Enhancement of Magnetization through Interface Exchange Interactions of Confined NiO Nanoparticles within the Mesopores of CoFe₂O₄

Abstract

A bimagnetic nanostructure was designed where the antiferromagnetic (AFM) NiO nanoparticles (NPs) are confined within the pores of a mesoporous ferrimagnetic (FiM) CoFe2O4 matrix. An amount of 3.4 wt % of 9 ± 1 nm NiO NPs was inserted into pores of 35 ± 5 nm clustered CoFe2O4 NPs when the −NH3 + groups of cysteamine on the NiO NP surface electrostatically bind to the −OSO3 – of sodium dodecyl sulfate (SDS) attached to CoFe2O4 NPs. The role of in situ embedded NiO NPs is 3-fold: (i) to nearly double the saturation magnetization (M S) and coercivity (H C) by suppressing the frozen disordered spins on the surface of CoFe2O4 NPs surrounding the NiO NPs inside the pores at the cost of enhanced FiM ordering, (ii) to introduce AFM/FiM exchange coupling by breaking the spin glass surface layer to provide exchange bias (EB) of 233.0 ± 0.2 Oe at 5 K with a cooling field of 2 T, and (iii) to provide symmetry to the asymmetric nature of the hysteresis loop of CoFe2O4. In the absence of cooling field, the pristine CoFe2O4 NP porous matrix shows hysteresis loop shifts of >1000 Oe and asymmetric magnetization reversal which are uncommon in spinel oxides.

Efficient Dye Degradation Catalyzed by Manganese Oxide Nanoparticles and the Role of Cation Valence

“…The catalytic activity usually depends on the available active sites which is directly proportional to the specific surface area of the NP catalysts . Figure shows the nitrogen adsorption‐desorption isotherms at 77 K. According to IUPAC classification, Mn 3 O 4 , MnO and δ‐MnO 2 show Type IV isotherm with H2 hysteresis loop for Mn 3 O 4 and MnO and H4type loop for δ‐MnO 2 , in the 0.5‐0.8 relative pressure (P/P 0 ) range which suggests that capillary condensation occurs inside the mesopore with a narrow pore distribution of 3.6‐3.9 nm (Figure insets), corroborating the TEM observations of Figure .…”

Oxygen‐Defect‐Rich Cobalt Ferrite Nanoparticles for Practical Water Electrolysis with High Activity and Durability

“…The formation of as-prepared CoFe 2 O 4 (AP-CoFe 2 O 4 )N Ps by the coprecipitation techniquei ss chematically illustrated in Figure 1a.F igure 1b shows the FESEM image of AP-CoFe 2 O 4 NPs, the well-definedc rystallinity of which is already shown from the Rietveld-refinedX RD pattern in our previous work on the magnetism of thesea s-prepared NPs. [36] AP-CoFe 2 O 4 was calcined under N 2 at 350, 550, and 650 8Cf or 5h to obtain samples CoF-1, CoF-2, and CoF-3, respectively.T he calcined NPs crystallize in the spinel structure with space group Fd3 m,a ccording to JCPDS card no. 22-1086 ( Figure 1c).…”

“…Adapting the synthetic protocol partly from our earlier report, [36] CoCl 2 •6H 2 O( 0.95 g) and FeCl 2 •4H 2 O( 1.58 g) were added to a1 m aqueous solution of SDS (5 mL) and stirred at RT.T he solution temperature was increased to 80 8Cu nder continuous stirring and an excess quantity of ah ot solution of NH 4 OH was added to the solution of mixed-metal chloride until the color turned green. Within a few minutes, the slurry turned brown.…”

Tweaking Nickel with Minimal Silver in a Heterogeneous Alloy of Decahedral Geometry to Deliver Platinum‐like Hydrogen Evolution Activity

“…During synthesis, DDD helps in forming the anisotropic structure by lowering the difference in redox pair potentials of Ag + /Ag 0 and Ni 2+ /Ni 0 , which otherwise forms a core–shell morphology by faster reduction of Ag than Ni (Supporting Information, Figure S11) . Both DDD and TBAP stabilize the hetero‐alloy structures even though OAm triggers the rate of nucleation . Without OAc and OAm, larger circa 100 nm NCs are obtained and absence of TBAP leads to Ag and Ni phase segregation.…”