S.F. Lee

In situ real-time investigation of cancer cell photothermolysis mediated by excited gold nanorod surface plasmons

The photothermolysis of living EMT-6 breast tumor cells triggered by gold nanorods (AuNRs) with two-photon irradiation was conducted in situ and under real-time observation. The morphology and plasma membrane permeability of the cells were key indicators to the phenomena. AuNRs with an aspect ratio of 3.92, and a longitudinal absorption peak at 800 nm were synthesized with a seed-mediated method. The nanorods surfaces were further modified with polystyrenesulfonate (PSS) for biocompatibility. The prepared nanorods displayed excellent two-photon photoluminescence imaging. In situ real-time results revealed cavities internal to the cells were created from thermal explosions triggered by AuNRs localized photothermal effect. The cavitation dynamic is energy dependent and responsible for the perforation or sudden rupture of the plasma membrane. The energy threshold for cell therapy depended significantly on the number of nanorods taken up per cell. For an ingested AuNR cluster quantity N approximately 10-30 per cell, it is found that energy fluences E larger-than 93 mJ/cm(2) led to effective cell destruction in the crumbled form within a very short period. As for a lower energy level E = 18 mJ/cm(2) with N approximately 60-100, a non-instant, but progressive cell deterioration, is observed.

Magnetic flux penetration depth study in Nb/Co system

A series of Co/Nb bilayers, Nb/Co/Nb and Co/Nb/Co trilayer thin films are made by dc sputtering. Magnetic hysteresis loops are measured to study the interplay between superconductor and ferromagnet. Our results show the influence of large exchange field and small spin-orbit interaction on superconductivity. We inferred a magnetic penetration depth of ∼35–40 nm in Nb. Suppression of superconducting signal by 0.6-nm-thick Co between two 30 nm Nb films suggests confinement of the superconducting wave function within individual layers.

Thickness dependence of superconducting transition temperature in Co/SC/Co trilayers and SC/Co bilayers with SC=NbTi, Nb

Superconducting transition temperatures Tc of sputtered Co/SC/Co trilayers and SC/Co bilayers with SC=Nb and NbTi were studied by the electrical resistivity and magnetic susceptibility. For a fixed Co layer thickness, Tc decreases with decreasing SC layer thickness. By applying a published model for the effects of pair breaking, the critical SC layer thickness dSC was deduced. The effect of interface roughness on Tc(dSC) is discussed from the viewpoint of the superconducting coherence length.

Magnetoresistance study in Co–Al–Co and Al–Co–Al double tunneling junctions

Magnetoresistance (MR) in Co–Al–Co and Al–Co–Al double tunneling junctions has been studied at temperatures between 65 and 750 mK and in magnetic fields up to 3 T. The electrical resistance decreases with increasing temperature. In the low magnetic field region, the electrical resistance hysteresis behavior is attributed to a typical TMR for ferromagnetic Co and insulator Al2O3 elements. In the high magnetic field region, a sharp resistance variation roughly near 2.0 T for the Co–Al–Co system and 1.75 T for the Al–Co–Al system has been observed and is attributed to the electron tunneling effect. From the current–voltage and dI/dV characteristics, the superconductivity energy gap is roughly 0.5 meV in the Co–Al–Co system and roughly 0.3 meV in the Al–Co–Al system; and magnetic tunneling energy is roughly 0.01 meV in the Co–Al–Co system and roughly 0.06 meV in the Al–Co–Al system.

Spin Pumping Induced Inverse Spin-Hall Effects in

Ferromagnetic/paramagnetic bilayer systems have been used to investigate inverse spin-Hall effect (ISHE) extensively with the technique of spin-pumping which is based on a mechanism driving the spin moment from ferromagnetic layers into paramagnetic layers via the ferromagnetic resonance procession. When the spin current is induced in the paramagnetic layer, a transversal electrical potential difference is generated and can be measured. Among many, platinum is the most effective paramagnetic metal with a strong inverse spin-Hall effect due to its strong spin-orbit coupling. In this work, we study ISHE in two kinds of bilayer films, Ni81Fe19(Py)/Pt and La0.7Sr0.3MnO3(LSMO)/Pt. Our experimental results show that the voltage induced by ISHE in LSMO/Pt ( ~ 1.0 μV) is one order smaller than that Py/Pt ( ~ 10 μV) at 100 mW of microwave power, despite the fact that LSMO has much higher spin polarization than Py. Based on our fitting results, the reason for the reduction of spin-pumping effect in LSMO/Pt may be the strong anomalous Hall Effect in LSMO.

{\rm La}_{0.7}{\rm Sr}_{0.3}{\rm MnO}_{3}

Spin pumping effect in Bi2Se3/Fe3Si and Fe/Bi2Te3 heterostructures was studied. High quality films of Bi2Se3(001) on ferromagnetic Fe3Si(111) layer and Fe(111) films on Bi2Te3(001) layer were grown epitaxially by molecular beam epitaxy. Using a microwave cavity source, large voltages due to the Inverse Spin Hall Effect (VISHE) were detected in Bi2Se3(001)/Fe3Si(111) bi-layer at room temperature. VISHE of up to 63.4 ± 4.0 μV at 100 mW microwave power (PMW) was observed. In addition, Fe(111)/Bi2Te3(001) bi-layer also showed a large VISHE of 3.0 ± 0.1 μV at PMW of 25 mW. VISHE of both structures showed microwave linear power dependence in accordance with the theoretical model of spin pumping. The spin Hall angle was calculated to be 0.0053 ± 0.002 in Bi2Se3 and was estimated to be 0.0068 ± 0.003 in Bi2Te3. The charge current density (Jc) of Bi2Se3/Fe3Si and Fe/Bi2Te3 structures are comparable and are about 2–5 times higher than the Fe3Si/normal metal and Fe3Si/GaAs results. The significant enhancement of spi...

/Platinum Bilayer Film

Domain wall pinning force in the junctions (corners), with different shapes of square, semicircle, or triangle, of half-ring in-series wires is considered to study the current injection induced wall movements. This geometry has less thermal activation at the region of domain wall nucleation in contrast to notch structures. The wires with square corners have the largest domain pinning force to resist polarized current-induced magnetization reversal, judging from the largest slope in the current-field dependence (ΔI∕ΔH=0.274).

Strongly enhanced spin current in topological insulator/ferromagnetic metal heterostructures by spin pumping

Cobalt films have been grown on yttria-stabilized cubic zirconia (YSZ) (100) and (110) substrates by molecular beam epitaxy. Both hcp(0001) and fcc(111) twin structures and fcc(110) films have been successfully fabricated on the YSZ(100) and (110), respectively. For the Co on YSZ(100) case, the Co films possess either hcp(0001) or fcc(111) crystals with in-plane 30° rotation. For the Co on YSZ(110) case, the structural relationship is YSZ(110)[100] ‖ Co(110)[1–10]. All the films display an isotropiclike magnetic anisotropy with the coercivity increasing abruptly above its martensitic transition temperature. The coercivity decreases with increasing the thickness of Co films from 100 A to 500 A; and increases as the deposited temperature above 500 °C. Co films grown on YSZ(100) are in favor of the layer by layer growth, and Co films grown on YSZ(110) are in favor of the island growth.

Vortex domain wall depinning by polarized current in submicron half-ring wires

The magnetic properties of ultrathin Co/Ag/Si[111] films were studied by surface magneto-optic Kerr effect. A magnetic phase diagram for binary-metal Co/Ag films deposited on Si[111] surfaces has been successfully established. The phase diagram can be divided into four regions: nonferromagnetic Co-Si compound; low Curie temperature Co film; canted out-of-plane anisotropy; in-plane anisotropy. The ferromagnetic inactive layers at the Co/Si interface are formed due to intermixing of Co and Si; and can be efficiently reduced by the Ag buffer layer. We have demonstrated that the inactive layer thickness is reduced from 2.1 ML for Co/Si[111], to 1.0 for Co/2.8 MLAg/Si[111], and 0.0 for Co/5.6 MLAg/Si[111].

Structure and magnetic properties of Co grown on yttria-stabilized cubic zirconia substrates

Epitaxial Co/Cr superlattices CO (1 l?O)/Cr(100) on MgO (100) and Co(l:OO)/Cr (211) on MgO(110) have been grown by molecular beam epitaxy technique. Buffer layer of MO or CrMo alloy was first deposited on top of the substrate which is crucial to prepare a smooth and well-ordered Cr surfaces and the following superlattices. The epitaxial orientation of Co/Cr (100) superlattices is (1001, Co(liOO)//Cr ( 0 1 l)//MgO ( 0 101 and CO( 000 1)//Cr ( Ol:)//MgO( 0011, while that for Co/Cr( 21 1) CO ( l?OO)//Cr ( 2 1 l)//MgO ( 11 01, CO( ll~O)//Cr(ill)// MgO(li~) and Co(OOOl)// Cr(Ol~)//MgO(OOl). (C0xCry)n superlattices with different CO thickness (x), Cr thickness (y) and number of layers (n) have been deposited. The maximum magnetoresistance of the Co/Cr(211) superlattices is 18% comparing with the 4.8% for Co/Cr(100) superlattices. The magnetization measurements also show that the antiferromagnetic coupling in Co/Cr(211) superlattices is stronger than in Co/Cr(100) superlattices. The magnetic properties are strongly influenced by the crystal orientation of the multilayers.