Issue when SOT current is applied along x direction
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Aarthi Tamil maran
Jun 24, 2026, 9:30:46 AM (10 days ago) Jun 24
to mumax2
Hi, when SOT current is applied along the x-direction, the system (mx) switches from the +1 to +0.96 state, not even near zero for J = 2e12 A/m2 and pulse duration (80 ps).
If current is applied along the z-direction without changing any parameter, then the system switches from +1 to -1 state for J = 2e10 A/m2 and pulse duration (80 ps). i have enclosed my code for reference. Kindly clarify this and give some suggestions.
Josh Lauzier
Jun 24, 2026, 5:30:50 PM (10 days ago) Jun 24
to mumax2
Hi,
In mumax3, the Slonczewski STT only works with currents in the z direction. When you use this type of set up for SOT, you are repuporpising the existing Slonczewski STT to do SOT (which is not natively built into mumax3). This is normally fine, but with the one limitation is that it still only sees currents in the z directions.
To fix this, there are two options. One is to rotate your entire sample, so that the x direction becomes z. The second is instead of repurposing STT, you use a Custom Fields approach. An example of Custom fields to do STT is given in the mumax tutorial here. See session 4. Custom fields does not have any restrictions in terms of directions and but is otherwise equivalent to reusing STT.
The current effect you're seeing is due solely to Zhangli STT, which is not currently disabled and has a very different form from STT (see Eqs 26 and 28 in the mumax paper "The Design and verification of mumax3". Slonczewski type torques go as mxm_pxm and mxm_p, where m_p is the polarization layer , whereas Zhangli go as mx(mx(udotgrad))m and mx(udotgrad)m ). You can set disableZhanglitorque=true to fully disable this, if you don't think it plays any role in your simulation.
Best regards,
Josh L.
In mumax3, the Slonczewski STT only works with currents in the z direction. When you use this type of set up for SOT, you are repuporpising the existing Slonczewski STT to do SOT (which is not natively built into mumax3). This is normally fine, but with the one limitation is that it still only sees currents in the z directions.
To fix this, there are two options. One is to rotate your entire sample, so that the x direction becomes z. The second is instead of repurposing STT, you use a Custom Fields approach. An example of Custom fields to do STT is given in the mumax tutorial here. See session 4. Custom fields does not have any restrictions in terms of directions and but is otherwise equivalent to reusing STT.
The current effect you're seeing is due solely to Zhangli STT, which is not currently disabled and has a very different form from STT (see Eqs 26 and 28 in the mumax paper "The Design and verification of mumax3". Slonczewski type torques go as mxm_pxm and mxm_p, where m_p is the polarization layer , whereas Zhangli go as mx(mx(udotgrad))m and mx(udotgrad)m ). You can set disableZhanglitorque=true to fully disable this, if you don't think it plays any role in your simulation.
Best regards,
Josh L.
Aarthi Tamil maran
Jun 27, 2026, 6:14:09 AM (7 days ago) Jun 27
to mum...@googlegroups.com
Thank you for your suggestion. Hope this will be helpful.
Thank you.
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