Manipulating magnetic anisotropy and ultrafast spin dynamics of magnetic nanostructures

Abstract

We present our extensive research into magnetic anisotropy. We tuned the terrace width of Si(111) substrate by a novel method: varying the direction of heating current and consequently manipulating the magnetic anisotropy of magnetic structures on the stepped substrate by decorating its atomic steps. Laser-induced ultrafast demagnetization of a CoFeB/MgO/CoFeB magnetic tunneling junction was explored by the time-resolved magneto-optical Kerr effect (TR-MOKE) for both the parallel state (P state) and the antiparallel state (AP state) of the magnetizations between two magnetic layers. It was observed that the demagnetization time is shorter and the magnitude of demagnetization is larger in the AP state than those in the P state. These behaviors are attributed to the ultrafast spin transfer between two CoFeB layers via the tunneling of hot electrons through the MgO barrier. Our observation indicates that ultrafast demagnetization can be engineered by the hot electron tunneling current. This opens the door to manipulate the ultrafast spin current in magnetic tunneling junctions. Furthermore, an all-optical TR-MOKE technique provides the flexibility for exploring the nonlinear magnetization dynamics in ferromagnetic materials, especially with metallic materials.

Study of magnetization reversal and anisotropy of single crystalline ultrathin Fe/MgO (001) film by magneto-optic Kerr effect

“…The rotational magneto-optic Kerr effect (ROTMOKE) is a powerful method to determine the magnetic anisotropy in magnetic thin films by realizing the coherent rotation of magnetization. [22][23][24] In the present paper, the magnetization reversal process in Fe/MgO (001) film is investigated by MOKE. Firstly, the normalized angular-dependent longitudinal and transverse magnetization hysteresis loops are measured with the applied field parallel and perpendicular to the incident plane.…”

Tunable in-plane spin orientation in Fe/Si (557) film by step-induced competing magnetic anisotropies

“…[1,2] Since the spin orientation in ferromagnetic film is directly determined by the magnetic anisotropy, a better controlling and understanding of magnetic anisotropy becomes one of the challenging topics to engineer the spin order orientation of magnetic material. [1][2][3] Surface/interface effect has a strong bearing on the magnetic properties of low-dimensional system, and consequently can be taken as an effective method to engineer the magnetic anisotropy of ultrathin film. [4][5][6][7] Epitaxial growth of the ferromagnetic film on stepped substrate is one of the most common methods to form a periodical surface morphology of film, resulting in an in-plane uniaxial magnetic anisotropy (UMA) originating from the magnetic shape anisotropy, [8][9][10] bulk strain, [11,12] and/or Néel pair-bonding of surface atomic.…”

“…[14] Due to the importance of Fe/Si films in magnetoelectronics and the integration of magnetic devices in silicon technology, [16] the magnetic anisotropy of Fe/Si film has been largely reported. [3,[7][8][9][10][17][18][19][20] In particular, the manipulation of spin-reorientation transition (SRT) processes from out-ofplane to in-plane in Fe/Si film has already been fully understood and studied. For example, for Fe films deposited on flat Si (111) substrate, due to the competition between surface magnetic anisotropy and shape anisotropy, an SRT process from out-of-plane to in-plane with a critical thickness of about 7 monolayer (ML) was observed.…”