Abstract
In order to prominently investigate the effects of the surface spin on the magnetic properties, the weak magnetic ZnLa0.02Fe1.98O4 nanoparticles were chosen as studying objects which benefit to reduce as possibly the effects of interparticle dipolar interaction and crystalline anisotropy energies. By annealing the undiluted and diluted ZnLa0.02Fe1.98O4 nanoparticles at different temperatures, we observed the rich variations of magnetic ordering states (superparamagnetism, weak ferromagnetism, and paramagnetism). The magnetic properties can be well understood by considering the effects of the surface spin of the magnetic nanoparticles. Our results indicate that in the nano-sized magnets with weak magnetism, the surface spin plays a crucial rule in the magnetic properties.
Highlights
Ferrite nanocrystals have been extensively studied due to their tunable and remarkable magnetic properties as well as catalytic properties not existing in the corresponding bulk materials [1,2,3,4,5]
Our results indicate that the surface spins significantly affect the macromagnetism of ZLFO NPs
The ZLFO NPs were synthesized by the hydrothermal method
Summary
Ferrite nanocrystals have been extensively studied due to their tunable and remarkable magnetic properties as well as catalytic properties not existing in the corresponding bulk materials [1,2,3,4,5]. In the fundamental research field, magnetic nanoparticles (NPs) usually serve as ideal model systems, e.g., the Stoner-Wohlfarth [6,7] and Néel-Brown model [8], or to study the finite-size effect [9]. 36 mmol Zn(NO3)2 · 6H2O, 72 mmol Fe(NO3)3 · 6H2O, 7.2 mmol La(OOCCH3)3 · 1.5H2O, and 108 mmol C2H3NaO2 · 3H2O were dissolved in 300-mL anhydrous C2H6O2 with magnetic stirring. The solution was transferred into 50-ml Teflon-lined stainless steel autoclave and maintained at 200°C for 24 h to obtain the ZLFO NPs. The typical synthesis procedure can be shown by the following [20]: Zn(NO3)2 · 6H2O + 0.02 La(OOCCH3)3 · 1.5H2O + 1.98 Fe(NO3)3 · 6H2O + C2H3NaO2 · 3H2O + C2H6O2 → ZnLa0.02 Fe1.98(OOCH2CH3)8 · nH2O + NaNO3. The obtained ZLFO NPs were divided into two parts. High-resolution transmission electron microscopy (HRTEM) (JEOL JEM-2100, JEOL, Akishima-shi, Tokyo, Japan) was used to observe the morphology, selected area electronic diffraction (SAED), and lattice fringes
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