We present a detailed low-energy muon spin rotation and x-ray magnetic circular dichroism (XMCD) investigation of the magnetic structure in ultrathin tetragonal (T)-CuO films. The measured muon-spin polarization decay indicates an antiferromagnetic (AFM) order with a transition temperature higher than 200 K. The XMCD signal obtained around the $\mathrm{Cu}{L}_{2,3}$ edges indicates the presence of pinned ${\mathrm{Cu}}^{2+}$ moments that are parallel to the sample surface, and additionally, isotropic paramagnetic moments. The pinning of some of the Cu moments is caused by an AFM ordering consisting of moments that lie most likely in plane of the film. Moreover, pinned moments show a larger orbital magnetic moment contribution with an approximate ratio of $m_{\mathrm{orb}}/m_{\mathrm{spin}}=1.5$, indicating that these spins are located at sites with reduced symmetry. Some fractions of the pinned moments remain pinned from an AFM background even at 360 K, indicating that $T_{\mathrm{N}}>360\mathrm{K}$. We propose a simple model that explains these experimental findings, showing that the magnetic order of the $T$-CuO ultrathin films differs from the theoretical predictions.

中文翻译：

---

四方CuO超薄膜的磁序

我们对超薄四方 (T)-CuO 薄膜中的磁性结构进行了详细的低能 μ 子自旋旋转和 X 射线磁圆二色性 (XMCD) 研究。测量的μ子自旋极化衰减表明转变温度高于 200 K 的反铁磁 (AFM) 阶。在周围获得的 XMCD 信号$铜{升}_{2,3}$ 边缘表示存在固定 ${铜}^{2+}$平行于样品表面的磁矩，以及各向同性的顺磁矩。一些 Cu 矩的钉扎是由 AFM 排序引起的，该排序由最有可能位于薄膜平面内的矩组成。此外，钉扎矩显示出更大的轨道磁矩贡献，大约为${米}_{\mathrm{球体}}/{米}_{\mathrm{旋转}}=1.5$，表明这些自旋位于对称性降低的位置。即使在 360 K 时，固定力矩的某些部分仍然固定在 AFM 背景中，表明${吨}_{\mathrm{N}}>360\mathrm{钾}$. 我们提出了一个简单的模型来解释这些实验结果，表明$吨$-CuO 超薄膜不同于理论预测。