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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 CodeInt. 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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