Enhancement of exchange coupling and hard magnetic properties in nanocomposites by magnetic annealing

Textured anisotropic FePd/α-Fe nanocomposite foils by sheath repetitive cold-rolling

“…In particular, the SRCR can introduce strong pre-textures in as-fabricated samples which provide significant numbers of favorable nucleation sites for the texture formation of hard magnetic phases in the subsequent solid-state phase transformation during the HMFA. By influencing nucleation and grain growth during the phase transformation, the subsequent HMFA also results in both nanostructure refinements and a new hard phase preferential formation in certain orientations [3][4][5][6][7][8][9][10]. Thus, both fine and highly textured nanostructure is expected to form.…”

“…A high field of 8 T or above is usually required for nanocomposites in order to obtain sufficient magnetic torque to align the hard grains with critical grain sizes [3,4]. In addition, the magnetic field during the annealing promotes homogeneous nucleation of nanocrystals by increasing the nucleation rate to form fine nanoscaled grain sizes and uniform grain configuration [3,4].…”

“…Because of magnetic anisotropy of the nuclei, magnetic fields could introduce textures in the materials by changing the habit plane of nucleation. In order to align the hard grains, the driving force due to magnetocrystalline anisotropy energy of the hard phases should be larger than those due to the energy associated with shape anisotropy and thermal disordering effects [3][4][5][6][7][8][9][10]. A high field of 8 T or above is usually required for nanocomposites in order to obtain sufficient magnetic torque to align the hard grains with critical grain sizes [3,4].…”

“…In order to align the hard grains, the driving force due to magnetocrystalline anisotropy energy of the hard phases should be larger than those due to the energy associated with shape anisotropy and thermal disordering effects [3][4][5][6][7][8][9][10]. A high field of 8 T or above is usually required for nanocomposites in order to obtain sufficient magnetic torque to align the hard grains with critical grain sizes [3,4]. In addition, the magnetic field during the annealing promotes homogeneous nucleation of nanocrystals by increasing the nucleation rate to form fine nanoscaled grain sizes and uniform grain configuration [3,4].…”

“…The scale of the soft phase should be in a range of twice the domain wall width of the hard magnetic phase and the hard nanograins should have a strong Caxis texture and magnetic anisotropy [1,2]. The alignment of the hard nanograins to achieve strong C-axis texture and magnetic anisotropy is one of the most important and difficult factors in attainment of record-high (BH) max in either anisotropic nanocomposites or single-phase nanostructured magnets [1][2][3][4][5][6][7][8][9][10]. To achieve the required nanostructure parameters, a combination process of the sheath repetitive cold-rolling process (SRCR) with high magnetic field annealing (HMFA) was developed in this work as a unique technique to fabricate textured anisotropic FePd/␣-Fe nanocomposite bulk foils.…”