electron spin resonance

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1、ElectronSpinResonanceKatrinaSliwa1,andBenoitRichard1,y1DepartmentofPhysicsandAstronomy,UniversityofRochester,Rochester,NY14627Electronspinresonance(ESR)isaphenomenonresultingfromcouplingbetweenamagneticeldandthespinofamaterial'selectrons.WeattemptedtomeasuretheLandeg-factorof-diphenyl--picrylh

2、ydrazyl(DPPH)bymicrowavespectroscopy.Despiteseeingasignalchangethatindicatedagfactorof2.011,itwasnotasignaldip,andassuchwecouldnotcorroboratetheacceptedvalueof2.INTRODUCTIONQuantumtheorytellsuselectronshavecertainprop-ertiessuchasspin.Anytypeofangularmomentum,in-cludingspin,canbecoupledwithamagn

3、eticeld.Suchacoupling,alongwithmicrowavespectroscopy,canbeusedtostudyspecicattributesofcertaintypesofma-terials.Thisphenomenonisexploitedinelectronspinresonance(ESR)microwavespectroscopy.Amongthematerialsthatcanbestudiedaretheparamagneticmate-rialssuchasDPPH.UsingESRmicrowavespectroscopy,FIG.1

4、:Energylevelsplittingseenduetothecouplingofthephysicalvariablessuchasthemagneticeldandresonantelectronspinwithanexternalmagneticeldfrequencyaredirectlymeasuredinordertocalculatetheso-calledLandeg-factor.Weaimedtomeasurethelatterobservables,andcomputedtheLandeg-factor.Thiswillandthezprojectiono

5、fspincanbeeither1hor1hso22bediscussedinthefollowingparagraphs.oursplittingis
E=(z+z)
H(6)THEORY11Maxwell'sequationstellusthatmovingchargespro-=(gbgb)
H(7)22ducemagneticelds.Fromthequantizedorbitalangularmomentumandspinofanelectronweseequantizedmag-neticmoments.Whenanexternaleldisapp

6、lied,weget,=(gb)
H=h:(8)fromRussell-Saunderscoupling,anewmagneticmomentWeneedapopulationdierencetoobserveaneect,ofandtherateoftransitionisproportionaltothepopu-11lationofthedierentenergystates.Thepresenceofan=gb[j[j+]](1)22alternatingmagneticeldwillexertatorqueonourmag-neticdipoles.This

7、torquecausessomeofthemtochangewhereorientation,andthiswhatwemeanbyresonance.Whenj(j+1)+s(s+1)l(l+1)wehaveanensembleofelectrons,Boltzmannstatisticsg=1+(2)giveusthepopulationsofthedierentstates.2j(j+1)BistheLandeg-factoran