Reversed (Negative) Magnetization for Electrochemically Deposited High-Tc Thin Films of Chromium Hexacyanide Magnets
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- 作者：Wayne E. Buschmann ; Scott C. Paulson ; Charles M. Wynn ; Mihai A. Girtu ; Arthur J. Epstein ; Henry S. White ; and Joel S. Miller
- 刊名：Chemistry of Materials
- 出版年：1998
- 出版时间：May 1998
- 年：1998
- 卷：10
- 期：5
- 页码：1386 - 1395
- 全文大小：194K
- 年卷期：v.10,no.5(May 1998)
- ISSN：1520-5002
文摘
Thin films of chromium cyanide Prussian blue-like materials,KnCrx[Cr(CN)6](ca. 1.0 ±0.5 
m thick) are electrodeposited on glassy carbon electrodes inamorphous (a) andcrystalline (
) forms. The crystalline film shows a X-raydiffraction pattern typical of aface-centered cubic (fcc) Prussian blue-type cubic lattice[a = 10.41(2) Å]. The filmsexhibitquasi-reversible cyclic voltammetric waves, distinct morphologies inSEM images, and strongfield-dependent magnetic behavior. The films undergo twoone-electron processes,CrII[CrII(CN)6]2-
CrIII[CrII(CN)6]-+ e-, andCrIII[CrII(CN)6]- CrIII[CrIII(CN)6]+ e-, withsome residual CrII being present. The composition isdetermined from an analysis of the
CN IR data{[CrII(CN)6]4-:CN = 2072s cm-1;[CrIII(CN)6]3-:CN = 2185m cm-1} andX-rayphotoelectron (XPS) spectral data. The composition of the oxidizedand reduced films areCrIII[CrIII(CN)6]0.98[CrII(CN)6]0.02andK2.0CrII[CrII(CN)6],respectively, for both amorphous andcrystalline forms. These materials exhibit broad intervalencecharge-transfer bands in theiroxidized [
max = 18 800cm-1 (
~ 1280cm-1 M-1); 35 500cm-1 ( ~ 1180cm-1 M-1)]andreduced [max = 20 200 cm-1( ~ 870 cm-1M-1); 36 700 cm-1( ~ 770 cm-1M-1)] forms.The crystal field splitting 
o's forCrII(NC)6 andCrIII(NC)6 are 19 500 and 26 600cm-1,respectively. The magnetic ordering temperatures,Tc, are a function of Cr oxidationstateand range between 135 and 260 K for both film types. TheTc's are independent ofcrystallinity, suggesting that the magnetic domains are smaller thanthe short-rangestructural order for both a- and -films. Hysteresis is observedfor the films, with coercivefields as high as 830 Oe at 20 K, confirming the existence of bulkferrimagnetic behaviorbelow Tc. We determined that the coercivityof the amorphous films is larger than that ofthe crystalline films and suggest that this due to the larger number ofdefects in the a-films.
m thick) are electrodeposited on glassy carbon electrodes inamorphous (a) andcrystalline () forms. The crystalline film shows a X-raydiffraction pattern typical of aface-centered cubic (fcc) Prussian blue-type cubic lattice[a = 10.41(2) Å]. The filmsexhibitquasi-reversible cyclic voltammetric waves, distinct morphologies inSEM images, and strongfield-dependent magnetic behavior. The films undergo twoone-electron processes,CrII[CrII(CN)6]2-CrIII[CrII(CN)6]-+ e-, andCrIII[CrII(CN)6]- CrIII[CrIII(CN)6]+ e-, withsome residual CrII being present. The composition isdetermined from an analysis of theCN IR data{[CrII(CN)6]4-:CN = 2072s cm-1;[CrIII(CN)6]3-:CN = 2185m cm-1} andX-rayphotoelectron (XPS) spectral data. The composition of the oxidizedand reduced films areCrIII[CrIII(CN)6]0.98[CrII(CN)6]0.02andK2.0CrII[CrII(CN)6],respectively, for both amorphous andcrystalline forms. These materials exhibit broad intervalencecharge-transfer bands in theiroxidized [max = 18 800cm-1 ( ~ 1280cm-1 M-1); 35 500cm-1 ( ~ 1180cm-1 M-1)]andreduced [max = 20 200 cm-1( ~ 870 cm-1M-1); 36 700 cm-1( ~ 770 cm-1M-1)] forms.The crystal field splitting o's forCrII(NC)6 andCrIII(NC)6 are 19 500 and 26 600cm-1,respectively. The magnetic ordering temperatures,Tc, are a function of Cr oxidationstateand range between 135 and 260 K for both film types. TheTc's are independent ofcrystallinity, suggesting that the magnetic domains are smaller thanthe short-rangestructural order for both a- and -films. Hysteresis is observedfor the films, with coercivefields as high as 830 Oe at 20 K, confirming the existence of bulkferrimagnetic behaviorbelow Tc. We determined that the coercivityof the amorphous films is larger than that ofthe crystalline films and suggest that this due to the larger number ofdefects in the a-films.