Tokyo, July 1, 2003 - JFE Steel Corporation and JFE Ferrite Corporation announced today the development of "MBT2," a soft ferrite¹⁾ that reduces core loss²⁾ by 15 % compared to conventional "MBT1." MBT2 features little change in initial permeability³⁾ due to temperature, making it suitable for a wide range of electronic devices, including switching power supplies⁴⁾, telecommunication equipment and car electronics. The companies have also developed a mass-production system for the material.

MBT2 will serve as one of JFE's "number one" products, combining unique ferrite technology based on high-purity iron oxide materials and the excellent sintering technologies of the JFE Group.

JFE Ferrite, a subsidiary responsible for manufacturing and marketing ferrite materials, will produce MBT2 at its Kurashiki Plant, which has a capacity of 1 million units per month. Mass production will begin in July.

Background
Automotive electronics, telecommunication equipment and other electronic devices are used in a wide range of temperatures - from below 0°C to above 100°C. The soft ferrite that such equipment employs has low core loss in the key frequency range between 10 kHz and 10 MHz as well as excellent initial permeability. Unfortunately, soft ferrite also has a critical defect in that its magnetic properties change significantly according to the temperature. This defect has proved an impediment to equipment design, and researchers have been searching for soft ferrite with minimal change in magnetic properties over a wide temperature range in order to help reduce electric power loss and develop more compact, efficient electronic equipment.

JFE-developed MBT1 was the first material in the world to meet all of its customers' requirements, and its excellent temperature properties are highly regarded by industry.

Features of MBT2
Newly-developed MBT2 is manganese zinc ferrite similar to conventional MBT1 and MB3⁵⁾, a general-use low-loss material.

While maintaining the excellent temperature properties of MBT1, core loss of MBT2 is reduced by 15 % (Fig. 1). Core loss when driven at frequency of 100 kHz in the sinusoidal⁶⁾ magnetic flux density of 0.2 T (tesla) was 300 kW/m³ at 40 °C, 280 kW/m³ at 80 °C, and 340 kW/m³ at 120 °C, indicating low core loss over a wide range of temperatures. The material is effective in reducing power loss from the transformers of the switching power supplies. Compared to the conventional low-loss ferrite, it has one and a half times higher initial permeability at room temperature with one-third the change in initial permeability over temperature from 0 °C to 100°C (Fig. 2). It will therefore contribute to smaller and more stable choke coils⁷⁾.

For MBT2, it has been possible to reduce changes in core loss and initial permeability by optimizing chemical composition and alleviating the change due to temperature in the magnetic anisotropy constant⁸⁾. Also, precise control of temperature and oxygen concentration during the sintering process has enabled production of an optimized precision structure made up of crystal grains with an average diameter of approximately 10 micrometers and electrical insulating crystal grain boundaries⁹⁾ of several nanometers thickness, thereby realizing MBT2 with low core loss.

Applications
MBT2's low loss regardless of environmental temperature makes the material an excellent choice for the cores of the switching power supply transformers and choke coils listed below. In addition, its stable inductance¹⁰⁾ makes the material suitable for telecommunication antennas and noise filters. When used in power supply transformers, MBT2 is able to reduce the magnetizing current required to realize high inductance over a wide range of temperature, thereby constraining power loss. It is particularly suited for the transformers for forward converters^11).

Fig.1: Comparison of temperature dependence of core loss (Pcv) at
100 kHz and 200 mT for MBT2 and conventional materials

Fig.2: Comparison of temperature dependence of initial permeability
(mi) for MBT2 and conventional materials