Electron spin resonance is a technique used for the studying of materials with unpaired electrons. In the presence of an external magnetic field the electrons magnetic moment aligns itself either parallel or antiparallel to the field resulting in the splitting of energy levels that is directly proportional to the magnetic field. The proportionality constant that relates the magnetic moment of a particle to its angular momentum quantum number and fundamental quantum unit of magnetism is known as the g-factor. Through the use of ESR and a known magnetic field strength the electron spin g-factor can be approximated using a paramagnetic free radical molecule such as DPPH. The electron g-factor for DPPH was determined to be 1.96 ± 0.01 which is not consistent with the known value for DPPH of 2.0036(2)1 but systematically off due to thermal effects in the apparatus.
Paramagnetic substances consist of atoms with unpaired electrons and magnetic moments that are randomly oriented if no external magnetic field is present. If a magnetic field is applied, then the electron’s magnetic moment is subjected to a torque such that
However, an electron’s angular momentum cannot have an arbitrary projection along the magnetic field; only integer or half integer projections are allowed. The potential energy associated with the interaction between the magnetic moment and the magnetic field is such that the energy levels take on discrete or quantized values shown by different projections of the magnetic moments onto the magnetic field. In electron spin resonance, an oscillating magnetic field is used to induce transition between energy levels. If an oscillating magnetic field is applied between two energy levels such that its frequency corresp...
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...ermined using linear regression.
The g-factor for DPPH was determined to be 1.96 ± 0.01. The known value of DPPH is 2.0036(2).1 The experimental value is not in agreement with the known value. The y-intercept of Fig.5 suggests a systematic error associated with each measurement. This is most likely due to thermal effects which tend to randomize the directions of the magnetic moments and oppose the alignment of the magnetic moment with the magnetic field. A prolonged amount of current traveling though the apparatus would dissipate over time resulting in a change in temperature. The temperature dependence of paramagnetic material is related by Curie’s law where is the magnetization of the material, proportional to , and is the Curie constant. An increase in temperature would result in a decrease in the measured magnetic moment and a smaller calculated g-factor.
a) The excitation of electrons of both metal ion and ligand is influenced by their interactions.
Furthermore, AMR should be recognized as the combined solid -fluid system, whereby, in essence, a temperature gradient is established throughout the AMR and a fluid is used to transfer heat from the cold end to the hot. This subtle but important idea produced a new magnetic cycle distinct from Carnot, Ericsson, Brayton, or Stirling [6].
Throughout the past century, investigations of quantum and particle physics phenomena have proven to show the most significant concepts and ideas in the physical and sub-atomic world. However, the discoveries yet to be made are endless. One of the most fascinating concepts in the sub-atomic universe is the idea of spintronics. Spintronics is the quantum study of the independent angular momentum (not to be confused with the orbital angular momentum of the electron) of a particle, typically that of an electron (Introduction). An electron is a fundamental particle, with a negative charge, and is independently studied in the process of spintronic devices. The spin angular momentum of electrons is ±½ћ. Devices that use the properties
Magnetic resonance imaging (MRI) is considered as one of the pioneers in medical imaging for diagnosis of pathologies involving soft tissues and internal structures. MRI provides good contrast resolution between different soft tissues of the body especially in brain, muscles, heart etc compared to other medical imaging modalities like computed tomograpgy (CT) and conventional radiography which utilizes x-rays for imaging. The other important aspect of MRI versus other imaging modalities like CT and conventional radiography is that MRI uses no ionizing radiation like x-rays for imaging, instead it uses a strong magnetic field to align the magnetization of some atoms within the body , then uses radiofrequency pulses to systematically alter the alignment of this magnetization. This process causes the nuclei of certain atoms to produce a magnetic field which can be detected by the scanner, and all this information is used to reconstruct an MR image of the scanned area of the body. The initial experiments by Sir Otto Stern in the year 1922 stated that physically the magnetic resonance ima...
The Pauli exclusion principle is defined by Dr. Steven S. Zumdahl, "In a given atom no two electrons can have the same set of four quantum numbers." Due to this principle, only two electrons can inhabit a single energy level. The electrons that share the same energy level have opposite intrinsic angular momentums which is more commonly known as "spin". To determine the direction of the spin the angular momentum vector is analyzed.
Polman, H., Orobio De Castro, B. & Van Aken, M. A.G. (2008). Experimental Study of the
In 1971, scientists were motivated to use magnetic resonance for detection of diseases after discovering the difference in nuclear magnetic relaxation times of tissues and tumors (Dr. J. Hornak, n.d). In 1973, Lauterbur and Mansfield defined the use of magnetic field gradients for spatial localization of NMR signals, laying the foundation for MRI in the future. Two years later, Richard Ernst used Fourier Transform (an algorithm for the analysis of heat transfer between solid bodies) to encode and reconstruct 2D images, which underpins MRI today (Geva, 2006).
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Electric currents produce magnetic fields, they can be as small as macroscopic currents in wires, or microscopic currents in atomic orbits caused by electrons. The magnetic field B is described in terms of force on a moving charge in the Lorentz force law. The relationship of magnetic field and charges leads to many practical applications. Magnetic field sources are dipolar in nature, with a north and south magnetic pole. The magnetic field SI unit is the Tesla, it can be seen in the magnetic part of the Lorentz force law F magnetic = qvB composed of (Newton x second)/(Coulomb x meter). The smaller magnetic field unit is the
Ionic compounds, when in the solid state, can be described as ionic lattices whose shapes are dictated by the need to place oppositely charged ions close to each other and similarly charged ions as far apart as possible. Though there is some structural diversity in ionic compounds, covalent compounds present us with a world of structural possibilities. From simple linear molecules like H2 to complex chains of atoms like butane (CH3CH2CH2CH3), covalent molecules can take on many shapes. To help decide which shape a polyatomic molecule might prefer we will use Valence Shell Electron Pair Repulsion theory (VSEPR). VSEPR states that electrons like to stay as far away from one another as possible to provide the lowest energy (i.e. most stable) structure for any bonding arrangement. In this way, VSEPR is a powerful tool for predicting the geometries of covalent molecules.