Global ETD Search
Search theses and dissertations gathered from participating repositories worldwide. Every result links back to the library that holds it. No account is needed.
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Showing 1 to 20 of 59 for “"Spin glass"”.
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Dynamics in quantum spin glass systems
… of the equilibrium dynamics of quantum spin glass systems. To this end a generic fermionic SU(2), spin 1/2 spin glass model with infinite-range interactions is defined in the first part. The model is treated in the framework of imaginary-time Grassmann field theory along with the replica …
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Electrical noise in the spin-glass AuFe
… fluctuations have been performed on the spin-glass AuFe in order to compare with prior results in CuMn. Macroscopic AuFe samples showed a sharp increase in the noise with the onset of the noise at a temperature corresponding to the peak in the magnetic susceptibility as a function of …
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Experimental study of the spin-glass phase diagram
The spin-glass phase diagram is examined as a function of temperature, magnetic field, random anisotropy, and uniaxial anisotropy and the results are compared to recent mean-field theories. It is clearly demonstrated through measurements of the magnetic relaxation processes in the amorphous …
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Probing Spin Glass Energy Landscapes with 1/f Noise
The spin-glass transition is a dynamical phase transition, similar in nature to that of structural glasses and other systems. Upon quenching from above the transition temperature Tg to a measurement temperature T < Tg, experiments and simulations have unveiled an underlying length scale, the …
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Stirred spin glass models of in vivo protein folding
"The similarity between spin glasses and proteins is that both have complex energy landscapes with multiple energy minima and barriers. The approach to equilibrium in such systems has been previously studied. We present here a ""stirred"" spin glass whose equilibrium is constantly being perturbed …
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Electrical noise study of spin glass dynamics in mesocopic CuMn
The electrical resistance of the archetypal spin glass CuMn is surprisingly sensitive to small changes in the spin configuration. This enhanced sensitivity results from long-range electron quantum interference at low temperatures. Due to this effect, substantial resistance noise is produced by …
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Self-organized fine-tuned response in a driven spin glass
… when an external drive is applied. I consider a spin glass as a prototypical model of such a system, and investigate these principles through simulation. I find that spins differentiate into slow spins which decouple from the drive and fast spins which couple more strongly to the drive, resulting …
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Electrical noise study of spin glass dynamics in mesoscopic copper manganese
The electrical resistance of the archetypal spin glass $\underline{\rm Cu}$Mn is surprisingly sensitive to small changes in the spin configuration. This enhanced sensitivity results from long-range electron quantum interference at low temperatures. Due to this effect, substantial resistance noise …
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Cluster expansion approach and fluctuation results in mean field spin glass theory
Submission published under a 24 month embargo labeled 'U of I Access', the embargo will last until 2025-08-01
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Zero Field Nmr Study on a Spin Glass: Iron-Doped 2hydrogen-Niobium Diselenide
We have used spin echoes to study the ('93)Nb NQR in 2H-NbSe(,2)Fe(,x). We measured (intensity) x (temperature), and T(,1P) (spin-lattice relaxation parameter) and T(,2) (spin-spin relaxation time) as a function of temperature. Our data reveal dramatic difference between non-spin glass samples (x = …
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Zero field NMR study on a spin glass: Iron-doped 2H-niobium diselenide
We have used spin echoes to study the 93Nb NQR in 2H-NbSe2Fex. We measured (intensity)x(temperature), and T1P (spin-lattice relaxation parameter) and T2 (spin-spin relaxation time) as a function of temperature. Our data reveal dramatic difference between non-spin glass samples (x=O, 0.25%, 1% and …
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57Fe Mössbauer spectroscopic study of the spin-glass transitions in the mixed spinel series Mg0.9+xFe2(1-x)Ni0.1Ti0.1O4
Magnetically diluted materials with spinel structure can fulfil the conditions for spin-glass behaviour. On the other hand, such spinels were also reported to exhibit a superparamagnetic behaviour due to the existence of small magnetic clusters in the spinel lattice. In order to gain some insight …
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Magnetic resonance in amorphous iron-nickel alloys
… Fe8Ni72P20 and Fe10Ni70P20 show paramagnetic to spin-glass transitions, while Fe16N~4P20 shows paramagnetic to ferromagnetic and ferromagnetic to spin-glass transitions. The lineshape, at both frequencies, undergoes a progressive distortion as the temperature is reduced. We use an improved …
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Mesoscopic noise probe of an inhomogeneous colossal magnetoresistance phase
… the mixed phase. A separate experiment on the spin glass CuMnAu investigates the effect of strong local anisotropy on spin glass dynamics. The result demonstrates that altering the symmetry of a spin glass Hamiltonian on the scale of the two-spin interaction has a strong qualitative effect on …
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Statistical and Algorithmic Thresholds in Spin Glasses
This thesis studies spin glasses, disordered complex systems originating in statistical physics. Such systems model optimization, sampling, and inference problems from probability and statistics, which are of fundamental importance to modern data science. In particular, spin glasses provide natural …
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Synthesis and Characterization of Heusler Compounds with Non-Collinear Magnetic Structure - From Spin Glasses to Spin Reorientation
… free permanent magnets, magnetocalorics, spin transfer torque devices and tunnel junctions. Apart from that, magnetic Heusler systems are also interesting for fundamental research since some members host skyrmion lattices and other magnetically complex orders. The search for new Heusler …
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Aging and Barkhausen noise in the relaxor ferroelectrics
… than Arrhenius cooperative freezing into a glassy relaxor regime instead. It is not understood how the random fields and random interactions present in these dielectrics inhibit the formation of long-range ferroelectric order. This thesis presents two types of experi- ments aimed at shedding …
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Mechanical relaxations, spin glasses and 1/f resistance noise
… resistance changes in mesoscopic samples of the spin glass CuMn. A large sensitivity of the resistance to the relative configuration of spins in the sample was found with a magnitude and temperature dependence in accordance with predictions of universal conductance fluctuations. Predictions of …
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Investigation and Optimization of Extraordinary Electroconductance (EEC) Sensors & The Role of Magnetic Disorder in the Formation of Spin Glasses
… Role of Magnetic Disorder in the Formation of Spin Glasses</underline></p><p>This thesis presents data on the magnetic properties of two classes of layered spin S=1/2 antiferromagnetic quasi-triangular lattice materials: Cu<sub>2(1-x)</sub>Zn<sub>2x</sub>(OH)<sub>3</sub>NO<sub>3</sub> …
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Microstructural characteristics of gold-rich gold-iron alloys
As a typical spin-glass alloy system with diverse controversies on its magnetic properties and atomic arrangements, Au-rich Au-Fe alloys with Fe content from 10.7 to 33at% were studied to clarify their microstructural characteristics. As a consequence and in comparison with previous work, some …
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