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Greedy embedding is the key of geometric greedy routing in p2p networks It embeds a graph (the topological structure of the p2p network) in a metric space such that between any source-destination pair, there is a distance decreasing path for message delivery It is known that any graph can be greedily embedded in the hyperbolic plane with using O(logn) bits for each node's coordinates [7] Interestingly, on greedy embedding in the Euclidean plane, existing embedding algorithms result in coordinates with ${\it \Omega}(n)$ bits It was recently proved that ${\it \Omega}(n)$ is a lower bound of the coordinates' bit length if one uses Cartesian or polar coordinate system and preserves the planar embedding of a planar graph when greedily embedding it in the Euclidean plan [2] In this paper we strengthen this result by further proving that ${\it \Omega}(n)$ is still a lower bound even if the graph is allowed to take free embedding in the plane.

We give a sufficient condition, which guarantees that for arbitrary Hamiltonian cycle C, there exists a [k, k + 1]-factor containing C. This improves a previous result of Cai, Li, and Kano [7].

We study the problem of securely searching for resources in p2p networks where a constant fraction of the peers may act maliciously. We present two novel hashing-based schemes that can be employed to reliably support resource location and content retrieval queries, limiting the ability of adversarial nodes to carry out attacks. Our schemes achieve scalability and load balancing and have small authentication overhead. In particular, for a network with n peers, resources are securely located with O(log2 n) messages and content from a collection of m data items is securely retrieved with O(logn logm) messages.

Thermal-magnetic noise at ferromagnetic resonance (T-FMR) can be used to measure magnetic perpendicular anisotropy of nanoscale magnetic tunnel junctions (MTJs). For this purpose, T-FMR measurements were conducted with an external magnetic field up to 14 kOe applied perpendicular to the film surface of MgO-based MTJs under a dc bias. The observed frequency-field relationship suggests that a 20 A CoFeB free layer has an effective demagnetization field much smaller than the intrinsic bulk value of CoFeB, with 4PiMeff = (6.1 +/- 0.3) kOe. This value is consistent with the saturation field obtained from magnetometry measurements on extended films of the same CoFeB thickness. In-plane T-FMR on the other hand shows less consistent results for the effective demagnetization field, presumably due to excitations of more complex modes. These experiments suggest that the perpendicular T-FMR is preferred for quantitative magnetic characterization of nanoscale MTJs., Comment: 10 pages, 3 figures, accepted by APL

Geometric greedy routing uses (virtual) geographic point locations as addresses for the purposes of routing, while routing decisions are made by each node individually based only on local information. It requires that the network topology is greedily embedded in a metric space through assigning virtual coordinates to the nodes in the network. Recent research pointed out that such scheme is significantly more efficient than other traditional routing schemes only if the virtual coordinates are succinctly represented (i.e., using $O(poly(\log n))$ bits per coordinate) in the greedy embedding, an issue that has been overlooked for a long time. In this paper we prove that such succinctness is not achievable in Euclidean plane, assuming that Cartesian or polar coordinate system is used, the network topology is a planar graph, and the planar embedding is preserved during the process of greedy embedding. Indeed, we provide a counter example to show that in this situation, some coordinates must take $\Omega(n)$ bits to represent.

Spin-valve based nanojunctions incorporating Co|Ni multilayers with perpendicular anisotropy were used to study spin-torque driven ferromagnetic resonance (ST-FMR) in a nonlinear regime. Perpendicular field swept resonance lines were measured under a large amplitude microwave current excitation, which produces a large angle precession of the Co|Ni layer magnetization. With increasing rf power the resonance lines broaden and become asymmetric, with their peak shifting to lower applied field. A nonhysteretic step jump in ST-FMR voltage signal was also observed at high powers. The results are analyzed in in terms of the foldover effect of a forced nonlinear oscillator and compared to macrospin simulations. The ST-FMR nonhysteretic step response may have applications in frequency and amplitude tunable nanoscale field sensors., Comment: 4 pages, 3 figures, to appear in Applied Physics Letters

We report significant enhancements of magnetoresistance in granular (La0.67Ca0.33MnO3)x/(SrTiO3)1−x. The system exhibits a conduction threshold at x=xc∼60%, around which magnetoresistance versus x has a maximum. The composition xc at which maximum enhancement in magnetoresistance is observed is the same at high (around 5 T) and at low (a few hundred Oersted) fields. The enhancement is consistent with the disorder-driven amplification of spin-dependent transport at the structural boundaries of the mixture.

We have demonstrated a robust magnetic tunnel junction (MTJ) with a resistance-area product RA=8 Omega-mum2 that simultaneously satisfies the statistical requirements of high tunneling magnetoresistance TMR > 15sigma(Rp), write threshold spread sigma(Vw)/

We use spin-transfer-driven ferromagnetic resonance (ST-FMR) to measure the spin-transfer torque vector T in MgO-based magnetic tunnel junctions as a function of the offset angle between the magnetic moments of the electrodes and as a function of bias, V. We explain the conflicting conclusions of two previous experiments by accounting for additional terms that contribute to the ST-FMR signal at large |V|. Including the additional terms gives us improved precision in the determination of T(V), allowing us to distinguish among competing predictions. We determine that the in-plane component of has a weak but non-zero dependence on bias, varying by 30-35% over the bias range where the measurements are accurate, and that the perpendicular component can be large enough to be technologically significant. We also make comparisons to other experimental techniques that have been used to try to measure T(V)., 30 pages, 8 figures. Expanded with additional data and discussion. In press at PRB

High current density spin-polarized transport in current-perpendicular nanomagnetic junctions reveals an interaction between the spin-polarized current and the nanomagnet electrodes. This interaction causes a current-induced magnetic excitation in the ferromagnetic electrodes, leading either to persistent magnetic precession or to a complete magnetic reversal, under a dc current bias. This article gives a brief review of the basic understanding of this so-called spin-transfer phenomenon, including the basic mechanism, its early theoretical prediction and experimental discovery, and the significance of this interaction for applications in modern electronics. This review uses a framework of phenomenological analyses, bridging experimental observations and first-principle-based theoretical work. Keywords: Spin angular momentum; spin torque; spin transfer; current-induced magnetic switching; spin polarized transport; spintronics

Spin-torque driven ferromagnetic resonance (ST-FMR) is used to study thin Co/Ni synthetic layers with perpendicular anisotropy confined in spin-valve based nanojunctions. Field swept ST-FMR measurements were conducted with a magnetic field applied perpendicular to the layer surface. The resonance lines were measured under low amplitude rf excitation, from 1 to 20 GHz. These results are compared with those obtained using conventional rf field driven FMR on extended films with the same Co/Ni layer structure. The layers confined in spin valves have a lower resonance field, a narrower resonance linewidth and approximately the same linewidth vs frequency slope, implying the same damping parameter. The critical current for magnetic excitations is determined from measurements of the resonance linewidth vs dc current and is in accord with the one determined from I-V measurements., 3 pages, 3 figures

Spin-polarized currents can transfer spin angular momentum to a ferromagnet, generating a torque that can efficiently reorient its magnetization. Achieving quantitative measurements of the spin-transfer-torque vector in magnetic tunnel junctions (MTJs) is important for understanding fundamental mechanisms affecting spin-dependent tunneling, and for developing magnetic memories and nanoscale microwave oscillators. Here we present direct measurements of both the magnitude and direction of the spin torque in Co60Fe20B20/MgO/Co60Fe20B20 MTJs. At low bias V, the differential torque vector d{tau}/dV lies in the plane defined by the electrode magnetizations, and its magnitude is in excellent agreement with a prediction for highly-spin-polarized tunneling. With increasing bias, the in-plane component d{tau}_{parallel}/dV remains large, in striking contrast to the decreasing magnetoresistance ratio. The differential torque vector also rotates out of the plane under bias; we measure a perpendicular component tau_{perp}(V) with bias dependence proportional to V^2 for low V, that becomes as large as 30% of the in-plane torque., 33 pages, 9 figures

Checking value-sensitive data structures in sublinear space has been an open problem for over a decade. In this paper, we suggest a novel approach to solving it. We show that, in combination with other techniques, a previous method for checking value-insensitive data structures in log space can be extended for checking the more complicated value-sensitive data structures, using log space as well. We present the theoretical model of checking data structures and discuss the types of invasions a checker might bring to the data structure server. We also provide our idea of designing sublinear space checkers for value-sensitive data structures and give a concrete example - a log space checker for the search data structures (SDS).

Spin-torque driven ferromagnetic resonance (ST-FMR) is used to study magnetic excitations in Co/Ni synthetic layers confined in nanojunctions. Field swept ST-FMR measurements were conducted with a magnetic field applied perpendicular to the layer surface. The resonance lines were measured under low amplitude excitation in a linear response regime. The resulting resonance fields were compared with those obtained using conventional rf field driven FMR on extended films with the same Co/Ni layer structure. A lower resonance field is found in confined structures. The effect of both dipolar fields acting on the Co/Ni layer emanating from other magnetic layers in the device and finite size effects on the spin wave spectrum are discussed., Comment: 3 pages, 3 figures

Thin film trilayer junction of La$%_{0.67}$Sr$_{0.33}$MnO$_3$ - SrTiO$_3$ - La$_{0.67}$Sr$_{0.33}$MnO$_3$ shows a factor of 9.7 change in resistance, in a magnetic field around 100 Oe at 14K. The junction magnetoresistance is bias and temperature dependent. The energy scales associated with bias and temperature dependence are an order of magnitude apart. The same set of energies also determine the bias and temperature dependence of the differential conductance of the junction. We discuss these results in terms of metallic cluster inclusions at the junction-barrier interface., Comment: 3 pages, 4 figures

We have carried out a study of composite, granular films made by depositing LCMO (a colossal magnetoresistive perovskite) and pure, metallic Au onto MgO and LaAlO3 substrates. Elevated temperature caused the Au to segregate into small, micron-sized granules. The films were studied by atomic force microscopy, magnetoresistivity, superconducting quantum interference device magnetization measurements, and magnetically modulated microwave absorption.

The switching probability of a single-domain ferromagnet under spin-current excitation is evaluated using the Fokker-Planck equation(FPE). In the case of uniaxial anisotropy, the FPE reduces to an ordinary differential equation in which the lowest eigenvalue $\lambda_1$ determines the slowest switching events. We have calculated $\lambda_1$ by using both analytical and numerical methods. It is found that the previous model based on thermally distributed initial magnetization states \cite{Sun1} can be accurately justified in some useful limiting conditions., Comment: The 10th Joint MMM/Intermag, HA-09

The temperature dependence of current-induced magnetization switching of ferrimagnetic CoGd free layers in spin valves is explored. At temperatures well above and well below the magnetization compensation temperature (${T}_{\mathrm{MC}}$) of CoGd, a current flowing from the free layer to the CoFe fixed layer aligns the moments of the two layers parallel, and a current flowing in the opposite direction aligns them antiparallel. However, for intermediate temperatures just above ${T}_{\mathrm{MC}}$, the current-induced alignment of the moments is reversed. We attribute this effect to the different compensation temperatures of the net magnetization and angular momentum of CoGd.

In addition to the huge resistivity changes, the phase-change switching process is accompanied by a significant volume change (Pedersen et al., 2001), which in turn can result in large stresses. This can become a serious reliability issue, particularly in small device cells utilizing under- and over-layers of suitable contact metals. It is important then to evaluate the magnitude and the sign of stress during the phase changes, and to ascertain the effect of capping layers. In this paper, we report distinct stress signatures in a phase change material, Ge2Sb2Te5 (GST). As GST may be integrated in devices with Ti/TiN (for adhesion and diffusion barrier considerations), the stress evolution in such sandwiched structures is addressed

When injected spin polarized electrons interact with the magnetic moment of a free layer, their angular momentum becomes transferred to the free layer. If sufficient current is applied, the exerted torque switches the free layer either parallel or anti-parallel to the pinned layer depending on the direction of flow of the current. This type of localized current switching is attractive for an MRAM application. This paper focuses on the fabrication and characterization of sub-100nm spin-transfer switching devices. These fabricated tunnel junctions were characterized at room temperature with a quasi-static electrical measurement setup.

Spin transfer in asymmetric Co/Cu/Co bilayer magnetic nanopillars junctions has been studied at low temperature as a function of free-layer thickness. The phase diagram for current-induced magnetic excitations has been determined for magnetic fields up to 7.5 T applied perpendicular to the junction surface and free-layers thicknesses from 2 to 5 nm. The junction magnetoresistance is independent of thickness. The critical current for magnetic excitations decreases linearly with decreasing free-layer thickness, but extrapolates to a finite critical current in the limit of zero thickness. The limiting current is in quantitative agreement with that expected due to a spin-pumping contribution to the magnetization damping. It may also be indicative of a decrease in the spin-transfer torque efficiency in ultrathin magnetic layers., Comment: 5 Pages, 4 Figures

We report the observation of a large magnetoresistance (83%) at low magnetic fields of tens of Oe at 4.2 K in the epitaxial trilayer junction structure, La0.67Sr0.33MnO3/SrTiO3/La0.67Sr0.33MnO3. The spin-polarization parameter of the manganite has been determined from the magnetoresistance value. The switching fields of the two magnetic layers were designed by using the magnetic shape anisotropy. By limiting the sweeping field in a low field range (∼100 Oe), we have achieved bistable resistive states at zero field, which is of potential interest for magnetoelectronic applications.

We report spin-dependent perpendicular transport in the magnetic trilayer junction structure La0.67Sr0.33MnO3/SrTiO3/La0.67Sr0.33MnO3. Large (factor of 5) changes of magnetoresistance induced by a field of ∼200 Oe are observed at 4.2 K. Junction I–V characteristics at low temperatures are consistent with a metal–insulator–metal tunneling process with a large spin-polarization factor of 0.81 for the conduction electrons. Above 100 K, a variable range-hopping conduction shunts out the magnetoresistance contribution. This second conduction channel comes from the impurity states within SrTiO3 barrier and therefore is not an intrinsic limit to the magnetoresistance performance of the device at high temperatures.

We present a new multi-dimensional data structure, which we call the skip quadtree (for point data in R^2) or the skip octree (for point data in R^d, with constant d>2). Our data structure combines the best features of two well-known data structures, in that it has the well-defined "box"-shaped regions of region quadtrees and the logarithmic-height search and update hierarchical structure of skip lists. Indeed, the bottom level of our structure is exactly a region quadtree (or octree for higher dimensional data). We describe efficient algorithms for inserting and deleting points in a skip quadtree, as well as fast methods for performing point location and approximate range queries., 12 pages, 3 figures. A preliminary version of this paper appeared in the 21st ACM Symp. Comp. Geom., Pisa, 2005, pp. 296-305

Current-induced magnetic excitations in Co/Cu/Co bilayer nanopillars ($\sim$50 nm in diameter) have been studied experimentally at low temperatures for large applied fields perpendicular to the layers. At sufficiently high current densities excitations, which lead to a decrease in differential resistance, are observed for both current polarities. Such bipolar excitations are not expected in a single domain model of spin-transfer. We propose that at high current densities strong asymmetries in the longitudinal spin accumulation cause spin-wave instabilities transverse to the current direction in bilayer samples, similar to those we have reported for single magnetic layer junctions., Comment: 4 pages, 4 figures+ 2 additional jpg figures (Fig. 2d and Fig. 3) high resolution figures and recent related articles are available at: http://www.physics.nyu.edu/kentlab/news.html

We present room temperature ferromagnetic resonance (FMR) studies of polycrystalline ||Pt/10 nm Cu/t Co/10 nm Cu/Pt|| films as a function of Co layer thickness (1 < t < 10 nm) grown by evaporation and magnetron sputtering. FMR was studied with a high frequency broadband coplanar waveguide (up to 25 GHz) using a flip-chip method. The resonance field and the linewidth were measured as a function of the ferromagnetic layer thickness. The evaporated films exhibit a lower magnetization density (Ms = 1131 emu/cm^3) compared to the sputtered films (Ms= 1333 emu/cm^3), with practically equal perpendicular surface anisotropy (Ks ~ -0.5 erg/cm^2). For both series of films, a strong increase of the linewidth was observed for Co layer thickness below 3 nm. For films with a ferromagnetic layer thinner than 4 nm, the damping of the sputtered films is larger than that of the evaporated films. The thickness dependence of the linewidth can be understood in term of the spin pumping effect, from which the interface spin mixing conductance g^{\uparrow\downarrow}S^{-1} is deduced.

We report on the fabrication of a new class of trilayer epitaxial thin film devices based on the doped perovskite manganates La–Ca–Mn–O and La–Sr–Mn–O. We show that large resistance changes, up to a factor of 2, can be induced by a moderate applied magnetic field below 200 Oe in these trilayers supporting current‐perpendicular‐to‐plane transport. These results show that low‐field spin‐dependent transport in manganates can be accomplished, the magnitude of which is suitable for magnetoresistive field sensors.

We report results of quantitative magnetization studies on epitaxial thin films of La0.60Y0.07Ca0.33MnO3−δ and La1−x⧠xMnO3−δ, with ⧠ standing for vacancy on the La site. The magnetization in all samples shows significant field dependent broadening of the ferromagnetic transition. Classical mean‐field analysis of magnetization data in applied fields above a few Tesla leads to a magnetic cluster size of the order of a few unit cells. The density of such a magnetic cluster correlates with the doping concentration x in the compound series La1−x⧠xMnO3−δ. In thin films of La0.60Y0.07Ca0.33MnO3−δ, a magnetic field dependent, non‐Curie–Weiss susceptibility was found in the paramagnetic state, indicating local ferromagnetic cluster formation above macroscopic ferromagnetic ordering temperature.

Based on macroscopic quantum coherence effects arising from pair tunneling and flux quantization, a series of tricrystal experiments have been designed and carried out to test the order parameter symmetry in high-Tc cuprate superconductors. By using a scanning SQUID microscope, we have directly and non-invasively observed the spontaneously generated half-integer flux quantum effect in controlled-orientation tricrystal cuprate superconducting systems. The presence or absence of the half-integer flux quantum effect as a function of the tricrystal geometry allows us to prove that the order parameter symmetry in the YBCO and Tl2201 systems is consistent with that of the dx2−y2 pair state.

We present a method to measure the effective field contribution to spin-transfer-induced interactions between the magnetic layers in a bilayer nanostructure, which enables spin current effects to be distinguished from the usual charge-current-induced magnetic fields. This technique is demonstrated on submicron $\mathrm{Co}∕\mathrm{Cu}∕\mathrm{Co}$ nanopillars. The hysteresis loop of one of the magnetic layers in the bilayer is measured as a function of current while the direction of magnetization of the other layer is kept fixed, first in one direction and then in the opposite direction. These measurements show a current-dependent shift of the hysteresis loop which, based on the symmetry of the magnetic response, we associate with spin transfer. The observed loop shift with applied current at room temperature is reduced in measurements at $4.2\phantom{\rule{0.3em}{0ex}}\mathrm{K}$. We interpret these results both in terms of a spin-current-dependent effective activation barrier for magnetization reversal and a spin-current-dependent effective magnetic field. From data at $4.2\phantom{\rule{0.3em}{0ex}}\mathrm{K}$, we estimate the magnitude of the spin-transfer-induced effective field to be $\ensuremath{\sim}1.5\ifmmode\times\else\texttimes\fi{}{10}^{\ensuremath{-}7}\phantom{\rule{0.3em}{0ex}}\mathrm{Oe}\phantom{\rule{0.2em}{0ex}}{\mathrm{cm}}^{2}∕\mathrm{A}$, about a factor of 5 less than the spin torque.

Spin-angular momentum transfer (or spin-transfer for short) describes the angular momentum exchange between a spin-polarized current and a ferromagnetic conductor. When the conductor dimensions are reduced to around 100nm or below, the spin-angular momentum transfer effect becomes significant compared to the current-induced magnetic field. This paper describes some recent spin-transfer experimental findings in sub-100nm current-perpendicular spin-valve systems consisting of Co-Cu-Co nanopillars. The spin-transfer current is shown to cause a magnetic reversal of the thinner magnetic layer inside the nanopillar. The reversal is experimentally shown to reach sub-nanosecond speed. The effect of spin-transfer is best understood in terms of its modification to the effective Landau-Lifshiz-Gilbert damping coefficient, either increasing or decreasing its value depending on the direction and magnitude of the spin-polarized current. For sufficiently large spin-current, the net damping coefficient may change sign, resulting in amplification of magnetic precession, leading to a magnetic reversal. At finite temperatures, the effect of spin-transfer is to either increase or decrease the thermal agitation of the nanomagnet. A quantitative model is developed that adequately describes the finite temperature experimental observations of the dynamic spin-transfer effect.

Nanotubes and nanowires with both elemental1,2 (carbon or silicon) and multi-element3,4,5 compositions (such as compound semiconductors or oxides), and exhibiting electronic properties ranging from metallic to semiconducting, are being extensively investigated for use in device structures designed to control electron charge6,7,8. However, another important degree of freedom—electron spin, the control of which underlies the operation of ‘spintronic’ devices9—has been much less explored. This is probably due to the relative paucity of nanometre-scale ferromagnetic building blocks10 (in which electron spins are naturally aligned) from which spin-polarized electrons can be injected. Here we describe nanotubes of vanadium oxide (VOx), formed by controllable self-assembly11, that are ferromagnetic at room temperature. The as-formed nanotubes are transformed from spin-frustrated semiconductors to ferromagnets by doping with either electrons or holes, potentially offering a route to spin control12 in nanotube-based heterostructures13.

We report direct experimental evidence of an energy threshold for spin-transfer-induced magnetic excitations in Co/Cu/Co nanopillars from temperature dependent measurements of current-induced excitations. The current threshold of excitations decreases when the temperature is increased from 4.2 to 300 K. However, the product of the current threshold and the pillar resistance stays almost temperature independent up to a temperature of $\ensuremath{\sim}150\mathrm{K}.$ This behavior supports the energy-threshold mechanism for spin-transfer-induced magnetic excitations.

Current-induced excitations in Cu/Co/Cu single ferromagnetic layer nanopillars ( approximately 50 nm in diameter) have been studied experimentally as a function of Co layer thickness at low temperatures for large applied fields perpendicular to the layers. For asymmetric junctions current-induced excitations are observed at high current densities for only one polarity of the current and are absent at the same current densities in symmetric junctions. These observations confirm recent predictions of spin-transfer torque induced spin-wave excitations in single layer junctions with a strong asymmetry in the spin accumulation in the leads.

We study the problem of broadcasting confidential information to a collection of n devices while providing the ability to revoke an arbitrary subset of those devices (and tolerating collusion among the revoked devices). In this paper, we restrict our attention to low-memory devices, that is, devices that can store at most O(log n) keys. We consider solutions for both zero-state and low-state cases, where such devices are organized in a tree structure T. We allow the group controller to encrypt broadcasts to any subtree of T, even if the tree is based on an multi-way organizational chart or a severely unbalanced multicast tree.

Epitaxial thin films of lanthanum‐deficient LaxMnO3−δ (0.67≤x≤1) have been grown on (100) SrTiO3 substrates by pulsed laser deposition. The as‐deposited films exhibit a ferromagnetic transition at temperatures ranging from 115 to 240 K, with the transition temperature (Tc) increasing with higher La deficiency. A sharp drop in resistivity and negative magnetoresistance is observed close to Tc, a behavior similar to that observed in divalent substituted La1−xMxMnO3−δ (M=Ba, Sr, Ca, Pb) films. Postannealing the films in O2 reduces the resistivity and raises the Tc to values close to room temperature. A magnetoresistance value of 130% (Δρ/ρH) has been obtained at 300 K at 4 T for a post‐annealed film with x=0.75.

We report a large magnetoresistance in in situ grown La0.60Y0.07Ca0.33MnOx thin films made at a low substrate temperature of 600 °C without postdeposition annealing. The zero‐field resistivity peaks around 120 K. The resistivity peak is reduced by two orders of magnitude by a 6 T field. Comparison of transport and magnetization data reveals a correlation of conductivity versus magnetization below the ferromagnetic transition temperature, which may suggest a double‐exchange‐based conduction mechanism. Above the ferromagnetic transition at low fields, a quadratic dependence of conductivity on magnetization is found, consistent with a spin‐scattering‐limited conductivity.

Record values of colossal magnetoresistance (CMR) have been achieved in the antiferromagnetic phase of the La1−xCaxMnO3 system. At 125 K, the CMR of the La0.5Ca0.5MnO3 reaches nearly 1 000 000%. It increases exponentially to 100 000 000% at 57 K. While the ground state is primarily an antiferromagnet, application of a magnetic field induces a ferromagnetic alignment of spins that is highly beneficial to the electron conduction. Other ferromagnetic samples exhibit very sharp magnetic phase transitions, with which the magnetotransport is closely correlated.

In situ planarization of epitaxial films has been demonstrated. This is a critical technology for the processing of any epitaxial multilayer device. Ion beam assisted deposition (IBAD) has been used to planarize patterned yttria‐stabilized ZrO2 (YSZ)(001) substrates using YSZ films. X‐ray diffraction measurements have shown that the IBAD YSZ grows homoepitaxially. The IBAD planarization mechanism has similarities to those previously observed for rf bias sputtering. Critical current densities of up to 7×105 A/cm2 at 77 K have been measured for Ba2YCu3O7−x (BYC) films deposited on planarized patterned YSZ substrates using pulsed laser deposition. In contrast, BYC deposited on unplanarized patterned YSZ substrates did not become fully superconducting for measurements down to 25 K.

This letter discusses the effects of a moderate magnetic field applied to a SQUID magnetometer and introduces the invention of the ‘‘flux dam.’’ A flux dam is a weak link or Josephson junction in series with the pickup loop which allows magnetic flux to enter and leave the inside of the superconducting loop easily for moderate changes in magnetic field. This largely prevents the flux lines from entering and being pinned in the superconducting parts of the magnetometer which would create extra low frequency noise. SQUID magnetometers with flux dams in the pickup loop can be operated in the Earth’s magnetic field without a significant increase in low frequency flux noise.

We have combined a novel low temperature positioning mechanism with a single‐chip miniature superconducting quantum interference device (SQUID) magnetometer to form an extremely sensitive new magnetic microscope, with a demonstrated spatial resolution of ∼10 μm. The design and operation of this scanning SQUID microscope will be described. The absolute calibration of this instrument with an ideal point source, a single vortex trapped in a superconducting film, will be presented, and a representative application will be discussed.

We study experimentally the current-driven magnetic excitations in symmetric $\mathrm{C}\mathrm{o}/\mathrm{C}\mathrm{u}/\mathrm{C}\mathrm{o}$ nanopillars. In contrast with all the previous observations where the current of only one polarity is capable of exciting a multilayer system saturated by an externally applied magnetic field, we observe that both polarities of the applied current trigger excitations in a symmetric multilayer. This may indicate that in symmetric structures the current propels high-frequency magnetic oscillations in all magnetic layers. We argue, however, that only one layer is excited in our multilayers but, interestingly, currents of opposite polarities excite different layers. This hypothesis is supported by modeling the spin accumulation in symmetric magnetic multilayers.

Angular momentum transfer in magnetic nanostructures mediated by an electric current has become the subject of intense research. Slonscewski and Berger first considered this theoretically in 1996 [1,2]. Its experimental observation a few years later [3–7] has boosted efforts to understand the influence of the conduction electron spin on the magnetization dynamics of ferromagnetic nanostructures in the presence of high electric currents. A spin current has been demonstrated to switch the magnetization direction of a small magnetic element. Reversible changes in multilayer resistance have also been observed and associated with magnetic excitations or the generation of spin waves. However, an in-depth understanding of the relationship between these two phenomena — reversible excitations of the magnetization and irreversible switching of the magnetization—is still missing. In the initial experiments a point contact was employed to inject high current densities into a magnetic multilayer [3,6,7]. Subsequent experiments have concentrated on the reduction of the lateral size of Co=Cu=Co trilayers to the submicron scale, resulting in the fabrication of nanopillar devices [8–14]. In the point-contact experiments the applied magnetic field was oriented perpendicular to the thin film plane and was larger than the film demagnetization fields (H � 2T ). In this high field regime a peak structure in the differential resistance (dV=dI) at a critical current was interpreted as the onset of current induced excitation of spin waves in which the current induced spin-transfer torque leads to the uniform precession of the magnetization [3,6,15]. Spin-transfer torque studies on pillar devices concentrated on magnetic fields applied in the thin film plane. In the low-field regime, a hysteretic jump in the differential resistance was observed; clear evidence for current induced magnetization reversal of one of the magnetic layers [8–14]. Hence, the effect of the spin-polarized current on the magnetization seemed to be quite distinct in the low and high field regimes. Experimentally, a current induced hysteretic magnetization reversal was observed only at low in-plane fields in nanopillar devices. In this Letter we report detailed studies of current induced dynamics of the magnetization in submicron size pillar devices at high magnetic fields in the field perpendicular to the plane geometry. For sufficiently large currents of one polarity hysteretic magnetic switching of the layers is observed at high magnetic fields. In contrast to previous results in this geometry with mechanical point contacts, these results cannot be understood as small amplitude excitations of the magnetization. Micromagnetic modeling suggests that spin-transfer torques induce precessional states which evolve into a static state of antiparallel alignment of the layers.

Time-resolved measurements of spin-transfer-induced (STI) magnetization reversal were made in current-perpendicular spin-valve nanomagnetic junctions subject to a pulsed current bias. These results can be understood within the framework of a Landau-Lifshitz-Gilbert equation that includes STI corrections and a Langevin random field for finite temperature. Comparison of these measurements with model calculations demonstrates that spin-transfer induced excitation is responsible for the observed magnetic reversal in these samples.

The effects of radio frequency radiation on the dc SQUID are examined. Simulations show how the shape of the SQUID transfer characteristic is distorted by radio frequency interference (RFI). How this affects three commonly used SQUID modulation methods is discussed, and the results explain why we experimentally observe the bias current reversing readout method to be the least susceptible to RFI. The commonly seen increase in the low frequency flux noise power spectrum of dc SQUIDs in unshielded environments is also explained.

All high‐Tc, multilevel edge junction superconducting quantum interference devices (SQUIDs) which now operate at 77 K have been fabricated using laser‐ablated YBaCuO electrodes and in situ laser‐ablated SrTiO3 for the barrier material. Devices with a SQUID inductance of about 70 pH have a peak to peak voltage swing, VΦ, up to 8 μV (dV/dΦ≂25 μV) and a flux noise (SΦ) of about 3×10−10 Φ20/Hz in the white noise region. IcRn, products for these devices are about 35 μV at 77 K with Ic in the range of 3–100 μA and operation to temperatures as high as 84 K observed. Scaling of the junction conductance and critical current with junction size has been measured on many devices and we observe an IcRn product that varies approximately as J0.89c.

In this work, we demonstrate a 6.9 sq. /spl mu/m embedded SRAM cell in a 0.25 /spl mu/m physical design-rule salicide high-performance CMOS technology. The scalability of this salicide-CMOS embedded-SRAM technology is demonstrated by functionality of the same SRAM cell implemented in 0.35 /spl mu/m and 0.25 /spl mu/m design rules. To our knowledge this is the smallest reported SRAM cell in a salicide-only technology, and is achieved using deep-UV lithography, shallow-trench isolation, damascene tungsten low-resistance local interconnect, and optimization of design-rules. Process and structure studies indicate process extendability to 0.18 /spl mu/m lithography generation. The CMOS technology is a 1.8 V, 0.12 /spl mu/m nominal L/sub EFF/, dual work-function CMOS with 4.0 nm gate oxide. The unloaded inverter and 2-way NAND gate delays are 24 and 45 ps respectively with 1.8 V power supply, and 57 and 98 ps with 1.0 V power supply.

An integrated 0.35 /spl mu/m CMOS technology with 0.15 /spl mu/m effective channel length (L/sub EFF/) is demonstrated in a 200 mm line. X-ray lithography is used for the critical gate level, along with conventional deep-UV and mid-UV lithography for other levels. Shallow Trench Isolation (STI) is used to achieve 0.35 /spl mu/m design rules. The NFET and PFET devices are designed for operation with a scaled power supply of 1.8 V. This technology provides 50% performance improvement relative to a 2.5 V, 0.5 /spl mu/m design rule, 0.25 /spl mu/m L/sub EFF/ high-performance CMOS technology. >

We have developed a process for the fabrication of YBaCuO high‐Tc junctions based on the step‐edge weak‐link concept. The process emphasizes the creation of sharp and straight step edges on a substrate, and the restoration of oxygen content for superconducting materials at the step edges. A diamond‐like carbon film is used as an ion milling mask for the creation of steps on substrates such as LaAlO3 and SrTiO3. Room‐temperature plasma oxidation is shown to be effective in restoring Tc from processing related degradation for grains residing at the step edge. Using this process, dc SQUIDs were fabricated with 77 K electrical performances matching, and in certain cases exceeding, similar SQUIDs made using bicrystal‐based tilt‐boundary weak‐link junctions.