共查询到15条相似文献,搜索用时 992 毫秒
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实验研究了石榴石磁泡薄膜中不同脉冲宽度下产生的硬磁畴的动态特性.结果表明:由零偏场下产生的枝状畴收缩而成的哑铃畴均逆时针转动,与产生枝状畴时所用的脉冲偏场的脉冲宽度无关.而固定直流偏场下由软畴段硬化而成的哑铃畴的转动状态,则与所用的硬化脉冲偏场的脉冲宽度有关.低脉冲宽度下硬化成的哑铃畴均逆时针转动,随硬化脉冲宽度的升高,出现混合转动向顺时针转动的过渡.由此揭示了直流偏场和脉冲偏场在石榴石磁泡薄膜中形成正、负垂直布洛赫线的作用.
关键词:
磁畴
磁泡
垂直布洛赫线 相似文献
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前 言 磁泡材料的畴壁迁移率和磁泡状态的测定是磁泡动态测量的两个重要内容.早先的阶梯函数响应法[1]和磁泡破灭法[2]虽然都能测量畴壁迁移率μω,但用作常规测试都不理想,并且都不能用来确定磁泡的状态. 本文所介绍的脉冲梯度场磁泡传输法[3],直接测量孤立磁泡在脉冲梯度场中的运动速度,从而测得迁移率.同时又从磁泡的运动方向确定磁泡的状态,方法简便,原理直观,所以这个方法被广泛地应用于常规测试和基础研究. 一、测量原理 1.用脉冲梯度场磁泡传输法测迁移率μω。 在梯度为 H的不均匀偏场中,磁泡将受力而沿- H的方向运动.磁泡速度V… 相似文献
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M. Carbucicchio R. Ciprian G. Palombarini 《Journal of magnetism and magnetic materials》2010,322(9-12):1307-1310
Ultrathin films of L10-ordered FePt alloy with different thickness were grown by UHV e-beam evaporation technique. In this ultrathin regime, the increase of the thickness induces a strong improvement of the magnetic properties followed by a decrease of the grain size. Starting from these hard layers, FePt/Fe/FePt trilayers with different thickness of the outermost layer have been grown. The samples show a single-phase magnetic behaviour and a strong perpendicular anisotropy thanks to the exchange-coupling that established at the soft/hard interfaces. By increasing the thickness of the outer layer, a strong reduction of the switching field distribution has been obtained with the appearance of a predominant exchange-type interaction among the magnetic grains. The morphology is characterized by well separated and elongated islands, while the magnetic pattern shows finely dispersed bubble domains. 相似文献
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Boiling histotripsy is a High Intensity Focused Ultrasound (HIFU) technique which uses a number of short pulses with high acoustic pressures at the HIFU focus to induce mechanical tissue fractionation. In boiling histotripsy, two different types of acoustic cavitation contribute towards mechanical tissue destruction: a boiling vapour bubble and cavitation clouds. An understanding of the mechanisms underpinning these phenomena and their dynamics is therefore paramount to predicting and controlling the overall size of a lesion produced for a given boiling histotripsy exposure condition. A number of studies have shown the effects of shockwave heating in generating a boiling bubble at the HIFU focus and have studied its dynamics under boiling histotripsy insonation. However, not much is known about the subsequent production of cavitation clouds that form between the HIFU transducer and the boiling bubble. The main objective of the present study is to examine what causes this bubble cluster formation after the generation of a boiling vapour bubble. A numerical simulation of 2D nonlinear wave propagation with the presence of a bubble at the focus of a HIFU field was performed using the k-Wave MATLAB toolbox for time domain ultrasound simulations, which numerically solves the generalised Westervelt equation. The numerical results clearly demonstrate the appearance of the constructive interference of a backscattered shockwave by a bubble with incoming incident shockwaves. This interaction (i.e., the reflected and inverted peak positive phase from the bubble with the incoming incident rarefactional phase) can eventually induce a greater peak negative pressure field compared to that without the bubble at the HIFU focus. In addition, the backscattered peak negative pressure magnitude gradually increased from 17.4 MPa to 31.6 MPa when increasing the bubble size from 0.2 mm to 1.5 mm. The latter value is above the intrinsic cavitation threshold of –28 MPa in soft tissue. Our results suggest that the formation of a cavitation cloud in boiling histotripsy is a threshold effect which primarily depends (a) the size and location of a boiling bubble, and (b) the sum of the incident field and that scattered by a bubble. 相似文献
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Ha Yong Lee Se Hun Jung Soo Yong Lee Young Ho You Kyung Hyun Ko 《Applied Surface Science》2005,252(5):1891-1898
Al-Al2O3 composite coatings with different Al2O3 particle shapes were prepared on Si and Al substrate by cold spray. The powder compositions of metal (Al) and ceramic (Al2O3) having different sizes and agglomerations were varied into ratios of 10:1 wt% and 1:1 wt%. Al2O3 particles were successfully incorporated into the soft metal matrix of Al. It was found that crater formation between the coatings and substrate, which is typical characteristic signature of cold spray could be affected by initial starting Al2O3 particles. In addition, when the large hard particles of fused Al2O3 were employed, the deep and big craters were generated at the interface between coatings and hard substrates. In the case of pure soft metal coating such as Al on hard substrate, it is very hard to get proper adhesion due to lack of crater formation. Therefore, the composite coating would have certain advantages. 相似文献