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Title: Verwey type transition in nano-particle spinel ferrite Fe<sub>2.2</sub>Co<sub>0.8</sub>O<sub>4</sub>
Authors: Chander, Subhash
Krishnamurthy, Anjali
Srivastava, Bipin K
Gupta, Ajay
Nigam, Arun Kumar
Issue Date: Aug-2004
Publisher: CSIR
Series/Report no.: Int. Cl.<sup>7</sup> H01F 10/20
Abstract: Results are presented on magnetization and Mössbauer measurements on two multi-disperse nano-particle samples of Co substituted spinel ferrite Fe<sub>2.2</sub>Co<sub>0.8</sub>O<sub>4</sub> with average particle sizes of ~ 50 Ǻ and ~ 80 Ǻ. In these nono-particle samples Co occupies the octahedral site B with ~ 60% preference. The 50 Ǻ average particle sized sample Co50 is largely in super-paramagnetic state at 300 K and its blocking temperature <i style="">T</i><sub>B  </sub>is<sub> </sub>~ 260 K. 80 Ǻ average particle sized sample Co80 has its <i style="">T</i><sub>B </sub>above 300 K. The two samples exhibit magnetic relaxation. Much smaller moments of the two samples than saturation magnetization for the bulk particle sample and a loop shift observed in <i style="">M</i>-<i style="">H</i> curves of Co50 recorded in zero field and field cooling modes are suggestive of spin disordered surfaces. The nano-particle sample Co80, of the ferrite Fe<sub>2.2</sub>Co<sub>0.8</sub>O<sub>4</sub> which in its bulk particle state is known to have more than an order of magnitude higher magneto-crystalline anisotropy than Fe<sub>3</sub>O<sub>4</sub>, shows signature of a ‘Verwey’ type transition with enhanced magnetic anisotropy below ~ 90 K. Co50 does not show a ‘Verwey’ type transition. A weak hump in <i style="">M</i>-<i style="">T</i> curve at a lower temperature of ~ 50 K in Co50 is attributed to disordered spin freezing.
Description: 343-348
ISSN: 0975-1017 (Online); 0971-4588 (Print)
Appears in Collections:IJEMS Vol.11(4) [August 2004]

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