Why Is The Curie Temperature of Manganese Zinc Power Core Above 200 Degrees, And The High Permeability Core Only over 100 Degrees?

The initial permeability μi is a fundamental parameter of soft ferrite materials. In communication equipment, most electronic transformers operate at low flux densities, where the material's permeability plays a crucial role. When the material has a high permeability, a smaller number of turns in the coil can achieve the required inductance, effectively reducing the coil's DC resistance and the associated losses. This means that for a given loss, using high-permeability materials can significantly reduce the transformer's size. Therefore, the performance requirements for high μi materials are: to maximize μi values and Curie temperature Tc, minimize the loss coefficient tanδ/μi and temperature coefficient, and ensure that the saturation flux density Bs is typically 0.32~0.42T. The μi-f curve should remain flat across a wide frequency range.

Why is there such a big difference between the Curie temperatures of the two?1. Component differences

Although both primarily consist of manganese-zinc ferrite (MnO-ZnO-Fe₂O₃), their specific compositions differ. Power cores typically contain a higher amount of iron oxide (Fe₂O₃) and moderate amounts of zinc oxide (ZnO) and manganese oxide (MnO). This composition helps form a stable crystal structure, maintaining the orderly arrangement of magnetic domains at higher temperatures, thus increasing the Curie temperature. To achieve high permeability, high-permeability cores adjust their composition ratios, such as by increasing the relative content of manganese oxide, which may reduce the material's Curie temperature to some extent.

Some high-performance manganese-zinc power cores also add a small amount of other elements, such as cobalt (Co), nickel (Ni), etc., which can further enhance the stability of crystal structure and improve the Curie temperature. However, high permeability cores generally add less of these elements that help to improve the Curie temperature, or the amount of addition is different.

The figure shows the high permeability mirror core RM10

Second, the microstructure is different

In the process of preparation of power magnetic core, the grain size is large and the grain boundary is clear after the specific sintering process. This microstructure makes it relatively difficult for the magnetic domain wall to move, and the thermal motion needs higher energy to destroy the ordered arrangement of magnetic domain, so the Curie temperature is high.

To achieve high magnetic permeability, the microstructure of the core typically features smaller grain sizes and a relatively complex grain boundary structure. Smaller grain sizes mean there are more and more mobile magnetic domain walls. At lower temperatures, thermal motion can significantly disrupt the ordered arrangement of magnetic domains, making them more prone to disintegration, thus lowering the Curie temperature.

Three. Performance requirements and design orientation

Power magnetic core is mainly used in power conversion and other fields. It needs to maintain good magnetic properties at high temperature to withstand large power and current. Therefore, the Curie temperature should be improved in material design and preparation to meet the requirements of practical application.

High-permeability cores are primarily used in applications requiring high permeability, such as signal processing and filtering. In these applications, the operating temperature is typically relatively low, and the requirement for a Curie temperature is less stringent compared to power cores. To achieve this critical performance of high permeability, material design involves trade-offs, resulting in a relatively lower Curie temperature.