Microwave-absorbing characteristics for the composites of TP(8)

34C.-H.Pengetal./MaterialsScienceandEngineeringB117(2005)

27–36

Fig.8.Permittivityandpermeabilityspectraofdoped-andundoped-NiZnferrite-TPUcomposites.(a)ε ,(b)ε ,(c)µ ,and(d)µ .( )Undoped,( )Co-doped,( )Cu-doped,and( )Mg-doped.(Allofthesesynthesizedferriteswereannealedat500 Cfor1h.).

ingthemagnetizingprocesses[26].Itisthoughtthatforsmallcrystallitesize(as-synthesizedferritewithoutheattreatment)onlyspinresonanceisobserved,however,bothspinrotationanddomainwallcanbeoperatedwithrespecttolarge

crystal-

litesize(annealedat500 Candabove).Notonlycannano-sizedpowdersincreaseunsaturatedcoordination,interfacepolarization,andmultiplescatternearthesizeoftransitionstage(～40nm),buttheyalsoexistquantumsizeeffectsuchaselectronicenergylevelsplit.TheRef.[25]alsoindicatesthatinthetransitionstagefromsingledomaintomultido-main,coerciveforcereachestoamaximum,whichmaylead

Table3

RelationshipbetweenmatchingfrequencyandmatchingthicknessinNi0.5Zn0.5Fe2O4-TPUcompositesSpecimen

SynthesizedferriteWithoutheattreatment

fm(GHZ)dm(mm)R.L.(dB)Bandwidtha

(GHZ)9.152.52

3.075.432.135.923.425.653.235.62

32.38 35.62 43.71 43.35 29.47 31.03 31.81 33.46

0.740.851.101.160.690.730.700.79

Annealedat500 C/1h9.43

3.16Annealedat900 C/1h8.89

2.27

Fig.9.AbsorptioncharacteristicsoftheNi0.5Zn0.5Fe2O4-TPUcompositewithmaximumattenuation.(Allofthesynthesizedferritewasannealedat500 Cfor1h.).

Commercialferrite

a

9.022.97

ForR.L.≤20dB.