J.C. Martínez-García

First-order reversal curves analysis in nanocrystalline ribbons

Differential analysis based on first-order reversal curves (FORC) is being increasingly used to study the internal interactions in magnetic systems. Traditionally, this technique has gone hand in hand with Preisach-type models which, although succeeding in describing weakly interacting systems, are not applicable to nanostructures or polycrystalline systems characterized by strong internal interactions. This paper is aimed at contributing to the physical understanding of the complex FORC diagrams of strongly interacting systems with a macromagnetic model based on a mean interaction field and a distribution of switching fields as intrinsic elements. The proposed idea is used to explain the FORC patterns of nanocrystalline Co-based systems.

Scanning Magneto-Inductive Sensor for Quantitative Assay of Prostate-Specific Antigen

Among analytical tests available for point-of-care diagnostics, the lateral flow immunoassay (LFIA) stands out for its low-cost, speed, portability, and ease of use. By its nature, this paper-based instrument is qualitative, intended to provide a positive/negative reading. LFIA, coupled to a quantitative readout device that did not compromise its advantages, would be a powerful tool for many clinical and biological applications. A promising enabling strategy is the use of superparamagnetic nanoparticles as labels. Their reduction of visual signal compared to gold or latex reporters is compensated by their magnetic induction, which enables absolute quantification with magnetic sensors. In this letter, a magnetic LFIA reader is presented that exploits spontaneous magnetic switching, a characteristic of superparamagnetism, to produce a quantifiable electromagnetic induction in an alternating current carrier. In contrast to other magnetic sensors, this approach does not require the application of external magnetic fields, which greatly reduces its complexity. The capability of the system for bioanalyte quantification has been proved by successfully measuring prostate-specific antigen levels in the interval of clinical interest.

Quasi-Static AC FORC Measurements for Soft Magnetic Materials and Their Differential Interpretation

A detailed analysis of the first-order reversal curve (FORC) measurements offers the possibility to separate the different magnetic interactions in multiphase or composite magnetic materials, and then to attain a precise interpretation of the role played by those interactions. In this paper, we present a modified setup based on a classical inductive magnetometer optimized for FORC measurements in soft magnetic materials, together with an improved differential method for the data analysis in order to get an accurate interpretation of the experimental results.