xov xwm

Ua tsaug rau koj tuaj saib Nature. Qhov browser version koj siv tau txwv kev txhawb nqa rau CSS. Rau qhov kev paub zoo tshaj plaws, peb pom zoo kom koj siv qhov browser tshiab (lossis kaw qhov kev sib raug zoo hauv Internet Explorer). Nyob rau tib lub sijhawm, txhawm rau ua kom muaj kev txhawb nqa txuas ntxiv, peb yuav tso saib cov chaw tsis muaj cov qauv thiab JavaScript.
Cov khoom sib nqus ntawm SrFe12O19 (SFO) nyuaj hexaferrite yog tswj los ntawm txoj kev sib raug zoo ntawm nws cov microstructure, uas txiav txim siab lawv qhov cuam tshuam rau daim ntawv thov hlau nplaum mus tas li. Xaiv ib pawg ntawm SFO nanoparticles tau txais los ntawm sol-gel spontaneous combustion synthesis, thiab ua qhov tob hauv cov qauv X-ray hmoov diffraction (XRPD) tus cwj pwm los ntawm G(L) kab kev tsom xam. Qhov tau txais crystallite loj faib qhia qhov pom tseeb ntawm qhov loj me raws li [001] kev taw qhia ntawm txoj kev sib txuas, ua rau tsim cov flaky crystallites. Tsis tas li ntawd, qhov loj ntawm SFO nanoparticles tau txiav txim siab los ntawm kev soj ntsuam kev sib kis ntawm electron microscopy (TEM), thiab qhov nruab nrab ntawm cov crystallites hauv cov khoom tau kwv yees. Cov txiaj ntsig no tau raug soj ntsuam los qhia txog qhov tsim ntawm ib lub xeev hauv qab tus nqi tseem ceeb, thiab qhov ua kom ntim tau los ntawm kev ntsuas lub sij hawm-sib nqus magnetization, tsom rau elucidating cov txheej txheem rov qab magnetization ntawm cov khoom siv hlau nplaum nyuaj.
Nano-scale magnetic cov ntaub ntawv muaj qhov tseem ceeb ntawm kev tshawb fawb thiab thev naus laus zis, vim tias lawv cov khoom sib nqus muaj cov cwj pwm txawv txawv piv nrog lawv qhov ntim loj, uas coj cov kev xav tshiab thiab kev siv 1,2,3,4. Ntawm cov ntaub ntawv nanostructured, M-hom hexaferrite SrFe12O19 (SFO) tau dhau los ua tus neeg sib tw txaus nyiam rau kev siv hlau nplaum tas mus li5. Qhov tseeb, nyob rau hauv xyoo tas los no, ntau txoj haujlwm tshawb fawb tau ua tiav ntawm kev hloov kho SFO-raws li cov ntaub ntawv ntawm nanoscale los ntawm ntau yam kev sib txuas thiab kev ua kom zoo tshaj qhov loj, morphology, thiab cov khoom sib nqus 6,7,8. Tsis tas li ntawd, nws tau txais kev saib xyuas zoo hauv kev tshawb fawb thiab kev loj hlob ntawm kev sib pauv coupling systems9,10. Nws lub siab magnetocrystalline anisotropy (K = 0.35 MJ / m3) taw qhia raws li c-axis ntawm nws hexagonal lattice 11,12 yog qhov ncaj qha tshwm sim ntawm kev sib raug zoo ntawm cov hlau nplaum thiab siv lead ua qauv, crystallites thiab grain loj, morphology thiab kev ntxhib los mos. Yog li ntawd, tswj cov yam ntxwv saum toj no yog lub hauv paus rau kev ua kom tau raws li cov kev cai tshwj xeeb. Daim duab 1 qhia txog qhov raug hexagonal space group P63/mmc ntawm SFO13, thiab lub dav hlau sib raug rau qhov kev xav ntawm txoj kab profile tsom xam.
Ntawm cov yam ntxwv cuam tshuam ntawm ferromagnetic particle txo qhov loj me, tsim ntawm ib lub xeev hauv qab tus nqi tseem ceeb ua rau muaj kev nce hauv cov hlau nplaum anisotropy (vim thaj tsam ntau dua rau qhov ntim piv), uas ua rau muaj kev quab yuam 14,15. Qhov dav hauv qab ntawm qhov tseem ceeb (DC) hauv cov ntaub ntawv nyuaj (tus nqi raug kwv yees li 1 µm), thiab txhais los ntawm qhov hu ua coherent size (DCOH) 16: qhov no yog hais txog qhov tsawg tshaj plaws ntim txoj kev rau demagnetization nyob rau hauv qhov loj coherent. (DCOH), Qhia tawm raws li qhov ua kom ntim (VACT) 14. Txawm li cas los xij, raws li qhia hauv daim duab 2, txawm hais tias cov siv lead ua loj me dua DC, cov txheej txheem inversion yuav tsis sib haum. Nyob rau hauv nanoparticle (NP) Cheebtsam, qhov tseem ceeb ntim ntawm reversal nyob ntawm lub magnetic viscosity (S), thiab nws magnetic teb dependence muab cov ntaub ntawv tseem ceeb txog kev hloov ntawm NP magnetization17,18.
Saum toj no: Schematic daim duab ntawm lub evolution ntawm lub coercive teb nrog particle loj, uas qhia tus coj magnetization reversal txheej txheem (hloov los ntawm 15). SPS, SD, thiab MD sawv cev rau lub xeev superparamagnetic, ib lub npe, thiab ntau lub npe, feem; DCOH thiab DC yog siv rau coherence txoj kab uas hla thiab tseem ceeb txoj kab uas hla, feem. Hauv qab: Sketches ntawm qhov sib txawv ntawm qhov ntau thiab tsawg, qhia txog kev loj hlob ntawm crystallites los ntawm ib qho siv lead ua rau polycrystalline. thiab qhia crystallite thiab particle loj, feem.
Txawm li cas los xij, ntawm nanoscale, cov txheej txheem tshiab kuj tau qhia, xws li muaj zog sib nqus sib nqus ntawm cov khoom, qhov loj me me, cov duab me me, qhov tsis zoo ntawm qhov chaw, thiab cov kev taw qhia ntawm qhov yooj yim axis ntawm magnetization, tag nrho cov no ua rau kev tsom xam nyuaj dua19, 20. Cov ntsiab lus no cuam tshuam rau lub zog thaiv kev faib tawm thiab tsim nyog tau txais kev saib xyuas kom zoo, yog li cuam tshuam rau hom magnetization thim rov qab. Rau lub hauv paus no, nws yog ib qho tseem ceeb tshwj xeeb kom nkag siab txog kev sib raug zoo ntawm cov khoom sib nqus thiab lub cev nanostructured M-hom hexaferrite SrFe12O19. Yog li ntawd, raws li ib tug qauv system, peb siv ib tug txheej ntawm SFOs npaj los ntawm ib tug hauv qab-up sol-gel txoj kev, thiab tsis ntev los no ua kev tshawb fawb. Cov txiaj ntsig yav dhau los qhia tau hais tias qhov loj ntawm cov crystallites yog nyob rau hauv nanometer ntau yam, thiab nws, nrog rau cov duab ntawm crystallites, nyob ntawm qhov kev kho cua sov siv. Tsis tas li ntawd, qhov crystallinity ntawm cov qauv no nyob ntawm txoj kev sib txuas, thiab kev soj ntsuam ntxaws ntxiv yuav tsum tau ua kom paub meej txog kev sib raug zoo ntawm crystallites thiab particle loj. Txhawm rau nthuav tawm qhov kev sib raug zoo no, los ntawm kev sib kis ntawm electron microscopy (TEM) kev tshuaj xyuas ua ke nrog Rietveld txoj kev thiab kab profile tsom ntawm cov ntaub ntawv siab X-ray hmoov diffraction, crystal microstructure tsis (ie, crystallites thiab particle loj, duab) tau ua tib zoo tshuaj xyuas. . XRPD) hom. Cov yam ntxwv ntawm tus yam ntxwv lub hom phiaj los txiav txim siab cov yam ntxwv anisotropic ntawm cov nanocrystallites tau txais thiab ua pov thawj qhov ua tau ntawm kab profile tsom xam raws li cov txheej txheem muaj zog rau kev ua kom pom lub ncov dav dav mus rau nanoscale ntau ntawm (ferrite) cov ntaub ntawv. Nws pom tau hais tias qhov ntim-hnyav crystallite loj faib G (L) muaj zog nyob ntawm crystallographic kev taw qhia. Hauv kev ua haujlwm no, peb pom tias cov txheej txheem ntxiv yog qhov yuav tsum tau ua kom raug rho tawm qhov loj me ntsig txog qhov ntsuas kom raug piav qhia cov qauv thiab cov yam ntxwv sib nqus ntawm cov qauv hmoov zoo li no. Cov txheej txheem ntawm thim rov qab magnetization kuj tau kawm kom paub meej txog kev sib raug zoo ntawm cov qauv morphological thiab tus cwj pwm sib nqus.
Rietveld tsom xam ntawm X-ray hmoov diffraction (XRPD) cov ntaub ntawv qhia tau hais tias cov crystallite loj raws c-axis tuaj yeem hloov kho los ntawm kev kho cua sov kom haum. Nws tshwj xeeb qhia tau hais tias lub ncov dav dav pom nyob rau hauv peb cov qauv zoo li yuav yog vim cov duab anisotropic crystallite. Tsis tas li ntawd, qhov sib xws ntawm qhov nruab nrab txoj kab uas hla los ntawm Rietveld thiab Williamson-Hall daim duab ( thiab hauv Table S1) qhia tau hais tias cov crystallites yuav luag tsis muaj strain thiab tsis muaj cov qauv deformation. Lub evolution ntawm crystallite loj faib raws cov lus qhia sib txawv tsom peb cov xim ntawm qhov tau txais particle loj. Kev tsom xam tsis yog yooj yim, vim hais tias cov qauv tau los ntawm sol-gel spontaneous combustion yog tsim los ntawm agglomerates hais nrog ib tug ntxeem tau qauv 6,9, nees nkaum ib. TEM yog siv los kawm cov qauv sab hauv ntawm cov qauv xeem kom ntxaws ntxiv. Cov duab ci ntsa iab raug tshaj tawm hauv daim duab 3a-c (rau cov lus piav qhia ntxaws ntxaws ntawm kev tshuaj xyuas, thov mus rau ntu 2 ntawm cov ntaub ntawv ntxiv). Cov qauv muaj cov khoom siv nrog cov duab me me. Cov platelets koom ua ke los tsim cov porous aggregates ntawm ntau qhov sib txawv thiab cov duab. Txhawm rau kwv yees qhov loj me ntawm cov platelets, thaj tsam ntawm 100 qhov ntawm txhua tus qauv tau ntsuas manually siv ImageJ software. Txoj kab uas hla ntawm lub voj voog sib npaug nrog tib thaj chaw raws li tus nqi raug ntaus nqi rau tus neeg sawv cev loj ntawm txhua qhov ntsuas. Cov txiaj ntsig ntawm cov qauv SFOA, SFOB thiab SFOC tau sau tseg hauv daim duab 3d-f, thiab qhov nruab nrab txoj kab uas hla tus nqi kuj tau tshaj tawm. Kev ua kom kub ua kom nce qhov loj ntawm cov khoom thiab lawv qhov dav dav. Los ntawm kev sib piv ntawm VTEM thiab VXRD (Table 1), nws tuaj yeem pom tau tias nyob rau hauv cov ntaub ntawv ntawm SFOA thiab SFOB cov qauv, qhov nruab nrab ntawm cov crystallites ib feem qhia tau hais tias polycrystalline xwm ntawm cov lamellae. Hauv qhov sib piv, qhov ntim ntim ntawm SFOC yog piv rau qhov nruab nrab crystallite ntim, qhia tias feem ntau ntawm cov lamellae yog ib leeg muaju. Peb taw qhia tias qhov loj me ntawm TEM thiab X-ray diffraction yog txawv, vim hais tias nyob rau hauv lub tom kawg, peb tab tom ntsuas lub coherent scattering block (nws tej zaum yuav me dua li ib txwm flake): Tsis tas li ntawd, qhov me me yuam kev taw qhia ntawm cov tawg. domains yuav suav nrog diffraction.
Cov duab ci ntsa iab TEM ntawm (a) SFOA, (b) SFOB thiab (c) SFOC qhia tias lawv muaj cov khoom sib xws nrog lub phaj zoo li. Cov kev faib loj sib xws tau pom nyob rau hauv histogram ntawm lub vaj huam sib luag (df).
Raws li peb tau pom nyob rau hauv kev tshuaj ntsuam yav dhau los, cov crystallites nyob rau hauv cov hmoov tiag tiag qauv tsim ib tug polydisperse system. Txij li thaum txoj kev X-ray yog qhov rhiab heev rau qhov sib xyaw ua ke ntawm kev sib cais, kev tshuaj xyuas zoo ntawm cov ntaub ntawv sib txawv ntawm cov hmoov yuav tsum tau piav qhia txog cov qauv zoo nanostructures. Ntawm no, qhov luaj li cas ntawm crystallites yog tham los ntawm tus yam ntxwv ntawm lub ntim-weighted crystallite loj faib muaj nuj nqi G (L) 23, uas yuav tsum tau txhais raws li qhov yuav tsum tau ceev ntawm nrhiav crystallites ntawm assumed puab thiab loj, thiab nws qhov hnyav yog proportional rau nws. Volume, nyob rau hauv tus qauv tsom xam. Nrog rau cov duab prismatic crystallite, qhov nruab nrab ntim hnyav crystallite loj (qhov nruab nrab sab ntev hauv [100], [110] thiab [001] cov lus qhia) tuaj yeem suav. Yog li ntawd, peb xaiv tag nrho peb cov qauv SFO nrog qhov sib txawv ntawm qhov sib txawv hauv daim ntawv ntawm anisotropic flakes (saib Daim Ntawv Qhia 6) los ntsuas qhov ua tau zoo ntawm cov txheej txheem no kom tau txais qhov tseeb crystallite loj faib ntawm cov ntaub ntawv nano-scale. Txhawm rau ntsuas qhov anisotropic orientation ntawm ferrite crystallites, kab profile tsom xam tau ua nyob rau hauv XRPD cov ntaub ntawv ntawm cov xaiv peaks. Cov qauv SFO kuaj tsis muaj qhov yooj yim (ntshiab) siab dua kev txiav txim siab los ntawm tib txheej ntawm cov siv lead ua dav hlau, yog li nws tsis tuaj yeem cais cov kab kev nthuav dav los ntawm qhov loj thiab qhov txawv txav. Nyob rau tib lub sijhawm, qhov pom kev nthuav dav ntawm cov kab diffraction feem ntau yuav yog vim qhov loj me, thiab qhov nruab nrab crystallite zoo raug txheeb xyuas los ntawm kev txheeb xyuas ntawm ntau kab. Daim duab 4 sib piv cov ntim hnyav crystallite loj faib ua haujlwm G(L) raws li cov lus qhia crystallographic. Daim ntawv ntawm crystallite loj faib yog lognormal faib. Ib tug yam ntxwv ntawm tag nrho cov tau txais kev faib loj yog lawv unimodality. Feem ntau, qhov kev faib tawm no tuaj yeem raug ntaus nqi rau qee qhov txheej txheem tsim particle. Qhov sib txawv ntawm qhov nruab nrab xam qhov loj ntawm lub ncov xaiv thiab tus nqi rho tawm los ntawm Rietveld refinement yog nyob rau hauv ib qho kev pom zoo (xav tias cov txheej txheem ntsuas ntsuas qhov sib txawv ntawm cov txheej txheem no) thiab yog tib yam li qhov sib thooj ntawm cov dav hlau los ntawm Debye Qhov nruab nrab qhov loj tau txais yog raws li qhov sib npaug Scherrer, raws li qhia hauv Table 2. Qhov sib txawv ntawm qhov ntim nruab nrab crystallite loj ntawm ob hom qauv sib txawv yog qhov sib txawv heev, thiab qhov sib txawv ntawm qhov loj me me heev. Txawm hais tias tej zaum yuav muaj kev tsis pom zoo nrog Rietveld, piv txwv li, nyob rau hauv rooj plaub ntawm (110) kev xav ntawm SFOB, nws yuav muaj feem xyuam rau qhov kev txiav txim siab ntawm keeb kwm yav dhau los ntawm ob sab ntawm qhov kev xaiv xaiv ntawm qhov deb ntawm 1 degree 2θ hauv txhua qhov. kev taw qhia. Txawm li cas los xij, qhov kev pom zoo zoo ntawm ob lub thev naus laus zis tau lees paub qhov tseeb ntawm txoj kev. Los ntawm kev tsom xam ntawm qhov siab tshaj plaws, nws pom tseeb tias qhov loj me nrog [001] muaj qhov tshwj xeeb nyob ntawm txoj kev sib xyaw ua ke, ua rau tsim cov flaky crystallites hauv SFO6,21 synthesized los ntawm sol-gel. Qhov tshwj xeeb no qhib txoj hauv kev rau kev siv cov qauv no los tsim cov nanocrystals nrog cov duab nyiam. Raws li peb txhua tus paub, cov qauv siv lead ua nyuaj ntawm SFO (raws li qhia hauv daim duab 1) yog qhov tseem ceeb ntawm tus cwj pwm ferromagnetic ntawm SFO12, yog li cov duab thiab qhov loj me tuaj yeem hloov kho kom zoo rau kev tsim cov qauv rau kev siv (xws li mus tas li. magnet hais txog). Peb taw qhia tias crystallite loj tsom xam yog ib txoj hauv kev zoo los piav qhia txog anisotropy ntawm crystallite duab, thiab ntxiv dag zog rau cov txiaj ntsig yav dhau los.
(a) SFOA, (b) SFOB, (c) SFOC xaiv qhov kev xav (100), (110), (004) ntim hnyav crystallite loj faib G(L).
Txhawm rau ntsuas qhov ua tau zoo ntawm cov txheej txheem kom tau txais qhov tseeb crystallite loj faib ntawm cov ntaub ntawv nano-hmoov thiab siv rau cov nanostructures nyuaj, raws li qhia hauv daim duab 5, peb tau txheeb xyuas tias txoj kev no muaj txiaj ntsig zoo hauv cov ntaub ntawv nanocomposite (tus nqi nominal). Qhov tseeb ntawm rooj plaub yog tsim los ntawm SrFe12O19 / CoFe2O4 40/60 w / w %). Cov txiaj ntsig no tau ua tiav raws li kev txheeb xyuas Rietveld (saib daim duab ntawm daim duab 5 rau kev sib piv), thiab muab piv rau ib-theem system, SFO nanocrystals tuaj yeem hais txog cov phaj zoo li morphology. Cov txiaj ntsig no yuav tsum siv cov kab ntawv txheeb xyuas no rau ntau lub tshuab ua haujlwm uas ntau qhov sib txawv siv lead ua theem tuaj yeem sib tshooj yam tsis tau poob cov ntaub ntawv hais txog lawv cov qauv.
Qhov ntim-hnyav crystallite loj faib G(L) ntawm cov kev xav tau xaiv ntawm SFO ((100), (004)) thiab CFO (111) hauv nanocomposites; rau kev sib piv, qhov sib thooj Rietveld tsom xam qhov tseem ceeb yog 70(7), 45(6) thiab 67(5) nm6.
Raws li pom nyob rau hauv daim duab 2, kev txiav txim siab ntawm qhov loj ntawm lub magnetic domain thiab qhov tseeb kwv yees ntawm lub cev ntim yog lub hauv paus rau piav txog cov complex systems thiab kom to taub meej txog kev sib cuam tshuam thiab cov qauv kev txiav txim ntawm magnetic particles. Tsis ntev los no, tus cwj pwm sib nqus ntawm SFO cov qauv tau kawm kom ntxaws, nrog rau kev saib xyuas tshwj xeeb rau cov txheej txheem thim rov qab ntawm cov hlau nplaum, txhawm rau kawm txog cov khoom tsis zoo ntawm cov hlau nplaum sib nqus (χirr) (Daim duab S3 yog ib qho piv txwv ntawm SFOC) 6. Txhawm rau kom nkag siab tob dua ntawm cov hlau nplaum thim rov qab mechanism hauv qhov ferrite-based nanosystem, peb tau ua qhov ntsuas kev sib nqus hauv qhov rov qab (HREV) tom qab saturation hauv ib qho kev taw qhia. Xav txog \(M\left(t\right)\proptoSln\left(t\right)\) (saib daim duab 6 thiab cov ntaub ntawv ntxiv kom paub meej ntxiv) thiab tom qab ntawd tau txais qhov qhib qhov ntim (VACT). Txij li thaum nws tuaj yeem txhais tau tias yog qhov ntim tsawg tshaj plaws ntawm cov khoom siv uas tuaj yeem hloov pauv tau hauv ib qho xwm txheej, qhov ntsuas no sawv cev rau "magnetic" ntim koom nrog hauv cov txheej txheem thim rov qab. Peb tus nqi VACT (saib Table S3) sib raug mus rau ib lub kheej kheej nrog ib txoj kab uas hla ntawm kwv yees li 30 nm, txhais raws li txoj kab uas hla (DCOH), uas piav qhia txog qhov txwv sab sauv ntawm lub kaw lus magnetization reversal los ntawm coherent rotation. Txawm hais tias muaj qhov sib txawv loj hauv lub cev ntim ntawm cov khoom (SFOA yog 10 npaug loj dua SFOC), cov txiaj ntsig no yog qhov tsis tu ncua thiab me me, qhia tau hais tias cov hlau nplaum thim rov qab ntawm txhua lub tshuab tseem zoo ib yam (raws li peb thov. yog ib tug sau system) 24 . Thaum kawg, VACT muaj lub cev me me dua li XRPD thiab TEM tsom xam (VXRD thiab VTEM hauv Table S3). Yog li, peb tuaj yeem txiav txim siab tias txoj kev hloov pauv tsis yog tshwm sim los ntawm kev sib hloov sib hloov. Nco ntsoov tias cov txiaj ntsig tau los ntawm kev siv cov hlau nplaum sib txawv (Daim duab S4) muab cov txiaj ntsig zoo sib xws ntawm DCOH. Hauv qhov no, nws yog ib qho tseem ceeb heev uas yuav tsum tau txiav txim siab qhov tseem ceeb ntawm txoj kab uas hla ntawm ib qho kev sib txuas lus (DC) txhawm rau txiav txim siab qhov tsim nyog tshaj qhov kev thim rov qab. Raws li peb qhov kev txheeb xyuas (saib cov khoom siv ntxiv), peb tuaj yeem pom tau tias qhov tau txais VACT cuam tshuam nrog kev sib hloov tsis sib haum, vim tias DC (~ 0.8 µm) nyob deb heev ntawm DC (~ 0.8 µm) ntawm peb cov khoom, uas yog, tsim cov phab ntsa tsis yog ces tau txais kev txhawb zog thiab tau txais ib qho kev teeb tsa ib leeg. Cov txiaj ntsig no tuaj yeem piav qhia los ntawm kev tsim ntawm kev sib cuam tshuam domain25, 26. Peb xav tias ib qho crystallite koom nrog hauv kev sib cuam tshuam, uas txuas mus rau cov khoom sib cuam tshuam vim qhov sib txawv ntawm microstructure ntawm cov ntaub ntawv no27,28. Txawm hais tias X-ray txoj kev tsuas yog rhiab rau qhov zoo ntawm microstructure ntawm domains (microcrystals), kev ntsuas kev sib nqus tau muab pov thawj ntawm cov xwm txheej nyuaj uas yuav tshwm sim hauv nanostructured SFOs. Yog li ntawd, los ntawm optimizing lub nanometer loj ntawm SFO nplej, nws muaj peev xwm tiv thaiv kev hloov mus rau lub multi-domain inversion txheej txheem, yog li tswj lub siab coercivity ntawm cov ntaub ntawv no.
(a) Lub sij hawm-dependent magnetization nkhaus ntawm SFOC ntsuas ntawm qhov sib txawv rov qab teb HREV qhov tseem ceeb tom qab saturation ntawm-5 T thiab 300 K (qhia ib sab ntawm cov ntaub ntawv sim) (magnetization yog normalized raws li qhov hnyav ntawm tus qauv); kom pom tseeb, Lub inset qhia cov ntaub ntawv sim ntawm 0.65 T teb (dub lub voj voog), uas muaj qhov zoo tshaj plaws haum (liab kab) (magnetization yog normalized rau thawj tus nqi M0 = M(t0)); (b) cov sib nqus sib nqus viscosity (S) yog qhov rov qab ntawm SFOC A kev ua haujlwm ntawm daim teb (kab yog ib qho kev qhia rau lub qhov muag); (c) cov txheej txheem ua kom muaj zog nrog lub cev / sib nqus qhov ntev cov ntsiab lus.
Feem ntau hais lus, magnetization thim rov qab tuaj yeem tshwm sim los ntawm cov txheej txheem hauv zos, xws li sau cov phab ntsa nucleation, propagation, thiab pinning thiab unpinning. Nyob rau hauv cov ntaub ntawv ntawm ib leeg-domain ferrite hais, lub activation mechanism yog nucleation-mediated thiab yog tshwm sim los ntawm ib tug magnetization hloov me dua tag nrho cov magnetic reversal ntim (raws li qhia nyob rau hauv daim duab 6c) 29.
Qhov sib txawv ntawm qhov tseem ceeb ntawm cov hlau nplaum thiab lub cev txoj kab uas hla ntawm lub cev txhais tau hais tias hom incoherent yog concomitant tshwm sim ntawm magnetic domain reversal, uas tej zaum yuav yog vim cov khoom inhomogeneities thiab deg unevenness, uas yuav correlated thaum particle loj nce 25, uas ua rau ib tug deviation los ntawm cov khoom. uniform magnetization xeev.
Yog li ntawd, peb tuaj yeem txiav txim siab tias nyob rau hauv cov txheej txheem no, cov txheej txheem thim rov qab magnetization yog qhov nyuaj heev, thiab kev siv zog los txo qhov loj hauv nanometer nplai ua lub luag haujlwm tseem ceeb hauv kev sib cuam tshuam ntawm microstructure ntawm ferrite thiab hlau nplaum. .
Kev nkag siab txog kev sib raug zoo ntawm cov qauv, daim ntawv thiab cov hlau nplaum yog lub hauv paus rau kev tsim thiab tsim cov kev siv yav tom ntej. Cov kab ntawv txheeb xyuas ntawm cov qauv XRPD xaiv ntawm SrFe12O19 tau lees paub cov duab anisotropic ntawm nanocrystals tau los ntawm peb txoj kev sib txuas. Ua ke nrog TEM tsom xam, qhov polycrystalline xwm ntawm cov khoom no tau ua pov thawj, thiab tom qab ntawd nws tau lees paub tias qhov loj ntawm SFO tshawb hauv qhov haujlwm no yog qis dua qhov tseem ceeb ntawm txoj kab uas hla, txawm tias muaj pov thawj ntawm kev loj hlob crystallite. Nyob rau hauv lub hauv paus no, peb xav kom ib tug irreversible magnetization txheej txheem raws li tsim los ntawm ib tug interconnection domain muaj li interconnected crystallites. Peb cov txiaj ntsig tau ua pov thawj qhov sib raug zoo ntawm cov particle morphology, cov qauv siv lead ua thiab crystallite loj uas muaj nyob ntawm qib nanometer. Txoj kev tshawb no tsom kom paub meej cov txheej txheem thim rov qab magnetization ntawm cov ntaub ntawv nyuaj nanostructured sib nqus thiab txiav txim siab lub luag haujlwm ntawm cov yam ntxwv ntawm microstructure hauv cov txiaj ntsig sib nqus.
Cov qauv tau tsim los siv citric acid ua tus neeg sawv cev chelating / roj raws li sol-gel spontaneous combustion method, qhia nyob rau hauv Reference 6. Cov txheej txheem synthesis tau optimized kom tau txais peb qhov ntau thiab tsawg ntawm cov qauv (SFOA, SFOB, SFOC), uas yog tau los ntawm kev kho kom zoo annealing ntawm qhov kub sib txawv (1000, 900, thiab 800 ° C, feem). Table S1 qhia txog cov khoom sib nqus thiab pom tias lawv zoo ib yam. Cov nanocomposite SrFe12O19/CoFe2O4 40/60 w/w% kuj tau npaj zoo ib yam.
Cov qauv diffraction tau ntsuas siv CuKα hluav taws xob (λ = 1.5418 Å) ntawm Bruker D8 hmoov diffractometer, thiab lub ntsuas ntsuas qhov dav tau teem rau 0.2 hli. Siv lub txee VANTEC los sau cov ntaub ntawv hauv 2θ ntau ntawm 10-140 °. Qhov ntsuas kub thaum sau cov ntaub ntawv tau khaws cia ntawm 23 ± 1 ° C. Qhov kev xav tau ntsuas los ntawm kev siv cov kauj ruam-thiab-scan, thiab cov kauj ruam ntev ntawm tag nrho cov qauv kuaj yog 0.013 ° (2theta); Qhov siab tshaj plaws tus nqi ntawm qhov ntsuas qhov deb yog -2.5 thiab + 2.5 ° (2theta). Rau txhua lub ncov, tag nrho ntawm 106 quanta yog xam, thaum tus Tsov tus tw muaj txog 3000 quanta. Ntau qhov kev sim siab (sib cais lossis ib nrab sib tshooj) raug xaiv rau kev tshuaj xyuas ntxiv ib txhij: (100), (110) thiab (004), uas tshwm sim ntawm lub kaum sab xis Bragg ze rau Bragg lub kaum sab xis ntawm SFO sau npe kab. Qhov kev sim siv zog tau raug kho rau Lorentz polarization yam, thiab keeb kwm yav dhau raug tshem tawm nrog qhov kev xav tau hloov pauv. NIST tus qauv LaB6 (NIST 660b) tau siv los ntsuas qhov ntsuas thiab ntsuas qhov dav dav. Siv LWL (Louer-Weigel-Louboutin) deconvolution txoj kev 30,31 kom tau txais cov kab ntshiab diffraction. Txoj kev no yog siv rau hauv qhov kev txheeb xyuas qhov profile PROFIT-software32. Los ntawm qhov haum ntawm cov ntaub ntawv ntsuas kev siv ntawm cov qauv thiab cov qauv nrog pseudo Voigt muaj nuj nqi, cov kab ncaj nraim contour f(x) raug rho tawm. Qhov loj me me muaj nuj nqi G(L) txiav txim siab los ntawm f(x) los ntawm kev ua raws li cov txheej txheem qhia hauv Kev Siv 23. Yog xav paub ntxiv, thov mus saib cov khoom siv ntxiv. Raws li ib qho ntxiv rau cov kab ntawv txheeb xyuas, FULLPROF program siv los ua Rietveld tsom xam ntawm XRPD cov ntaub ntawv (cov ntsiab lus tuaj yeem pom hauv Maltoni li al. 6). Hauv luv luv, nyob rau hauv tus qauv Rietveld, lub diffraction peaks tau piav qhia los ntawm kev hloov kho Thompson-Cox-Hastings pseudo Voigt muaj nuj nqi. LeBail refinement ntawm cov ntaub ntawv tau ua nyob rau hauv NIST LaB6 660b tus qauv los qhia txog cov cuab yeej pab txhawb rau qhov siab tshaj plaws. Raws li kev suav FWHM (tag nrho dav ntawm ib nrab ntawm qhov siab tshaj plaws), qhov sib npaug Debye-Scherrer tuaj yeem siv los xam qhov ntim-qhov hnyav nruab nrab qhov loj me ntawm qhov sib xyaw ua ke ntawm cov crystalline domain:
Qhov twg λ yog X-ray hluav taws xob wavelength, K yog qhov zoo tshaj plaws (0.8-1.2, feem ntau sib npaug rau 0.9), thiab θ yog lub kaum sab xis Bragg. Qhov no siv rau: qhov kev xaiv xaiv, cov txheej txheem sib txuas ntawm cov dav hlau thiab tag nrho cov qauv (10-90 °).
Tsis tas li ntawd, Philips CM200 microscope ua haujlwm ntawm 200 kV thiab nruab nrog LaB6 filament tau siv rau TEM tsom xam kom tau txais cov ntaub ntawv hais txog particle morphology thiab qhov loj me.
Magnetization relaxation ntsuas yog ua los ntawm ob lub cuab yeej sib txawv: Lub Cev Kev Ntsuas Lub Cev (PPMS) los ntawm Quantum Design-Vibrating Sample Magnetometer (VSM), nruab nrog 9 T superconducting hlau nplaum, thiab MicroSense Model 10 VSM nrog electromagnet. Lub teb yog 2 T, tus qauv yog saturated nyob rau hauv daim teb (μ0HMAX:-5 T thiab 2 T, feem rau txhua qhov ntsuas), thiab tom qab ntawd rov qab teb (HREV) yog siv los coj tus qauv mus rau qhov chaw hloov pauv (ze HC. ), thiab tom qab ntawd Cov hlau nplaum tawg tau kaw ua haujlwm ntawm lub sijhawm dhau 60 feeb. Kev ntsuas yog ua nyob rau ntawm 300 K. Qhov sib txuam ua kom ntim yog ntsuas raws li cov ntsuas ntsuas tau piav qhia hauv cov khoom siv ntxiv.
Muscas, G., Yaacoub, N. & Peddis, D. Sib nqus cuam tshuam hauv cov ntaub ntawv nanostructured. Nyob rau hauv lub tshiab magnetic nanostructure 127-163 (Elsevier, 2018). https://doi.org/10.1016/B978-0-12-813594-5.00004-7.
Mathieu, R. thiab Nordblad, P. Cov cwj pwm sib nqus sib nqus. Hauv cov qauv tshiab ntawm nanoparticle magnetism, nplooj 65-84 (2021). https://doi.org/10.1007/978-3-030-60473-8_3.
Dormann, JL, Fiorani, D. & Tronc, E. Sib nqus so hauv cov txheej txheem zoo. Progress in Chemical Physics, pp. 283-494 (2007). https://doi.org/10.1002/9780470141571.ch4.
Sellmyer, DJ, thiab lwm yam. Cov qauv tshiab thiab physics ntawm nanomagnets (thov caw). J. Daim Ntawv Thov Physics 117, 172 (2015).
de Julian Fernandez, C. thiab lwm yam. Thematic tshuaj xyuas: qhov kev vam meej thiab kev cia siab ntawm hard hexaferrite mus tas li hlau nplaum daim ntaub ntawv. J. Physics. D. Thov rau Physics (2020).
Maltoni, P. thiab lwm yam Los ntawm optimizing lub synthesis thiab sib nqus zog ntawm SrFe12O19 nanocrystals, dual magnetic nanocomposites yog siv raws li cov hlau nplaum mus tas li. J. Physics. D. Thov rau Physics 54, 124004 (2021).
Saura-Múzquiz, M. thiab lwm yam Qhia meej txog kev sib raug zoo ntawm nanoparticle morphology, nuclear / magnetic qauv thiab cov khoom sib nqus ntawm sintered SrFe12O19 hlau nplaum. Nano 12, 9481–9494 (2020).
Petrecca, M. thiab lwm yam. Ua kom zoo dua cov khoom sib nqus ntawm cov khoom siv tawv thiab muag muag rau kev tsim cov khoom sib pauv caij nplooj ntoos hlav hlau nplaum ruaj khov. J. Physics. D. Thov rau Physics 54, 134003 (2021).
Maltoni, P. thiab lwm yam. Kho cov khoom sib nqus ntawm cov tawv-mos SrFe12O19 / CoFe2O4 nanostructures los ntawm kev muaj pes tsawg leeg / theem coupling. J. Physics. Chemistry C 125, 5927–5936 (2021).
Maltoni, P. thiab lwm yam. Tshawb xyuas qhov sib nqus thiab sib nqus ntawm SrFe12O19 / Co1-xZnxFe2O4 nanocomposites. J. Mag. Mag. alma mav. 535, 168095 (2021).
Pullar, RC Hexagonal ferrites: Ib qho kev piav qhia ntawm kev sib txuas, kev ua tau zoo thiab kev siv ntawm hexaferrite ceramics. Kho kom raug. alma mav. kev kawm. 57, 1191–1334 (2012).
Momma, K. & Izumi, F. VESTA: 3D visualization system rau kev txheeb xyuas hluav taws xob thiab cov qauv. J. Applied Process Crystallography 41, 653–658 (2008).
Peddis, D., Jönsson, PE, Laureti, S. & Varvaro, G. Magnetic interaction. Frontiers in Nanoscience, pp. 129-188 (2014). https://doi.org/10.1016/B978-0-08-098353-0.00004-X.
Li, Q. thiab lwm yam Kev sib raug zoo ntawm qhov loj / tus qauv ntawm cov crystalline Fe3O4 nanoparticles thiab cov khoom sib nqus. kev kawm. Tus neeg sawv cev 7, 9894 (2017).
Coey, JMD Sib Nqus thiab cov khoom sib nqus. (Cambridge University Press, 2001). https://doi.org/10.1017/CBO9780511845000.
Lauretti, S. et al. Sib nqus sib nqus hauv silica-coated nanoporous Cheebtsam ntawm CoFe2O4 nanoparticles nrog cubic magnetic anisotropy. Nanotechnology 21, 315701 (2010).
O'Grady, K. & Laidler, H. Cov kev txwv ntawm kev sib nqus cov ntaubntawv povthawj siv-xov xwm xav txog. J. Mag. Mag. alma mav. 200, 616–633 (1999).
Lavorato, GC thiab lwm yam. Cov sib nqus sib nqus thiab lub zog thaiv hauv cov tub ntxhais / plhaub dual sib nqus nanoparticles yog txhim kho. J. Physics. Chemistry C 119, 15755–15762 (2015).
Peddis, D., Cannas, C., Musinu, A. & Piccaluga, G. Sib nqus cov khoom ntawm nanoparticles: dhau qhov cuam tshuam ntawm particle loj. Chemistry ib euro. J. 15, 7822–7829 (2009).
Eikeland, AZ, Stingaciu, M., Mamakhel, AH, Saura-Múzquiz, M. & Christensen, M. Txhim kho cov khoom sib nqus los ntawm kev tswj cov morphology ntawm SrFe12O19 nanocrystals. kev kawm. Tus neeg sawv cev 8, 7325 (2018).
Schneider, C., Rasband, W. thiab Eliceiri, K. NIH Duab rau ImageJ: 25 xyoo ntawm kev txheeb xyuas duab. A. Nat. Txoj Kev 9, 676–682 (2012).
Le Bail, A. & Louër, D. Smoothness thiab validity ntawm crystallite loj faib nyob rau hauv X-ray profile tsom xam. J. Applied Process Crystallography 11, 50-55 (1978).
Gonzalez, JM, thiab lwm yam. Sib nqus viscosity thiab microstructure: particle loj dependence ntawm activation ntim. J. Applied Physics 79, 5955 (1996).
Vavaro, G., Agostinelli, E., Testa, AM, Peddis, D. thiab Laureti, S. hauv ultra-high density magnetic recording. (Jenny Stanford Press, 2016). https://doi.org/10.1201/b20044.
Hu, G., Thomson, T., Rettner, CT, Raoux, S. & Terris, BD Co∕Pd nanostructures thiab zaj duab xis magnetization reversal. J. Application Physics 97, 10J702 (2005).
Khlopkov, K., Gutfleisch, O., Hinz, D., Müller, K.-H. & Schultz, L. Evolution ntawm kev sib koom ua ke hauv ib qho kev ntxhib los mos zoo-grained Nd2Fe14B hlau nplaum. J. Daim Ntawv Thov Physics 102, 023912 (2007).
Mohapatra, J., Xing, M., Elkins, J., Beatty, J. & Liu, JP Size-dependent magnetic hardening in CoFe2O4 nanoparticles: the effect of deg spin tilt. J. Physics. D. Thov rau Physics 53, 504004 (2020).