Spin–orbit coupling can convert a charge current into a spin current, thereby generating a spin–orbit torque (SOT). Energy-efficient, commercially viable SOT technology requires field-free switching of perpendicular magnetization at low current. In heterostructures incorporating ferromagnets, the polarization of spin current consists, in general, of three vectors: \(( {{{{\hat{\mathrm z}}}} \times {{{\hat{\mathrm E}}}}} )\), \({{{\hat{\mathrm m}}}}\) and \({{{\hat{\mathrm m}}}} \times ( {{{{\hat{\mathrm z}}}} \times {{{\hat{\mathrm E}}}}} )\), where \({{{\hat{\mathrm z}}}}\) is the film normal, \({{{\hat{\mathrm E}}}}\) is the electric-field direction and \({{{\hat{\mathrm m}}}}\) is the magnetization direction. Previous studies on SOT have used only part of all the three polarizations, because the two \({{{\hat{\mathrm m}}}}\)-dependent polarizations are mutually orthogonal. Here we show that all the three polarizations can be exploited in systems with ferromagnet/non-magnet/ferromagnet trilayers, having a bottom epitaxial ferromagnet layer with a tilted magnetic easy axis. The approach reduces the field-free SOT switching current compared with approaches that exploit only part of all the three polarizations. We also show that this technique can be used with a sputtered polycrystalline trilayer, illustrating its potential applicability to mass production.

自旋轨道耦合可以将充电电流转换为自旋电流，从而产生自旋轨道扭矩（SOT）。节能、商业上可行的 SOT 技术需要在低电流下进行垂直磁化的无场切换。在包含铁磁体的异质结构中，自旋电流的极化通常由三个向量组成：\(( {{{{\hat{\mathrm z}}}} \times {{{\hat{\mathrm E}}} }} )\) , \({{{\hat{\mathrm m}}}​​}\)和\({{{\hat{\mathrm m}}}​​} \times ( {{{{\hat{\ mathrm z}}}} \times {{{\hat{\mathrm E}}}}} )\)，其中\({{{\hat{\mathrm z}}}}\)是电影法线，\ ({{{\hat{\mathrm E}}}}\)是电场方向，\({{{\hat{\mathrm m}}}​​}\)是磁化方向。以前对 SOT 的研究仅使用了所有三个极化的一部分，因为两个与\({{{\hat{\mathrm m}}}​​}\)相关的极化是相互正交的。在这里，我们表明所有三种极化都可以在具有铁磁体/非磁体/铁磁体三层的系统中利用，该系统具有底部外延铁磁体层和倾斜的易磁轴。与仅利用所有三种极化中的一部分的方法相比，该方法降低了无场 SOT 开关电流。我们还表明，该技术可用于溅射多晶三层，说明其在大规模生产中的潜在适用性。