Chiral Magnetic Domain Wall and Skyrmion Memory Devices
183
Fig. 5 DW dynamics driven by STTs (a), and SOTs (b) in an out-of-plane magnetized thin film.
The colors on the strip represent the z component of the magnetization. The top and bottom panels
of a represent the torques arising from the adiabatic and non-adiabatic STTs, respectively. The
top and bottom panels of b represent the torques arising from the field—and damping-like SOTs,
respectively. The H d in a is attributed to the demagnetization field against to the increase of the
magnetic volume charge. The H eff in b is from the interfacial Dzyaloshinskii-Moriya interaction
that prefer the Néel wall than the Bloch wall. The orange—and green-colored arrows indicate the
precession and damping torques, respectively, induced by the STTs (or SOTs) and H d (H eff ). The
cone-arrows on the plane represent the local magnetization (m) within DWs
be discussed later). As seen in Fig. 5b, when the field-like torque is exerted on the
local magnetization, all torques are canceled out, therefore, this torque cannot solely
move the DWs as like the adiabatic STT. On the contrary, the damping-like torque
can drive the DW motion even at a very small current density, and the DW can move
against to the electron flow—this depends on the sign of a spin Hall angle (or a ISGE
coefficient) of the heavy metal adjacent to the ferromagnet and the chirality of the
DW.
Although these two mechanisms cannot fully explain the experimental data, it has
been experimentally shown that these two spin–orbit torques (SOTs), field-like and
damping-like torques, are indeed present in ferromagnetic multilayers, particularly
consisting of heavy metals and ferromagnetic metals. These SOTs play an important
role in driving DWs or switching magnetization in ferromagnetic thin films. Therefore
quantifying the SOT in different systems is critical to fully understand the DW
motion and magnetization switching. In the following sections, we will introduce
the experimental techniques to quantify these SOTs.
183
Fig. 5 DW dynamics driven by STTs (a), and SOTs (b) in an out-of-plane magnetized thin film.
The colors on the strip represent the z component of the magnetization. The top and bottom panels
of a represent the torques arising from the adiabatic and non-adiabatic STTs, respectively. The
top and bottom panels of b represent the torques arising from the field—and damping-like SOTs,
respectively. The H d in a is attributed to the demagnetization field against to the increase of the
magnetic volume charge. The H eff in b is from the interfacial Dzyaloshinskii-Moriya interaction
that prefer the Néel wall than the Bloch wall. The orange—and green-colored arrows indicate the
precession and damping torques, respectively, induced by the STTs (or SOTs) and H d (H eff ). The
cone-arrows on the plane represent the local magnetization (m) within DWs
be discussed later). As seen in Fig. 5b, when the field-like torque is exerted on the
local magnetization, all torques are canceled out, therefore, this torque cannot solely
move the DWs as like the adiabatic STT. On the contrary, the damping-like torque
can drive the DW motion even at a very small current density, and the DW can move
against to the electron flow—this depends on the sign of a spin Hall angle (or a ISGE
coefficient) of the heavy metal adjacent to the ferromagnet and the chirality of the
DW.
Although these two mechanisms cannot fully explain the experimental data, it has
been experimentally shown that these two spin–orbit torques (SOTs), field-like and
damping-like torques, are indeed present in ferromagnetic multilayers, particularly
consisting of heavy metals and ferromagnetic metals. These SOTs play an important
role in driving DWs or switching magnetization in ferromagnetic thin films. Therefore
quantifying the SOT in different systems is critical to fully understand the DW
motion and magnetization switching. In the following sections, we will introduce
the experimental techniques to quantify these SOTs.