Abstract
Large and sensitive magnetostriction (large strain induced by small magnetic fields) is highly desired for applications of magnetostrictive materials. However, it is difficult to simultaneously improve magnetostriction and reduce the switching field because magnetostriction and the switching field are both proportional to the magnetocrystalline anisotropy. To solve this fundamental challenge, we report that introducing tetragonal nanoprecipitates into a cubic matrix can facilitate large and sensitive magnetostriction even in random polycrystals. As exhibited in a proof-of-principle reference, Fe–Ga alloys, the figure of merit—defined by the saturation magnetostriction over the magnetocrystalline anisotropy constant—can be enhanced by over 5-fold through optimum aging of the solution-treated precursor. On the one hand, the aging-induced nanodispersive face-centered tetragonal (FCT) precipitates create local tetragonal distortion of the body-centered cubic (BCC) matrix, substantially enhancing the saturation magnetostriction to be comparable to that of single crystal materials. On the other hand, these precipitates randomly couple with the matrix at the nanoscale, resulting in the collapse of net magnetocrystalline anisotropy. Our findings not only provide a simple and feasible approach to enhance the magnetostriction performance of random polycrystalline ferromagnets but also provide important insights toward understanding the mechanism of heterogeneous magnetostriction.
Highlights
Magnetostrictive materials that can convert magnetic energy into mechanical energy or vice versa have been widely used in actuators, transducers, sensors, and energy harvesters[1,2,3]
It is desirable to have a combination of large strain and a small switching field (which can be evaluated by the critical field, at which d33 reaches a maximum[4], and is proportional to K/Ms for Correspondence: Tianyu Ma or Xiaobing Ren 1Frontier Institute of Science and Technology, State Key Laboratory for Mechanical Behavior of Materials, and MOE Key Laboratory for Nonequilibrium Synthesis and Modulation of Condensed Matter, Xi’an Jiaotong University, Xi’an 710049, China 2School of Materials and Environmental Engineering, Hangzhou Dianzi University, Hangzhou 310012, China Full list of author information is available at the end of the article random polycrystals, where K is the magnetocrystalline anisotropy constant and Ms is the saturation magnetization5)
This complex process can constrain the ferromagnetic domains within the plane perpendicular to the crystal axis and can yield a large magnetostriction up to the theoretical limit through pure 90° domain switches when applying a magnetic field along the crystal axis
Summary
Magnetostrictive materials that can convert magnetic energy into mechanical energy or vice versa have been widely used in actuators, transducers, sensors, and energy harvesters[1,2,3]. The usual approach to maximize the magnetostriction of a given material with a large spontaneous magnetostriction constant has been fabricating a single crystal and further applying prestress or performing postgrowth magnetic annealing[9,10,11] This complex process can constrain the ferromagnetic domains within the plane perpendicular to the crystal axis and can yield a large magnetostriction up to the theoretical limit through pure 90° domain switches when applying a magnetic field along the crystal axis. This approach has dominated the fabrication and application of the state-of-the-art magnetostrictive material Terfenol-D (e.g., Tb0.3Dy0.7Fe2) with a large rhombohedral spontaneous magnetostriction constant λ111 of 1640 ppm at room temperature[2]. It is highly desirable to find a feasible approach that can enhance the magnetostriction and reduce the switching field simultaneously
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