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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 in 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.
Remanence or remanent magnetization or residual magnetism is the magnetization left behind in a ferromagnetic material after an external magnetic field is removed. Colloquially, when a magnet is "magnetized" it has remanence. The remanence of magnetic materials provides the magnetic memory in magnetic storage devices, and is used as a source of information on the past Earth's magnetic field in paleomagnetism. The word remanence is from remanent + -ence, meaning "that which remains".
Coercivity, also called the magnetic coercivity, coercive field or coercive force, is a measure of the ability of a ferromagnetic material to withstand an external magnetic field without becoming demagnetized. Coercivity is usually measured in oersted or ampere/meter units and is denoted HC.
Iron(II,III) oxide is the chemical compound with formula Fe3O4. It occurs in nature as the mineral magnetite. It is one of a number of iron oxides, the others being iron(II) oxide (FeO), which is rare, and iron(III) oxide (Fe2O3) which also occurs naturally as the mineral hematite. It contains both Fe2+ and Fe3+ ions and is sometimes formulated as FeO ∙ Fe2O3. This iron oxide is encountered in the laboratory as a black powder. It exhibits permanent magnetism and is ferrimagnetic, but is sometimes incorrectly described as ferromagnetic. Its most extensive use is as a black pigment. For this purpose, it is synthesized rather than being extracted from the naturally occurring mineral as the particle size and shape can be varied by the method of production.
Exchange bias or exchange anisotropy occurs in bilayers of magnetic materials where the hard magnetization behavior of an antiferromagnetic thin film causes a shift in the soft magnetization curve of a ferromagnetic film. The exchange bias phenomenon is of tremendous utility in magnetic recording, where it is used to pin the state of the readback heads of hard disk drives at exactly their point of maximum sensitivity; hence the term "bias."
Spin-polarized scanning tunneling microscopy (SP-STM) is a type of scanning tunneling microscope (STM) that can provide detailed information of magnetic phenomena on the single-atom scale additional to the atomic topography gained with STM. SP-STM opened a novel approach to static and dynamic magnetic processes as precise investigations of domain walls in ferromagnetic and antiferromagnetic systems, as well as thermal and current-induced switching of nanomagnetic particles.
In magnetism the Stoner–Wohlfarth astroid curve is a curve that separates regions with two minima of the free energy density from those with only one energy minimum. It is a geometric representation of the Stoner–Wohlfarth model. This curve is of particular importance as discontinuous changes of the magnetization can take place when crossing it.
In condensed matter physics, magnetic anisotropy describes how an object's magnetic properties can be 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.
Magnetic-targeted carriers, also known as MTCs or magnetic vehicles, are micro- or nanoparticles that carry an anticancer drug to the target site by using an external magnetic field and field gradient to direct the desired drug. Usually the complex involves microscopic beads of activated carbon, which bind the anticancer drug. A magnet applied from outside the body then can direct the drug to the tumor site. This can keep a larger dose of the drug at the tumor site for a longer period of time, and help protect healthy tissue from the side effects of chemotherapy.
In physics, the Landau–Lifshitz–Gilbert equation, named for Lev Landau, Evgeny Lifshitz, and T. L. Gilbert, is a name used for a differential equation describing the precessional motion of magnetization M in a solid. It is a modification by Gilbert of the original equation of Landau and Lifshitz.
Magnetic nanoparticles are a class of nanoparticle that can be manipulated using magnetic fields. Such particles commonly consist of two components, a magnetic material, often iron, nickel and cobalt, and a chemical component that has functionality. While nanoparticles are smaller than 1 micrometer in diameter, the larger microbeads are 0.5–500 micrometer in diameter. Magnetic nanoparticle clusters that are composed of a number of individual magnetic nanoparticles are known as magnetic nanobeads with a diameter of 50–200 nanometers. Magnetic nanoparticle clusters are a basis for their further magnetic assembly into magnetic nanochains. The magnetic nanoparticles have been the focus of much research recently because they possess attractive properties which could see potential use in catalysis including nanomaterial-based catalysts, biomedicine and tissue specific targeting, magnetically tunable colloidal photonic crystals, microfluidics, magnetic resonance imaging, magnetic particle imaging, data storage, environmental remediation, nanofluids, optical filters, defect sensor, magnetic cooling and cation sensors.
Iron oxide nanoparticles are iron oxide particles with diameters between about 1 and 100 nanometers. The two main forms are magnetite (Fe3O4) and its oxidized form maghemite (γ-Fe2O3). They have attracted extensive interest due to their superparamagnetic properties and their potential applications in many fields (although Co and Ni are also highly magnetic materials, they are toxic and easily oxidized).
Single domain, in magnetism, refers to the state of a ferromagnet 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. Such particles are very small. 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.
The Journal of Magnetism and Magnetic Materials is a peer-reviewed scientific journal that covers both basic research on magnetism and technological applications including magnetic recording. In addition to full-length research articles, it publishes review articles and rapid communications. A special section, "Information Storage: Basic and Applied", covers topics on magnetic media. The editor-in-chief is S. D. Bader.
Cuprospinel is a mineral that occurs naturally in Baie Verte, Newfoundland, Canada. The mineral was found in an exposed ore dump, on the property of Consolidated Rambler Mines Limited near Baie Verte, Newfoundland. The mineral was first characterized by Ernest Henry Nickel, a mineralogist with the Department of Energy, Mines and Resources in Australia, in 1973.
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 ferromagnetic minerals that explained how these minerals could reliably record the geomagnetic field. He also modeled frequency-dependent susceptibility and alternating field demagnetization.
An exchange spring magnet is a magnetic material with high coercivity and high saturation properties derived from the exchange interaction between a hard magnetic material and a soft magnetic material, respectively.
Iron–platinum nanoparticles are 3D superlattices composed of an approximately equal atomic ratio of Fe and Pt. Under standard conditions, FePt NPs exist in the face-centered cubic phase but can change to a chemically ordered face-centered tetragonal phase as a result of thermal annealing. Currently there are many synthetic methods such as water-in-oil microemulsion, one-step thermal synthesis with metal precursors, and exchanged-coupled assembly for making FePt NPs. An important property of FePt NPs is their superparamagnetic character below 10 nanometers. The superparamagnetism of FePt NPs has made them attractive candidates to be used as MRI/CT scanning agents and a high-density recording material.
Superparamagnetic relaxometry (SPMR) is a technology combining the use of sensitive magnetic sensors and the superparamagnetic properties of magnetite nanoparticles (NP). For NP of a sufficiently small size, on the order of tens of nanometers (nm), the NP exhibit paramagnetic properties, i.e., they have little or no magnetic moment. When they are exposed to a small external magnetic field, on the order of a few millitesla (mT), the NP align with that field and exhibit ferromagnetic properties with large magnetic moments. Following removal of the magnetizing field, the NP slowly become thermalized, decaying with a distinct time constant from the ferromagnetic state back to the paramagnetic state. This time constant depends strongly upon the NP diameter and whether they are unbound or bound to an external surface such as a cell. Measurement of this decaying magnetic field is typically done by superconducting quantum interference detectors (SQUIDs). The magnitude of the field during the decay process determines the magnetic moment of the NPs in the source. A spatial contour map of the field distribution determines the location of the source in three dimensions as well as the magnetic moment.
Neptunium arsenide is a binary inorganic compound of neptunium and arsenic with the chemical formula NpAs. The compound forms crystals.
References
- ↑ Rancourt, D. G. (2001-01-01). "Magnetism of Earth, Planetary, and Environmental Nanomaterials". Reviews in Mineralogy and Geochemistry. 44 (1): 217–292. Bibcode:2001RvMG...44..217R. doi:10.2138/rmg.2001.44.07. ISSN 1529-6466.
- ↑ Bostanjoglo, O.; Röhkel, K. (1972-05-16). "Superferromagnetism in gadolinium films". Physica Status Solidi A. 11 (1): 161–166. Bibcode:1972PSSAR..11..161B. doi:10.1002/pssa.2210110117. ISSN 0031-8965.
- ↑ Mørup, Steen; Bo Madsen, Morten; Franck, Jørgen; Villadsen, Jørgen; Koch, Christian J.W. (1983). "A new interpretation of Mössbauer spectra of microcrystalline goethite: "Super-ferromagnetism" or "super-spin-glass" behaviour?". Journal of Magnetism and Magnetic Materials. 40 (1–2): 163–174. Bibcode:1983JMMM...40..163M. doi:10.1016/0304-8853(83)90024-0. ISSN 0304-8853.
- ↑ Rancourt, D. G.; Daniels, J. M. (1984-03-01). "Influence of unequal magnetization direction probabilities on the Mössbauer spectra of superparamagnetic particles". Physical Review B. 29 (5): 2410–2414. Bibcode:1984PhRvB..29.2410R. doi:10.1103/physrevb.29.2410. ISSN 0163-1829.
- ↑ Bedanta, S.; Seki, T.; Iwama, H.; Shima, T.; Takanashi, K. (2015-10-12). "Superferromagnetism in dipolarly coupled FePt nanodots with perpendicular magnetization". Applied Physics Letters. 107 (15): 152410. doi:10.1063/1.4933381. ISSN 0003-6951.
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