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Indian Journal of Engineering and Materials Sciences (IJEMS) >
IJEMS Vol.11 [2004] >
IJEMS Vol.11(4) [August 2004] >
| Title: | Verwey type transition in nano-particle spinel ferrite Fe2.2Co0.8O4 |
| Authors: | Chander, Subhash
Krishnamurthy, Anjali
Srivastava, Bipin K
Gupta, Ajay
Nigam, Arun Kumar |
| Issue Date: | Aug-2004 |
| Publisher: | CSIR |
| IPC Code: | Int. Cl.7 H01F 10/20 |
| Abstract: | Results are presented on magnetization and Mössbauer
measurements on two multi-disperse nano-particle samples of Co substituted
spinel ferrite Fe2.2Co0.8O4 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 TB is ~ 260 K. 80 Ǻ average
particle sized sample Co80 has its TB
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 M-H 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 Fe2.2Co0.8O4
which in its bulk particle state is known to have more than an order of
magnitude higher magneto-crystalline anisotropy than Fe3O4,
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 M-T
curve at a lower temperature of ~ 50 K in Co50 is attributed to disordered spin
freezing. |
| Page(s): | 343-348 |
| ISSN: | 0975-1017 (Online); 0971-4588 (Print) |
| Source: | IJEMS Vol.11(4) [August 2004]
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