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Magnetic Remanence



Magnetic remanence is the property that allows an attacker to recreate files that have been overwritten. For the Science of Security community, it is a topic relevant to the hard problem of resilience. The work cited here was presented in 2015.

J. Song, H. Kim and S. Park, “Enhancing Conformance Testing Using Symbolic Execution for Network Protocols,” in IEEE Transactions on Reliability, vol. 64, no. 3, pp. 1024-1037, Sept. 2015. doi: 10.1109/TR.2015.2443392
Abstract: Security protocols are notoriously difficult to get right, and most go through several iterations before their hidden security vulnerabilities, which are hard to detect, are triggered. To help protocol designers and developers efficiently find non-trivial bugs, we introduce SYMCONF, a practical conformance testing tool that generates high-coverage test input packets using a conformance test suite and symbolic execution. Our approach can be viewed as the combination of conformance testing and symbolic execution: (1) it first selects symbolic inputs from an existing conformance test suite; (2) it then symbolically executes a network protocol implementation with the symbolic inputs; and (3) it finally generates high-coverage test input packets using a conformance test suite. We demonstrate the feasibility of this methodology by applying SYMCONF to the generation of a stream of high quality test input packets for multiple implementations of two network protocols, the Kerberos Telnet protocol and Dynamic Host Configuration Protocol (DHCP), and discovering non-trivial security bugs in the protocols.
Keywords: conformance testing; cryptographic protocols; DHCP; Kerberos Telnet protocol; SYMCONF; conformance testing enhancement; dynamic host configuration protocol; hidden security vulnerability; high-coverage test input packets; network protocols; nontrivial security bugs; security protocols; symbolic execution; symbolic inputs; Computer bugs; IP networks; Interoperability; Protocols; Security; Software; Testing; Conformance testing; Kerberos; Telnet; protocol verification; test packet generation
(ID#: 16-9969)


L. Chen, D. Hopkinson, J. Wang, A. Cockburn, M. Sparkes and W. O’Neill, “Reduced Dysprosium Permanent Magnets and Their Applications in Electric Vehicle Traction Motors,” in IEEE Transactions on Magnetics, vol. 51, no. 11, pp. 1-4, Nov. 2015. doi: 10.1109/TMAG.2015.2437373
Abstract: Permanent magnet (PM) machines employing rare-earth magnets are receiving increasing interest in electrical vehicle (EV) traction applications. However, a significant drawback of PM machine-based EV tractions is the extremely high cost and volatile supply of rare-earth materials, especially for dysprosium (Dy), whose price is almost 6 times higher than neodymium. This paper describes a new Dy grain boundary-diffusion process for sintered Nd2Fe14B magnets to maximize its effect on coercivity enhancement. The new process gains an 81% reduction in Dy consumption normally required by the conventional Nd2Fe14B magnets for the equivalent performance and 17% higher remanence. The investigation into the application in an interior PM (IPM) machine for a small-sized EV traction shows that compared with the conventional Nd2Fe14B magnets, despite the relatively low coercivity, the low-Dy-content magnets still withstand the thermal and demagnetization challenge over various driving operations. In addition, with the magnet's high remanence and energy product, the machine gains significant torque and energy efficiency improvements. The analysis results are validated by a series of tests carried out on a prototype IPM machine with the new magnets.
Keywords: boron alloys; coercive force; demagnetisation; dysprosium; electric vehicles; iron alloys; neodymium alloys; permanent magnet machines; permanent magnets; remanence; traction motors; Dy; Dy consumption reduction; Dy grain boundary-diffusion process; Nd2Fe14B;coercivity enhancement; demagnetization; energy efficiency; interior PM machine; low-Dy-content magnets; magnet high remanence; reduced dysprosium permanent magnets; sintered magnets; small-sized electric vehicle traction motors; torque efficiency; Magnetic domains; Magnetic flux; Magnetic noise; Magnetic shielding; Perpendicular magnetic anisotropy; Torque; rare earth material (ID#: 16-9970)


J. Li, N. Chen, D. Wei and M. Futamoto, “Micromagnetic Studies of Ultrahigh Resolution Magnetic Force Microscope Tip Coated by Soft Magnetic Materials,” in IEEE Transactions on Magnetics, vol. 51, no. 1, pp. 1-5, Jan. 2015. doi: 10.1109/TMAG.2014.2337835
Abstract: Magnetic force microscope (MFM) tips coated by soft magnetic materials can achieve a spatial resolution above 10 nm. It is interesting to analyze why tips coated with soft magnetic materials can achieve such a high resolution. In experiment, an MFM tip coated by amorphous FeB can achieve a resolution of 8 nm; therefore, we chose an FeB tip as an example and establish a micromagnetic model to understand the measurement mechanism of the soft magnetic MFM tip. In the FeB film simulation, the random crystalline anisotropy results in a soft magnetic loop with an in-plane coercivity of 0.2 Oe, and the film surface roughness will raise the coercivity to the order of 1 Oe. In the tip simulation, it is found that the FeB-coated tip can be switched in a uniform field of the order of 100 Oe, but can remain near a remanent state in a stray field resulting from media. A simple model is set up to analyze the MFM images of bits in hard disk drivers using the simulated magnetic properties of the tip and resolution ~10 nm is confirmed.
Keywords: amorphous magnetic materials; boron alloys; coercive force; disc drives; hard discs; iron alloys; magnetic anisotropy; magnetic force microscopy; magnetic thin film devices; magnetic thin films; metallic thin films; micromagnetics; remanence; soft magnetic materials; surface roughness; FeB; amorphous film simulation; film surface roughness; hard disk driver bits; in-plane coercivity; magnetic properties; micromagnetic model; random crystalline anisotropy; remanent state; soft magnetic MFM tip; soft magnetic loop; soft magnetic materials; spatial resolution; stray field; tip simulation; ultrahigh resolution magnetic force microscopy tip; Amorphous magnetic materials; Educational institutions; Films; Magnetic force microscopy; Micromagnetics; Microscopy; Soft magnetic materials; Amorphous FeB; magnetic force microscope (MFM) tip; micromagnetic simulation; soft magnetic coating (ID#: 16-9971)


Q. Y. Zhou, Z. Liu, S. Guo, A. R. Yan and D. Lee, “Magnetic Properties and Microstructure of Melt-Spun Ce–Fe–B Magnets,” in IEEE Transactions on Magnetics, vol. 51, no. 11, pp. 1-4, Nov. 2015. doi: 10.1109/TMAG.2015.2447553
Abstract: A series of CexFebalB6 (x = 12, 14, 17, 19, and 23 wt%) ternary ribbons was prepared by melt-spinning. Magnetic properties and the microstructure of the Ce-Fe-B ribbons with different Ce contents were investigated. The X-ray diffraction results indicated that multiphase coexisted in the as-spun Ce-Fe-B ribbons, which contained Ce2Fe17, CeFe2, Ce-rich phase, Fe-rich phase, cerium oxide, and iron oxide. The magnetic properties, microstructure, and phase composition of the ribbons were directly affected by the cerium content. The magnetic properties could be obtained by exchange coupling between the hard and soft magnetic phases in the pure ternary Ce-Fe-B ribbons. Furthermore, by heat treatment, the magnetic properties of the as-spun Ce-Fe-B ribbons could be optimized. The highest magnetic properties of Hcj = 6.2 kOe, Br = 6.9 kGs, and (BH)m = 8.6 MGOe were obtained in Ce17FebalB6 magnets.
Keywords: X-ray diffraction; boron alloys; cerium alloys; coercive force; crystal microstructure; exchange interactions (electron); heat treatment; iron alloys; melt spinning; permanent magnets; remanence; soft magnetic materials; CexFeB6; X-ray diffraction; coercivity; exchange coupling; hard magnetic phase; heat treatment; magnetic energy product; magnetic properties; melt-spun magnets; microstructure; phase composition; soft magnetic phase; ternary ribbons; Heating; Magnetic properties; Microstructure; Perpendicular magnetic anisotropy; Saturation magnetization; Temperature; Ce-Fe-B magnets; Ce2Fe17B magnets; heat treatment; heat-treatment; magnetic properties; melt-spinning (ID#: 16-9972)


C. Wu et al., “Low-Temperature Sintering of Barium Hexaferrites with Bi2O3/CuO Additives,” in IEEE Transactions on Magnetics, vol. 51, no. 11, pp. 1-4, Nov. 2015. doi: 10.1109/TMAG.2015.2434834
Abstract: Barium hexaferrites BaFe12O19 with Bi2O3/CuO additives were synthesized by the conventional oxide ceramic process. The results manifest that Bi2O3 additives mainly concentrate on the grain boundary regions, while CuO additives could both enter into the grain and segregate at the grain boundary regions. The appropriate sintering temperature of barium hexaferrites with Bi2O3 and Bi2O3+ CuO additives reaches 1020 °C and 920 °C, respectively. As the amount of Bi2O3 is 3 wt%, the specimens of BaFe12O19 show saturation magnetization (Ms) of 346 kA/m, remanence (Mr) of 227 kA/m, and density (d) of 5.06 g/cm3. Meanwhile, the combination of 3 wt% Bi2O3 and 3 wt% CuO additives significantly promotes grain growth and sintering densification, with a high saturation magnetization of 371 kA/m and density of 5.23 g/cm3 for BaFe12O19, which are pretty close to the theoretical values (380 kA/m, 5.28 g/cm3). Moreover, the corresponding remanence could also rise by 10% compared with that in the sintered samples with 3 wt% Bi2O3.
Keywords: barium compounds; bismuth compounds; copper compounds; densification; ferrites; grain boundaries; grain growth; remanence; sintering; BaFe12O19-Bi2O3-CuO; barium hexaferrites; conventional oxide ceramic process; density; grain boundary regions; low-temperature sintering; saturation magnetization; sintering densification; temperature 1020 degC to 920 degC; Additives; Barium; Copper; Ferrites; Grain boundaries; Magnetic properties; Saturation magnetization; Barium hexaferrites; Bi2O3/CuO additives; Density; Low-temperature sintering; magnetic properties (ID#: 16-9973)


C. Yu, S. Niu, S. L. Ho, W. Fu and L. Li, “Hysteresis Modeling in Transient Analysis of Electric Motors with AlNiCo Magnets,” in IEEE Transactions on Magnetics, vol. 51, no. 3, pp. 1-4, March 2015. doi: 10.1109/TMAG.2014.2362615
Abstract: Electric motors fabricated with aluminum-nickel-cobalt (AlNiCo) permanent magnets (PMs) can be operated over a wide speed range, as the strong nonlinear demagnetization characteristics of AlNiCo allow effective and efficient airgap flux control. This paper presents a linear hysteresis model which is derived from the Preisach model for AlNiCo PMs, to be incorporated into the time-stepping finite element method to study the motor performance, especially transient performance, accurately and effectively. The proposed method can significantly reduce the computing time without scarifying the accuracy of the Preisach model. The validity and accuracy of the proposed method are verified by both simulation and experimentation.
Keywords: air gaps; aluminium alloys; cobalt alloys; demagnetisation; finite element analysis; magnetic flux; magnetic hysteresis; nickel alloys; permanent magnet motors; transient analysis; AlNiCo; Preisach model; airgap flux control; electric motors; linear hysteresis model; nonlinear demagnetization characteristics; permanent magnets; time stepping finite element method; transient performance analysis; Demagnetization; Hysteresis motors; Magnetic flux; Magnetic hysteresis; Magnetization; Permanent magnet motors; Remanence;  Aluminum-nickel-cobalt (AlNiCo); finite element method; hysteresis model; memory motor; permanent magnet; permanent magnet (PM) (ID#: 16-9974)


C. Yang et al., “Giant Converse Magnetoelectric Effect in PZT/FeCuNbSiB/FeGa/FeCuNbSiB/PZT Laminates Without Magnetic Bias Field,” in IEEE Transactions on Magnetics, vol. 51, no. 11, pp. 1-4, Nov. 2015. doi: 10.1109/TMAG.2015.2435010
Abstract: We reported a giant self-biased converse magnetoelectric (CME) effect in laminated composites consisting of graded magnetostrictive FeCuNbSiB/FeGa/FeCuNbSiB layers sandwiched between two electro-parallel-connected PZT piezoelectric plates. The great different magnetic characteristics (such as magnetic permeability and coercivity) in FeGa and nanocrystalline foil FeCuNbSiB result in a large internal magnetic field and remanent piezomagnetic coefficient in FeCuNbSiB/FeGa/FeCuNbSiB, which account for the giant self-biased CME effect. The experimental results show that: (1) a large remanent CME coefficient of 2.228 × 10-3 mGs · cm/V is achieved, which can be used for realizing miniature electrically controlled magnetic flux devices; (2) the dynamic switching of magnetic flux between bistable states in PZT/FeCuNbSiB/FeGa/FeCuNbSiB/PZT through a smaller ac voltage (1 Vrms) controlling is realized; and (3) the induced magnetic induction B has an excellent linear relationship with applied ac voltage Vin.
Keywords: boron alloys; coercive force; copper alloys; electromagnetic induction; gallium alloys; iron alloys; laminates; lead compounds; magnetic flux; magnetic multilayers; magnetic permeability; magnetic switching; magnetoelectric effects; magnetostriction; nanostructured materials; niobium alloys; remanence; silicon alloys; PZT-FeCuNbSiB-FeGa-FeCuNbSiB-PZT; PZT-FeCuNbSiB-FeGa-FeCuNbSiB-PZT laminates; applied ac voltage; bistable states; coercivity; dynamic switching; electroparallel-connected PZT piezoelectric plates; giant self-biased converse magnetoelectric effect; graded-magnetostrictive FeCuNbSiB-FeGa-FeCuNbSiB layers; induced magnetic induction; internal magnetic field; laminated composites; magnetic permeability; miniature electrically controlled magnetic flux devices; nanocrystalline foil FeCuNbSiB; remanent converse magnetoelectric coefficient; remanent piezomagnetic coefficient; Magnetic flux leakage; Magnetic hysteresis; Magnetic resonance; Magnetic switching; Magnetoelectric effects; Magnetostriction; Converse magnetoelectric (CME) effects; Converse magnetoelectric effects; magnetostrictive materials; nanocrystalline foil; switching of magnetic flux. (ID#: 16-9975)


X. Cui, S. Yakata and T. Kimura, “Detection of Vortex Core Oscillation Using Second-Harmonic Voltage Detection Technique,” in IEEE Transactions on Magnetics, vol. 51, no. 11, pp. 1-3, Nov. 2015. doi: 10.1109/TMAG.2015.2435024
Abstract: A sensitive and reliable detection method for magnetic vortex core dynamics at the remanent state has been demonstrated. Perfectly symmetric potential created in a circular-shaped disk produces twofold symmetry in the position dependence of the resistance of the ferromagnetic disk. We find that the detectable second-harmonic voltage can be induced by flowing the dc current when the circular-shaped core oscillation is excited by the microwave magnetic field. The consistent features have been observed in the current dependence and field dependence of the signals, indicating that the present method is a powerful technique to characterize the core dynamics, even at the remanent state.
Keywords: magnetic cores; remanence; circular-shaped core oscillation; circular-shaped disk; core dynamics; current dependence; dc current; ferromagnetic disk; field dependence; magnetic vortex core dynamics; microwave magnetic field; remanent state; second-harmonic voltage; second-harmonic voltage detection technique; twofold symmetry; vortex core oscillation detection; Magnetic cores; Magnetic resonance; Magnetic separation; Magnetostatics; Perpendicular magnetic anisotropy; 2nd harmonic; Anisotropic magnetoresistance (AMR) effect; RF magnetic field; anisotropic magnetoresistance effect; second harmonic; vortex dynamics
(ID#: 16-9976)


M. Nakano et al., “Nd–Fe–B Film Magnets with Thickness Above 100 μm  Deposited on Si Substrates,” in IEEE Transactions on Magnetics, vol. 51, no. 11, pp. 1-4, Nov. 2015. doi: 10.1109/TMAG.2015.2438099
Abstract: Although increase in thickness of a Nd-Fe-B film magnet is indispensable to provide a sufficient magnetic field, it was difficult to suppress the peeling phenomenon due to the different values of a linear expansion coefficient for a Si substrate and a Nd-Fe-B film even if a buffer layer such as a Ta film was used. In this report, it was confirmed that a control of the microstructure for pulsed laser deposition-fabricated Nd-Fe-B films enabled us to increase the thickness up to approximately 160 μm without a buffer layer on a Si substrate. Namely, we found that the precipitation of the Nd element at the boundary of Nd-Fe-B grains together with the triple junctions due to the composition adjustment is effective in suppressing the destruction of the samples through an annealing process. The magnetic properties of the prepared films were comparable with those of previously reported ones deposited on metal substrates. Although the mechanism is under investigation, the above-mentioned film had stronger adhesive force compared with that of a sputtering-made film. Resultantly, no deterioration of mechanical together with magnetic properties could be observed after a dicing process.
Keywords: annealing; boron alloys; crystal microstructure; iron alloys; magnetic thin films; metallic thin films; neodymium alloys; precipitation; pulsed laser deposition; remanence; Nd-Fe-B film magnets; NdFeB; Si substrates; adhesive force; annealing; linear expansion coefficient; magnetic field; magnetic properties; microstructure; precipitation; pulsed laser deposition; triple junctions; Magnetic films; Magnetic properties; Magnetic tunneling; Magnetomechanical effects; Silicon; Substrates; Film magnet; MEMS; Nd-Fe-B; Nd???Fe???B; PLD (Pulsed Laser Deposition); Si substrate; film magnet; pulsed laser deposition (PLD) (ID#: 16-9977)


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