Europhys. Lett.
Volume 75, Number 4, August 2006
Page(s) 618 - 623
Section Condensed matter: electronic structure, electrical, magnetic, and optical properties
Published online 12 July 2006
Europhys. Lett., 75 (4), pp. 618-623 (2006)
DOI: 10.1209/epl/i2006-10148-y

Deviation from Bloch $\mth{T^{3 / 2}}$ law in ferrite nanoparticles

K. Mandal, Subarna Mitra and P. Anil Kumar

Magnetism Laboratory, S. N. Bose National Centre for Basic Sciences Block JD, Sector III - Salt Lake, Kolkata 700 098, India

received 17 February 2006; accepted in final form 27 June 2006
published online 12 July 2006

The temperature dependence of saturation magnetization of ferrite nanoparticles has been studied to investigate the applicability of Bloch spin-wave theory to the finite-size systems. T3/2 law is valid above ~75$\un{K}$ for the smallest ferrite particles obtained in this experiment having size of ~2.5$\un{nm}$. The region of validity of Bloch law increases at the lower-temperature end with the increase in particle size and interparticle interactions. The anomaly from the spin-wave theory has been observed with an upturn at low temperature, which can be explained by considering the quantization of spin-wave spectrum due to the finite size of the particles.

75.30.Ds - Spin waves.
75.50.Gg - Ferrimagnetics.
75.50.Tt - Fine-particle systems; nanocrystalline materials.

© EDP Sciences 2006