Various series of permalloy thin films were grown by dc-sputtering on Si (100) and glass substrates at room temperature and different argon pressure values using a Fe₂₀ Ni₈₀ target. The increase of argon pressure leads to a decrease of the Fe concentration in the films from 17 at.% to 15 at.%, an increase of the root mean square roughness of film surfaces, and a decrease of the sharpness of the crystalline texture of the samples. The increase of the film thickness leads to an increase of the coercive field. The transition to the "transcritical" state was observed at a critical thickness that decreases from 220 to 50 nm as the argon pressure in the chamber increases. This state was confirmed by the characteristic shapes of hysteresis loops, rotatable magnetic anisotropy, and the appearance of stripe domains.

Magnetospirillum gryphiswaldense is a microorganism with the ability to biomineralize magnetite nanoparticles, called magnetosomes, and arrange them into a chain that behaves like a magnetic compass. Rather than straight lines, magnetosome chains are slightly bent, as evidenced by electron cryotomography. Our experimental and theoretical results suggest that due to the competition between the magnetocrystalline and shape anisotropies, the effective magnetic moment of individual magnetosomes is tilted out of the [111] crystallographic easy axis of magnetite. This tilt does not affect the direction of the chain net magnetic moment, which remains along the [111] axis, but explains the arrangement of magnetosomes in helical-like shaped chains. Indeed, we demonstrate that the chain shape can be reproduced by considering an interplay between the magnetic dipolar interactions between magnetosomes, ruled by the orientation of the magnetosome magnetic moment, and a lipid/protein-based mechanism, modeled as an elastic recovery force exerted on the magnetosomes.

Thin-film based magnetoimpedance (MI) sensors were used for quantitative determination of the concentration of magnetic nanoparticles (MNPs) in ferrogels. Ferrogels (model systems for biological tissue) were synthesized by radical polymerization of acrylamide in a stable aqueous suspension of γ-Fe₂O₃ MNPs fabricated by laser target evaporation. MI [FeNi/Ti]₃/Cu/[Ti/FeNi]₃/Ti sensitive elements were prepared by sputtering. Thorough structural and magnetic studies of MNPs, ferrogels, and multilayered sensitive element insure the complete characterization of biosensor prototype. The MI response of the sensitive element was carefully evaluated in initial state and in the presence of ferrogels with different concentration of iron oxide MNPs from 0 to 2.44 wt. %, which produced systematic changes of the MI in a frequency span of 300 kHz to 400 MHz.

Magnetotactic bacteria (MTB) are aquatic microorganisms that are able to biomineralize membrane-enclosed magnetic nanoparticles called magnetosomes. Inside the MTB, magnetosomes are arranged in a chain that allows MTB to align and navigate along the Earth's magnetic field. When isolated from the MTB, magnetosomes display a number of potential applications for targeted cancer therapies, such as magnetic hyperthermia, localized drug delivery, or tumor monitoring. The characteristics and properties of magnetosomes for these applications exceed in several aspects those of synthetic magnetic nanoparticles. Likewise, the whole MTB can also be considered as promising agents for cancer treatment, taking advantage of their self-propulsion capability provided by their flagella and the guidance capabilities ensured by their magnetosome chain. Indeed, MTB are envisaged as nanobiots that can be guided and manipulated by external magnetic fields and are naturally attracted toward hypoxic areas, such as the tumor regions, while retaining the therapeutic and imaging capacities of the isolated magnetosomes. Moreover, unlike most of the bacteria currently tested in clinical trials for cancer therapy, MTB are not pathogenic but could be engineered to deliver and/or express specific cytotoxic molecules. In this article, we will review the progress and perspectives of this emerging research field and will discuss the main challenges to overcome before the use of MTB can be successfully applied in the clinic.

Magnetic disks are a new generation of nanoparticles with outstanding properties to face biomedical challenges as a cancer treatment. The key features of their suitability are the ability of rotation (torque), the high dispersion capability, and the easy manipulation under low magnetic fields. These properties make disk-shaped particles ideal magnetomechanical actuators to damage cancer cell integrity, deliver antitumor drugs, generate heat (magnetic hyperthermia), or separate cancer cells for early detection. Since the experimental demonstration of the capability of destroying brain cancer cells by the force exerted from rotating Ni₈₀Fe₂₀ microdisks, important advances have been reported on disks composed of different magnetic materials and dimensions. Here, we present the evolution of a decade-old research field by combining the discussion of in vitro experiments available in the literature with our most recent results. More importantly, we compare the torque and dispersion capability of each type of magnetic disk in order to promote the investigation toward the most efficient magnetomechanical actuator to destroy cancer cells.

Detailed measurements of giant magnetoimpedance (GMI) in an amorphous ribbon and a magnetic/nonmagnetic multilayer are presented for frequencies up to $3\mathrm{GHz}$ . Through this frequency range, the transition from quasistatic to dynamic regime of GMI can be clearly distinguished, due to the appearance of the ferromagnetic resonance (FMR). The unambiguous experimental evidence presented mediates between conflicting interpretations of GMI: the ones that assume the existence of FMR even for low frequencies and the ones that consider that it is irrelevant. The frequency at which the transition takes place is shown to be related with the width of the resonance, which is substantially different for both samples. It is concluded that the large increase of permeability caused by the ferromagnetic resonance can be advantageous for GMI-based devices only for samples with a small, very well-defined perpendicular anisotropy.