Evidence of surface spin-glass behavior in NiFe2O4 nanoparticles determined using magnetic resonance technique

Autor: Menchu Martinez, Paulo C. Morais, Jose A. H. Coaquira, J. Mantilla, Paulo Eduardo Narcizo de Souza, Leandro Corrêa Figueiredo, Pedro Augusto Matos Rodrigues, L. León Félix, F. H. Aragón, S.W. da Silva
Rok vydání: 2019
Předmět:
Zdroj: Journal of Magnetism and Magnetic Materials. 476:392-397
ISSN: 0304-8853
DOI: 10.1016/j.jmmm.2019.01.001
Popis: Nanosized nickel ferrite (NiFe2O4) is successfully synthesized by the sol-gel method using citric acid (C6H8O7) as fuel. The X-ray diffraction pattern of the as-synthesized sample shows formation of NiFe2O4 nanoparticles (NPs) as the main phase, with mean crystalline size ∼50 nm. While transmission electron microscopy (TEM) reveals nearly spherical morphology with mean particle diameter of 41 ± 5 nm, high-resolution TEM shows inter-planar distance (2.55 A) corresponding to the (1 1 3) plane of the spinel structure. Additionally, the Raman spectrum exhibits five Raman active modes (two A1g at 575 cm−1 and 710 cm−1; two Eg at 345 cm−1 and 670 cm−1; and one T2g at 497 cm−1) typical of NiFe2O4. X-band magnetic resonance (MR) data reveal a single broad resonance line in the whole temperature range (3.8 K ≤ T ≤ 300 K), with g-value decreasing monotonically from 3.10 ± 0.01 at 3.8 K to 2.77 ± 0.01 at 300 K. The temperature dependence of both resonance field and resonance linewidth show a remarkable change in the range of 60–70 K, herein credited to surface spin-glass behavior. The model picture used to explain the MR data assumes NPs with a core-shell structure. Below about 60–70 K the shell’s spin system progressively reveals a paramagnetic to spin-glass-like transition upon cooling, with a freezing temperature estimated at 2.1 ± 0.1 K. However, above about 60–70 K spins in the paramagnetic shell align along the NP’s core dipolar field, resulting in an effective enlarged nanoparticle size.
Databáze: OpenAIRE
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