Magnetic Force Microscope Study on High-anisotropy UMn2Ge2 and Construction of a Spin Polarized Scanning Tunneling Microscope PDF Download
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Author: Xinzhou Tan
Publisher:
ISBN:
Category :
Languages : en
Pages : 156
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Book Description
The first part of this dissertation introduces the theoretical background for the Magnetic Force Microscope (MFM), the Spin Polarized Scanning Tunneling Microscope (SP-STM), and the theoretical basis for magnetic domains.The second part addresses issues on the design and construction of a low temperature magnetic force microscope (LT-MFM) and its operation. The third part focuses on the LT-MFM experimental investigation on ternary UMn2Ge2 crystals. The forth part describes the construction and implementation of a low temperature SP-STM system. Scanning probe microscopy (SPM), beginning with the invention of the STM, was first developed to study the electronic properties of different materials, such as imaging high T[subscript c] superconductors. But soon, as the SPM family expanded, some of them developed into powerful techniques to characterize magnetic features. This category includes MFM and SP-STM. The former was widely used for imaging surface magnetic properties from hundreds of micrometers down to the nanometer scale, ideal for imaging magnetic domains. With our homemade LT-MFM system, we studied UMn2Ge2 single crystals, in which both the Uranium and Manganese atoms are magnetic. Flower-like magnetic domain pattern were found at room temperature, and they persisted all the way down to low temperature. Around 150K, Uranium atom ordering was revealed in the form of magnetic domain wall jumps, by partially saturating the sample and warming it up in zero field. In addition, the underlying mechanism of the flower pattern was explained using the domain branching scheme. On the other hand, a Low temperature SP-STM (LT-SP-STM) was designed and constructed, paving the way for spin mapping at the atomic scale thus characterizing magnetic materials with ultra-resolution.
Author: Xinzhou Tan
Publisher:
ISBN:
Category :
Languages : en
Pages : 156
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Book Description
The first part of this dissertation introduces the theoretical background for the Magnetic Force Microscope (MFM), the Spin Polarized Scanning Tunneling Microscope (SP-STM), and the theoretical basis for magnetic domains.The second part addresses issues on the design and construction of a low temperature magnetic force microscope (LT-MFM) and its operation. The third part focuses on the LT-MFM experimental investigation on ternary UMn2Ge2 crystals. The forth part describes the construction and implementation of a low temperature SP-STM system. Scanning probe microscopy (SPM), beginning with the invention of the STM, was first developed to study the electronic properties of different materials, such as imaging high T[subscript c] superconductors. But soon, as the SPM family expanded, some of them developed into powerful techniques to characterize magnetic features. This category includes MFM and SP-STM. The former was widely used for imaging surface magnetic properties from hundreds of micrometers down to the nanometer scale, ideal for imaging magnetic domains. With our homemade LT-MFM system, we studied UMn2Ge2 single crystals, in which both the Uranium and Manganese atoms are magnetic. Flower-like magnetic domain pattern were found at room temperature, and they persisted all the way down to low temperature. Around 150K, Uranium atom ordering was revealed in the form of magnetic domain wall jumps, by partially saturating the sample and warming it up in zero field. In addition, the underlying mechanism of the flower pattern was explained using the domain branching scheme. On the other hand, a Low temperature SP-STM (LT-SP-STM) was designed and constructed, paving the way for spin mapping at the atomic scale thus characterizing magnetic materials with ultra-resolution.
Author: Peter, Moritz
Publisher: KIT Scientific Publishing
ISBN: 3731504103
Category : Physics
Languages : en
Pages : 164
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Book Description
The present work introduces a new concept for magnetic resonance measurements in the GHz regime inside a scanning tunneling microscope. It is based on heterodyne detection in a spin-polarized tunneling barrier. The experimental requirements, including a new method to suppress transmission effects, are explained. Measurements on three model systems which were studied to validate the new technique are presented and compared to simulations.
Author: Jacob John Repicky
Publisher:
ISBN:
Category : Magnetism
Languages : en
Pages : 0
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Book Description
As conventional electronics approach the physical limits of size and speed, desire for more capable and energy efficient technologies has driven studies of the individual and collective behavior of electron spins within solid state materials to achieve new forms of information processing. Recent developments in this field of spintronics have led to the discovery particle-like magnetic textures called magnetic skyrmions where spins are arranged in a swirling, vortex-like pattern. To advance the understanding of materials capable of stabilizing magnetic skyrmions and the mechanisms that govern their stability and dynamical properties, we use spin-polarized scanning tunneling microscopy. The research presented here builds on the connection between the physical and magnetic structure at the surface of materials. First, we observe novel surface structures and investigate the electronic and magnetic properties of Cr(001) and Fe/Ir(111), two systems that can be used to characterize the magnetic tip of the scanning tunneling microscope. Next, we detail a technique to determine the grain structure of B20-type magnetic materials FeGe and MnGe, where the structural chirality is known to determine the chirality of the magnetic textures. The surface termination, stacking order of the layered atomic lattice, and grain chirality can all be identified by analysis of the atomic corrugation and insights from density functional theory calculations. Finally, we observe novel topological spin textures at the surface of MnGe(111). The stabilization of these is correlated to structural deformation of the film, and their three-dimensional structure is deduced based on comparison of the spin-polarized imaging with micromagnetic simulations.
Author: Moritz Peter
Publisher:
ISBN: 9781013281310
Category : Science
Languages : en
Pages : 156
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Book Description
The present work introduces a new concept for magnetic resonance measurements in the GHz regime inside a scanning tunneling microscope. It is based on heterodyne detection in a spin-polarized tunneling barrier. The experimental requirements, including a new method to suppress transmission effects, are explained. Measurements on three model systems which were studied to validate the new technique are presented and compared to simulations. This work was published by Saint Philip Street Press pursuant to a Creative Commons license permitting commercial use. All rights not granted by the work's license are retained by the author or authors.
Author: Toyo Kazu Yamada
Publisher:
ISBN: 9789090190358
Category :
Languages : en
Pages : 193
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Book Description
Author: Lan Luan
Publisher: Stanford University
ISBN:
Category :
Languages : en
Pages : 118
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Book Description
Superconductivity is among the most fascinating properties that a material can have. Below the transition temperature $T_c$, electrons condensate into a macroscopic quantum mechanical state and flow without dissipation. The quantum nature of the superconducting state also manifests in its magnetic properties. Superconductors fully expels magnetic field in a weak applied field, referred as Meissner effect. In an intermediate field, superconductors often contain microscopic whirlpools of electrons that carry quantized magnetic flux, called vortices. In this thesis, I present magnetic-force-microscopy (MFM) studies of unconventional superconductors both in the Meissner state and in the mix state. We extend the application of MFM beyond the conventional imaging mode and use it for quantitative analysis. In the mix state, we use MFM manipulating individual vortices with a high level of control and a known force to study the mechanics and dynamics of a single vortex in cuprate superconductors. In the Messiner state, we establish MFM as a novel local technique to measure the magnetic penetration depth $\lambda$ and implement it to study the pairing mechanism of iron-pnictide superconductors. Chapter 1 contains a brief introduction of MFM and its conventional application of imaging. We demonstrate high-spatial resolution images of isolated superconducting vortices. We show that by integrating images of isolated vortices at consecutive heights we are able to reconstruct the force between the MFM tip and vortices. We can also obtain the force by using a tip-vortex model. The two methods agree and both allow us to obtain the force used in vortex manipulation discussed in Chapter 2 and Chapter 3. Chapter 2 discusses the behavior of individual vortices in fully doped YBa$_2$Cu$_3$O$_{7-\delta}$ when subject to a local force. Because the anisotropy of fully doped YBa$_2$Cu$_3$O$_{7-\delta}$ is moderate, the vortex motion can be well described as an elastic string moving through a uniform three dimensional pinning landscape. We find an unexpected and marked enhancement of the response of a vortex to pulling when we wiggle it transversely. In addition, we find enhanced vortex pinning anisotropy that suggests clustering of oxygen vacancies in our sample. We demonstrate manipulation at the nanoscale with a level of control far beyond what has been reported before. We show that a dragged vortex can be used to probe deep into the bulk of the sample and to interact with microscopic structures much smaller than the tip size. Chapter 3 shows the vortex behavior in another limit. In an very underdoped YBa$_2$Cu$_3$O$_{6+x}$ single crystal, a cuprate superconductor with strong anisotropy, a vortex can be regarded as a stack of two-dimensional pancakes with weak interlayer Josephson coupling. We use the MFM tip to split the pancake stacks composing a single vortex and to produce a kinked structure. Our measurements highlight the discrete nature of stacks of pancake vortices in layered superconductors. We also measure the required force in the process, providing the first measurement of the interlayer coupling at the single vortex level. The discovery of iron-pnictide superconductors in 2008 motivates my efforts to locally measure the magnetic penetration depth $\lambda$, one of the two fundamental length scales in superconductors and known to be difficult to measure. Chapter 4 discusses the methodology of measuring $\lambda$ by MFM, which is based on the time-reversed mirror approximation an analytical model of the MFM tip-superconductor interaction in the Meissner state. A calibration run was performed on \YBCO\ single crystals with known $\lambda$. The same time-reversed mirror approximation can be applied to scanning SQUID sysceptometry (SSS) to measure the temperature variation of penetration depth $\Delta\lambda(T)\equiv\lambda(T)-\lambda(0)$. Chapter 5 includes brief introduction of the iron-pnictide superconductors. The multiple conduction bands and the vicinity of the superconducting phase to magnetic phase give additional challenges in $\lambda$ measurements. We demonstrated in this chapter on single crystals of Ba(Fe$_{0.95}$Co$_{0.05}$)$_2$As$_2$ that MFM can measure the absolute value of $\lambda$, as well as obtain its temperature dependence and spatial homogeneity. We observe that $\Delta\lambda(T)$ varies 20 times slower with temperature than previously reported by bulk techniques, and that $\rho_s(T)$ over the full temperature range is well described by a clean two-band fully gapped model, consistent with the proposed $s\pm$ pairing symmetry. Chapter 6 extends the measurements of $\rho_s(T)$ to the family Ba(Fe$_{1-x}$Co$_x$)$_2$As$_2$ with Co doping level $x$ across the superconducting dome. We observe systematic evolution of $\rho_s(T)$ with $x$ that can be summarized as three main trends. First, $\rho_s(0)$ falls more quickly with $T_c$ on the underdoped side of the dome than on the overdoped. Second, the temperature variation of $\rho_s(T)$ at low temperature increases away from optimal doping. Third, $\rho_s(T)$ increases sharply with cooling through the superconducting transition temperature $T_c$ of both optimally doped and underdoped compounds. These observations hint an interplay between magnetism and superconductivity.
Author: Morgann Elizabeth Berg
Publisher:
ISBN:
Category :
Languages : en
Pages : 314
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Book Description
Magnetic force microscopy studies in varying temperature and applied external magnetic field of magnetic thin films of LaCoO3 under strain and single crystal UMn2Ge2 have been performed. In the case of LaCoO3 thin films the aim is an understanding of the response of the magnetic microstructure to different signs and degrees of strain and a further attempt to distinguish the effect of defects from strain-induced effects. In UMn2Ge2 the magnetic microstructure is imaged for the first time and signatures of a possible phase transition at 150 K and crystalline anisotropy are explored. The first portion of this dissertation focuses on the synthesis methods used to produce the samples investigated and the critical role of synthesis in producing high-quality samples. This is followed by a discussion of characterization techniques used to obtain local and global magnetic and structural characteristics, with particular emphasis on magnetic force microscopy including noise characteristics and a discussion of achieving a high force gradient sensitivity by optimizing the fiber-optic interferometer used for cantilever deflection detection. Design elements and features of the multi-mode variable-temperature atomic force microscope used to obtain magnetic force microscopy images are presented and results for LaCoO3 and UMn2Ge2 are discussed.
Author: Mike Gyamfi
Publisher:
ISBN:
Category :
Languages : en
Pages : 89
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Book Description
Author: Chen, Jinjie
Publisher: KIT Scientific Publishing
ISBN: 3731508192
Category : Molecules
Languages : en
Pages : 146
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Book Description
We worked on different magnetic molecules containing 3d and 4f magnetic centers. Their growth on metallic surfaces, topographies, spin states, magnetic properties and electron transport were locally investigated by using scanning tunneling microscopy (STM) at temperatures down to 30mK. The main achievement of this dissertation reveals the abrupt switching of crystal fields during formation of molecular contacts.
Author: Samuel H. Cohen
Publisher: Springer Science & Business Media
ISBN: 0306448904
Category : Science
Languages : en
Pages : 468
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Book Description
Papers presented at the first US Army Natick Research, Development and Engineering Center Symposium on [title], held in Natick, Mass., June 1993. The various symposium topics included application of AFM/STM in material sciences, polymers, physics, biology and biotechnology, along with recent developments including new probe microscopies. The procee.
