Effect of induced shape anisotropy on magnetic properties of ferromagnetic cobalt nanocubes

Tailoring nanoparticles design for enhanced heating efficiency and improved magneto-chemo therapy for glioblastoma

Development of multifunctional magnetic nanomaterials (MNPs) with improved heat-generating capabilities and effective combination with localized chemotherapy has emerged as a promising therapeutic regime for solid tumors like glioblastoma. In this regard, the shape-dependent hyperthermic and chemo-therapeutic potential of nanomaterials, has not been extensively explored. Here we present, development of various morphological designs of MNPs including spherical, clusters, rods and cubic; to compare the effect of shape on tuning the properties of MNPs that are relevant to many potential biomedical applications like drug delivery, cellular uptake and heat generation. The study includes extensive comparison of morpho-structural characteristics, size distributions, chemical composition, surface area measurements and magnetic properties of the variable shaped MNPs. Further the heating efficiencies in aqueous and cellular environments and heat triggered drug release profiles for successful magneto-chemotherapy were compared among all in-house synthesized MNPs. Under biosafety limit considerations given by Hergt's limit (H*f value <5 × 10⁹ Am^-1 s^-1), cuboidal shaped MNPs demonstrated highest heating efficiency owing to magnetosome-like chain formation along with sustained drug release profile as compared to other synthesized MNPs. The mechanism of cancer cell death mediated via magneto-chemotherapy was elucidated to be the oxidative stress-mediated apoptotic cell death pathway. In vivo studies further demonstrated complete tumor regression only in the magneto-chemotherapy treated group. These findings suggest the potential of combinatorial therapy to overcome the clinical limitations of the independent therapies for advanced thermotherapy of glioblastoma.

Influence of pH Adjustment Parameter for Sol-Gel Modification on Structural, Microstructure, and Magnetic Properties of Nanocrystalline Strontium Ferrite

Synthesis of nanocrystalline strontium ferrite (SrFe₁₂O₁₉) via sol-gel is sensitive to its modification parameters. Therefore, in this study, an attempt of regulating the pH as a sol-gel modification parameter during preparation of SrFe₁₂O₁₉ nanoparticles sintered at a low sintering temperature of 900 °C has been presented. The relationship of varying pH (pH 0 to 8) on structural, microstructures, and magnetic behaviors of SrFe₁₂O₁₉ nanoparticles were characterized by X-ray diffraction (XRD), field emission scanning microscope (FESEM), and vibrating sample magnetometer (VSM). Varying the pH of precursor exhibited a strong effect on the sintered density, crystal structure and magnetic properties of the SrFe₁₂O₁₉ nanoparticles. As the pH is 0, the SrFe₁₂O₁₉ produced relatively largest density, saturation magnetization, M_s, and coercivity, H_c, at a low sintering temperature of 900 °C. The grain size of SrFe₁₂O₁₉ is obtained in the range of 73.6 to 133.3 nm. The porosity of the sample affected the density and the magnetic properties of the SrFe₁₂O₁₉ ferrite. It is suggested that the low-temperature sintered SrFe₁₂O₁₉ at pH 0 displayed M_s of 44.19 emu/g and H_c of 6403.6 Oe, possessing a significant potential for applying in low-temperature co-fired ceramic permanent magnet.

A comparative work on the magnetic field-dependent properties of plate-like and spherical iron particle-based magnetorheological grease

In this study, a new magnetorheological (MR) grease was made featuring plate-like carbonyl iron (CI) particles, and its magnetic field-dependent rheological properties were experimentally characterized. The plate-like CI particles were prepared through high-energy ball milling of spherical CI particles. Then, three different ratios of the CI particles in the MR grease, varying from 30 to 70 wt% were mixed by dispersing the plate-like CI particles into the grease medium with a mechanical stirrer. The magnetic field-dependent rheological properties of the plate-like CI particle-based MR grease were then investigated using a rheometer by changing the magnetic field intensity from 0 to 0.7 T at room temperature. The measurement was undertaken at two different modes, namely, a continuous shear mode and oscillation mode. It was shown that both the apparent viscosity and storage modulus of the MR grease were heavily dependent on the magnetic field intensity as well as the CI particle fraction. In addition, the differences in the yield stress and the MR effect between the proposed MR grease featuring the plate-like CI particles and the existing MR grease with the spherical CI particles were investigated and discussed in detail.

Engineered magnetic shape anisotropy in BiFeO3-CoFe2O4 self-assembled thin films

We report growth of various phase architectures of self-assembled BiFeO3-CoFe2O4 (BFO-CFO) thin films on differently oriented SrTiO3 (STO) substrates. CFO forms segregated square, stripe, and triangular nanopillars embedded in a coherent BFO matrix on (001)-, (110)-, and (111)-oriented STO substrates, respectively. Nanostructures with an aspect ratio of up to 5:1 with a prominent magnetic anisotropy were obtained on both (001) and (110) STO along out-of-plane and in-plane directions. Magnetic easy axis rotation from in-plane to out-of-plane directions was realized through aspect ratio control. An intractable in-plane anisotropy was fixed in CFO on (111) STO due to the triangular shape of the ferromagnetic phase nanopillars. These studies established a detailed relationship of magnetic anisotropy with specific shape and dimensions of ordered magnetic arrays. The results suggest a way to effectively control the magnetic anisotropy in patterned ferromagnetic oxide arrays with tunable shape, aspect ratio, and elastic strain conditions of the nanostructures.