Microwave-absorbing characteristics for the composites of TP(5)

C.-H.Pengetal./MaterialsScienceandEngineeringB117(2005)27–36

Table1

GrainsizesofferriteanddetaildataforhysteresisloopsshowninFig.3Specimen

Synthesizedferrite

Withoutheat-treatmentAnnealedat500 C/1hAnnealedat900 C/1hCommercialferrite

a

31

Da(nm)254580–

Hc(Oe)52.1265.8228.0124.12

Ms(emu/g)44.2431.3538.8236.08

Mr(emu/g)3.4213.2161.4890.950

AH(kJ/m3)41.2557.7534.1737.73

EvaluatedbytheDebye–Scherrerformula.

onesinregardtowhichtheyareaboutthesamesizesastheonesestimatedbyusingXRDmethod.Inaddition,diffractionpatternsindicatethattheheat-treatedpowdershaveahigherdegreeofcrystallinitythandotheas-synthesizedpowderssincetheirdiffractionringsaresharperandbrighterascom-paredwiththoseofthepowderswithoutheattreatment.3.3.Measurementofhysteresisloop

ThehysteresisloopshowninFig.5illustrateswhataretherealtracesofthemagneticbehavioroftheas-synthesized

NiZnferriteaswellastheferritesamplesthatwereannealedat500 Cand900 Cfor1h.Table1presentstherelevantdata.Itisinterestingtorecognizethatthepowdersafteran-nealingat500 Cpossessthelargestcoerciveforce(Hc),thelargesthysteresislooparea(AH)andthesmallestremanence(Mr)thanthoseofothersamples,whiletheformertwofac-torsmayleadtothelargesthysteresisloss[24].Moreover,thesaturatedmagnetization(Ms)valuesofthecalcinedNiZnferritesaresmallerthanthatoftheonewithoutheattreatment.Fig.6showsthehysteresisloopsoftheundoped,Co-doped,Cu-doped,andMg-dopedNiZnferritesannealed

at

Fig.4.TEMimagesofsynthesizedpowderswithcorrespondingdiffractionpatterns.(a)Withoutheattreatment,and(b)annealedat500 Cfor1h(Takenatthesameoperationconditions).