Ultrathin films: magnetism on the microscopic scale

Structural aspects of elastic deformation of a metallic glass

Symmetry breaking is a fundamental concept that prevails in many branches of physics1–5. In magnetic materials, broken inversion symmetry induces the Dzyaloshinskii–Moriya interaction (DMI), which results in fascinating physical behaviours6–14 with the potential for application in future spintronic devices15–17. Here, we report the observation of a bulk DMI in GdFeCo amorphous ferrimagnets. The DMI is found to increase linearly with an increasing thickness of the ferrimagnetic layer, which is a clear signature of the bulk nature of DMI. We also found that the DMI is independent of the interface between the heavy metal and ferrimagnetic layer. This bulk DMI is attributed to an asymmetric distribution of the elemental content in the GdFeCo layer, with spatial inversion symmetry broken throughout the layer. We expect that our experimental identification of a bulk DMI will open up additional possibilities to exploit this interaction in a wide range of materials. A composition gradient is found to provide the necessary structural inversion asymmetry for a bulk Dzyaloshinskii–Moriya interaction to manifest itself.

Bulk Dzyaloshinskii-Moriya interaction in amorphous ferrimagnetic alloys.

Spin-orbit torques: Materials, mechanisms, performances, and potential applications

Recent Developments in Perpendicular Magnetic Anisotropy Thin Films for Data Storage Applications

Using x-ray-absorption fine-structure measurements we have obtained clear evidence for structural anisotropy in amorphous sputter-deposited TbFe films exhibiting perpendicular magnetic anisotropy. Modeling of the data shows that perpendicular anisotropy in these films is associated with Fe-Fe and Tb-Tb pair correlations which are greater in plane and Tb-Fe correlations which are greater perpendicular to the film plane. Upon annealing at 300 \ifmmode^\circ\else\textdegree\fi{}C the measured structural anisotropy disappears and the magnetic anisotropy decreases to a level consistent with magnetoelastic interactions between the film and substrate.

Structural origins of magnetic anisotropy in sputtered amorphous Tb-Fe films

The authors report the measurement and description of an anisotropy between the in-plane and out-of-plane atomic structure in as-deposited amorphous Tb-Fe alloy films. This anisotropy, measured using a conversion-electron extended X-ray absorption fine structure (EXAFS) technique, correlates closely with measured values of the perpendicular magnetic anisotropy energy as a function of both film composition and annealing temperature. Modeling of the EXAFS data using theoretical codes and structural standards suggests that the Tb-Tb and Fe-Fe pair correlations are greater parallel to the film plane and that the Tb-Fe pair correlations are greater perpendicular to the film plane. Upon annealing at 300 degrees C the structural anisotropy is eliminated, and the magnetic anisotropy is lowered to a level consistent with magnetoelastic interactions between the film and substrate. >

Determination of the structural anisotropy in amorphous Tb-Fe films

Correlation between structure and magnetic anisotropy in amorphous FeTb alloy films

We have employed extended x‐ray absorption fine structure (EXAFS) analysis to study the compositional dependence of the atomic structure in Fe–Tb alloy films. Fourier transforms of EXAFS data, relative to both the Fe K and the Tb LIII absorption edges, provide information about the local atomic environments relative to each atom. Results indicate the Fe EXAFS data to be dominated by Fe–Fe correlations, and consists of contributions from two Fe atomic shells at radial distances near 2.47 and 2.66 A and a Tb shell near 2.91 A. The coordination number of the Fe shells are measured to increase, while radial distances decrease, with increased Fe content. The Tb EXAFS data was found to have an atomic shells of Fe and Tb at 2.91 and 3.47 A, respectively. Analysis suggests that the Fe shell is very disordered and is comprised of approximately 9.5 atoms while the Tb shell has ≊3 atoms.

K. D. Aylesworth

Papers

Structural origins of magnetic anisotropy in sputtered amorphous Tb-Fe films

Determination of the structural anisotropy in amorphous Tb-Fe films

Correlation between structure and magnetic anisotropy in amorphous FeTb alloy films

Extended x-ray absorption fine structure studies of IBS Fe-Tb alloy films

Magnetic properties of ferrimagnetic rare-earth—transition-metal films and multilayers