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A general (t, n) secret sharing (SS) scheme with fixed threshold allows a secret to be shared without considering the time dynamic nature of the security environment. In this paper, we propose a threshold changeable secret sharing scheme whose threshold can be changed in an integer interval [t, t′] without updating the shares. In this scheme, a different threshold can be activated at any time through the public broadcast channel. At the heart of the proposed scheme is a novel matrix of primes. The validity of the share generation and secret reconstruction is provided by the Chinese Remainder Theorem (CRT). We prove the existence of the proposed matrix and present a method to efficiently construct it, which makes use of a proposed sequence of nested closed intervals generated by large co-prime numbers. We further use the structure to propose a scheme with computational security, without maintaining online dealer. Compared with previous methods, the proposed scheme has short share size and low complexity for recovery. For any changeable threshold in [t, t′], the increase in share size is at most 1 t − 1 of that from previous methods. Computational complexity for secret recovery is O(t), compared with O(tlog2t) of the best previous methods.

We apply known relations for voltage-driven current and torque to magnetic tunneling junctions (MTJs) symmetric in composition. Postulated are effects of possibly asymmetric microstructures of the two interfaces separating the two electrodes from a barrier composed of (0 0 1)MgO. Our model takes into account effects of (i) dependence of state density on energy, (ii) possible asymmetry of the elastic transfer Hamiltonian, and tunneling enabled by inelastic mechanisms (iii) within the barrier or (iv) within the electrodes. It leads to distinct observable signatures for these effects in the voltage dependences of current and torque. A parameter-free relation connecting torque with conductance makes possible direct experimental tests of the model. Additionally, a derived formula illustrates how coulomb-correlation may contribute to these effects at high voltage.

This report examines the current status and the future directions of the field of nanomagnetism and assesses the ability of hard X-ray synchrotron facilities to provide new capabilities for making advances in this field. The report first identifies major research challenges that lie ahead in three broadly defined subfields of nanomagnetism: confined systems, clusters and complex oxides. It then examines the relevant experimental capabilities that are currently available at hard X-ray synchrotron light sources, using the Advanced Photon Source (APS) at Argonne as an example. Finally, recommendations are made for future development in X-ray facilities that will enhance the study of nanomagnetism, including new experimental directions, modifications that would enable in situ sample preparation, and measurements at high magnetic fields and/or low temperatures. In particular, in situ sample preparation is of high priority in many experiments, especially those in the area of surface magnetism.

Trilayer junctions of doped manganites provide a model system for the study of spin-polarized transport across a half metallic interface. Novel phenomena observed in these systems include a large low-field magnetoresistance (MR), with nearly an order of magnitude change in junction resistance in 100 Oe at 14 K, and a strong temperature and bias dependence of the junction MR. They also enabled the first demonstration of a spin-angular momentum transfer-induced reversal of a magnetic moment. Systems containing both manganite and transition metal ferromagnetic electrodes demonstrate a complex interface structure between the perovskite oxide such as SrTiO 3 and the transition metal electrode such as Co or Fe. It reveals the important effect this interface has on the magnetotransport property of the junction.

Magnetic oxide materials possessing a high degree of spin polarization have been found to exhibit enhanced spin-dependent transport properties. For example, interfaces created by naturally occurring or artificial grain boundaries in the perovskite manganites, La 1− x A x MnO 3 , result in a large magnetoresistance (MR) at low fields. Extrinsic grain boundary MR has also been reported in other conducting magnetic oxides, such as chromium dioxide (CrO 2 ), pyrochlore Tl 2 Mn 2 O 7 , magnetite (Fe 3 O 4 ), and the ordered double-perovskite Sr 2 FeMoO 6 . Even larger changes in resistances at low fields are obtained in the layered manganite, La 2−2 x Sr 1+2 x Mn 2 O 7 for x =0.3, which possesses a natural tunnel junction structure in the c -axis direction. But, by far, the largest MR effect to date has been observed in thin film ferromagnetic/insulating/ferromagnetic tunnel junction structures, where resistance changes as high as a factor of 10 at low fields has been reported for the strontium-doped perovskite manganites. In most cases, the enhanced MR effect in these magnetic oxides is limited to rather low temperatures and decreases rapidly with increasing temperature. With a better understanding of the nature of the boundaries in these junctions, it might be possible to enhance the MR at higher temperatures.

A current-driven switching of magnetic state is observed in manganite trilayer junctions. The switching current threshold I c depends on applied magnetic field. The switching is due to the transfer of spin-momentum from spin-polarized carriers to a ferromagnetic cluster situated between the electrodes. A model developed based on the spin-momentum transfer process quantitatively describes the experimental observation.

We have designed and carried out a tricrystal experiment, based on macroscopic coherence effects, flux quantization, and pair tunneling, to study the microscopic phase of the pair wave function in high- T c cuprate superconductors. Using a high-resolution scanning SQUID microscope, we have made the first direct observation of spontaneously generated half-integer flux quanta in controlled-orientation tricrystal rings and blanket films. By varying the grain misorientation and the grain-boundary angles in the tricrystal, we have proved that the order parameter in YBa 2 Cu 3 O 7 and Tl 2 Ba 2 Cu 6 + δ has nodes and lobes consistent with d wave, but not with g wave pairing symmetry.

Based on macroscopic quantum coherence effects, flux quantization and pair tunneling, a tricrystal experiment has been designed and carried out to study the microscopic phase of the pair wavefunction in high T c cuprate superconductors. Using a high-resolution scanning SQUID microscope, we have made the first direct observation of spontaneously generated half integer flux quanta in controlled-orientation tricrystal rings. By varying the grain misorientation and the grain boundary angles in the tricrystal, we have proved that the order parameter in YBCO has nodes and lobes consistent with d-wave, but not with the g-wave pairing symmetry. The results of this work demonstrate that the half-integer flux quantum effect in superconducting systems containing multi-grains with deliberately designed grain orientation can be used as a general technique for probing the pairing symmetry.

Direct-coupled single-layer thin film SQUID magnetometers are the most reproducible high- T c magnetometers fabricated to-date. They also serve as a good model for early identification of critical device and fabrication needs for system applications. A step-edge weak-link junction is a single-layer junction technology that allows easy lithographic definition of device position. In this article we discuss the basic technologies involved in the fabrication of single-layer SQUID devices, as well as some issues in operating such SQUIDs in an ambient, unshielded environment.