Understanding the magnetic anisotropy in Fe-Si amorphous alloys

Abstract

transition metal. 3d electrons in transition metals have a much weaker spin-orbit interaction compared to the Rare Earths, and they interact more strongly with the crystal field which makes their orbital moments smaller so that their magnetism is dominated by the exchange interaction. In Transition MetalMetalloid (TM-M) alloys, the Metalloid (Si, B, P..) is introduced to amorphisize the TM structure. The exchange interaction is believed to still dominate in these compounds [2]. Their ferromagnetic correlation length is longer than in the RE-TM alloys, which also implies that their spatial spinspin correlation function decays more slowly. These materials have a quasi long range magnetic order and, also due to the dominant exchange interaction, they behave as very soft ferromagnets, i.e., their coercivity and anisotropy energy are very small. The TM-M alloys prepared in the form of thin films usually have a well defined easy axis that can not come about from the pure exchange interaction which is isotropic. The anisotropy of the films should come from either the spinorbit interaction, responsible of the magneto-crystalline anisotropy at each site, or from magnetic dipolar interactions [2]. The last one can be originated at an atomic level due to structural anisotropies, or on a microscopic scale, due to defects and inhomogeneities. Identifying the factors that cause the anisotropy in these films is important from a practical point of view because it allows the control of their magnetic characteristics.Abstract-The origin of the magnetic anisotropy in a very disordered Fe-Si alloy has been investigated. The alloy containing 40% at. Si was prepared in the form of a thin film in a DC magnetron sputtering chamber. Structural disorder was obtained from Extended X-ray Absorption Fine Structure spectroscopy. The uniformity and lack of inhomogeneities at a microscopic level was checked by measuring their transverse magnetic susceptibility and hysteresis loops. The orbital component of the magnetic moment was measured by X-ray Magnetic Circular Dichroism spectroscopy. The orbital moment was extraordinary high, 0.4µ B . Such a high value contrasted with the relatively small uniaxial anisotropy energy of the thin film (2kJ/m 3 ). This suggests that the cause of the magnetic anisotropy in this alloy was a small degree of correlation in the orientation of the local orbital moments along a preferential direction.

In-plane magnetic anisotropy and coercive field dependence upon thickness of CoFeB

“…Diaz et al [17] reported that in Fe-Si amorphous soft ferromagnetic films, due to large local anisotropy of Fe ions (10 6 J/m 3 ) caused due to structural disorder, a small degree in the orientational correlation of the local orbital moments can result in uniaxial anisotropy. By analogy, precipitation of even small fraction of Fe 2 B compound in CoFeB may contribute to the uniaxial anisotropy owing to its high magneto-crystalline anisotropy ( $ À4 Â 10 5 J/m 3 ) [15].…”

Phase separation inFe−SiandCo−Sisputtered ferromagnetic alloys and the origin of their magnetic aniso

“…Therefore, A u was proportional to the anisotropy energy K u , assuming that the TKE signal was proportional to the magnetization of the sample. 24 The anisotropy energy of the most anisotropic amorphous Fe-Si film was 15 2 ϫ 10 4 erg/ cm 3 and in the amorphous Co-Si film was 14 6 ϫ 10 3 erg/ cm 3 .…”

“…In the case of the Co-Si alloys, the easy axis is defined by the plane of incidence of the evaporated species for any Si concentration. 4,14 However, the Fe-Si amorphous alloys have a range of low Si concentrations where their easy axes does not point in such a direction, 15 and it can be oriented by externally applied magnetic fields of weak intensity ͑lower than 30 Oe͒ during film deposition. Since the anisotropy of Co-Si films, and Fe-Si with high enough Si concentrations, is unchanged by externally applied magnetic fields, it is proposed that its origin should be associated to the internal structure of the film.…”

“…Such a structure would probably be derived from fluctuations in the Si concentration, possibly at the nanometer scale, 16 where segregated nonmagnetic or poorly magnetic regions rich in Si would surround magnetic regions rich in Fe. 15,17 To determine the presence of such a possible segregation and its influence in the coercivity and anisotropy properties of these alloys, several films were deposited with Si concentrations above and below the amorphous concentration. The levels of such a segregation were measured by EXAFS spectroscopy, which is very sensitive to ordered atomic environments and much less sensitive to disordered or liquid-like environments.…”

Amorphous Co-Ni-P Alloys with High Saturation Magnetization Produced by Electrodeposition

“…This has been attributed to novel mechanical, [1][2][3][4] magnetic [5][6][7][8] and catalytic [9][10][11] properties and excellent corrosion resistance [12][13][14][15][16][17] for these materials. Among magnetic amorphous materials, Cobased alloys are important and have been produced by various techniques including rapid quenching, 18,19) physical vapor deposition, 20) chemical or electroless plating 21,22) and electrodepostion.…”