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11.
12.
Bruce T. Bolon M.A. HaugenA. Abin-Fuentes J. DeneenC.B. Carter C. Leighton 《Journal of magnetism and magnetic materials》2007
We have used ferromagnet/antiferromagnet/ferromagnet trilayers and ferromagnet/antiferromagnet multilayers to probe the grain size dependence of exchange bias in polycrystalline Co/Fe50Mn50. X-ray diffraction and transmission electron microscopy show that the Fe50Mn50 (FeMn) grain size increases with increasing FeMn thickness in the Co (30 Å)/FeMn system. Hence, in Co(30 Å)/FeMn(tAF Å)/Co(30 Å) trilayers the two Co layers sample different FeMn grain sizes at the two antiferromagnet/ferromagnet interfaces. For FeMn thicknesses above 100 Å, where simple bilayers have a thickness-independent exchange bias, we are therefore able to deduce the influence of FeMn grain size on the exchange bias and coercivity (and their temperature dependence) simply by measuring trilayer and multilayer samples with varying FeMn thicknesses. This can be done while maintaining the (1 1 1) orientation, and with little variation in interface roughness. Increasing the average grain size from 90 to 135 Å results in a fourfold decrease in exchange bias, following an inverse grain size dependence. We interpret the results as being due to a decrease in uncompensated spin density with increasing antiferromagnet grain size, further evidence for the importance of defect-generated uncompensated spins. 相似文献
13.
Dynamic nuclear polarization studies of nitroxyl spin probes in agarose gel using Overhauser‐enhanced magnetic resonance imaging
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V. Meenakumari Hideo Utsumi Fuminori Hyodo A. Jawahar A. Milton Franklin Benial 《Magnetic resonance in chemistry : MRC》2017,55(11):1022-1028
Agarose is a tissue‐equivalent material and its imaging characteristics similar to those of real tissues. Hence, the dynamic nuclear polarization studies of 3‐carboxy‐2,2,5,5‐tetramethyl‐pyrrolidine‐1‐oxyl (carboxy‐PROXYL) in agarose gel were carried out. The dynamic nuclear polarization parameters such as spin lattice relaxation time, longitudinal relaxivity, leakage factor, saturation parameter and coupling parameter were estimated for 2 mM carboxy‐PROXYL in phosphate‐buffered saline solution and water/agarose mixture (99 : 1). From these results, the spin probe concentration was optimized as 2 mM, and the reduction in enhancement was observed for carboxy‐PROXYL in water/agarose mixture (99 : 1) compared with phosphate‐buffered saline solution. Phantom imaging was also performed with 2 mM concentration of carboxy‐PROXYL in various concentrations of agarose gel at various radio frequency power levels. The results from the dynamic nuclear polarization measurements agree well with the phantom imaging results. These results pave the way for designing model system for human tissues suited to the biological applications of electron spin resonance/Overhauser‐enhanced magnetic resonance imaging. 相似文献
14.
We consider the realization of a quantum computer in a chain of nuclear spins coupled by an Ising interaction. Quantum algorithms
can be performed with the help of appropriate radio-frequency pulses. In addition to the standard nearest-neighbor Ising coupling,
we also allow for a second neighbor coupling. It is shown, how to apply the 2π
k method in this more general setting, where the additional coupling eventually allows to save a few pulses. We illustrate
our results with two numerical simulations: the Shor prime factorization of the number 4 and the teleportation of a qubit
along a chain of 3 qubits. In both cases, the optimal Rabi frequency (to suppress non-resonant effects) depends primarily
on the strength of the second neighbor interaction. 相似文献
15.
Very large resistance maxima can be observed in the longitudinal magnetoresistance of a narrow single quantum well. They exist only at certain fractional filling factors and are clearly related to the coupling of the electron to the nuclear spin system. In resistively detected NMR experiments, which are possible in this system, a very unusual fine structure of the resonance lines is observed, which hints towards an unusual coupling between the electron and nuclear system. 相似文献
16.
Hydrophobicity‐Driven Self‐Assembly of an Eighteen‐Membered Honeycomb Lattice with Almost Classical Spins
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Guo‐Jun Zhou Prof. Dr. Johannes Richter Prof. Dr. Jürgen Schnack Prof. Dr. Yan‐Zhen Zheng 《Chemistry (Weinheim an der Bergstrasse, Germany)》2016,22(42):14846-14850
The design and synthesis of model compounds that do not exist naturally is one of the important targets in modern coordination chemistry. Herein, an eighteen‐membered honeycomb structure with equal numbers of MnII (s=5/2) and GdIII (s=7/2) metal centers has been prepared, for the first time, by using a hydrophobic force‐directed self‐assembling process. Due to the weakly coupled GdIII pairs, the magnetic properties are mainly determined by eight‐membered chains in the experimentally considered temperature range. These [Mn4Gd4] ”finite‐size“ chains, albeit with large Hilbert space, can be fully resolved by the high‐temperature series expansion and the powerful finite‐temperature Lanczos method, which reveal that the exchange‐couplings between the metal centers are antiferromagnetic and consistent with the magnetization measurement. Interestingly, from the surface‐engineering point of view, the [Mn4Gd4] chains are ”precisely“ assembled into a 2D honeycomb pattern, which is potentially desirable in the design of weakly coupled qubits. 相似文献
17.
Studies on the magnetic properties of the molecular antiferromagnetic material {N(n-C5H11)4[MnIIFeIII(ox)3]}∞, carried out by various physical techniques (AC/DC magnetic susceptibility, magnetization, heat capacity measurements and Mössbauer spectroscopy) at low temperatures, have been presented. Different experimental observations complement each other and provide a clue for the observation of an uncompensated magnetization below the Néel temperature and short-range correlations persisting high above TN. It is understood that the honeycomb layered structure of the compound contains non-equivalent magnetic sub-lattices, (MnII–ox–FeIIIA–...) and (MnII–ox–FeIIIB–...), where different responses of the FeIIIA and FeIIIB spin sites towards an external magnetic field might be responsible for the observation of the uncompensated magnetization in this compound at T < TN. The present magnetic system is an S = 5/2 2-D Heisenberg antiferromagnet system with the intralayer exchange parameter J/kB = −3.29 K. A very weak interlayer exchange interaction was anticipated from the spin wave modeling of the magnetic heat capacity for T < 0.5TN. The positive sign of the coupling between the layers has been concluded from the Mössbauer spectrum in the applied magnetic field. Frustration in the magnetic interactions gives rise to the uncompensated magnetic moment in this compound at low temperatures. 相似文献
18.
Room‐temperature magnetization hysterisis measurements were conducted on Mn0.5Zn0.5GdxFe(2‐x)O4 ferrite nanoparticles, with x = 0, 0.5, 1.0, 1.5. The structure of this ferrite is normal spinel where the added of Gd3+ ions occupied the octahedral sites and replaces Fe3+ ions. The saturation magnetization was found to increase with the initial addition of the Gd3+ ions followed by a sharp decrease with further addition of Gd3+ ions. The Curie temperature was found to increase up to Gd3+ concentration of x = 1.0, and then decreases at x = 1.5. These results were attributed to the surface spins. Because the size of Gd3+ ions is larger than that of Fe3+ ions, the substitution of Fe3+ ions with the Gd3+ ions results in surface disorder which results in surface spins. A core‐shell magnetization model was introduced where several factors were combined to explain our results. (© 2009 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim) 相似文献
19.
20.
We propose a scheme to engineer a non-local two-qubit
phase gate between two remote quantum-dot spins. Along with
one-qubit local operations, one can in principal perform various
types of distributed quantum information processing. The scheme
employs a photon with linearly polarisation interacting one after
the other with two remote quantum-dot spins in cavities. Due to the
optical spin selection rule, the photon obtains a Faraday rotation
after the interaction process. By measuring the polarisation of the
final output photon, a non-local two-qubit phase gate between the
two remote quantum-dot spins is constituted. Our scheme may has very
important applications in the distributed quantum information
processing. 相似文献