Field-dependent low-field enhancement in effective paramagnetic moment with nanoscaled Co 3 O 4

• Published in: Journal of applied physics 2010-10, Vol.108 (7), p.073907-073907-5
• Main Authors: Chen, Weimeng, Chen, Chinping, Guo, Lin
• Format: Article
• ISSN: 0021-8979; 1089-7550
• DOI: 10.1063/1.3475249

Paramagnetic (PM) properties of columnar cobaltosic oxide ( Co 3 O 4 ) nanoparticles, about 75 nm in diameter, have been investigated by magnetization measurements at T > T N = 39   K . In zero or low applied field, the effective PM moment per formula unit (FU), μ eff , enhances significantly from the bulk value of 4.14   μ B / FU . It decreases asymptotically from 5.96   μ B / FU at H app = 50   Oe down to 4.21   μ B / FU as the applied field increases to H app = 10   kOe . The field-dependent PM properties are explained by a structural inversion, from the normal spinel (spin-only moment ∼ 3.9   μ B / FU ) to the inverse spinel structure (spin-only moment ∼ 8.8   μ B / FU ). The structural inversion is reversible with the variation in the applied field. The lattice structure becomes almost 100% normal spinel in the high field exceeding 10 kOe, as revealed by the magnitude of the effective PM moment. The reversible, field-dependent structure inversion is an important property with promising application potential. It is interesting for the future investigations.