We have investigated the effects of high frequency strain on domain wall (DW) textures in ferromagnetic thin films with perpendicular anisotropy. Matched pairs of interdigital transducers are lithographically patterned on 128 Y cut LiNbO3. Excitation at the resonance frequency drives surface acoustic waves (SAW). We describe the response of domain walls (DW) and magnetic bubbles. SAW lower the pinning energy barriers of DWs, showing a monotonic decrease in the characteristic depinning time with SAW amplitude. Application of SAW in a different sample rapidly increases the density of bubbles. We measure SAW driven dynamics of bubble domains.
The ability to control magnetic domain patterns with high frequency strain waves could result in a novel, fast method for moving domain walls. We examine the motion of magnetic domain walls in Co/Pt multilayers when subject to a high frequency strain standing wave generated by a focused surface acoustic wave transducer. Our ability to map focused strain waves using optical methods allow us to make subsequent magnetic measurements without losing the location of strain nodes and antinodes. Our results indicate that domain walls move preferentially towards strain antinodes and away from the nodes.
Materials possessing perpendicular anisotropy have applications in high density magnetic data storage technology. In this paper, we present initial attempts to measure the fast magnetization switching from out-of-plane to in-plane in perpendicular anisotropy Co/Pt multilayers. Interaction with surface acoustic waves (SAW) results in strain induced anisotropy changes in Co/Pt multilayers arising from the magnetostrictive properties of ferromagnetic Co, and changing the easy axis of magnetization. The strain amplitude required to overcome perpendicular magnetic anisotropy is close to 1%. Such large strains are achievable using annular interdigital transducers (AIDT), in which the electrodes follow the velocity curve of the piezoelectric substrate. When excited at the fundamental resonance frequency, SAW propagating towards the center undergo constructive interference and create an intense strain at the focal center. We successfully fabricated AIDT using photolithography with a fundamental resonance of 87.56 MHz. An elliptic structure of Co/Pt multilayers was deposited at the focal center using electron beam lithography (EBL) and magnetron sputtering. The magnetization of the elliptic patterned Co/Pt was measured using focused MOKE and magnetic force microscopy (MFM), confirming that the ellipse is in a single domain state with out of plane anisotropy. Preliminary attempts to measure the magnetization rotation arising from the strain waves did not show the expected magnetization rotation signature. Possible reasons for this are discussed.
KEYWORDS: Diodes, Boron, Sensors, Semiconductors, Heterojunctions, Lithium, Solid state electronics, Electronics, Signal processing, Analytical research
We report further studies on the neutron detection capabilities of boron carbide/Si heterjunction diodes. In particular, we investigate the behavior of these diodes in the presence of low neutron flux. The spectrum is compared with previous data obtained in the high neutron flux environment in the irradiation sample well of a TRIGA reactor.
Semiconducting boron-rich boron-carbon alloys have been deposited by plasma-enhanced chemical vapor deposition. Heterojunction diodes made with 276nm thick nanocrystalline layers of these alloys have been used as real-time solid-state neutron detectors. Individual neutrons were detected and signals induced by gamma rays were determined to be insignificant. Linearity of detection was demonstrated over more than two orders of magnitude in flux. The neutron detection performance was unaffected by > 1 x 1015 neutrons / cm2. The source gas closo-1,2-dicarbadodecaborane (ortho-carborane) was used to fabricate the boron carbon alloys with only the natural isotopic abundance of 10B. Devices made of thicker boron carbon alloy layers enriched in 10B could lead to increased detection efficiency.
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