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Anisotropic magnetism of graphite irradiated with medium-energy hydrogen and helium ions

机译：中能氢和氦离子辐照石墨的各向异性磁性

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We have studied the changes in the magnetic behavior of highly oriented pyrolytic graphite (HOPG) samples subjected to medium-energy proton and helium irradiation. The variations of the ferromagneticlike magnetization curves with the irradiation dose have been studied for two configurations: magnetic fields parallel and perpendicular to graphitic planes. For high irradiation doses, the values of magnetization at saturation are close for both geometries. At low irradiation fluences an orientationally dependent magnetic response is obtained. Directional dependence of magnetization indicates that the magnetism in irradiated graphite is triggered by vertically aligned intrinsic carbon defects induced by irradiation. This physical picture has been verified by the observation of a local stray field near linear defects by means of magnetic force microscopy. Similar results obtained with hydrogen and helium ions confirm that the chemical nature of projectiles is not crucial for formation of ferromagnetic order in oriented graphite. The dependence of induced magnetic moment versus irradiation dose shows a maximum; the optimal dose is an order of magnitude less for helium ions than for protons, being in line with simulations showing that He~+ generates 8 times more defects than H~+. Raman studies indicate that the degradation of magnetic ordering at large irradiation doses occurs much earlier than graphite amorphization but coincides with the destruction of graphene sheet stacking.
机译：我们已经研究了中能质子和氦气辐照的高取向热解石墨（HOPG）样品的磁行为变化。对于两种配置，研究了铁磁性类磁化曲线随辐照剂量的变化：平行和垂直于石墨平面的磁场。对于高辐照剂量，两种几何结构的饱和磁化强度值均接近。在低辐照通量下，可获得取向依赖性的磁响应。磁化的方向依赖性表明，被辐照的石墨中的磁是由辐照引起的垂直排列的固有碳缺陷触发的。通过磁力显微镜观察线性缺陷附近的局部杂散场，已验证了该物理图像。用氢和氦离子获得的类似结果证实，抛射体的化学性质对于定向石墨中铁磁有序化的形成不是至关重要的。感应磁矩对辐照剂量的依赖性最大。氦离子的最佳剂量要比质子的最佳剂量少一个数量级，这与模拟表明He〜+产生的缺陷比H〜+多出8倍的模拟相符。拉曼研究表明，在大剂量辐照下，磁有序性的退化发生的时间比石墨的非晶化要早得多，但与石墨烯片堆叠的破坏相吻合。

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