Direct imaging of current-driven domain walls in ferromagnetic nanostripes

Abstract

To better understand the response of domain walls to current induced spin transfer torques, we have directly imaged the internal magnetic structure of domain walls in current-carrying ferromagnetic nanostripes. Domain wall images were acquired both while a constant current was flowing through the wire, and after applying current pulses. Domain walls ranging from vortices in wide (1 m) wires, to transverse walls in narrow (100 nm) wires were quantitatively analyzed using scanning electron microscopy with polarization analysis (SEMPA). The domain wall motion is characterized by strong interactions with random pinning sites along the wire. The walls either jump with the electron flow between pinning sites, or the pinned walls are distorted by the current. The domain wall propagation is also associated with transverse motion of the vortex core.

Approach to writing-induced different types of spin vortex structure into ferromagnetic nanostripes

“…Uhlig et al [1] gave a stripe geometry domain wall phase diagram in their experimental study. Their result shows that the stripe width and thickness of the sample determine the type of static domain wall, i.e., thicker or wider stripe favors VW and TW is more likely to appear in thinner and narrower stripe.…”

“…Recently, magnetic domain-wall Racetrack memory is proposed, in which the movement of domain walls in magnetic nanostripes is controlled by short pulses of spin-polarized current instead of applying external magnetic fields [1][2][3][4][5][6][7][8][9][10][11][12][13][14][15][16]. In ferromagnetic nanostripes, two basic magnetic domain walls are transverse wall (TW) and vortex wall (VW) [1][2][3][4][5][6][7][8]17], which consists of two TWs and a spin vortex core [3,18]. According to some present reports, the spin vortex structure (SVS) has two common types: single vortex (SV) and double vortex(DV), which can be found in both numerical and experimental results [1,9,[19][20][21][22][23][24][25][26][27][28][29][30][31][32].…”

“…In ferromagnetic nanostripes, two basic magnetic domain walls are transverse wall (TW) and vortex wall (VW) [1][2][3][4][5][6][7][8]17], which consists of two TWs and a spin vortex core [3,18]. According to some present reports, the spin vortex structure (SVS) has two common types: single vortex (SV) and double vortex(DV), which can be found in both numerical and experimental results [1,9,[19][20][21][22][23][24][25][26][27][28][29][30][31][32]. It was proved that the current-induced domain wall motion depends on the domain wall structure [3,10,19], i.e., different domain walls may result in different domain wall motions.…”

“…In fact, the digital information is stored by the magnetic domain, and the writing of digital information is implemented (performed) by the magnetic domain wall motion. Recently, magnetic domain-wall Racetrack memory is proposed, in which the movement of domain walls in magnetic nanostripes is controlled by short pulses of spin-polarized current instead of applying external magnetic fields [1][2][3][4][5][6][7][8][9][10][11][12][13][14][15][16]. In ferromagnetic nanostripes, two basic magnetic domain walls are transverse wall (TW) and vortex wall (VW) [1][2][3][4][5][6][7][8]17], which consists of two TWs and a spin vortex core [3,18].…”

Magnetometry of single ferromagnetic nanoparticles using magneto-optical indicator films with spatial amplification

“…Bulk measurements are typically complicated by particle interactions and small signal strengths. 11,12 Microscopic techniques such as electron microscopy, 13,14 scanning probe magnetometry, 15 micro-superconducting quantum interference device (SQUID) [16][17][18] magnetometry, and magneto-optical Kerr effect (MOKE) 19 magnetometry can yield useful information about individual particles, but typically require low temperatures, high vacuum environments, or long measurement times.…”