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Title: Effect of heavy metal layer thickness on spin-orbit torque and current-induced switching in Hf|CoFeB|MgO structures

Abstract

We study the heavy metal layer thickness dependence of the current-induced spin-orbit torque (SOT) in perpendicularly magnetized Hf broken vertical bar CoFeB broken vertical bar MgO multilayer structures. The damping-like (DL) current-induced SOT is determined by vector anomalous Hall effect measurements. A non-monotonic behavior in the DL-SOT is found as a function of the thickness of the heavy-metal layer. The sign of the DL-SOT changes with increasing the thickness of the Hf layer in the trilayer structure. As a result, in the current-driven magnetization switching, the preferred direction of switching for a given current direction changes when the Hf thickness is increased above similar to 7 nm. Although there might be a couple of reasons for this unexpected behavior in DL-SOT, such as the roughness in the interfaces and/or impurity based electric potential in the heavy metal, one can deduce a roughness dependence sign reversal in DL-SOT in our trilayer structure.

Authors:
ORCiD logo; ; ORCiD logo; ; ; ; ;
Publication Date:
Research Org.:
Argonne National Lab. (ANL), Argonne, IL (United States)
Sponsoring Org.:
USDOE Office of Science - Office of Basic Energy Sciences - Materials Sciences and Engineering Division; National Science Foundation (NSF); U.S. Department of Defense (DOD) - Defense Advanced Research Projects Agency (DARPA)
OSTI Identifier:
1376723
DOE Contract Number:
AC02-06CH11357
Resource Type:
Journal Article
Resource Relation:
Journal Name: Applied Physics Letters; Journal Volume: 109; Journal Issue: 2
Country of Publication:
United States
Language:
English

Citation Formats

Akyol, Mustafa, Jiang, Wanjun, Yu, Guoqiang, Fan, Yabin, Gunes, Mustafa, Ekicibil, Ahmet, Khalili Amiri, Pedram, and Wang, Kang L. Effect of heavy metal layer thickness on spin-orbit torque and current-induced switching in Hf|CoFeB|MgO structures. United States: N. p., 2016. Web. doi:10.1063/1.4958295.
Akyol, Mustafa, Jiang, Wanjun, Yu, Guoqiang, Fan, Yabin, Gunes, Mustafa, Ekicibil, Ahmet, Khalili Amiri, Pedram, & Wang, Kang L. Effect of heavy metal layer thickness on spin-orbit torque and current-induced switching in Hf|CoFeB|MgO structures. United States. doi:10.1063/1.4958295.
Akyol, Mustafa, Jiang, Wanjun, Yu, Guoqiang, Fan, Yabin, Gunes, Mustafa, Ekicibil, Ahmet, Khalili Amiri, Pedram, and Wang, Kang L. Mon . "Effect of heavy metal layer thickness on spin-orbit torque and current-induced switching in Hf|CoFeB|MgO structures". United States. doi:10.1063/1.4958295.
@article{osti_1376723,
title = {Effect of heavy metal layer thickness on spin-orbit torque and current-induced switching in Hf|CoFeB|MgO structures},
author = {Akyol, Mustafa and Jiang, Wanjun and Yu, Guoqiang and Fan, Yabin and Gunes, Mustafa and Ekicibil, Ahmet and Khalili Amiri, Pedram and Wang, Kang L.},
abstractNote = {We study the heavy metal layer thickness dependence of the current-induced spin-orbit torque (SOT) in perpendicularly magnetized Hf broken vertical bar CoFeB broken vertical bar MgO multilayer structures. The damping-like (DL) current-induced SOT is determined by vector anomalous Hall effect measurements. A non-monotonic behavior in the DL-SOT is found as a function of the thickness of the heavy-metal layer. The sign of the DL-SOT changes with increasing the thickness of the Hf layer in the trilayer structure. As a result, in the current-driven magnetization switching, the preferred direction of switching for a given current direction changes when the Hf thickness is increased above similar to 7 nm. Although there might be a couple of reasons for this unexpected behavior in DL-SOT, such as the roughness in the interfaces and/or impurity based electric potential in the heavy metal, one can deduce a roughness dependence sign reversal in DL-SOT in our trilayer structure.},
doi = {10.1063/1.4958295},
journal = {Applied Physics Letters},
number = 2,
volume = 109,
place = {United States},
year = {Mon Jul 11 00:00:00 EDT 2016},
month = {Mon Jul 11 00:00:00 EDT 2016}
}
  • We study the heavy metal layer thickness dependence of the current-induced spin-orbit torque (SOT) in perpendicularly magnetized Hf|CoFeB|MgO multilayer structures. The damping-like (DL) current-induced SOT is determined by vector anomalous Hall effect measurements. A non-monotonic behavior in the DL-SOT is found as a function of the thickness of the heavy-metal layer. The sign of the DL-SOT changes with increasing the thickness of the Hf layer in the trilayer structure. As a result, in the current-driven magnetization switching, the preferred direction of switching for a given current direction changes when the Hf thickness is increased above ∼7 nm. Although there might bemore » a couple of reasons for this unexpected behavior in DL-SOT, such as the roughness in the interfaces and/or impurity based electric potential in the heavy metal, one can deduce a roughness dependence sign reversal in DL-SOT in our trilayer structure.« less
  • We study the effect of the oxide layer on current-induced perpendicular magnetization switching properties in Hf|CoFeB|MgO and Hf|CoFeB|TaO{sub x} tri-layers. The studied structures exhibit broken in-plane inversion symmetry due to a wedged CoFeB layer, resulting in a field-like spin-orbit torque (SOT), which can be quantified by a perpendicular (out-of-plane) effective magnetic field. A clear difference in the magnitude of this effective magnetic field (H{sub z}{sup FL}) was observed between these two structures. In particular, while the current-driven deterministic perpendicular magnetic switching was observed at zero magnetic bias field in Hf|CoFeB|MgO, an external magnetic field is necessary to switch the CoFeBmore » layer deterministically in Hf|CoFeB|TaO{sub x}. Based on the experimental results, the SOT magnitude (H{sub z}{sup FL} per current density) in Hf|CoFeB|MgO (−14.12 Oe/10{sup 7} A cm{sup −2}) was found to be almost 13× larger than that in Hf|CoFeB|TaO{sub x} (−1.05 Oe/10{sup 7} A cm{sup −2}). The CoFeB thickness dependence of the magnetic switching behavior, and the resulting  H{sub z}{sup FL} generated by in-plane currents are also investigated in this work.« less
  • We study the effect of the oxide layer on the current-induced spin-orbit torques (SOTs) in perpendicularly magnetized Hf|CoFeB|MgO (MgO-capped) or Hf|CoFeB|TaO{sub x} (TaO{sub x}-capped) structures. The effective fields corresponding to both the field-like and damping-like current-induced SOTs are characterized using electric transport measurements. Both torques are found to be significantly stronger in MgO-capped structures than those in TaO{sub x}-capped structures. The difference in field-like and damping-like SOTs in the different structures may be attributed to the different Rashba-like Hamiltonian, arising from the difference in the electric potential profiles across the oxide|ferromagnet interfaces in the two cases, as well as possiblemore » structural and oxidation differences in the underlying CoFeB and Hf layers. Our results show that the oxide layer in heavy-metal|ferromagnet|oxide trilayer structures has a very significant effect on the generated SOTs for manipulation of ferromagnetic layers. These findings could potentially be used to engineer SOT devices with enhanced current-induced switching efficiency.« less
  • We report that strong perpendicular magnetic anisotropy of the ferromagnetic layer in a W/CoFeB/MgO multilayer structure can be established by inserting a Hf layer as thin as 0.25 nm between the W and CoFeB layers. The Hf spacer also allows transmission of spin currents generated by an in-plane charge current in the W layer to apply strong spin torque on the CoFeB, thereby enabling current-driven magnetic switching. The antidamping-like and field-like components of the spin torque exerted on a 1 nm CoFeB layer are of comparable magnitudes in this geometry. Both components originate from the spin Hall effect in the underlying Wmore » layer.« less
  • We study the device size dependence of spin-orbit torque induced magnetization switching in a Ta/CoFeB/MgO structure with perpendicular easy axis. The miniaturization of the device from micrometer-sized wire to 80-nm dot results in the increase of the threshold current density J{sub th} by one order, whereas J{sub th} increases only slightly with further reducing the device size down to 30 nm. No significant increase in J{sub th} is seen, as the current pulse width decreases from 100 ms down to 3 ns. We reveal that the switching in devices at reduced size is reasonably well explained by the macrospin model, in which themore » effects of both the Slonczewski-like torque and field-like torque are included.« less