Surface anisotropy and resonance modes in Co − SiO 2 heterogeneous films
Surface anisotropy and resonance modes in Co − SiO 2 heterogeneous films
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DOI：
10.1103/physrevb.70.054428
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发表时间：
2004-08
影响因子：
3.7
通讯作者：
J. Gómez;A. Butera;J. Barnard
中科院分区：
文献类型：
--
作者：
J. Gómez;A. Butera;J. Barnard
我们研究了${\mathrm{Co}\text{\ensuremath{-}}\mathrm{SiO}}_{2}$薄膜的磁性随掺杂浓度的变化规律。用射频溅射法制备了薄膜，获得了$0.18\ensuremath{\leqslant}x\ensuremath{\leqslant}0.62$范围内的体积浓度。样品在X波段$(\ensuremath{\nu}=9.5\phantom{\rule{0.3em}{0ex}}\mathrm{GHz})$和Q波段$(\ensuremath{\nu}=35\phantom{\rule{0.3em}{0ex}}\mathrm{GHz})$.处使用铁磁共振进行测量在所有薄膜中都观察到了与磁矩的均匀进动有关的主要吸收。从该共振场出发，我们求出了有效各向异性场$({H}{\mathm{Jeff}})$作为$x$的函数。对于低浓度的{Co}，形状各向异性是对{H}_{\mathm{Jeff}}$的主要贡献。然而，在临界浓度${x}_{p}\Ensureath{\sim}0.37$(与$\mathm{Co}$颗粒的渗流重合)以上，有必要假设存在额外的各向异性来解释实验数据。在相同的浓度下，共振谱随高于均匀共振模的场的额外吸收而发生变化。对于较大的{Co}浓度，在中间场观察到另一种吸收。我们使用表面不均匀模型分析了这些额外的线，该模型考虑了表面矩的不同环境。表面各向异性被确定为$x$的函数，其行为与从${H}_{\mathm{Jeff}}$获得的附加各向异性非常相似。原位退火研究支持这样的假设，即观察到的行为起源于表面的影响，并表明两种薄膜表面的不等价性。
We have studied the magnetic properties of ${\mathrm{Co}\text{\ensuremath{-}}\mathrm{SiO}}_{2}$ films as a function of the $\mathrm{Co}$ concentration. Films were prepared using rf sputtering and $\mathrm{Co}$ volume concentrations in the range $0.18\ensuremath{\leqslant}x\ensuremath{\leqslant}0.62$ were obtained. The samples were measured using ferromagnetic resonance at X-band $(\ensuremath{\nu}=9.5\phantom{\rule{0.3em}{0ex}}\mathrm{GHz})$ and Q-band $(\ensuremath{\nu}=35\phantom{\rule{0.3em}{0ex}}\mathrm{GHz})$. A main absorption associated to the uniform precession of the magnetic moments was observed in all films. From this resonance field we have evaluated an effective anisotropy field $({H}_{\mathrm{eff}})$ as a function of $x$. For low $\mathrm{Co}$ concentrations the shape anisotropy is the major contribution to ${H}_{\mathrm{eff}}$. However, above a critical concentration ${x}_{p}\ensuremath{\sim}0.37$ (coincident with the percolation of the $\mathrm{Co}$ granules) it is necessary to assume the presence of an additional anisotropy to explain the experimental data. At this same concentration the resonance spectra change with the appearance of an extra absorption at fields higher than that of the uniform resonance mode. For larger $\mathrm{Co}$ concentrations another absorption is observed at intermediate fields. We have analyzed these extra lines using the surface inhomogeneity model that takes into account the different environment of the surface moments. The surface anisotropy was determined as a function of $x$ with a behavior quite similar to the additional anisotropy obtained from ${H}_{\mathrm{eff}}$. In situ annealing studies support the assumption that the observed behavior originates in the effects of the surface and suggest the nonequivalence of both film surfaces.