Coexistence of Superparmagnetism and Spin-Glass Like Magnetic Ordering Phenomena in a CoFe2O4-SiO2 Nanocomposite
详细信息 查看全文
- 作者：D. Peddis ; C. Cannas ; A. Musinu ; G. Piccaluga
- 刊名：Journal of Physical Chemistry C
- 出版年：2008
- 出版时间：April 3, 2008
- 年：2008
- 卷：112
- 期：13
- 页码：5141 - 5147
- 全文大小：291K
- 年卷期：v.112,no.13(April 3, 2008)
- ISSN：1932-7455
文摘
The effect of interparticle interactions on the magnetic behavior of cobalt ferrite nanoparticles was investigatedin a CoFe2O4/SiO2 nanocomposite with 50 wt % of magnetic phase. A sample of pure cobalt ferrite nanoparticlesprepared by the same method was also studied, as reference. Both samples show irreversible magnetic behavior,when the DC magnetization, M(T), is observed by the zero field cooling-field cooling (ZFC-FC)measurements. For a field higher than 0.2 T, the ZFC curves of the two samples show a maximum and thecorresponding temperature is proportional to the magnetic field raised to the 2/3 power (Tmax 
H2/3). Thisstudy shows that in both samples the MZFC(T) maxima are due to magnetic ordering phenomena rather thansuperparamagnetic blocking, pointing out that strong interactions among particles are present also in thenanocomposite. However, the presence of the silica matrix gives rise to the coexistence of two differentmagnetic behaviors. In fact, a secondary maximum at low temperature is observed in the MZFC(T) curvesmeasured for the silica supported sample. The study of the Tmax vs H2/3 plot of such secondary MZFC(T)maximum shows that it is not due to collective magnetic ordering but rather to a superparamagnetic transitionof a fraction of small nanoparticles. The coexistence of two populations of nanoparticles is in agreement withMössbauer spectroscopy and TEM analysis.
H2/3). Thisstudy shows that in both samples the MZFC(T) maxima are due to magnetic ordering phenomena rather thansuperparamagnetic blocking, pointing out that strong interactions among particles are present also in thenanocomposite. However, the presence of the silica matrix gives rise to the coexistence of two differentmagnetic behaviors. In fact, a secondary maximum at low temperature is observed in the MZFC(T) curvesmeasured for the silica supported sample. The study of the Tmax vs H2/3 plot of such secondary MZFC(T)maximum shows that it is not due to collective magnetic ordering but rather to a superparamagnetic transitionof a fraction of small nanoparticles. The coexistence of two populations of nanoparticles is in agreement withMössbauer spectroscopy and TEM analysis.