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Hybrid nanocomposites of nickel nanoparticles (Ni NPs) embedded in a carbon matrix hold significant promise for environmental remediation by integrating the adsorption capacity of carbon with the antimicrobial effects induced by localized heating of Ni NPs under magnetic hyperthermia. In this work, we investigate the evolution of the structural, magnetic and thermal properties of Ni@C nanocomposites as a function of the carbonization temperature. Samples within the magnetic single domain and multidomain regimes have been used to explore their potential for magnetic hyperthermia-assisted water remediation. To assess the influence of these different regimes on the tranverse suscepbility (TS) and magnetic heating performance, two representative samples, S600 and S1000, were selected to span the single-domain to multi-domain particle regimes. TS measurements show that S1000 exhibits a higher effective anisotropy field (HKeff ), attributed to its larger particle size and enhanced magnetic anisotropy. However, calorimetric magnetic heating studies reveal that S600 demonstrates significantly higher specific absorption rate (SAR) and intrinsic loss power (ILP) values, especially at lower concentrations. This enhanced heating efficiency is linked to its smaller particle size, reduced dipolar interactions, and magnetically soft behavior at room temperature. Consequently, more effective magnetic relaxation under moderate fields is enabled, highlighting the importance of optimizing nanoparticle size, anisotropy, and matrix dispersion to improve magnetic heating performance, offering design strategies for non-biomedical applications such as water purification and microbial inactivation. 

ABSTRACT While broadband electromagnetic (EM) loss mechanisms have critical implications for both electromagnetic absorbers and magnetic hyperthermia, integrating diverse loss channels into single material architecture remains a key challenge for next‐generation multifunctional composites. Herein, we introduce carbon confinement of Cobalt Ferrite nanoparticles (CFO@C) as a design principle to simultaneously address the performance‐processability trade‐off for broadband functionality. Mesoporous activated carbon acts as a reactive template that constrains CFO nanoparticle growth (), mitigates agglomeration, and provides conductive pathways for complementary dielectric response (ε). Static magnetometry reveals complex magnetic behavior driven by coexisting hard and soft phases, which is quantitatively resolved using Voigt‐profile deconvolution of the wasp‐waisted hysteresis loops, enabling phase‐resolved analysis of reversal processes. Ferromagnetic Resonance (18–30 GHz) reveals a stable g‐factor and large damping (α  =  0.14) indicative of efficient GHz‐frequency energy dissipation governed by spin–lattice relaxation. Low‐frequency magnetic hyperthermia validates linear‐response relaxation as the dominant loss channel under physiological field conditions (310 kHz, 400–800 Oe). These results establish CFO@C as a multifunctional nanocomposite that unifies broadband EM dissipation with efficient low‐frequency heating, establishing the pathway for μ − ε co‐design in frequency‐adaptive materials relevant to printed electronics, EMI mitigation, and magnetically driven functional devices. 

Tailoring the magnetic properties of iron oxide nanosystems is essential to expanding their biomedical applications. In this study, 34 nm iron oxide nanocubes with two phases consisting of Fe3O4 and α-Fe2O3 were annealed for 2 h in the presence of O2, N2, He, and Ar to tune the respective phase volume fractions and control their magnetic properties. X-ray diffraction and magnetic measurements were carried out post-treatment to evaluate changes in the treated samples compared to the as-prepared samples, showing an enhancement of the α-Fe2O3 phase in the samples annealed with O2 while the others indicated a Fe3O4 enhancement. Furthermore, the latter samples indicated enhancements in crystallinity and saturation magnetization, while coercivity enhancements were the most significant in samples annealed with O2, resulting in the highest specific absorption rates (of up to 1000 W/g) in all the applied fields of 800, 600, and 400 Oe in agar during magnetic hyperthermia measurements. The general enhancement of the specific absorption rate post-annealing underscores the importance of the annealing atmosphere in the enhancement of the magnetic and structural properties of nanostructures. 

The inherent existence of multi phases in iron oxide nanostructures highlights the significance of them being investigated deliberately to understand and possibly control the phases. Here, the effects of annealing at 250 °C with a variable duration on the bulk magnetic and structural properties of high aspect ratio biphase iron oxide nanorods with ferrimagnetic Fe3O4 and antiferromagnetic α-Fe2O3 are explored. Increasing annealing time under a free flow of oxygen enhanced the α-Fe2O3 volume fraction and improved the crystallinity of the Fe3O4 phase, identified in changes in the magnetization as a function of annealing time. A critical annealing time of approximately 3 h maximized the presence of both phases, as observed via an enhancement in the magnetization and an interfacial pinning effect. This is attributed to disordered spins separating the magnetically distinct phases which tend to align with the application of a magnetic field at high temperatures. The increased antiferromagnetic phase can be distinguished due to the field-induced metamagnetic transitions observed in structures annealed for more than 3 h and was especially prominent in the 9 h annealed sample. Our controlled study in determining the changes in volume fractions with annealing time will enable precise control over phase tunability in iron oxide nanorods, allowing custom-made phase volume fractions in different applications ranging from spintronics to biomedical applications. 

We investigate the spatial distribution of spin orientation in magnetic nanoparticles consisting of hard and soft magnetic layers. The nanoparticles are synthesized in a core–shell spherical morphology where the target stoichiometry of the magnetically hard, high anisotropy layer is CoFe2O4 (CFO), while the synthesis protocol of the lower anisotropy material is known to produce Fe3O4. The nanoparticles have a mean diameter of ∼9.2–9.6 nm and are synthesized as two variants: a conventional hard/soft core–shell structure with a CFO core/FO shell (CFO@FO) and the inverted structure FO core/CFO shell (FO@CFO). High-resolution electron microscopy confirms the coherent spinel structure across the core–shell boundary in both variants, while magnetometry indicates the nanoparticles are superparamagnetic at 300 K and develop a considerable anisotropy at reduced temperatures. Low-temperature M vs H loops suggest a multistep reversal process. Small angle neutron scattering (SANS) with full polarization analysis reveals a considerable alignment of the spins perpendicular to the field even at fields approaching saturation. The perpendicular magnetization is surprisingly correlated from one nanoparticle to the next, though the interaction is of limited range. More significantly, the SANS data reveal a pronounced difference in the reversal process of the magnetization parallel to the field for the two nanoparticle variants. For the CFO@FO nanoparticles, the core and shell magnetizations appear to track each other through the coercive region, while in the FO@CFO variant, the softer Fe3O4 core reverses before the higher anisotropy CoFe2O4 shell, consistent with expectations from mesoscale magnetic modeling. These results highlight the interplay between interfacial exchange coupling and anisotropy as a means to tune the composite properties of the nanoparticles for tailored applications including biomedical/theranostic uses. 

The magnetic proximity effect (MPE) has recently been explored to manipulate interfacial properties of two-dimensional (2D) transition metal dichalcogenide (TMD)/ferromagnet heterostructures for use in spintronics and valleytronics. However, a full understanding of the MPE and its temperature and magnetic field evolution in these systems is lacking. In this study, the MPE has been probed in Pt/WS2/BPIO (biphase iron oxide, Fe3O4 and α-Fe2O3) heterostructures through a comprehensive investigation of their magnetic and transport properties using magnetometry, four-probe resistivity, and anomalous Hall effect (AHE) measurements. Density functional theory (DFT) calculations are performed to complement the experimental findings. We found that the presence of monolayer WS2 flakes reduces the magnetization of BPIO and hence the total magnetization of Pt/WS2/BPIO at T > ~120 K—the Verwey transition temperature of Fe3O4 (TV). However, an enhanced magnetization is achieved at T < TV. In the latter case, a comparative analysis of the transport properties of Pt/WS2/BPIO and Pt/BPIO from AHE measurements reveals ferromagnetic coupling at the WS2/BPIO interface. Our study forms the foundation for understanding MPE-mediated interfacial properties and paves a new pathway for designing 2D TMD/magnet heterostructures for applications in spintronics, opto-spincaloritronics, and valleytronics.