve maximum magnetization strength with the minimum external magnetic field. Soft magnetic material is a magnetic material with low coercivity and high permeability. Soft magnetic materials are easy to magnetize and demagnetize and are widely used in electrical and electronic equipment. The most widely used soft magnetic materials are iron-silicon alloys (silicon steel sheet) and a variety of soft magnetic ferrites and so on.

2.2.1 Silicon steel soft magnet

Silicon steel soft magnet has several significant advantages, making it widely used in the power electronics industry. First, the high saturation magnetic induction of silicon steel means that less material cross-section can be used under the same magnetic flux conditions, which effectively saves material and enables miniaturization of components. Secondly, silicon steel has low magnetic losses, especially in AC magnetic fields, and its high resistivity effectively reduces eddy current losses, while low hysteresis losses ensure excellent performance during operation. In addition, silicon steel also has good processing performance, easy to be processed into sheet materials, suitable for punching, cutting and other processing techniques, common forms include cold rolled silicon steel sheet, cold rolled non-oriented electrical steel strip and cold rolled oriented electrical steel strip, widely used in electronic systems and home appliances in the low-frequency transformers and chokes and other components. Finally, silicon steel performs particularly well in low-frequency, high-power applications, especially in cores for power transformers, distribution transformers and current transformers, which are commonly used in power electronics with frequencies up to 400Hz.

Fig. 4 Silicon Steel Soft Magnet

2.2.2 Soft magnetic ferrite

Soft magnetic ferrite is characterized by low saturation flux density, low permeability, low Curie temperature, low loss at medium and high frequencies, and low cost. The first three low is its shortcomings, limiting the scope of its use, and now (early 21st century) is trying to improve. The last two lows are its advantages, facilitating access to the high-frequency market, which is now (at the beginning of the 21st century) being worked on for expansion.

Fig. 5 Soft Magnetic Ferrite

Soft magnetic materials are widely used in electronics because of their excellent magnetic properties. They are commonly used as core materials for transformers, inductors, and current and voltage transformers, where their low hysteresis loss and high saturation magnetic induction strength improve the efficiency of these components and reduce energy loss. Soft magnetic materials are also widely used in the stator and rotor sections of electric motors and generators to enhance power density and efficiency, especially in high-frequency motors. In addition, they are used for electromagnetic shielding to reduce electromagnetic interference (EMI) in electronic equipment and ensure stable operation. Soft magnetic materials also play an important role in induction heating technology, improving heating efficiency by interacting with high-frequency currents in a wide range of applications such as metal heating, plastic molding and welding. In power management systems, soft magnetic materials are used in filters and power supply equipment to improve stability and efficiency through their low magnetic loss characteristics. In addition, soft magnetic materials are used in magnetic sensors, passive components and other electronic assemblies, such as position sensors, speed sensors, and magnetic capacitors and switches. Overall, with their excellent magnetic properties and processability, soft magnetic materials play a key role in the electronics industry in a variety of areas, from power management to communications, automation and medical devices.

2.3 Magnetic Alloys

Magnet alloys are alloys composed of iron and other metal elements (e.g. cobalt, nickel, rare earth elements, etc.), which have excellent magnetic properties and are widely used in many fields, such as electronics, communications, and energy. According to the different magnetic properties, magnet alloys are usually divided into two categories: soft magnetic alloys and hard magnetic alloys.

Soft Magnetic Alloys: These alloys are characterized by low hysteresis loss and good permeability, making them excellent for applications such as transformers, motors, and inductors. Common soft magnetic alloys such as silicon steel and iron-nickel alloys are mainly used in power electronics, home appliances, automotive electronics and other fields.

Hard Magnetic Alloys: Hard magnetic alloys have high magnetic energy product and magnetic field strength, can maintain stable magnetic properties, and are usually used in the manufacture of permanent magnets. Common hard magnetic alloys include neodymium-iron-boron (NdFeB), aluminum-nickel-cobalt (AlNiCo) and cobalt-based alloys. They are widely used in high-tech fields such as electric motors, sensors, loudspeakers, and magnetic resonance imaging (MRI).

Magnet alloys show different performance characteristics in practical applications. For example, neodymium-iron-boron (NdFeB) magnets have become indispensable materials in modern industry and electronics with their high magnetic energy product and powerful magnetic force, and are widely used in electric motors, wind turbines, speakers and other products. Alnico alloys, on the other hand, are commonly used for magnetic components in high-temperature and special environments due to their good temperature resistance and stability.

Fig. 6 Neodymium-Iron-Boron (NdFeB) Magnets

3 Properties of Magnetic Materials for Electronics

3.1 Magnetic permeability

Magnetic permeability is a physical quantity that characterizes the magnetic properties of a magnetic medium. Indicates the resistance to magnetic flux or the ability to conduct magnetic lines of force in a magnetic field after current flows through a coil in space or the core space. Its formula μ = B / H, where H = magnetic field strength, B = magnetic induction strength, commonly used symbols μ, μ for the permeability of the medium, or absolute permeability.

Magnetic permeability in electronic products on the impact of electromagnetic properties is very important, mainly in electromagnetic induction, inductance and magnetic closure, electromagnetic shielding, and other aspects. In the process of electromagnetic induction, magnetic permeability determines the ability of the material to respond to changes in the magnetic field, which in turn affects the size of the induced current.

Selecting materials with appropriate permeability can improve the efficiency and performance of devices such as transformers and inductors. In inductors, high permeability materials can enhance the relationship between the induced current in the coil and the strength of the magnetic field, improving the efficiency and sensitivity of the device. In magnetic confinement materials, materials with higher magnetic permeability can effectively reduce magnetic field leakage and enhance the concentration and effectiveness of the magnetic field.

In addition, magnetic permeability also plays an important role in electromagnetic shielding, and the selection of high magnetic permeability materials can effectively absorb, reflect, or disperse the energy of electromagnetic waves, and reduce the interference and damage of electromagnetic radiation on electronic equipment, communication equipment, and aerospace equipment. Therefore, magnetic permeability plays a crucial role in optimizing the electromagnetic performance of electronic products, improving equipment efficiency and reducing electromagnetic interference.

Fig. 7 Magnetic Permeability

3.2 Saturation Magnetic Flux Density

Saturation Magnetic Flux Density (SMFD) refers to a limit value of the magnetic induction strength (magnetic field strength) within a magnetic material that is gradually reached as the applied magnetic field strength increases. When the magnetic field strength is further increased, the magnetic field strength inside the material will no longer increase, and this limit value is the saturation magnetic flux density of the material. In short, saturation magnetic induction is the maximum magnetic field strength that a material can withstand. The saturation magnetic induction strength has an important impact on the application, which is mainly reflected in several aspects.

First of all, the saturation magnetic induction strength of a material determines the maximum magnetic energy it can store in a strong magnetic field, beyond which the material is unable to further enhance its magnetic properties, which is crucial for the design of high-performance magnetic components (e.g., inductors, transformers, permanent magnets, etc.). Materials with high saturation magnetic induction strength can operate at higher magnetic field strengths, providing greater magnetic flux for high-power and high-efficiency devices.

Second, in magnetic components such as inductors and transformers, high saturation magnetic induction strength means that more magnetic energy can be stored in the same volume, allowing for miniaturized designs. For example, the use of high-saturation magnetic induction strength materials in transformers reduces core size and lowers the weight of the device while maintaining high performance and efficiency.

In addition, different applications have different requirements for saturation magnetic induction strength, and in high-frequency electronic equipment, signal processing, and high-power electrical equipment, the choice of high saturation magnetic induction strength materials can effectively improve system performance. In power transformers, this characteristic can increase the magnetic flux density, reduce core losses, and thus improve the efficiency of the transformer.

Finally, saturation magnetic induction is also affected by temperature, with most materials decreasing in saturation magnetic induction as the temperature rises, which is particularly important for applications in high-temperature operating environments, especially in automotive electronics, aerospace and energy equipment, where it is critical to select materials that maintain a high saturation magnetic induction at high temperatures.

Fig. 8 Saturation Magnetic Flux Density

3.3 Coercivity

Coercivity is one of the important properties of magnetic materials and refers to the ability of a material to retain its magnetic properties after the magnetic field has been removed, or the minimum external magnetic field strength required to reverse the direction of the material's magnetization. It reflects the material's ability to resist reversal of magnetization and is therefore critical to the performance of permanent magnets. The influence of coercivity on permanent magnets is mainly reflected in magnetic stability, resistance to demagnetization, magnetic field strength versus volume, and application selection. Higher coercivity means that the material can maintain strong magnetic properties, even under the influence of external ambient magnetic field or temperature changes, for a longer period, which is critical for applications requiring long-term stability, such as electric motors, generators, and sensors.

In addition, the higher the coercivity, the stronger the demagnetization ability of the material, even at high temperatures or strong external magnetic fields and other harsh environments, the material does not easily lose its magnetic properties, so the performance of high coercivity permanent magnets in complex operating environments is more superior, widely used in automotive, aerospace and other fields. High-coercivity permanent magnets can achieve stronger magnetic fields in a smaller volume, which is especially important for miniaturized equipment, precision instruments, and mobile devices. For example, in miniature motors, sensors, and high-efficiency magnetic drives, permanent magnets with high coercivity can provide sufficient magnetic force to improve equipment efficiency and performance. Coercivity requirements vary from application to application, with higher coercivity materials often chosen for applications that require strong, stable magnetic fields, such as electric motors, permanent magnet generators, and magnetic drives, while lower coercivity materials are sufficient for applications that do not require strong magnetic fields, reducing costs.

4 Magnetic Materials in Electronic Devices

Magnetic materials play a crucial role in various electronic devices, including power supplies, transformers, data storage systems, motors, sensors, and wireless communication devices, due to their ability to interact with magnetic fields and facilitate energy conversion, data storage, and signal transmission.

4.1 Power supplies and transformers

In power supplies and transformers, magnetic materials are essential for voltage conversion and regulation. Transformers, for example, rely on magnetic cores made of soft magnetic materials like silicon steel or ferrite. These materials enhance the efficiency of electromagnetic induction, enabling the transformer to step up or step down voltage effectively. The magnetic properties allow the transfer of electrical energy from one coil to another without direct electrical contact, making transformers indispensable in power distribution systems, where they convert high-voltage electricity for safe use in homes and industries.

4.2 Data storage 

Magnetic materials are also vital in data storage applications, particularly in hard disk drives (HDDs) and magnetic tapes. In HDDs, thin layers of magnetic material are used to store digital information. The read/write heads of the drive alter the magnetic alignment on the disk surface, allowing data to be written or retrieved. Magnetic tapes, commonly used for backup storage, also utilize similar principles to store data in a magnetic field, enabling long-term data preservation.

4.3 Motors and Sensors

In motors and sensors, magnetic materials facilitate the conversion of electrical energy into mechanical motion and vice versa. For example, permanent magnets and electromagnets are used in the design of electric motors, including brushless motors, which are widely used in applications ranging from automotive to robotics. Sensors, such as current sensors, use magnetic materials to detect and measure the magnetic fields produced by electrical currents, providing critical feedback in control systems.

Fig. 9 Magnetic Sensors

Magnetic materials are equally significant in wireless communication technologies. In wireless devices, components like antennas, modulators, demodulators, and radio-frequency (RF) components rely on magnetic materials to optimize signal transmission and reception. These materials help to focus and guide electromagnetic waves, improving the performance of communication systems, such as mobile phones, Wi-Fi routers, and satellite communications.

5 Conclusion

Magnetic materials are essential in a wide array of electronic devices, playing key roles in energy conversion, data storage, motion control, and signal transmission. In power supplies and transformers, they enable efficient voltage regulation, while in data storage systems like hard drives and magnetic tapes, they facilitate reliable data recording and retrieval. In motors and sensors, magnetic materials are integral to energy conversion and precise measurement, powering everything from electric vehicles to industrial robots. Additionally, magnetic components in wireless communication devices improve the performance of antennas and RF components, ensuring optimal signal transmission and reception. Overall, magnetic materials are foundational to the functionality and performance of modern electronics.

Stanford Advanced Materials (SAM) is a key provider of high-quality magnetic materials, supporting these critical applications with reliable material solutions.

Further Reading:

Essential Electronic Materials: Part 1 - Silicon

Essential Electronic Materials: Part 2 - Silicon Carbide

Essential Electronic Materials: Part 3 - Germanium

Essential Electronic Materials: Part 4 - Gallium Compounds

Essential Electronic Materials: Part 5 - Carbon-Based Materials

Essential Electronic Materials: Part 6 - Conductive and Insulating Materials