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Superparamagnetic
Superparamagnetism is a form of magnetism which appears in small ferromagnetic or ferrimagnetic nanoparticles. In sufficiently small nanoparticles, magnetization can randomly flip direction under the influence of temperature. The typical time between two flips is called the Néel relaxation time. In the absence of an external magnetic field, when the time used to measure the magnetization of the nanoparticles is much longer than the Néel relaxation time, their magnetization appears to be on average zero; they are said to be in the superparamagnetic state. In this state, an external magnetic field is able to magnetize the nanoparticles, similarly to a paramagnet. However, their magnetic susceptibility is much larger than that of paramagnets. Néel relaxation in the absence of magnetic field Normally, any ferromagnetic or ferrimagnetic material undergoes a transition to a paramagnetic state above its Curie temperature. Superparamagnetism is different from this standard transit ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Néel Relaxation Theory
Néel relaxation theory is a theory developed by Louis Néel in 1949 to explain time-dependent magnetic phenomena known as ''magnetic viscosity''. It is also called ''Néel-Arrhenius theory'', after the Arrhenius equation, and ''Néel-Brown theory'' after a more rigorous derivation by William Fuller Brown, Jr. Néel used his theory to develop a model of thermoremanent magnetization in single-domain (magnetic), single-domain magnetic mineralogy, ferromagnetic minerals that explained how these minerals could reliably record the geomagnetic field. He also modeled frequency-dependent Magnetic susceptibility, susceptibility and alternating field demagnetization. Superparamagnetism Superparamagnetism occurs in ferromagnetic and ferrimagnetic nanoparticles which are single domain (magnetic), single-domain, i.e. composed of a single magnetic domain. This is possible when their diameter is below 3–50 nm, depending on the materials. In this condition, it is considered that the magnetiz ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Ferrofluid
Ferrofluid is a dark liquid that is attracted to the poles of a magnet. It is a colloidal liquid made of nanoscale ferromagnetic or ferrimagnetic particles suspended inside a carrier fluid (usually an organic solvent or water). Each magnetic particle is thoroughly coated with a surfactant to inhibit clumping. Large ferromagnetic particles can be ripped out of the homogeneous colloidal mixture, forming a separate clump of magnetic dust when exposed to strong magnetic fields. The magnetic attraction of tiny nanoparticles is weak enough that the surfactant's Van der Waals force is sufficient to prevent magnetic clumping or agglomeration. Ferrofluids usually do not retain magnetization in the absence of an externally applied field and thus are often classified as " superparamagnets" rather than ferromagnets. In contrast to ferrofluids, magnetorheological fluids (MR fluids) are magnetic fluids with larger particles. That is, a ferrofluid contains primarily nanoparticles, while ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Perpendicular Recording
Perpendicular recording (or perpendicular magnetic recording, PMR), also known as conventional magnetic recording (CMR), is a technology for data recording on magnetic media, particularly hard disks. It was first proven advantageous in 1976 by Shun-ichi Iwasaki, then professor of the Tohoku University in Japan, and first commercially implemented in 2005. The first industry-standard demonstration showing unprecedented advantage of PMR over longitudinal magnetic recording (LMR) at nanoscale dimensions was made in 1998 at IBM Almaden Research Center in collaboration with researchers of Data Storage Systems Center (DSSC) – a National Science Foundation (NSF) Engineering Research Center (ERCs) at Carnegie Mellon University (CMU). Advantages Perpendicular recording can deliver more than three times the storage density of traditional longitudinal recording. In 1986, Maxell announced a floppy disk using perpendicular recording that could store . Perpendicular recording was later us ... [...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 hard disk drive platter, platters coated with magnetic material. The platters are paired with disk read-and-write head, 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 Block (data storage), 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 disk enclosure, rectangular box. Hard disk drives were introduced by IBM in 1956, and were the dominant secondary storage device for History of general-purpose CPUs, general-purpose computers beginning in the early 1960s. HDDs maintained this position into the modern er ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Heat-assisted Magnetic Recording
Heat-assisted magnetic recording (HAMR) (pronounced "''hammer''") is a magnetic storage technology for greatly increasing the amount of data that can be stored on a magnetic device such as a hard disk drive by temporarily heating the disk material during writing, which makes it much more receptive to magnetic effects and allows writing to much smaller regions (and much higher levels of data on a disk). The technology was initially seen as extremely difficult to achieve, with doubts expressed about its feasibility in 2013. The regions being written must be heated in a tiny area – small enough that diffraction prevents the use of normal laser focused heating – and requires a heating, writing and cooling cycle of less than 1 nanosecond, while also controlling the effects of repeated spot-heating on the drive platters, the drive-to-head contact, and the adjacent magnetic data which must not be affected. These challenges required the development of nano-scale surface plasmons (surf ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Ferromagnetic
Ferromagnetism is a property of certain materials (such as iron) that results in a significant, observable magnetic permeability, and in many cases, a significant magnetic coercivity, allowing the material to form a permanent magnet. Ferromagnetic materials are noticeably attracted to a magnet, which is a consequence of their substantial magnetic permeability. Magnetic permeability describes the induced magnetization of a material due to the presence of an external magnetic field. For example, this temporary magnetization inside a steel plate accounts for the plate's attraction to a magnet. Whether or not that steel plate then acquires permanent magnetization depends on both the strength of the applied field and on the coercivity of that particular piece of steel (which varies with the steel's chemical composition and any heat treatment it may have undergone). In physics, multiple types of material magnetism have been distinguished. Ferromagnetism (along with the similar effec ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Single Domain (magnetic)
In magnetism, single domain refers to the state of a ferromagnet (in the broader meaning of the term that includes ferrimagnetism) in which the magnetization does not vary across the magnet. A magnetic particle that stays in a single domain state for all magnetic fields is called a single domain particle (but other definitions are possible; see below). Such particles are very small (generally below a micrometre in diameter). They are also very important in a lot of applications because they have a high coercivity. They are the main source of hardness in hard magnets, the carriers of magnetic storage in tape drives, and the best recorders of the ancient Earth's magnetic field (see paleomagnetism). History Early theories of magnetization in ferromagnets assumed that ferromagnets are divided into magnetic domains and that the magnetization changed by the movement of domain walls. However, as early as 1930, Frenkel and Dorfman predicted that sufficiently small particles could only ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Magnetic Anisotropy
In condensed matter physics, magnetic anisotropy describes how an object's magnetic properties can be anisotropy, different depending on direction. In the simplest case, there is no preferential direction for an object's magnetic moment. It will respond to an applied magnetic field in the same way, regardless of which direction the field is applied. This is known as magnetic isotropy. In contrast, magnetically anisotropic materials will be easier or harder to magnetize depending on which way the object is rotated. For most magnetically anisotropic materials, there are two easiest directions to magnetize the material, which are a 180° rotation apart. The line parallel to these directions is called the easy axis. In other words, the easy axis is an energetically favorable direction of spontaneous magnetization. Because the two opposite directions along an easy axis are usually equivalently easy to magnetize along, the actual direction of magnetization can just as easily settle int ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Magnetism
Magnetism is the class of physical attributes that occur through a magnetic field, which allows objects to attract or repel each other. Because both electric currents and magnetic moments of elementary particles give rise to a magnetic field, magnetism is one of two aspects of electromagnetism. The most familiar effects occur in ferromagnetic materials, which are strongly attracted by magnetic fields and can be magnetized to become permanent magnets, producing magnetic fields themselves. Demagnetizing a magnet is also possible. Only a few substances are ferromagnetic; the most common ones are iron, cobalt, nickel, and their alloys. All substances exhibit some type of magnetism. Magnetic materials are classified according to their bulk susceptibility. Ferromagnetism is responsible for most of the effects of magnetism encountered in everyday life, but there are actually several types of magnetism. Paramagnetic substances, such as aluminium and oxygen, are weakly attracted ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Longitudinal Recording
Magnetic storage or magnetic recording is the storage of data on a magnetized medium. Magnetic storage uses different patterns of magnetisation in a magnetizable material to store data and is a form of non-volatile memory. The information is accessed using one or more read/write heads. Magnetic storage media, primarily hard disks, are widely used to store computer data as well as audio and video signals. In the field of computing, the term ''magnetic storage'' is preferred and in the field of audio and video production, the term ''magnetic recording'' is more commonly used. The distinction is less technical and more a matter of preference. Other examples of magnetic storage media include floppy disks, magnetic tape, and magnetic stripes on credit cards. History Magnetic storage in the form of wire recording—audio recording on a wire—was publicized by Oberlin Smith in the Sept 8, 1888 issue of ''Electrical World''. Smith had previously filed a patent in September, 1878 b ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Hitachi
() is a Japanese Multinational corporation, multinational Conglomerate (company), conglomerate founded in 1910 and headquartered in Chiyoda, Tokyo. The company is active in various industries, including digital systems, power and renewable energy, railway systems, Health care, healthcare products, and Financial system, financial systems. The company was founded as an electrical machinery manufacturing subsidiary of the Kuhara Mining Plant in Hitachi, Ibaraki by engineer Namihei Odaira in 1910. It began operating as an independent company under its current name in 1920. Hitachi is listed on the Tokyo Stock Exchange and is a key component of the Nikkei 225 and TOPIX Core30 indices. As of June 2024, it has a market capitalisation of 16.9 trillion yen, making it the fourth largest Japanese company by market value. In terms of global recognition, Hitachi was ranked 38th in the 2012 Fortune Global 500 and 129th in the 2012 Forbes Global 2000. Hitachi is a highly globalised conglomerat ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Bit-patterned Recording
Patterned media (also known as bit-patterned media or BPM) is a potential future hard disk drive technology to record data in magnetic islands (one bit per island), as opposed to current hard disk drive technology where each bit is stored in within a continuous magnetic film. The islands would be patterned from a precursor magnetic film using nanolithography. It is one of the proposed technologies to succeed perpendicular recording due to the greater storage densities it would enable. BPM was introduced by Toshiba in 2010. Comparison with existing HDD technology In existing hard disk drives, data is stored in a thin magnetic film. This film is deposited so that it consists of isolated (weakly exchange coupled) grains of material of around diameter. One bit of data consists of around that are magnetized in the same direction (either "up" or "down", with respect to the plane of the disk). One method of increasing storage density has been to reduce the average grain volume. However ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
