Tuning The Magnetic Anisotropy And Magnetization Reversal Mechanism Investigation Of Patterned FeTa Films

With miniaturization and high frequency of electromagnetic devices, the requirements for high frequency soft magnetic thin films are more demanding. This requires that the materials have a higher saturation magnetization (Ms), permeability (μ), the resistivity (ρ) and appropriately magnetic anisotropy field (Hk), so that the materials has a higher cut-off frequency. In order to meet the requirements of high-frequency magnetic thin film device, the film materials with the resonance frequency in the GHz or above have become research hotspots in this field.In this work, A series of FeTa films with the thickness of130nm have been fabricated on glass substrates by magnetron sputtering at ambient condition. Conventional optical lithography was used to fabricate the strip array with different length and width. The crystal structure of the samples was examined using X-ray diffraction (XRD) with Cu-Ka radiation. We used atomic force microscope (AFM) to observe the surface topographies, At the same time, we use magnetic force microscope (MFM) to study the domain structure of samples. Magnetic properties of the FeTa films were measured by a vibrating sample magnetometer (VSM)(MicroSense EV-9) with the magnetic field resolution and sweep rates around7.8A/m and96.0A/m per second, respectively. A Durham micro-focused Magneto-optical Kerr Effect (MOKE) equipment NanoMOKE2TM was utilized to study the magnetic properties of a single strip with a3μm sized laser spot focused on the middle and end parts of the strip, respectively. The longitude Kerr signal was recorded with the applied field along the length direction of strips. The high frequency properties were observed by using the shorted microstrip transmission-line perturbation method. All measurements were performed at room temperature. The results are shown as follow:1、The as deposited continuous FeTa films show the isotropic magnetic properties with crystallized bcc structure and FeTa grain size around15.7nm. The saturation magnetization (47iMs) and coercivity (He) obtained from the hysteresis loop are19kGs and9.8Oe, respectively.2、In order to study the influence of the length of magnetic strip on magnetic anisotropy, we etch the continuous films into strip arrays with the length of strip from30μm to2500μm while the widths of strip are kept at30μm. The results indicate that the in plane uniaxial anisotropy of sample gradually become strong with change the aspect ratio from1:1to167:1. When the aspect ratio up to20:1, the hysteresis loop is basically no longer change, we consider that the magnetic moment almost arranged along the easy axis by the shape anisotropy. At the same time, the anisotropy field is keeping constant as the aspect ratio larger than20:1. The constant anisotropy field was understood by the constant demagnetizing factor of t/W, since the film thickness and strip width are constant with the change of the strip length.3、In order to research the influence of the width of strip on the magnetic anisotropy of sample, we etch the continuous films into strip arrays with the width of strip from50p.m to10μm while the lengths of strip are kept at5000μm. The results show that all the samples have obvious in-plane uniaxial anisotropy, the anisotropy field of samples gradually increasing as the width of strip decreasing. At the same time, the in-plane anisotropy field is proportional to the reciprocal of the strip width, i.e., the anisotropy is proportional to the aspect ratio. The linear increase of anisotropy field was understood by the linear increase of demagnetizing factor of t/W, since the film thickness is constant with the decrease of the strip width.4、The magnetization reversal mechanism has been investigated. The angular dependence of the coercivity shows a characteristic "M-shaped" curve. When the magnetic field is near the easy axis, the angular dependence of coercivity (ADC) curve is can be described by the Kondorsky model, indicating the domain wall nucleation mechanism of magnetization reversal. When the magnetic field is near the hard axis, ADC curve can be described by the Stoner-Wolfth model, indicating the coherent rotation of magnetization reversal mechanism. However, these two models can not explain all the data. The M-shaped ADC curve is finally well explained in terms of the two-phase model for all angles. 5、The high-frequency magnetic measurements show that the resonant frequency is moved to the higher frequency direction as the width of strip decreasing. For the sample with the aspect ratio of500:1, the resonance frequency is more than7GHz. Therefore tuning anisotropy can be achieved by changing the aspect of the strip, so as to realize the tuning of the high frequency soft magnetic properties.