|
Spin Engineering
Spin engineering describes the control and manipulation of quantum spin systems to develop devices and materials. This includes the use of the spin degrees of freedom as a probe for spin based phenomena. Because of the basic importance of quantum spin for physical and chemical processes, spin engineering is relevant for a wide range of scientific and technological applications. Current examples range from Bose–Einstein condensation to spin-based data storage and reading in state-of-the-art hard disk drives, as well as from powerful analytical tools like nuclear magnetic resonance spectroscopy and electron paramagnetic resonance spectroscopy to the development of magnetic molecules as qubits and magnetic nanoparticles. In addition, spin engineering exploits the functionality of spin to design materials with novel properties as well as to provide a better understanding and advanced applications of conventional material systems. Many chemical reactions are devised to create bulk ma ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Quantum Spin
Spin is a conserved quantity carried by elementary particles, and thus by composite particles (hadrons) and atomic nuclei. Spin is one of two types of angular momentum in quantum mechanics, the other being ''orbital angular momentum''. The orbital angular momentum operator is the quantum-mechanical counterpart to the classical angular momentum of orbital revolution and appears when there is periodic structure to its wavefunction as the angle varies. For photons, spin is the quantum-mechanical counterpart of the polarization of light; for electrons, the spin has no classical counterpart. The existence of electron spin angular momentum is inferred from experiments, such as the Stern–Gerlach experiment, in which silver atoms were observed to possess two possible discrete angular momenta despite having no orbital angular momentum. The existence of the electron spin can also be inferred theoretically from the spin–statistics theorem and from the Pauli exclusion principle—and vic ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Single-molecule Magnet
A single-molecule magnet (SMM) is a metal-organic compound that has superparamagnetic behavior below a certain blocking temperature at the molecular scale. In this temperature range, a SMM exhibits magnetic hysteresis of purely molecular origin.Introduction to Molecular Magnetism by Dr. Joris van Slageren. In contrast to conventional bulk s and molecule-based magnets, collective long-range magnetic ordering of s is not necessary. [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Magnetoresistive Random-access Memory
Magnetoresistive random-access memory (MRAM) is a type of non-volatile random-access memory which stores data in magnetic domains. Developed in the mid-1980s, proponents have argued that magnetoresistive RAM will eventually surpass competing technologies to become a dominant or even universal memory. Currently, memory technologies in use such as flash RAM and DRAM have practical advantages that have so far kept MRAM in a niche role in the market. Description Unlike conventional RAM chip technologies, data in MRAM is not stored as electric charge or current flows, but by magnetic storage elements. The elements are formed from two ferromagnetic plates, each of which can hold a magnetization, separated by a thin insulating layer. One of the two plates is a permanent magnet set to a particular polarity; the other plate's magnetization can be changed to match that of an external field to store memory. This configuration is known as a magnetic tunnel junction and is the simplest st ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Disk Read-and-write Head
A disk read-and-write head is the small part of a disk drive which moves above the disk platter and transforms the platter's magnetic field into electrical current (reads the disk) or, vice versa, transforms electrical current into magnetic field (writes the disk). The heads have gone through a number of changes over the years. In a hard drive, the heads ''fly'' above the disk surface with clearance of as little as 3 nanometres. The flying height has been decreasing with each new generation of technology to enable higher areal density. The flying height of the head is controlled by the design of an air bearing etched onto the disk-facing surface of the ''slider''. The role of the air bearing is to maintain the flying height constant as the head moves over the surface of the disk. The air bearings are carefully designed to maintain the same height across the entire platter, despite differing speeds depending on the head distance from the center of the platter. If the head h ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Hard Disk Drive
A hard disk drive (HDD), hard disk, hard drive, or fixed disk is an electro-mechanical data storage device that stores and retrieves digital data using magnetic storage with one or more rigid rapidly rotating platters coated with magnetic material. The platters are paired with magnetic heads, usually arranged on a moving actuator arm, which read and write data to the platter surfaces. Data is accessed in a random-access manner, meaning that individual blocks of data can be stored and retrieved in any order. HDDs are a type of non-volatile storage, retaining stored data when powered off. Modern HDDs are typically in the form of a small rectangular box. Introduced by IBM in 1956, HDDs were the dominant secondary storage device for general-purpose computers beginning in the early 1960s. HDDs maintained this position into the modern era of servers and personal computers, though personal computing devices produced in large volume, like cell phones and tablets, rely on ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Science And Technology Of Advanced Materials
''Science and Technology of Advanced Materials'' is a peer-reviewed scientific journal in materials science that was established in 2000. In 2008 it became an open access journal through the sponsorship of the National Institute for Materials Science (NIMS). The journal is international; it is managed by NIMS, which was joined in 2014 by the Swiss Federal Laboratories for Materials Science and Technology (Empa). Currently STAM is an electronic journal, its articles are continuously published online. Its sister journal, ''STAM Methods'', has been launched in 2021. Scope The journal covers all aspects of materials science, including theoretical analysis, synthesis and processing, phase and structure analyses, characterization, properties, engineering, and applications. It covers advances in research on solids, liquids and colloids, with emphasis on the interdisciplinary nature of materials science and issues at the forefront of the field, such as nano-, bio- and eco- and energy ma ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Spin Hall Effect
The spin Hall effect (SHE) is a transport phenomenon predicted by Russian physicists Mikhail I. Dyakonov and Vladimir I. Perel in 1971. It consists of the appearance of spin accumulation on the lateral surfaces of an electric current-carrying sample, the signs of the spin directions being opposite on the opposing boundaries. In a cylindrical wire, the current-induced surface spins will wind around the wire. When the current direction is reversed, the directions of spin orientation is also reversed. Definition The spin Hall effect is a transport phenomenon consisting of the appearance of spin accumulation on the lateral surfaces of a sample carrying electric current. The opposing surface boundaries will have spins of opposite sign. It is analogous to the classical Hall effect, where ''charges'' of opposite sign appear on the opposing lateral surfaces in an electric-current carrying sample in a magnetic field. In the case of the classical Hall effect the charge build up at the ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Magnonics
Magnonics is an emerging field of modern magnetism, which can be considered a sub-field of modern solid state physics. Magnonics combines the study of waves and magnetism. Its main aim is to investigate the behaviour of spin waves in nano-structure elements. In essence, spin waves are a propagating re-ordering of the magnetisation in a material and arise from the precession of magnetic moments. Magnetic moments arise from the orbital and spin moments of the electron, most often it is this spin moment that contributes to the net magnetic moment. Following the success of the modern hard disk, there is much current interest in future magnetic data storage and using spin waves for things such as 'magnonic' logic and data storage. Similarly, spintronics looks to utilize the inherent spin degree of freedom to complement the already successful charge property of the electron used in contemporary electronics. Modern magnetism is concerned with furthering the understanding of the behaviour of ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Spin Wave
A spin wave is a propagating disturbance in the ordering of a magnetic material. These low-lying collective excitations occur in magnetic lattices with continuous symmetry. From the equivalent quasiparticle point of view, spin waves are known as magnons, which are bosonic modes of the spin lattice that correspond roughly to the phonon excitations of the nuclear lattice. As temperature is increased, the thermal excitation of spin waves reduces a ferromagnet's spontaneous magnetization. The energies of spin waves are typically only in keeping with typical Curie points at room temperature and below. Theory The simplest way of understanding spin waves is to consider the Hamiltonian \mathcal for the Heisenberg ferromagnet: :\mathcal = -\frac J \sum_ \mathbf_i \cdot \mathbf_j - g \mu_ \sum_i \mathbf \cdot \mathbf_i where is the exchange energy, the operators represent the spins at Bravais lattice points, is the Landé -factor, is the Bohr magneton and is the internal fi ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Spin Pumping
Spin pumping is the dynamical generation of pure spin current by the coherent precession of magnetic moments, which can efficiently inject spin from a magnetic material into an adjacent non-magnetic material. The non-magnetic material usually hosts the spin Hall effect that can convert the injected spin current into a charge voltage easy to detect. A spin pumping experiment typically requires electromagnetic irradiation to induce magnetic resonance, which converts energy and angular momenta from electromagnetic waves (usually microwaves) to magnetic dynamics and then to electrons, enabling the electronic detection of electromagnetic waves. The device operation of spin pumping can be regarded as the spintronic analog of a battery. Spin pumping involves an AC effect and a DC effect: * The AC effect generates a spin current that oscillates at the same frequency with the microwave source. * The DC effect requires that the magnetic dynamic is circularly polarized or elliptically pol ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Spin Torque Transfer
Spin-transfer torque (STT) is an effect in which the orientation of a magnetic layer in a magnetic tunnel junction or spin valve can be modified using a spin-polarized current. Charge carriers (such as electrons) have a property known as spin which is a small quantity of angular momentum intrinsic to the carrier. An electric current is generally unpolarized (consisting of 50% spin-up and 50% spin-down electrons); a spin polarized current is one with more electrons of either spin. By passing a current through a thick magnetic layer (usually called the “fixed layer”), one can produce a spin-polarized current. If this spin-polarized current is directed into a second, thinner magnetic layer (the “free layer”), the angular momentum can be transferred to this layer, changing its orientation. This can be used to excite oscillations or even flip the orientation of the magnet. The effects are usually seen only in nanometer scale devices. Spin-transfer torque memory Spin-tra ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Spin Valve
A spin valve is a device, consisting of two or more conducting magnetic materials, whose electrical resistance can change between two values depending on the relative alignment of the magnetization in the layers. The resistance change is a result of the giant magnetoresistive effect. The magnetic layers of the device align "up" or "down" depending on an external magnetic field. In the simplest case, a spin valve consists of a non-magnetic material sandwiched between two ferromagnets, one of which is fixed (pinned) by an antiferromagnet which acts to raise its magnetic coercivity and behaves as a "hard" layer, while the other is free (unpinned) and behaves as a "soft" layer. Due to the difference in coercivity, the soft layer changes polarity at lower applied magnetic field strength than the hard one. Upon application of a magnetic field of appropriate strength, the soft layer switches polarity, producing two distinct states: a parallel, low-resistance state, and an antiparallel, h ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
