Related Research Articles
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.
A magnet is a material or object that produces a magnetic field. This magnetic field is invisible but is responsible for the most notable property of a magnet: a force that pulls on other ferromagnetic materials, such as iron, steel, nickel, cobalt, etc. and attracts or repels other magnets.
In physics and materials science, the Curie temperature (TC), or Curie point, is the temperature above which certain materials lose their permanent magnetic properties, which can (in most cases) be replaced by induced magnetism. The Curie temperature is named after Pierre Curie, who showed that magnetism is lost at a critical temperature.
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.
Ferrofluid is a liquid that is attracted to the poles of a magnet. It is a colloidal liquid made of nanoscale ferromagnetic or ferrimagnetic particles suspended in a carrier fluid. 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.
Iron(II,III) oxide, or black iron 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 (see: Mars Black). 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.
Magnetic semiconductors are semiconductor materials that exhibit both ferromagnetism and useful semiconductor properties. If implemented in devices, these materials could provide a new type of control of conduction. Whereas traditional electronics are based on control of charge carriers, practical magnetic semiconductors would also allow control of quantum spin state. This would theoretically provide near-total spin polarization, which is an important property for spintronics applications, e.g. spin transistors.
Magnetic particle imaging (MPI) is an emerging non-invasive tomographic technique that directly detects superparamagnetic nanoparticle tracers. The technology has potential applications in diagnostic imaging and material science. Currently, it is used in medical research to measure the 3-D location and concentration of nanoparticles. Imaging does not use ionizing radiation and can produce a signal at any depth within the body. MPI was first conceived in 2001 by scientists working at the Royal Philips Research lab in Hamburg. The first system was established and reported in 2005. Since then, the technology has been advanced by academic researchers at several universities around the world. The first commercial MPI scanners have recently become available from Magnetic Insight and Bruker Biospin.
A ferrite is one of a family of iron oxide-containing magnetic ceramic materials. They are ferrimagnetic, meaning they are attracted by magnetic fields and can be magnetized to become permanent magnets. Unlike many ferromagnetic materials, most ferrites are not electrically conductive, making them useful in applications like magnetic cores for transformers to suppress eddy currents.
Multiferroics are defined as materials that exhibit more than one of the primary ferroic properties in the same phase:
Superferromagnetism is the magnetism of an ensemble of magnetically interacting super-moment-bearing material particles that would be superparamagnetic if they were not interacting. Nanoparticles of iron oxides, such as ferrihydrite, often cluster and interact magnetically. These interactions change the magnetic behaviours of the nanoparticles and lead to an ordered low-temperature phase with non-randomly oriented particle super-moments.
Molecule-based magnets (MBMs) or molecular magnets are a class of materials capable of displaying ferromagnetism and other more complex magnetic phenomena. This class expands the materials properties typically associated with magnets to include low density, transparency, electrical insulation, and low-temperature fabrication, as well as combine magnetic ordering with other properties such as photoresponsiveness. Essentially all of the common magnetic phenomena associated with conventional transition-metal magnets and rare-earth magnets can be found in molecule-based magnets. Prior to 2011, MBMs were seen to exhibit "magnetic ordering with Curie temperature (Tc) exceeding room temperature".
Magnetic nanoparticles (MNPs) 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 composed of magnetite and its oxidized form maghemite. They have attracted extensive interest due to their superparamagnetic properties and their potential applications in many fields including molecular imaging.
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 materials or single molecules with well defined spin properties, such as a single-molecule magnet. The aim of this article is to provide an outline of fields of research and development where the focus is on the properties and applications of quantum spin.
Magnetic material synthesis and characterization technology continue to improve, allowing for the production of various shapes, sizes, and compositions of magnetic material to be studied and tuned for improved properties. One of the places which has seen great advancement is in the synthesis of magnetic materials at nanometer length scales. Nanoparticle research has seen a great deal of interest in a number of fields as many phenomena can be explained by what is occurring on the nanoscale, which can be probed more effectively using nanometer sized materials. One unique type of materials which have seen a recent surge in research interest have been known as "nanoflakes" where they resemble flakes or discs of nanometer thickness and micrometer dimensions. Nanomaterials of this shape have seen use in a number of fields including energy storage, as [electrodes] of electrochemical cells, and in cancer therapy to kill cancer cells.
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.
Mohindar Singh Seehra is an Indian-American Physicist, academic and researcher. He is Eberly Distinguished Professor Emeritus at West Virginia University (WVU).
Bernard Dieny is a research scientist and an entrepreneur. He is Chief Scientist at SPINTEC, a CEA/CNRS/UGA research laboratory that he co-founded in 2002 in Grenoble, France. He is also co-founder of two startup companies: Crocus Technology on MRAM and magnetic sensors in 2006 and EVADERIS on circuits design in 2014.
References
- ↑ "Bio" (PDF).
- 1 2 "South Asia Center".
- ↑ "Kannan M. Krishnan". ETHW. 2 February 2016.
- ↑ Blomqvist, P.; Krishnan, Kannan M.; Ohldag, H. (16 March 2005). "Direct Imaging of Asymmetric Magnetization Reversal in Exchange-Biased F e / M n P d Bilayers by X-Ray Photoemission Electron Microscopy". Physical Review Letters. 94 (10): 107203. doi:10.1103/PhysRevLett.94.107203. PMID 15783516.[ non-primary source needed ]
- 1 2 "NSF Award Search: Award # 0501490 - Diluted Magnetic Dielectrics : New Spintronics Materials and Devices". nsf.gov.
- ↑ "Kannan Krishnan | IEEE Magnetics Society". ieeemagnetics.org.
- 1 2 Harker, A. H. (3 April 2017). "Fundamentals and applications of magnetic materials, by Kannan M. Krishnan: Scope: textbook. Level: advanced undergraduate, postgraduate, early career researcher". Contemporary Physics. 58 (2): 188–189. doi:10.1080/00107514.2017.1290690.
- 1 2 Harker, A.H. (2 October 2021). "Principles of materials characterization and metrology: by Kannan M. Krishnan, Oxford, UK, Oxford University Press, 2021, 20 + 849 pp., ISBN 978–0–19–883025–2 (hbk), ISBN 978–0–19–883026–9 (pbk). Scope: textbook. Level: undergraduate, early postgraduate". Contemporary Physics. 62 (4): 242. doi:10.1080/00107514.2022.2081723.
- ↑ "Materials Science & Engineering Roberts Hall Spring 2008 Review" (PDF).
- 1 2 "Kannan M". IEEE .
- 1 2 3 "MSA | Society Awards Recipients By Year". microscopy.org.
- ↑ "APS Council Announces 2009 APS Fellows" (PDF).
- ↑ "Journal of Materials Science". SpringerLink.
- 1 2 3 "Lodespin Labs". CoMotion.
- ↑ "Alumni".
- ↑ "Kannan M. Krishnan Biosketch". faculty.washington.edu.
- ↑ Krishnan, K. M. (February 1992). Ceramic Microstructures and Their Elucidation by Imaging, Diffraction and Spectroscopic Methods (Report).[ non-primary source needed ]
- ↑ "Kannan M. Krishnan - Professor, Washington, USA | eMedEvents". emedevents.com.
- ↑ "Tuned multifunctional magnetic nanoparticles for biomedicine".
- ↑ "Coated magnetic nanoparticles".
- ↑ "Iron oxide nanoparticles and their synthesis by controlled oxidation".
- ↑ "Research". faculty.washington.edu.
- ↑ "Fundamentals and Applications of Magnetic Materials Kannan M. Krishnan". MRS Bulletin. 42 (7): 540. July 2017. doi:10.1557/mrs.2017.156.[ non-primary source needed ]
- ↑ Puntes, Victor F.; Krishnan, Kannan M.; Alivisatos, A. Paul (16 March 2001). "Colloidal Nanocrystal Shape and Size Control: The Case of Cobalt". Science. 291 (5511): 2115–2117. doi:10.1126/science.1058495. PMID 11251109.[ non-primary source needed ]
- 1 2 Zhang, Wei; Krishnan, Kannan M (September 2014). "Epitaxial patterning of thin-films: conventional lithographies and beyond". Journal of Micromechanics and Microengineering. 24 (9): 093001. Bibcode:2014JMiMi..24i3001Z. doi:10.1088/0960-1317/24/9/093001.[ non-primary source needed ]
- ↑ Kusinski, Greg J.; Krishnan, Kannan M.; Denbeaux, Gregory; Thomas, Gareth (April 2003). "Magnetic reversal of ion beam patterned Co/Pt multilayers". Scripta Materialia. 48 (7): 949–954. doi:10.1016/S1359-6462(02)00607-3.[ non-primary source needed ]
- ↑ "NSF Award Search: Award # 1063489 - Magnetic Behavior of Nanoengineered Lithographic Particles and Arrays in the Single Domain Limit". nsf.gov.
- ↑ Li, Zheng; Kwon, Byung Seok; Krishnan, Kannan M. (7 May 2014). "Misalignment-free signal propagation in nanomagnet arrays and logic gates with 45°-clocking field". Journal of Applied Physics. 115 (17). doi:10.1063/1.4859996.[ non-primary source needed ]
- ↑ Li, Zheng; Krishnan, Kannan M. (14 January 2017). "A 3-input all magnetic full adder with misalignment-free clocking mechanism". Journal of Applied Physics. 121 (2). doi:10.1063/1.4974109.[ non-primary source needed ]
- ↑ Zhang, Wei; Krishnan, Kannan M. (July 2016). "Epitaxial exchange-bias systems: From fundamentals to future spin-orbitronics". Materials Science and Engineering: R: Reports. 105: 1–20. doi:10.1016/j.mser.2016.04.001.[ non-primary source needed ]
- ↑ USpatent 5374472,Krishnan, Kannan M,"Ferromagnetic thin films",issued 1994[ non-primary source needed ]
- ↑ Krishnan, Kannan M. (9 November 1992). "Ferromagnetic δ-Mn1− x Ga x thin films with perpendicular anisotropy". Applied Physics Letters. 61 (19): 2365–2367. doi:10.1063/1.108245.[ non-primary source needed ]
- ↑ Griffin, K. A.; Pakhomov, A. B.; Wang, C. M.; Heald, S. M.; Krishnan, Kannan M. (22 April 2005). "Intrinsic Ferromagnetism in Insulating Cobalt Doped Anatase TiO 2". Physical Review Letters. 94 (15): 157204. doi:10.1103/PhysRevLett.94.157204. PMID 15904182.[ non-primary source needed ]
- 1 2 "Kannan M. Krishnan – John Simon Guggenheim Memorial Foundation…". gf.org.
- ↑ Ju, H. L.; Sohn, H.-C.; Krishnan, Kannan M. (27 October 1997). "Evidence for O 2 p Hole-Driven Conductivity in La 1 − x Sr x MnO 3 ( 0 ≤ x ≤ 0.7 ) and La 0.7 Sr 0.3 MnO z Thin Films". Physical Review Letters. 79 (17): 3230–3233. doi:10.1103/PhysRevLett.79.3230.[ non-primary source needed ]
- ↑ Krishnan, Kannan M. (2001). "Magnetism and Microstructure: Imaging Techniques and Structure-Property Correlations in Information Storage Materials". Magnetic Storage Systems Beyond 2000. pp. 251–270. doi:10.1007/978-94-010-0624-8_18. ISBN 978-1-4020-0118-5.[ non-primary source needed ]
- ↑ Krishnan, Kannan M.; Thomas, Gareth (October 1984). "A generalization of atom location by channelling enhanced microanalysis". Journal of Microscopy. 136 (1): 97–101. doi:10.1111/j.1365-2818.1984.tb02549.x.[ non-primary source needed ]
- ↑ Gao, Youhui; Bao, Yuping; Pakhomov, Alec B.; Shindo, Daisuke; Krishnan, Kannan M. (7 April 2006). "Spiral Spin Order of Self-Assembled Co Nanodisk Arrays". Physical Review Letters. 96 (13): 137205. doi:10.1103/PhysRevLett.96.137205. PMID 16712029.[ non-primary source needed ]
- ↑ Takeno, Yumu; Murakami, Yasukazu; Sato, Takeshi; Tanigaki, Toshiaki; Park, Hyun Soon; Shindo, Daisuke; Ferguson, R. Matthew; Krishnan, Kannan M. (3 November 2014). "Morphology and magnetic flux distribution in superparamagnetic, single-crystalline Fe3O4 nanoparticle rings". Applied Physics Letters. 105 (18): 183102. doi:10.1063/1.4901008. PMC 4224681 . PMID 25422526.[ non-primary source needed ]
- ↑ Grogger, W.; Krishnan, K.M. (July 2001). "Scatter diagram analysis of Cr segregation in Co-Cr based recording media". IEEE Transactions on Magnetics. 37 (4): 1465–1467. doi:10.1109/20.950872.[ non-primary source needed ]
- ↑ Varela, M.; Grogger, W.; Arias, D.; Sefrioui, Z.; León, C.; Ballesteros, C.; Krishnan, K. M.; Santamaría, J. (28 May 2001). "Direct Evidence for Block-by-Block Growth in High-Temperature Superconductor Ultrathin Films" (PDF). Physical Review Letters. 86 (22): 5156–5159. doi:10.1103/PhysRevLett.86.5156. PMID 11384445.[ non-primary source needed ]
- ↑ Santamaria, J.; Gómez, M. E.; Vicent, J. L.; Krishnan, K M.; Schuller, Ivan K. (16 October 2002). "Scaling of the Interface Roughness in Fe-Cr Superlattices: Self-Affine versus Non-Self-Affine". Physical Review Letters. 89 (19): 190601. doi:10.1103/PhysRevLett.89.190601. PMID 12443108.[ non-primary source needed ]
- ↑ "Kannan M. Krishnan: Materials Science H-index & Awards - Academic Profile | Research.com".
- ↑ "Historians and memoirists, for example, rarely attend the same ..." yumpu.com.
- ↑ "FMD Distinguished Scientist/Engineer Award". tms.org.
- ↑ "Awards and Distinctions". forschungsbericht.uni-due.de.
- ↑ "Endowments". Materials Engineering IISc.
- ↑ "Julia and Johannes Weertman Educator Award". tms.org.
