Quantum Magnetics

Can the simple vector presentation be used to display the effects of a 90° pulse on zero- or multiple-quantum magnetizations ... 

No. The vector presentation is suitable for depicting single-quantum magnetizations but is not appropriate when considering zero-, double-, and higher-order quantum coherences. Quantum mechanical treatment can be employed when such magnetizations are considered. 

The last 90° pulse applied on the 13C channel is aimed to convert the heteronuclear multiple quantum magnetization into observable proton AP magnetization. 

In contrast, within (p-EPYNN)[Ni(dmit)2], first synthesized in 1996 [79], it has been proven that spin-ladder chains of the Ni(dmit)2 moiety coexist with the ferromagnetic one-dimensional chain of the p-EPYNN radical cation. Spin-ladders are of interest because of their potential applications in the area of quantum magnets and because it has been predicted that holes doped into even-leg ladders may pair and possibly superconduct [90-92]. 

Keywords fluxon gas in thermalized Josefson systems the criteria of degeneracy of the relativistic ideal gas absolute minimum realization of the most probable state in the equilibrium system temperature of the primary microwave cosmic background primary quantum magnetic flow. 

As follows from the previous analysis for quasi and ordinary particles gases there exists a critical value of parameters a and b for which the least value of the distribution function for observable frequencies is observed. From the physical point of view this is in agreement with the absolute minimal realization of the most probable state. As in any equilibrium distribution, there is an unique most probable state which the system tends to achieve. In consequence we conclude that the observable temperature of the relic radiation corresponds to this state. Or, what is the same, the temperature of such radiation correspond to the temperature originated in the primary microwave cosmic background and the primitive quantum magnetic flow. 

Detection of TNT and RDX Landmines by Stand-off Nuclear Quadrupole Resonance. Preprint given author by Andy Hibbs, Quantum Magnetics Inc., San Diego, 1999. Hill, H. H., Jr., W. F. Siems, and R. H. St. Louis. Ion mobility spectrometry. Anal Chem. 21(5), 321-355 (1990). 

Schollwock, U. Richter, J. Famell, D. J. J. Bishop, R. F. (Eds.) Quantum Magnetism Springer Berlin/Heidelberg, 2004. Volume 645 of Lecture Notes in Physics. 

In the following we will discuss three systems that on one hand can be regarded as model systems, however, on the other hand have extraordinary and unusual magnetic properties that distinguish them from other more classical materials. This exotic behavior is the basis for the fascination they raised in the community devoted to quantum magnetism. 

The most spectacular example of such a directed chemical approach toward quantum magnetism is Cu2Te205Br2, a system with weakly connected Cu2+ tetrahedra, as sketched in Fig. 2a) [39], The magnetic susceptibility data given in Fig. 2b) show a broad maximum at Tmax=30 K and a decrease at low temperatures, a behavior that is consistent with weakly coupled tetrahedra of AF coupled spins. A fit to this temperature dependence gives a typical energy scale for the intra-tetrahedra coupling of J=40 K for this compound. A kink at Tc=14.4 K in the susceptibility marks a transition [32],... 

P. Lemmens and P. Millet, in Quantum Magnetism Microscopic Techniques for Novel States of Matter (Springer, Heidelberg, 2004), Chap. Spin - Orbit - Topology, a triptych, and references within. 

Chou, S. Y., Krauss, P. R., and Kong, L. S., Nanolithograpically defined magnetic structures and quantum magnetic disk. J. Appl. Phys 79,6101 (1996). 

The basic magnetic-bead patent appears to be the property of Dynal, but Clemente Associates (formerly Quantum Magnetics, Madison, CT) produces Ni-bearing magnetic particles of 3- to 5-pm diameter for... 

For quantum magnets, quantum Monte Carlo (QMC) methods are also the method of choice whenever they are applicable. Over the last decade... 

While the mapping from the quantum average to a classical average in (46) can be performed for any quantum system, it can happen in frustrated quantum magnets, that some of the weights W(C) in the quantum system are negative, as is shown in Fig. 11. 

The loop, worm and directed loop algorithms can be used for the simulation of a wide class of quantum magnets. They are of interest not only to theoretical physicists, but also to experimentalists who want to fit experimental measurements to theoretical models. The wide applicability of these methods has led to the publication of open-source versions of these algorithms as part of the ALPS project (Algorithms and Libraries for Physics Simulations) [10] on the web page http //alps.comp-phys.org/. 

Another interesting application is to simulate realistic models for quantum magnets, using exchange constants calculated by ab-initio methods. Comparing these ab-initio QMC data to experimental measurements, as done for a series of vanadates [73] and for ladder compounds [71] allows to quantitatively check the ab-initio calculations. 

The worm and directed loop algorithms are applied when magnetic fields are present. Typical examples include the calculation of magnetization curves of quantum magnets [74], the determination of the first order nature of the spin flop transition in two dimensions [75] and the calculation of phase diagrams of dimerized quantum magnets in a magnetic field [76]. 

Another advantage of extended ensemble simulations is the ability to directly calculate the density of states and from it thermodynamic properties such as the entropy or the free energy that are not directly accessible in canonical simulations. In the following we will again use quantum magnets as concrete examples. A generalization to bosonic and fermionic models will always be straightforward. 

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