Shen Wu

Nd2Fe17 nanograins effect on the coercivity of HDDR NdFeB magnets with low boron content

Relationships between the coercivity of hydrogenation disproportionation desorption recombination (HDDR) Nd12.5Fe81.5−xCo6Bx bonded magnets and boron content were investigated. Nd2Fe17 phase with planar magnetic anisotropy is present in the microstructure when x= 4at%–5.88at%, which does not reduce the coercivity of the bonded magnets. High-resolution transmission electron microscopy (TEM) images show that Nd2Fe17 phase exists in the form of nanocrystals in the Nd2Fe14B matrix. There is an exchange-coupling interaction between the two phases so that the coercivity of HDDR Nd12.5Fe81.5−xCo6Bx bonded magnets is hardly reduced with a decrease in boron content.

Influence of Coating Content on the Magnetic Properties of Iron-MnZn Ferrite Soft Magnetic Composites

In this paper, iron powder with high purity is covered by a Mn-Zn ferrite layer, and the effect of amount of ferrite on the microstructure and magnetic properties are investigated. The morphology of the samples was characterized by scanning electron microscopy coupled with energy dispersive X-ray spectroscopy. It was shown that the particle surface layer contains a thin insulating layer of Mn-Zn ferrite, with high particle surface coverage. The magnetic measurements on samples were carried out using a B-H curve analyzer and an AC performance tester at Bm=50mT. The results indicate that the Mn-Zn ferrite coated samples have excellent frequency characteristics compared with uncoated samples. Also, the composites with 4wt% ferrite show a good combination of magnetic permeability and magnetic loss in the range 0.8-150 kHz.

Magnetic properties and loss separation in iron-silicone-MnZn ferrite soft magnetic composites

This paper investigates the magnetic and structural properties of iron-based soft magnetic composites coated with silicone-MnZn ferrite hybrid. The organic silicone resin was added to improve the flexibility of the insulated iron powder and causes better adhesion between particles to increase the mechanical properties. Scanning electron microscopy and distribution maps show that the iron particle surface is covered with a thin layer of silicone-MnZn ferrite. Silicone-MnZn ferrite coated samples have higher permeability when compared with the non-magnetic silicone resin coated compacts. The real part of permeability increases by 34.18% when compared with the silicone resin coated samples at 20 kHz. In this work, a formula for calculating the total loss component by loss separation method is presented and finally the different parts of total losses are calculated. The results show that the eddy current loss coefficient is close to each other for the silicone-MnZn ferrite, silicone resin and MnZn ferrite coa...

Measurement Error of the Coercivity Hcj of NdFeB Permanent Magnet Caused by Air Gap

Regular rare earth permanent magnet measurement systems are only able to measure standard samples with a fixed size. But NdFeB materials are usually processed into various kinds of shapes. Bonding magnets are even often formed together with the shaft or other parts. So there will be a distinct error in conventional measurement. The magnetic field intensity distribution between two poles of the system was analyzed. Because of the existence of air gap between the magnet and the poles of the measurement system, the measurement magnetic circuit is open in this experiment. By changing the height of the magnet and air gap, the measurement error of the intrinsic coercivity Hcj of NdFeB magnets is researched under this condition.