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Characterizing the optical response of magneto-optic and magnetic materials usually relies on semi-classical models (e.g. Lorentz oscillator model) involving few parameters or models based on a detailed quantum mechanical description of the underlying response. These models typically involve a few parameters that are estimated via fitting the experimental data to provide a qualitative understanding of the underlying physics. Such a few-parameters fitting approach falls short of accurately capturing all elements of the complex-valued permittivity tensor across a range of wavelengths. Accurate characterization of the permittivity tensor elements across a broad range of wavelengths is invariably imperative for designing optical elements such as isolators, circulators, etc. Here, we propose and demonstrate a ubiquitous and accessible method based on a combination of spectroscopic ellipsometry and spectroscopic Magneto-Optic Kerr Effect (MOKE) measurements coupled with rigorous numerical parameter extraction techniques. To this end, we use the combined MOKE ellipsometry measurements conducted at different angles of incidence with a gradient-descent minimization algorithm to provide the inverse solution to the complete dielectric permittivity tensor. Further, we demonstrate model re-verification to ensure the estimated dielectric permittivity values reliably predict the measured experimental data. Our method is a simplified bench-top counterpart to the otherwise complex measurement systems., Comment: 17 pages, 6 figures

Information encoding in barcodes using magnetic-based technology is a unique strategy to read data buried underneath non-transparent surfaces since a direct line-of-sight between the code and the reader is not required. This technology is of particular interest in secure labelling and recyclable packaging applications. However, current magnetic reading heads, such as those employed for magnetic ink character recognition, need to be placed in contact with the magnetic structures, limiting the depths at which the information can be read. This paper describes a strategy to overcome that limitation by replacing the traditional inductive heads with tunnel magnetoresistive (TMR) sensors. Soft-magnetic codes can be printed using conventional LaserJet toners and, by having their magnetisation set with a permanent magnet included in the device, the resulting magnetic field can be read using a TMR sensor. We demonstrate that such a device can read barcodes at depths of at least 1 mm. It can also resolve individual structures as thin as 200 {\mu}m when used in contact., Comment: 4 pages, 5 figures, Manuscript accepted for publication in IEEE Transactions on Magnetics

Automated technologies for quality inspection of fruits have attracted great interest in the food industry. The development of nondestructive mechanisms to assess the quality of individual fruit prior to sale may lead to an increase in overall product quality, value, and consequently, producer competitiveness. However, the existing methods have limitations. Herein, a texture sensor based on highly sensitive hair-like cilia receptors, to allow a quick quality evaluation of fruit is proposed. The texture sensor consists of up to 100 magnetized nanocomposite cilia attached to a chip with magnetoresistive sensors in a full Wheatstone bridge architecture. In this paper we demonstrate the use of ciliary sensors in scanning fruits (blueberries and strawberries) in different maturation stages. The contact of the cilia with the fruit skin provided qualitative information about its texture in terms of ripeness stage. Less mature fruits exhibited, on average, a highest peak voltage of 0.14 mV for blueberries and 0.12 mV for strawberries, while overripe fruits exhibited 0.58 mV and 0.56 mV, respectively. The results were confirmed by sensorial assessment of the fruit freshness, and therefore attesting the application potential of the sensing technology for fruit quality control.

We present a magnetic tunnel junction (MTJ) where its two ferromagnetic layers are in the form of a single ellipse (SE) and two-crossing ellipses (TCE). The MTJ exhibits four distinct resistance states corresponding to the four remanent states of the TCE structure. Flowing current in an underlying Ta layer generates in the adjacent TCE structure spin-orbit torques which induce field-free switching of the four-state MTJ between all its resistance states. The demonstrated four-state MTJ is an important step towards fabricating multi-level MTJs with numerous resistance states which could be important in various spintronics applications, such as multi-level magnetic random access or neuromorphic memory., Comment: 4 pages, 3 figures, This article may be downloaded for personal use only. Any other use requires prior permission of the author and AIP Publishing. This article appeared in (Appl. Phys. Lett. 117, 072404 (2020)) and may be found at (https://aip.scitation.org/doi/10.1063/5.0014771)

Magnetic encoders currently provide accurate positioning information by reading periodic patterns with equally spaced structures or bits. As this technology evolves to fulfill industrial demands for cheaper and more accurate systems, variations of this concept with non-periodic and non-predetermined patterns emerge. In this work, we take the first step towards the development of such devices using equally sized bits with different separations. We show magnetic scans of 1000 {\mu}m wide and 2000 {\AA} thick CoCrPt structures with separations between 63 and 3000 {\mu}m, obtained with tunnel magnetoresisistive sensors. A theoretical model to describe the magnetic field created by these structures is also proposed, which matches the trend of the experimental signals. We also show that there is a spatial resolution loss for reading distances higher than a threshold that depends on the minimum feature size of the sample., Comment: Accepted manuscript