Structural, Magnetic, and Electronic Properties of Mixed Spinel NiFe_2–xCr_xO₄ Nanoparticles Synthesized by Chemical Combustion

Abstract

A series of nickel-chromium-ferrite NiFeCrO (with x = 1.25) nanoparticles (NPs) with a cubic spinel structure and with size d ranging from 1.6 to 47.7 nm was synthesized by the solution combustion method. A dual structure of all phonon modes revealed in Raman spectra is associated with metal cations of different types present in the spinel lattice sites. Mössbauer spectra of small NPs exhibit superparamagnetic behavior. However, the transition into the paramagnetic state occurs at a temperature that is unusually high for small particles (T is about 240 K in the d = 4.5 nm NPs). The larger NPs with d > 20 nm do not exhibit superparamagnetic properties up to the Neel temperature. From the magnetic and Mössbauer data, the cation occupation of the tetrahedral (A) and octahedral [B] sites was determined (FeNi)[NiCr]O. The saturation magnetization M in the largest NPs is about (0.98-0.95) μ, which is more than twice higher the value in bulk ferrite (Fe)[CrNi]O. At low temperatures the total magnetic moment of the ferrite coincides with the direction of the B-sublattice moment. In the NPs with d > 20 nm, the compensation of the magnetic moments of A- and B-sublattices was revealed at about T = 360-365 K. This value significantly exceeds the point T in bulk ferrites NiFeCrO (about 315 K) with the similar Cr concentration. However, in the smaller NPs NiFeCrO with d ≤ 11.7 nm, the compensation effect does not occur. The magnetic anomalies are explained in terms of highly frustrated magnetic ordering in the B sublattice, which appears due to the competition of AFM and FM exchange interactions and results in a canted magnetic structure.

Magnetic properties of Sn- and Mn-incorporated Co2TiO4 from single-step calcination

“…They can merge, resulting in the Raman line broadening. 50 The XPS results of CTO are presented in Fig. S6 (ESI †).…”

“…57 The compensation temperature sometimes depends on the product's crystallite size. 50 The magnetic ions in these spinels result in several exchange interactions in the sublattices that differ in sign and strength. Our samples are intrinsically disordered or frustrated due to the competing magnetic interactions in the B sublattice.…”

Correlation between Cation Distribution and Magnetic and Dielectric Properties of Dy3+-Substituted Fe-Rich Cobalt Ferrite

“…Spinel ferrites continue to attract the attention of the scientific and research community for the design and development of smart materials for application in numerous technologies. − All spinel ferrites, which can be represented by the universal chemical formula MFe 2 O 4 (where Fe exists in the trivalent state (Fe 3+ ), and “M” represents divalent cations such as Zn 2+ , Ni 2+ , Co 2+ , etc. ), crystallize (see Figure ) in the Fd 3̅ m space group. , By virtue of tunable magnetic properties and the ability to obtain materials with variable morphology and magnetic behavior, cobalt ferrites (CFO) have been subjected to extensive studies in recent years.…”

“…Furthermore, cobalt ferrite, owing to its magnetocrystalline anisotropy, high coercivity, and chemical stability, has been used widely in automotive and environmental engineering. , In these fields, special attention is given to device applications, such as sensors, environmental protection, catalysis, microwave absorption, etc . However, the properties and performance characteristics of these ferrites are dependent on the structure, chemistry, and cation distribution, which in turn depend on the methods of preparation, processing conditions, and dopant ions (if any). − ,, Most importantly, the structural, magnetic, electrical, and dielectric properties of spinel ferrite materials greatly depend on the chemistry and precise distribution of cations. ,, Furthermore, in the spinel ferrite system, which exhibits two crystallographically distinguishable sublattices such as tetrahedral site (A-site) and octahedral site (B-site) (Figure ) in the general MFe 2 O 4 spinel structure, the distribution of cations is also highly important, especially when using other dopant ions to derive tunable properties. , Structurally, depending on the distribution of cations at tetrahedral or octahedral sites (Figure ), the resulting material may be in a normal, inverse, or mixed spinel structure.…”

Nanoscale Metastable ε-Fe3N Ferromagnetic Materials by Self-Sustained Reactions

“…The proposed method is based on the concept of solution combustion synthesis (SCS). The SCS approach has attracted substantial attention as a simple route for fabrication of nanostructured materials. − A typical SCS formulation includes preparation of homogeneous solutions of an oxidizer (metal nitrates) and organic fuel (e.g., glycine, urea, citric acid) in a solvent and placing the solutions in a preheated muffle furnace or on a hot plate. ,− After evaporation of the solvent, a viscous gel-like material forms, and initiation of the combustion reaction yields a porous solid and a significant amount of gases. This regime of an exothermic reaction is known as volume combustion .…”