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Large spin Hall magnetoresistance and its correlation to the spin-orbit torque in W/CoFeB/MgO structures.

Cho S, Baek SH, Lee KD, Jo Y, Park BG - Sci Rep (2015)

Bottom Line: This implies the existence of an inverse effect, in which the conductivity in such structures should depend on the magnetization orientation.We observe that the MR is independent of the angle between the magnetization and current direction but is determined by the relative magnetization orientation with respect to the spin direction accumulated by the spin Hall effect, for which the symmetry is identical to that of so-called the spin Hall magnetoresistance.The MR of ~1% in W/CoFeB/MgO samples is considerably larger than those in other structures of Ta/CoFeB/MgO or Pt/Co/AlOx, which indicates a larger spin Hall angle of W.

View Article: PubMed Central - PubMed

Affiliation: Department of Materials Science and Engineering, KAIST, Daejeon 305-701, Korea.

ABSTRACT
The phenomena based on spin-orbit interaction in heavy metal/ferromagnet/oxide structures have been investigated extensively due to their applicability to the manipulation of the magnetization direction via the in-plane current. This implies the existence of an inverse effect, in which the conductivity in such structures should depend on the magnetization orientation. In this work, we report a systematic study of the magnetoresistance (MR) of W/CoFeB/MgO structures and its correlation with the current-induced torque to the magnetization. We observe that the MR is independent of the angle between the magnetization and current direction but is determined by the relative magnetization orientation with respect to the spin direction accumulated by the spin Hall effect, for which the symmetry is identical to that of so-called the spin Hall magnetoresistance. The MR of ~1% in W/CoFeB/MgO samples is considerably larger than those in other structures of Ta/CoFeB/MgO or Pt/Co/AlOx, which indicates a larger spin Hall angle of W. Moreover, the similar W thickness dependence of the MR and the current-induced magnetization switching efficiency demonstrates that MR in a non-magnet/ferromagnet structure can be utilized to understand other closely correlated spin-orbit coupling effects such as the inverse spin Hall effect or the spin-orbit spin transfer torques.

No MeSH data available.


Related in: MedlinePlus

Switching experiments utilizing spin-orbit torque induced by in-plane current.(a) The magnetization direction detected by AHE measurement after each pulsed current of 10μs while sweeping current. The in-plane magnetic field Hx of 200 Oe is continuously applied during the measurement. Each line is independent AHE measurement as a function of Hz, which is designated in the top axis. The arrows indicate the critical current density for magnetization switching. (b) The inverse ratio of critical current density (Jc) to magnetic anisotropy (Hk) as a function of the W thickness, which is corresponded to the SOT-switching efficiency or the magnitude of SOT.
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f6: Switching experiments utilizing spin-orbit torque induced by in-plane current.(a) The magnetization direction detected by AHE measurement after each pulsed current of 10μs while sweeping current. The in-plane magnetic field Hx of 200 Oe is continuously applied during the measurement. Each line is independent AHE measurement as a function of Hz, which is designated in the top axis. The arrows indicate the critical current density for magnetization switching. (b) The inverse ratio of critical current density (Jc) to magnetic anisotropy (Hk) as a function of the W thickness, which is corresponded to the SOT-switching efficiency or the magnitude of SOT.

Mentions: Thus far, we have investigated the transport characteristics of W/CoFeB/MgO samples. Next, we examine an inverse effect of SMR, i.e., the in-plane current-induced spin-orbit torque (SOT). In order to evaluate the SOT magnitude, we perform a switching experiment using the same samples shown in Fig. 5. We first initialize the magnetization in the + z direction, and then sweep a pulsed current with a pulse width of 10 μs from a positive to a negative value, and vice versa, while maintaining a longitudinal magnetic field Hx of 200 Oe, which is necessary for deterministic switching35. After each current pulse, the magnetization direction is detected by measuring the AHE voltage. When the applied negative pulsed current exceeds a certain threshold, a reversal of the magnetization from + z to –z direction is observed. The AHE measured as a function of Hz is plotted as a line on the graph, indicating complete magnetization switching by the current-induced SOT. Note that a negative current and a positive Hx favor the -z direction of magnetization, which corresponds to the SOT with a negative spin Hall angle. We repeat the switching experiments for samples with various W thicknesses as shown in Fig. 6(a). We find that the critical current density (Jc) for magnetization switching (marked by arrow) strongly depends on the W thickness. For example, switching can be done at a Jc value of ~11 MA/cm2 for samples with a W value of 5 nm, while it exceeds 42 MA/cm2 when W for such samples is 7 nm. In order to compare the SOT magnitude from the switching experiment, the relative amount of the critical current density with respect to magnetic anisotropy (Hk) is plotted in Fig. 6(b), as the ratio of (Jc/Hk)−1 is a rough estimate of the SOT strength31. Here, Hk is obtained from the resistance vs. Hy curves in Fig. 5(a), where the resistance is saturated. This shows that the ratio (Jc/Hk)−1 reaches its maximum at 5 nm W, where SMR is also the largest (see Fig. 5(b)). Given that the ratio corresponds to the SOT efficiency, this finding indicates that the W thickness dependence of the SOT magnitude is identical to that of SMR, suggesting that the SMR and the SOT share the same physical origin of the SHE.


Large spin Hall magnetoresistance and its correlation to the spin-orbit torque in W/CoFeB/MgO structures.

Cho S, Baek SH, Lee KD, Jo Y, Park BG - Sci Rep (2015)

Switching experiments utilizing spin-orbit torque induced by in-plane current.(a) The magnetization direction detected by AHE measurement after each pulsed current of 10μs while sweeping current. The in-plane magnetic field Hx of 200 Oe is continuously applied during the measurement. Each line is independent AHE measurement as a function of Hz, which is designated in the top axis. The arrows indicate the critical current density for magnetization switching. (b) The inverse ratio of critical current density (Jc) to magnetic anisotropy (Hk) as a function of the W thickness, which is corresponded to the SOT-switching efficiency or the magnitude of SOT.
© Copyright Policy - open-access
Related In: Results  -  Collection

License
Show All Figures
getmorefigures.php?uid=PMC4589767&req=5

f6: Switching experiments utilizing spin-orbit torque induced by in-plane current.(a) The magnetization direction detected by AHE measurement after each pulsed current of 10μs while sweeping current. The in-plane magnetic field Hx of 200 Oe is continuously applied during the measurement. Each line is independent AHE measurement as a function of Hz, which is designated in the top axis. The arrows indicate the critical current density for magnetization switching. (b) The inverse ratio of critical current density (Jc) to magnetic anisotropy (Hk) as a function of the W thickness, which is corresponded to the SOT-switching efficiency or the magnitude of SOT.
Mentions: Thus far, we have investigated the transport characteristics of W/CoFeB/MgO samples. Next, we examine an inverse effect of SMR, i.e., the in-plane current-induced spin-orbit torque (SOT). In order to evaluate the SOT magnitude, we perform a switching experiment using the same samples shown in Fig. 5. We first initialize the magnetization in the + z direction, and then sweep a pulsed current with a pulse width of 10 μs from a positive to a negative value, and vice versa, while maintaining a longitudinal magnetic field Hx of 200 Oe, which is necessary for deterministic switching35. After each current pulse, the magnetization direction is detected by measuring the AHE voltage. When the applied negative pulsed current exceeds a certain threshold, a reversal of the magnetization from + z to –z direction is observed. The AHE measured as a function of Hz is plotted as a line on the graph, indicating complete magnetization switching by the current-induced SOT. Note that a negative current and a positive Hx favor the -z direction of magnetization, which corresponds to the SOT with a negative spin Hall angle. We repeat the switching experiments for samples with various W thicknesses as shown in Fig. 6(a). We find that the critical current density (Jc) for magnetization switching (marked by arrow) strongly depends on the W thickness. For example, switching can be done at a Jc value of ~11 MA/cm2 for samples with a W value of 5 nm, while it exceeds 42 MA/cm2 when W for such samples is 7 nm. In order to compare the SOT magnitude from the switching experiment, the relative amount of the critical current density with respect to magnetic anisotropy (Hk) is plotted in Fig. 6(b), as the ratio of (Jc/Hk)−1 is a rough estimate of the SOT strength31. Here, Hk is obtained from the resistance vs. Hy curves in Fig. 5(a), where the resistance is saturated. This shows that the ratio (Jc/Hk)−1 reaches its maximum at 5 nm W, where SMR is also the largest (see Fig. 5(b)). Given that the ratio corresponds to the SOT efficiency, this finding indicates that the W thickness dependence of the SOT magnitude is identical to that of SMR, suggesting that the SMR and the SOT share the same physical origin of the SHE.

Bottom Line: This implies the existence of an inverse effect, in which the conductivity in such structures should depend on the magnetization orientation.We observe that the MR is independent of the angle between the magnetization and current direction but is determined by the relative magnetization orientation with respect to the spin direction accumulated by the spin Hall effect, for which the symmetry is identical to that of so-called the spin Hall magnetoresistance.The MR of ~1% in W/CoFeB/MgO samples is considerably larger than those in other structures of Ta/CoFeB/MgO or Pt/Co/AlOx, which indicates a larger spin Hall angle of W.

View Article: PubMed Central - PubMed

Affiliation: Department of Materials Science and Engineering, KAIST, Daejeon 305-701, Korea.

ABSTRACT
The phenomena based on spin-orbit interaction in heavy metal/ferromagnet/oxide structures have been investigated extensively due to their applicability to the manipulation of the magnetization direction via the in-plane current. This implies the existence of an inverse effect, in which the conductivity in such structures should depend on the magnetization orientation. In this work, we report a systematic study of the magnetoresistance (MR) of W/CoFeB/MgO structures and its correlation with the current-induced torque to the magnetization. We observe that the MR is independent of the angle between the magnetization and current direction but is determined by the relative magnetization orientation with respect to the spin direction accumulated by the spin Hall effect, for which the symmetry is identical to that of so-called the spin Hall magnetoresistance. The MR of ~1% in W/CoFeB/MgO samples is considerably larger than those in other structures of Ta/CoFeB/MgO or Pt/Co/AlOx, which indicates a larger spin Hall angle of W. Moreover, the similar W thickness dependence of the MR and the current-induced magnetization switching efficiency demonstrates that MR in a non-magnet/ferromagnet structure can be utilized to understand other closely correlated spin-orbit coupling effects such as the inverse spin Hall effect or the spin-orbit spin transfer torques.

No MeSH data available.


Related in: MedlinePlus