Enhancement of low-frequency magnetic permeability and absorption by texturing flaky carbonyl iron particles

Abstract

We have fabricated flaky carbonyl iron particles (CIPs) with (200) crystal planes and easy axes preferred to parallel to the flake surfaces by developing a slip-induced grain orientation method. The method involves heat-treatment and subsequent wet milling of spherical CIPs. The heat-treatment in inert atmosphere is used to grow the grain sizes of raw spherical CIPs. During the wet milling process, the large grains in the heat-treated spherical CIPs are preferred to slip along directions {110} and rotate to produce (200) preferred orientation while they are being compressed into flaky shape. The grain orientation factor (a) increases from 0 to 0.42 with grain sizes grown up by controlled heat-treatment temperature. The texture decreases the in-plane magnetic anisotropy field of the flaky CIPs. The aligned flaky textured CIPs brings about an additional magnetic resonance at low frequency with respect to the non-textured counterpart, and exhibit enhanced double magnetic resonances. When a = 0.42, the imaginary permeability peak reaches 3.52 at 0.7 GHz, which is 2 times larger than previously reported values. The reflection loss less than −10 dB for their-based absorbing composite slab at thickness of 1 mm can cover a wide low frequency range between 0.4 and 2 GHz when the volume fraction of aligned textured flaky CIPs changes from 40 to 50%. This work provides an effective route to enhance magnetic permeability and loss at low frequencies, which has been a great challenge in recent years.