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Topic: Superparamagnetism


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In the News (Fri 19 Dec 14)

  
  Superparamagnetism
Superparamagnetism is a phenomenon by which magnetic materials may exhibit a behavior similar to paramagnetism at temperatures below the Curie or the Neel temperature.
Superparamagnetism occurs when the material is composed of very small crystallites (1-10 nm).
The energy required to change the direction of magnetization of a crystallite is called the Crystalline anisotropy energy[?] and depends both on the material properties and the crystallite size.
www.ebroadcast.com.au /lookup/encyclopedia/su/Superparamagnetism.html   (262 words)

  
 Magnetic Resonance TIP - MRI Database : Superparamagnetism
The material behaves in a manner similar to paramagnetism, except that instead of each individual atom being independently influenced by an external magnetic field, the magnetic moment of the entire crystallite tends to align with the magnetic field.
In MRI superparamagnetic iron oxide is used as a contrast agent.
Through interactions between the electron spins of the paramagnetic gadolinium and the water nuclei nearby, the relaxation rates (T1 and T2) of the water protons are increased (T1 and T2 times are decreased), causing an increase in signal on T1 weighted images.
www.mr-tip.com /serv1.php?type=db1&dbs=Superparamagnetism   (747 words)

  
 Superparamagnetism - Wikipedia, the free encyclopedia
Superparamagnetism is a phenomenon by which magnetic materials may exhibit a behavior similar to paramagnetism even when at temperatures below the Curie or the Néel temperature.
The idea of superparamagnetism is used in SuperParamagnetic Clustering algorithm (SPC) as well as in its extension global SPC.
In particular, it is a function of the exponential of the grain volume.
en.wikipedia.org /wiki/Superparamagnetism   (591 words)

  
 High density magnetic recording medium - Patent 5830588
The method of claim 19, wherein the filtering is assisted by placing a series of angled slits forming a venetian blind assembly in the path of the beam, wherein clusters that deflect away from a zero-field trajectory pass through the slits and cluster which maintain a zero-field trajectory are stopped.
The clusters with fixed moments can be separated from the superparamagnetic clusters also present in the beam by passing the beam through a conventional, superconducting quadrupole, superconducting hexapole, or other gradient field magnet, and collecting only those clusters which are deflected by a large amount.
The signature of superparamagnetic behavior is a small deflection of the beam that does not broaden its profile and that is linear in both the applied field and the field gradient.
www.freepatentsonline.com /5830588.html   (8006 words)

  
 NVE for GMR spintronics magnetic sensors isolators & mram
The Superparamagnetic Devices patent is number 7,054,118 and is the first patent granted from the application published by the USPTO under number 2004-0023065.
Superparamagnetism is the magnetic state of a material between highly ordered parallel spins (ferromagnetism) and randomly ordered spins (paramagnetism).
The NVE invention utilizes the superparamagnetic effect to improve the accuracy of spintronic sensors where a small sensed field is sufficient to order the spins in a superparamagnetic material.
www.nve.com /2006prs/may30-2006-patents.htm   (358 words)

  
 Superparamagnetism Information - superparamagnetism
In this case even though the temperature is below the Curie or Neel temperature and the thermal energy is not sufficient to overcome the coupling forces between neighboring atoms, the thermal energy is sufficient superparamagnetism to change the direction of magnetization of the entire crystallite.
The field of electronics is the study and use of systems that operate by controlling the flow of electrons or other electrically charged particles in devices such as thermionic valves and semiconductors.
The study of new semiconductor devices and their technology is sometimes considered as a branch of physics.
www.inanot.com /Ina-Electronics_Topics_Sk_-_Sy-/Superparamagnetism.html   (339 words)

  
 Superparamagnetism of magnetite nanoparticles: dependence on surface modification.
Superparamagnetic iron oxide nanoparticles (SPION) with an average particle diameter of 6 nm are prepared by controlled chemical coprecipitations.
The superparamagnetic blocking temperature, the coercivity, and the bias field radically increase with increasing coverage.
Magnetization measurements indicated that the superparamagnetic nature of the nanospheres had high saturation magnetization of 40 emu/g at 300 K. The procedures of the novel synthesis are described in detail.
antineoplastic.lib.bioinfo.pl /auid:4931734   (1843 words)

  
 Magnetic Resonance TIP - MRI Database : Superparamagnetism p2
Since hepatic tumors either do not contain RES cells or their activity is reduced, the contrast between liver and lesion is improved.
Superparamagnetic iron oxides cause noticeable shorter T2 relaxation times with signal loss in the targeted tissue (e.g., liver and spleen) with all standard pulse sequences.
Superparamagnetic iron oxide contrast agents: physicochemical characteristics and applications in MR imaging
www.mr-tip.com /serv1.php?type=db1&dbs=Superparamagnetism&set=2   (285 words)

  
 Storage Technology
Superparamagnetism occurs when the microscopic magnetic grains on the disk become so tiny that random thermal vibrations at room temperature cause them to lose their ability to hold their magnetic orientations.
The superparamagnetic barrier is drawing nearer, forcing the industry to slow the historically rapid pace of growth in disk drive capacity – a pace that, at its peak over the past decade, doubled capacity every 12 months.
Using perpendicular recording, scientists at Hitachi GST and other companies believe that the effects of superparamagnetism can be further forestalled, which would create opportunities for continued robust growth in areal density at a rate of about 40 percent each year.
hitachigst.com /hdd/research/recording_head/pr/PerpendicularPaper.html   (1834 words)

  
 Magnetic element, and magnetic head and magnetic memory device using thereof - Patent 6114056
However, because of superparamagnetism of conventional ultra-fine particles, saturation magnetization is intrinsically very large, resulting in a problem when being put into practical use.
In such a magnetic element 1, since a granular magnetic film 3 is not superparamagnetic but is ferromagnetic, a problem that saturation magnetic field is large like a conventional granular GMR material can be cancelled.
On the granular magnetic film, Ag(3 nm)/Co.sub.80 Pt.sub.20 (5 nm) was stacked and Ag layer of 100 nm thickness was formed as a gap layer to obtain a sample.
www.freepatentsonline.com /6114056.html   (11905 words)

  
 Perpendicular recording: Why it matters: Insight - Hardware - ZDNet Australia
Superparamagnetism occurs when the microscopic magnetic grains on the disk become so tiny that random thermal vibrations at room temperature cause them to lose their ability to hold their magnetic orientations.
Today, the hard-drive industry’s ability to push out the superparamagnetic limit is more critical than ever as capacity requirements continue to grow dramatically.
The superparamagnetic barrier is drawing nearer, forcing the industry to slow the historically rapid pace of growth in disk drive capacity.
www.zdnet.com.au /insight/hardware/soa/Perpendicular-recording-Why-it-matters/0,139023759,139191652,00.htm   (802 words)

  
 Perpendicular recording: Why it matters - TechEnclave
What results are "flipped bits"–-bits whose magnetic north and south poles suddenly and spontaneously reverse–-that corrupt data, rendering it and the storage device unreliable.
Though it departs from the current method of recording, perpendicular recording is technically the closest alternative to longitudinal recording, enabling the industry to capitalize on current knowledge while delaying the superparamagnetic effect.
The superparamagnetic barrier is drawing nearer, forcing the industry to slow the historically rapid pace of growth in disk drive capacity-–a pace that, at its peak over the past decade, doubled capacity every 12 months.
www.techenclave.com /forums/perpendicular-recording-why-it-matters-3301.html   (1059 words)

  
 How Perpendicular Recording Works | Hardware Secrets   (Site not responding. Last check: 2007-10-14)
Superparamagnetism occurs when the particles are so small that temperature variations can reverse the magnetic fields from the particles, what would corrupt stored data.
Superparamagnetism prevents manufactures from building hard disk drives with higher capacities.
Total or partial reproduction of the contents of this site, as well as that of the texts available for downloading, be this in the electronic media, in print, or any other form of distribution, is expressly forbidden.
www.hardwaresecrets.com /printpage/347/2   (309 words)

  
 SAMSUNG’s Digital World - Hard Disk Drive / White Paper   (Site not responding. Last check: 2007-10-14)
The primary reason why density is limited through LMR is a result of what is called superparamagnetism.
Superparamagnetism refers to the phenomenon by which magnetized materials move closer as the density increases, to the point where they eventually interfere with one another.
By avoiding superparamagnetism, PMR enables one to further increase recording density.
www.samsung.com /Products/HardDiskDrive/whitepapers/WhitePaper_11.htm   (251 words)

  
 The Future of Computing
At some point, the bits may become so small that thermal energy may cause it to demagnetize -- a phenomenon known as superparamagnetism.
To combat this, manufacturers have been increasing the coercivity (the "field" required to write a bit) of the disks they produce.
When the media is heated, the coercivity, or field required to write on the media is reduced.
www.businessweek.com /technology/tc_special/04future_pe/04future_a.htm   (204 words)

  
 Beating Superparamagnetism
In this case, the magnetic field of each grain is oriented up or down rather than right or left.
Because the grains are vertical, many more can be squeezed into a given area before superparamagnetism begins to take its toll.
Interestingly, perpendicular recording is more than 100 years old, with roots in the work of late 19th-century Danish scientist Valdemar Poulsen, who was the first person to record sound magnetically using this technique.
emusician.com /mag/emusic_beating_superparamagnetism/index.html   (745 words)

  
 LLN : Thin films : Micromagnetism : Brillouin versus Langevin function   (Site not responding. Last check: 2007-10-14)
Superparamagnetism is a long-standing issue in magnetism, that has benefited from countless contributions over the last decades.
In this contribution we discuss what kind of fitting function should be used in the superparamagnetic state of such nanoparticles, with a view to clarifying a misunderstanding about the Langevin function that is sometimes found in the literature.
It is sometimes believed that the Langevin function should be used whenever classical nanoparticles are involved, because their spin is very large compared to a 1/2 spin.
lab-neel.grenoble.cnrs.fr /themes/couches/ext/subjects/micromagnetism/brillouinlangevin/brillouinlangevin-en.html   (735 words)

  
 X-ray Photoelectron Spectroscopy and Magnetic Studies on the Effect of Pore Size, Wall Thickness, and Wall Composition ...   (Site not responding. Last check: 2007-10-14)
A series of mesoporous niobium oxide materials were synthesized in order to understand the role of pore size and thickness of the walls in the mesostructure on the magnetic properties.
The results of this study showed that variation of wall thickness or pore size in the Nb system had little effect on the properties and that superparamagnetism most likely arises from mixed oxidation state cobaltocene grains residing in the individual pores and not from the free electrons in the mesostructure or much larger domains.
The Langevin function was applied to the isothermal magnetic data from the Nb composites and gave mean superparamagnetic particle sizes of ca.
pubs.acs.org /cgi-bin/abstract.cgi/inocaj/2000/39/i26/abs/ic000678f.html   (338 words)

  
 Superparamagnetism   (Site not responding. Last check: 2007-10-14)
Superparamagnetic materials consist of individual domains of elements that have ferromagnetic properties in bulk.
The figure to the left illustrates the effect of a superparamagnetic material (grey circle) on the magnetic field flux lines (blue).
Examples of a superparamagnetic materials include iron containing contrast agents for bowel, liver, and lymph node imaging.
www.mritutor.org /mritutor/superpar.htm   (81 words)

  
 Superparamagnetism and the Mössbauer spectrum of goethite: a comment on a recent proposal by Coey et al   (Site not responding. Last check: 2007-10-14)
Superparamagnetism and the Mössbauer spectrum of goethite: a comment on a recent proposal by Coey et al
The distinctive Mössbauer spectra of goethite cannot be explained on the basis of superparamagnetism.
Consideration of superparamagnetic fluctuations in only the transverse components of the sublattice magnetization (`mode superparamagnetism', proposed by Coey et al), or of possible interactions between superparamagnetic particles, does not alter this conclusion.
stacks.iop.org /0953-8984/8/111   (246 words)

  
 4.4 Superparamagnetism or spin glass behaviour in europium fullerides   (Site not responding. Last check: 2007-10-14)
Furthermore, analysis of magnetization below 20T, at low temperatures allows one to conclude to the existence of superparamagnetic clusters of two to four ferromagnetically coupled Eu ions with a spin S=7/2.
A systematic study of the relaxation of magnetization versus field and temperature reveals that the preceding equation always accounts for the observed time effects.
As structural disorder is necessary to observe relaxation effects, the observed magnetic properties are due to the amorphous phase.
www.magniel.com /hmtj/annual/404.html   (299 words)

  
 DailyTech - First Holographic Drives and Media to Ship in 2006
Magnetic recording methods are approaching their physical limits because of the superparamagnetism phenomenon.
Superparamagnetism occurs when the magnetic bits of data on magnetic media, such as hard disk drives, are placed so close together that they disrupt each others' "on/off" state, corrupting the data and making the media unreadable.
This method ultimately conserves surface area and effectively increases the storage density without the occurrence of superparamagnetism.
www.dailytech.com /article.aspx?newsid=1478   (2466 words)

  
 Superparamagnetism in Fe_2-xV_1+xAl; MFM and NMR studies   (Site not responding. Last check: 2007-10-14)
These measurements indicate that two populations of clusters occur: "wrong-site" Fe atoms appear as isolated small clusters, with moment 3.7 \mu_B, and also as agglomerated large clusters of approximately10^4 \mu_B.
The large-moment clusters produce superparamagnetic behavior in these materials, and are also responsible for the GMR effect.
These images help to identify the superparamagnetic glass and ferromagnetic transitions for different compositions of this material.
flux.aps.org /meetings/YR99/TSF99/abs/S220005.html   (165 words)

  
 AnandTech: High Density Storage Technologies; Pixie Dust and Perpendicular Recording
When the areal density -- the number of bits that can be stored on a square inch of disk media -- of a disk medium reaches 150 gigabits per square inch, the magnetic energy holding the bits in place on the medium becomes equal to the ambient thermal energy within the disk drive itself.
What perpendicular recording does is it records, or magnetizes, bits vertically through the platter instead of horizontally which efficiently conserves surface area which, in turn, results in the effective doubling of the areal density of the platter.
As the head of the disk moves from bit to bit it detects the change in direction of the magnetic pull of each of the layers.
www.anandtech.com /storage/showdoc.aspx?i=2474   (1233 words)

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