Tunable single-phase magnetic behavior in chemically synthesized AFeO3-MFe2O4 (A = Bi or La, M = Co or Ni) nanocomposites

Magnetic nanocomposite for lead (II) removal from water

A magnetic perovskite-spinel oxide nanocomposite synthesized through a sol-gel self-combustion process is used for the first time as an adsorbent to remove toxic heavy metals (i.e., Pb2+). The synthesized LaFeO3:CoFe2O4 ((LFO)1:(CFO)x) (x = 0.11-0.87) nanocomposites possess good stability, abundant oxygenated active binding sites, and unique structural features, making them suitable for removing divalent Pb2+ ions. Scanning electron microscopy, X-ray diffraction, BET surface area, magnetization measurements, zeta-potential analyses, and X-ray photoelectron spectroscopy were used to analyze the nanocomposites, and their structural changes after Pb2+ ions adsorption. Batch tests confirmed that (LFO)1:(CFO)x efficiently removes Pb2+ from water with a maximum adsorption capacity of 105.96 mg/g. The detailed quantitative study indicates that the interaction of hydroxyl groups with Pb2+ ions occurs through electrostatic interactions and complex formation. We also demonstrate a new ring-magnetic separator system that allows magnetic separation of the toxic ions at a higher speed compared to traditional block magnets. The unique structure, high porosity, large specific surface area, and oxygenated functional groups of (LFO)1:(CFO)x nanocomposites make them promising materials for removal of heavy metal ions and possibly other environmental pollutants. This study provides a new approach to preparing nanocomposites of magnetic spinel ferrites with perovskite oxides for environmental applications.

Combined Bottom-Up and Top-Down Approach for Highly Ordered One-Dimensional Composite Nanostructures for Spin Insulatronics

Engineering magnetic proximity effects-based devices requires developing efficient magnetic insulators. In particular, insulators, where magnetic phases show dramatic changes in texture on the nanometric level, could allow us to tune the proximity-induced exchange splitting at such distances. In this paper, we report the fabrication and characterization of highly ordered two-dimensional arrays of LaFeO3 (LFO)-CoFe2O4 (CFO) biphasic magnetic nanowires, grown on silicon substrates using a unique combination of bottom-up and top-down synthesis approaches. The regularity of the patterns was confirmed using atomic force microscopy and scanning electron microscopy techniques, whereas magnetic force microscopy images established the magnetic homogeneity of the patterned nanowires and absence of any magnetic debris between the wires. Transmission electron microscopy shows a close spatial correlation between the LFO and CFO phases, indicating strong grain-to-grain interfacial coupling, intrinsically different from the usual core-shell structures. Magnetic hysteresis loops reveal the ferrimagnetic nature of the composites up to room temperature and the presence of a strong magnetic coupling between the two phases, and electrical transport measurements demonstrate the strong insulating behavior of the LFO-CFO composite, which is found to be governed by Mott-variable range hopping conduction mechanisms. A shift in the Raman modes in the composite sample compared to those of pure CFO suggests the existence of strain-mediated elastic coupling between the two phases in the composite sample. Our work offers ordered composite nanowires with strong interfacial coupling between the two phases that can be directly integrated for developing multiphase spin insulatronic devices and emergent magnetic interfaces.

The role of chemical and microstructural inhomogeneities on interface magnetism

The study of interfacing effects arising when different magnetic phases are in close contact has led to the discovery of novel physical properties and the development of innovative technological applications of nanostructured magnetic materials. Chemical and microstructural inhomogeneities at the interfacial region, driven by interdiffusion processes, chemical reactions and interface roughness may significantly affect the final properties of a material and, if suitably controlled, may represent an additional tool to finely tune the overall physical properties. The activity at the Nanostructured Magnetic Materials Laboratory (nM²-Lab) at CNR-ISM of Italy is aimed at designing and investigating nanoscale-engineered magnetic materials, where the overall magnetic properties are dominated by the interface exchange coupling. In this review, some examples of recent studies where the chemical and microstructural properties are critical in determining the overall magnetic properties in core/shell nanoparticles, nanocomposites and multilayer heterostructures are presented.

High Magnetic Field Sensitivity in Ferromagnetic-Ferroelectric Composite with High Mechanical Quality Factor

In this study, composite devices were fabricated using ferromagnetic FeSiB-based alloys (Metglas) and ferroelectric ceramics, and their magnetic field sensitivity was evaluated. Sintered 0.95Pb(Zr_0.52Ti_0.48)O₃-0.05Pb(Mn_1/3Sb_2/3)O₃ (PZT-PMS) ceramic exhibited a very dense microstructure with a large piezoelectric voltage coefficient (g₃₁ = −16.8 × 10⁻³ VmN⁻¹) and mechanical quality factor (Q_m > 1600). Owing to these excellent electromechanical properties of the PZT-PMS, the laminate composite with a Metglas/PZT-PMS/Metglas sandwich structure exhibited large magnetoelectric voltage coefficients (α_ME) in both off-resonance and resonance modes. When the length-to-width aspect ratio (l/w) of the composite was controlled, α_ME slightly varied in the off-resonance mode, resulting in similar sensitivity values ranging from 129.9 to 146.81 VT⁻¹. Whereas in the resonance mode, the composite with small l/w exhibited a large reduction of α_ME and sensitivity values. When controlling the thickness of the PZT-PMS (t), the α_ME of the composite showed the largest value when t was the smallest in the off-resonance mode, while α_ME was the largest when t is the largest in the resonance mode. The control of t slightly affected the sensitivity in the off-resonance mode, however, higher sensitivity was obtained as t increased in the resonance mode. The results demonstrate that the sensitivity, varying with the dimensional control of the composite, is related to the mechanical loss of the sensor. The composite sensor with the PZT-PMS layer exhibited excellent magnetic field sensitivity of 1.49 × 10⁵ VT⁻¹ with a sub-nT sensing limit, indicating its potential for application in high-performance magnetoelectric sensor devices.

A first-principles study on the magnetoelectric coupling induced by Fe in a two-dimensional BaTiO3(001) ultrathin film

A first-principles approach is utilized to study the magnetoelectric coupling induced by Fe in two-dimensional BaTiO₃(001) ultrathin film. It is observed that the Fe impurity increases the total magnetic moment but suppresses the spontaneous polarization. Furthermore, the total magnetic moment of Fe replacing Ti is influenced by the distance between dopants and decreases with reducing distance. A study of spin-orbit coupling under bi-axial compressive strain shows strong magnetoelectric coupling with Ti substitution and the configuration with neighbouring Fe is more readily adjusted than that with Fe distant from each other. Meanwhile, the replacement of Ba exhibits negligible interaction between spontaneous polarization and magnetic moment. Clearly, our current work may indicate that the careful substitution of Ti with Fe atoms can realize two-dimensional BaTiO₃ behaving as a multiferroic material.

Symbiotic, low-temperature, and scalable synthesis of bi-magnetic complex oxide nanocomposites

Functional oxide nanocomposites, where the individual components belong to the family of strongly correlated electron oxides, are an important class of materials, with potential applications in several areas such as spintronics and energy devices. For these materials to be technologically relevant, it is essential to design low-cost and scalable synthesis techniques. In this work, we report a low-temperature and scalable synthesis of prototypical bi-magnetic LaFeO₃-CoFe₂O₄ nanocomposites using a unique sol-based synthesis route, where both the phases of the nanocomposite are formed during the same time. In this bottom-up approach, the heat of formation of one phase (CoFe₂O₄) allows the crystallization of the second phase (LaFeO₃), and completely eliminates the need for conventional high-temperature annealing. A symbiotic effect is observed, as the second phase reduces grain growth of the first phase, thus yielding samples with lower particle sizes. Through thermogravimetric, structural, and morphological studies, we have confirmed the reaction mechanism. The magnetic properties of the bi-magnetic nanocomposites are studied, and reveal a distinct effect of the synthesis conditions on the coercivity of the particles. Our work presents a basic concept of significantly reducing the synthesis temperature of bi-phasic nanocomposites (and thus also the synthesis cost) by using one phase as nucleation sites for the second one, as well as using the heat of formation of one phase to crystallize the other.

Controlling magnetic coupling in bi-magnetic nanocomposites

Magnetic nanocomposites constitute a vital class of technologically relevant materials, in particular for next-generation applications ranging from biomedicine, catalysis, and energy devices. Key to designing such materials is determining and controlling the extent of magnetic coupling in them. In this work, we show how the magnetic coupling in bi-magnetic nanocomposites can be controlled by the growth technique. Using four different synthesis strategies to prepare prototypical LaFeO3-CoFe2O4 and LaFeO3-Co0.5Zn0.5Fe2O4 nanocomposite systems, and by performing comprehensive magnetic measurements, we demonstrate that the final material exhibits striking differences in their magnetic coupling that is distinct to the growth method. Through structural and morphological studies, we confirm the link between the magnetic coupling and growth methods due to distinct levels of particle agglomeration at the very microscopic scale. Our studies reveal an inverse relationship between the strength of magnetic coupling and the degree of particle agglomeration in the nanocomposites. Our work presents a basic concept of controlling the particle agglomeration to tune magnetic coupling, relevant for designing advanced bi-magnetic nanocomposites for novel applications.