Influence of Shape Anisotropy and Temperature on Magnetostrictive Behaviors in Single Crystal Galfenol Alloys
Fe-Ga (Galfenol) is a rare-earth-free alloy with useful magnetostrictive properties of nominal cost with robust mechanical properties advantageous for sensing, actuating and energy harvesting. Magnetostriction in the polycrystalline form is enhanced by abnormal grain growth of Goss texture (110)  by rolling and recrystallization of thin sheets. Prior research shows that magnetostriction of Fe81Ga19 was maximized when introduced to a uniform compressive stress in an external field, yielding an increase in magnetostriction with increasing stress as well as increasing magnetic susceptibility, which corresponds to a larger d33 transduction coefficient. Temperature-dependence of magnetostriction and magnetization was also previously investigated, resulting in a 12.9% decrease in magnetostriction from −21°C to +80°C and a corresponding 3.6% decrease in magnetization, demonstrating minimal dependence at low temperatures. Understanding magnetostriction and magnetization behaviors under stresses at the extended temperature ranges from −40°C to 300°C introduces the potential of harsh environment applications of magnetostrictive non-contact torque sensor for use in aerospace rotorcraft designs which operate at extreme temperatures. Galfenol thin patches have the potential to operate in engines and rotator shafts, but device performance at these temperature ranges has not been studied. Thus, in this work, we investigate simultaneous effects of temperature and external stresses on magnetic and magnetostrictive behaviors at temperatures from −40°C to 300°C for single crystal Fe-Ga samples. Prior to these works, (001)-oriented Galfenol single crystals with different shapes were examined for evaluating magnetostrictive performance when magnetized. Preliminary data from a Vibrating Sample Magnetometer (VSM) produced linear regions of magnetostriction versus normalized magnetization for a rectangular single crystal Fe80.2Ga19.8 sample of different orientations through a range of applied fields, as shown in Fig. 1. Figure 1(b) more closely illustrates the largest linear portion from normalized magnetism of about 0.35 to 0.8 of the sample corresponding to applied fields along the short direction and likewise Figure 1(c) more closely illustrates the largest linear portions of normalized magnetism of about 0.55 to 0.8 for the long direction orientation. For a circular Fe Fe82.5Ga17.5 sample, the linear region of normalized magnetism extends from 0 to around 0.7, as shown in Fig. 2. This data indicates that shape anisotropy effects are most evident in the circular sample and the rectangular sample aligned along the short direction with a parallel applied field, based on increased dλ/dH and thus faster magnetization from external fields, H. This proportionality between magnetostriction and normalized magnetism suggests a higher magnetic susceptibility corresponding to high shape anisotropy, an important relationship for sensing applications. Building upon this observation, this work attempts to relate temperature-dependence and shape anisotropy to determine the effect on magnetic susceptibility at extreme temperatures. To study this dependence, an insulated thermal chamber enclosing a heat source and pre-stress device will constrain the rectangular single crystal Fe80.2Ga19.8 sample. Despite a larger dλ/dH for the circular sample the testing of stress requires a rectangular single crystal Galfenol sample, which is oriented in the (001) plane with a magnetostriction value of about ~260 ppm. The sample will be subjected to various temperatures up to ~300 °C where simultaneous magnetostriction and magnetization values will be acquired. Based on previously observed models, a Magnetic Optic Kerr Effect (MOKE) system will confirm hypothesized effects of shape anisotropy and observed magnetic susceptibility by illustrating magnetic domain wall rotation throughout the procedure. Understanding the roles of extreme temperatures and compressive stress on magnetostrictive alloys will provide an enhanced understanding of the material properties and thus allow a wider range of beneficial applications.
A. Orr et al., "Influence of Shape Anisotropy and Temperature on Magnetostrictive Behaviors in Single Crystal Galfenol Alloys," Proceedings of the 2017 IEEE International Magnetics Conference( 2017, Dublin, Ireland), article no. 8007897, Institute of Electrical and Electronics Engineers (IEEE), Aug 2017.
The definitive version is available at https://doi.org/10.1109/INTMAG.2017.8007897
2017 IEEE International Magnetics Conference, INTERMAG 2017 (2017: Apr. 24-28, Dublin, Ireland)
Keywords and Phrases
Magnetostriction; Perpendicular magnetic anisotropy; Magnetometers; Magnetic susceptibility; Magnetization
International Standard Book Number (ISBN)
Article - Conference proceedings
© 2017 Institute of Electrical and Electronics Engineers (IEEE), All rights reserved.
10 Aug 2017