Magnetostriction and Magnetic Domain Structure in an Fe-Ga Alloy Single Crystal Grown by the Czochralski Method

Fe-Ga alloys are gathering much attention because of good machinability and superior magnetostrictive property for application to actuators and vibration energy harvesters. Recently, Fe-Ga alloy single crystals were successfully grown by the Czochralski (CZ) method [1]. In this study, the relationship between the magnetostrictive property and magnetic domain structure in an Fe-16 at%Ga alloy single crystal grown by the CZ method was investigated. To evaluate the magnetostrictive property, a strain gauge was attached on the (001) plane in the [100] direction. The magnetic domain structure on the (001) plane was observed by a magneto-optic Kerr effect microscope. In the mentioned-above experiments, magnetic fields were applied in the [100] direction on the plane. Figure 1 shows the magnetostriction curve of the specimen. The magnetostriction rapidly increases in the vicinity of 1250 Oe with increasing magnetic field and reaches the saturation value of about 109 ppm at about 2000 Oe. As shown in Fig. 2, 90° domain walls are aligned with the <;110> direction at zero magnetic field. Additionally, 180° domain walls form a staircase-like structure. When a magnetic field was applied along the [100] direction, 180° domain walls primarily moved, and they almost disappeared at about 1100 Oe. In other words, a striped domain structure composed of 90° domain walls was observed. The single domain structure was obtained after motion of 90° domain walls under the magnetic field above about 2000 Oe. Therefore, the mentioned-above change of magnetic domain structure corresponds to the magnetostrictive property. It is clear that 180° domain walls easily moved compared to 90° domain walls by applying the magnetic field in the Fe-16 at%Ga alloy single crystal.