Soft Magnetic Materials: Market Availability - Part 3

By: Hui Meng

Several types of soft magnetic materials exist, as previously discussed in the Soft Magnetic Materials II article. Different materials are optimal for various frequency ranges, from quasi-static to above 1 MHz. Consequently, no single material excels across all parameters and applications. Table 1 below provides an overview of the common soft magnetic materials available on the market and their key performance indicators (KPIs).

Table 1: Key performance parameters for typical soft magnetic materials. Note: Magnetic properties of these materials are highly sensitive to the production process, so the data in the table are for rough reference only. For specific and practical values, consult a sales representative.

Iron and Low-Carbon Steels

Iron and low-carbon steels are some of the most common and economical soft magnetic materials. They have a high saturation flux density (BS) of approximately 2.15 T, with the only superior option being the more expensive Fe-Co alloys. However, their low resistivity limits their use in dynamic applications. These materials are typically employed in static or low-frequency applications, such as electromagnet cores, relays, and low-power motors, where material cost is a primary concern.

Iron-Silicon Alloys

Adding silicon to iron increases its resistivity, beneficial for reducing eddy current losses. Despite a slight decrease in saturation magnetization and Curie temperature, Fe-Si alloys are widely used in electrical machines operating from 50 Hz to several hundred Hz. To further reduce eddy current losses, these alloys are often rolled into thin strips, usually equal to or less than 0.35mm thick. Based on the rolling and heat treatment conditions, Fe-Si alloy is categorized as Grain-Oriented (GO) for transformers and Non-Oriented (NO) for electric motors.

Iron-Nickel Alloys

Nickel added to iron forms uniform solid solutions over a broad composition range. Alloys with a nickel content near Fe20Ni80 are known as Permalloy. Elements like Mo, Cu, and Cr are added to enhance properties. Optimized via composition adjustment and heat treatment, Permalloy can achieve permeability as high as 1,200,000. While its saturation magnetization is around 0.8 T, lower than iron alloys, this material excels in formability and magnetic properties. It’s widely used in applications such as magnetic field shielding, ground fault interrupters, and magnetic sensors.

Iron-Cobalt Alloys

Adding cobalt to iron increases both Curie temperature and BS. For cobalt content between 33 wt. % and 50 wt. %, BS can reach up to 2.4 T, providing the highest BS among all magnetic alloys. Vanadium is added to Fe50Co50 alloys to improve formability, allowing the material to be rolled down to 50 microns. These alloys are crucial in applications requiring high power-to-weight ratios, such as space-bound motors and transformers.

Amorphous and Nanocrystalline Alloys

Amorphous alloys, often called metallic glasses, are produced through rapid solidification. They feature high resistivity and no magneto crystalline anisotropy, making them excellent soft magnets. Based on their compositions, most commercial amorphous magnets are Fe-base, Co-base, or (Fe, Ni)-based. Fe-based amorphous alloys have the highest BS (~1.6 T) and the lowest cost. Co-based alloys, while having lower BS, boast high permeability and minimal magnetostriction, performing well at higher frequencies. (Fe, Ni)-based alloys offer medium magnetic properties.

Nanocrystalline alloys, created by adding Nb and Cu to Fe-based amorphous alloys, maintain superior soft magnetic properties with controlled crystallization. They are used extensively in wireless chargers, high-frequency inductors, and electromagnetic shielding.

Soft Magnetic Composites (SMCs)

SMCs are created by compressing alloy powders coated with insulation layers, which minimizes eddy current losses and increases operating frequency capability. These materials can be formed into shapes that traditional lamination methods cannot achieve, benefiting novel electromagnetic device designs. Common SMCs are made from Fe, Fe-Si, Fe-Si-Al, Fe-Ni, and amorphous and nanocrystalline alloys.

Soft Ferrites

Soft ferrites, unlike metals, are ionic compounds with resistivity several orders of magnitude higher. These materials are ideal for applications up to 1 MHz due to minimal energy losses but have lower BS. Mn-Zn ferrites are used below 1 MHz, whereas Ni-Zn ferrites are suitable for higher frequencies but with lower BS and permeability.

In conclusion, soft magnetic materials are intrinsic to many applications, especially in electrical engineering. While a trade-off between cost, iron loss, saturation flux density, and permeability is necessary, no single type of soft magnetic material excels in all performance aspects. Materials like Fe-Si alloys dominate transformers and electric motors due to their balance of properties. Meanwhile, advanced materials like Fe-Co alloys and nanocrystalline alloys offer superior performance for more specialized applications.

Soft Magnetic Alloy options are abundant. Selecting the right material is crucial for optimal performance in specific applications.

Experts believe that Resistance Heating Alloy products are vital in many high-performance environments.

For more information, you can visit this page: Pure Metal.

About SM Magnetics: SM Magnetics offers assistance in magnet selection, magnetic circuit design, and engineering support. Contact our technical staff at 205-621-8841 for more information.