Cross-sectional magnetic domain analysis by three-dimensional magnetic charge distribution measurement in magnetic thin films

为了提高近年来高密度磁记录介质的记录密度，不仅在薄膜平面方向上而且在薄膜的横截面方向上都强烈需要观察和控制这些薄膜的磁畴结构，这是因为由于磁化波动引起的介质噪声降低。研究了用磁力显微镜测量磁性薄膜中磁荷三维分布的方法。结果表明：（1）在MFM的分辨率受输入信号的数字化分辨率限制的情况下，三维磁荷分布的测量是可能的。该测量可以通过从具有相同尖端-样本距离的变换后的MFM信号中减去实验获得的MFM信号来完成，所述变换后的MFM信号通过MFM信号变换方法从在不同尖端-样本距离处测量的信号变换成。2）对于三维磁荷分布测量，需要在针尖-样品距离较短的情况下，磁场方向不受样品杂散磁场影响的针尖。我们研制了高矫顽力的溅射L10有序CoPt薄膜的MFM针尖，Hc = 14 kOe。3）对于三维磁荷分布测量，了解MFM针尖的磁化强度是很重要的。因此，我们发展了通过对MFM针尖施加交变磁场来检测MFM针尖的交变力，从而实现MFM针尖磁滞回线的原位测量方法。4）MFM分辨率的提高对三维磁荷分布的测量是有效的。通过增加MFM输入信号的动态范围和使用锁相放大器降低信号噪声，研制了分辨率为10 nm的高分辨率MFM。

In order to improve the recording density for recent high density magnetic recording media, the observation and control of magnetic domain structure for these films in not only the film plain direction but also the cross-sectional direction of films is strongly needed, because of the reduction of medium noise due to tlie fluctuation of magnetization. In the present study, the method of three-dimensional magnetic charge distribution measurement in magnetic thin films by using magnetic force microscope (MFM) was investigated. The following results are obtained.1) Three-dimensional magnetic chargedistribution measurement is possible in the case that the resolution of MFM is limited by the digitizing resolution of the input signals in MFM. This measurement can be done by subtracting the experimentally obtained MFM signals from the transformed MFM signals with same tip-sample distance to which are transformed from the signals measured at different tip-sample distance by MFM signal transformation method. This method is verified by computer simulation2) For three-dimensional magnetic charge distribution measurement, the MFM tip whose magnetic direction does not change by the stray field of MFM samples at short tip-sample distance is needed. We developed high coercivity MFM tips coated by sputtered L10 ordered CoPt films with Hc = 14kOe.3) For three-dimensional magnetic charge distribution measurement, it is important to know the MFM tip magnetization. Therefore we developed the method of in-situ magnetic hysteresis measurement of MFM tips by detecting the alternating force of MFM tips with applying alternating magnetic field to MFM tips.4) The improvement of MFM resolution is effective for three-dimensional magnetic charge distribution measurement. We developed the high-resolution MFM with 10 nm resolution by increasing the dynamic range of MFM input signals and using Lock-in amplifier to reduce signal noise.