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| '''Ferromagnetic resonance''', or FMR, is a [[spectroscopic]] technique to probe the [[magnetization]] of [[ferromagnetic]] materials. It is a standard tool for probing [[spin wave]]s and spin dynamics. FMR is very broadly similar to [[electron paramagnetic resonance]] (EPR), and also somewhat similar to [[nuclear magnetic resonance]] (NMR) except that FMR probes the sample magnetization resulting from the [[magnetic moment]]s of dipolar-coupled but unpaired [[electron]]s whereas NMR probes the magnetic moment of [[Nucleus (atomic structure)|atomic nuclei]] screened by the atomic or molecular orbitals surrounding such nuclei of non-zero nuclear spin. | | Jayson Berryhill is how I'm called and my spouse doesn't like it at all. One of [http://www.january-yjm.com/xe/index.php?mid=video&document_srl=158289 psychic readings online] the very best issues in the globe for him is performing ballet and he'll be starting some thing else alongside with it. I am presently a good psychic - [http://hknews.classicmall.com.hk/groups/some-simple-tips-for-personal-development-progress/ hknews.classicmall.com.hk] - travel agent. I've always cherished living in Kentucky but now I'm considering other options.<br><br>Visit my webpage; free tarot readings ([http://findyourflirt.net/index.php?m=member_profile&p=profile&id=117823 click through the following website page]) |
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| == History ==
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| Ferromagnetic resonance was unknowingly discovered by V. K. Arkad'yev when he observed the [[Absorption (optics)|absorption]] of [[Ultra high frequency|UHF]] radiation by ferromagnetic materials in 1911. A qualitative explanation of FMR along with an explanation of the results from Arkad'yev was offered up by Ya. G. Dorfman in 1923 when he suggested that the [[optical]] transitions due to [[Zeeman effect|Zeeman]] splitting could provide a way to study ferromagnetic structure.
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| == Description ==
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| FMR arises from the precessional motion of the (usually quite large) magnetization <math>\scriptstyle\vec{M}</math> of a ferromagnetic material in an external magnetic field <math>\scriptstyle\vec{H}</math>. The magnetic field exerts a [[torque]] on the sample magnetization which causes the magnetic moments in the sample to [[precess]]. The precession frequency of the magnetization depends on the orientation of the material, the strength of the magnetic field, as well as the macroscopic magnetization of the sample; the effective precession frequency of the ferromagnet is much lower in value from the precession frequency observed for free electrons in EPR. Moreover, linewidths of absorption peaks can be greatly affected both by dipolar-narrowing and exchange-broadening (quantum) effects. Furthermore, not all absorption peaks observed in FMR are caused by the precession of the magnetic moments of electrons in the ferromagnet. Thus, the theoretical analysis of FMR spectra is far more complex than that of EPR or NMR spectra.
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| The basic setup for an FMR experiment is a [[Microwave cavity|microwave resonant cavity]] with an [[electromagnet]]. The resonant cavity is fixed at a frequency in the [[super high frequency]] band. A detector is placed at the end of the cavity to detect the microwaves. The magnetic sample is placed between the poles of the electromagnet and the [[magnetic field]] is swept while the resonant absorption intensity of the microwaves is detected. When the magnetization precession frequency and the resonant cavity frequency are the same, absorption increases sharply which is indicated by a decrease in the intensity at the detector.
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| Furthermore, the resonant absorption of microwave energy causes local heating of the ferromagnet. In samples with local magnetic parameters varying on the nanometer scale this effect is used for spatial dependent spectroscopy investigations.
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| The resonant frequency of a film with parallel applied external field <math>B</math> is given by the [[Charles Kittel|Kittel]] formula:<ref>Kittel, Charles; (2004). Introduction to Solid State Physics (8th ed.). Wiley. ISBN 047141526X</ref>
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| :<math> f = \frac{\gamma} {2 \pi} \sqrt{B (B + \mu_0 M)}</math>
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| where <math>M</math> is the magnetization of the ferromagnet and <math>\gamma</math> is the [[gyromagnetic ratio]].<ref>[http://link.aps.org/doi/10.1103/PhysRev.73.155 Phys. Rev. 73, 155 (1948): On the Theory of Ferromagnetic Resonance Absorption<!-- Bot generated title -->]</ref>
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| == See also ==
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| * [[Electron paramagnetic resonance]]
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| * [[Nuclear magnetic resonance]]
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| == References ==
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| *{{cite book
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| |first = S. V.
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| |last=Vonsovskii
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| |title= Ferromagnetic Resonance: The Phenomenon of Resonant Absorption of a High-Frequency Magnetic Field in Ferromagnetic Substances
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| |publisher = [[Pergamon Press|Pergamon]]
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| |location = Oxford
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| |year = 1966
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| }}
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| *{{cite book
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| |last = Chikazumi
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| |first = Sōshin
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| |title = Physics of Ferromagnetism
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| |publisher = [[Clarendon Press]]
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| |year = 1997
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| |isbn = 0-19-851776-9
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| }}
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| == External links ==
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| * [http://igorbarsukov.com/fmr.html Calculation of some important resonance fields]
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| * [http://igorbarsukov.com/sthm.html Spatially resolved ferromagnetic resonance technique]
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| * [http://www.physik.fu-berlin.de/einrichtungen/ag/ag-kuch/research/techniques/fmr.html Some information about FMR]
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| == References == | |
| <references />
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| {{BranchesofSpectroscopy}}
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| [[Category:Condensed matter physics]]
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| [[Category:Magnetic ordering]]
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| [[ro:Rezonanță electronică de spin]]
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