The 2007 Nobel Prize in Physics can be understood as a global recognition to the rapid development of the Giant Magnetoresistance (GMR), from both the physics and engineering points of view. Behind the utilization of GMR structures as read heads for massive storage magnetic hard disks, important applications as solid state magnetic sensors have emerged. Low cost, compatibility with standard CMOS technologies and high sensitivity are common advantages of these sensors. This way, they have been successfully applied in a lot different environments. In this work, we are trying to collect the Spanish contributions to the progress of the research related to the GMR based sensors covering, among other subjects, the applications, the sensor design, the modelling and the electronic interfaces, focusing on electrical current sensing applications.

The absorption edge of hexagonal (NiAs structure) antiferromagnetic MnTe has been measured by means of light transmission experiments carried out at different temperatures in the range 16–420 K $(P=1\mathrm{}\mathrm{bar})$ and hydrostatic pressures up to 9 GPa $(T=295\mathrm{}\mathrm{K}).\mathrm{}$ An indirect band gap has been found, in agreement with previous band-structure calculations, with an energy of $E_{\mathrm{ig}}=1.272\mathrm{}\pm 0.013\mathrm{eV}$ at room temperature and pressure. The temperature dependence of the absorption edge is linear above the Néel temperature $T_N=310\mathrm{}\mathrm{K},$ with a temperature coefficient $dE/dT=-(3.5\mathrm{}\pm 0.1)\times {10}^{-4}\mathrm{e}\mathrm{V}/\mathrm{K}.$ Below $T_N$ an additional blueshift is found, with a maximum value of 0.1 eV at low temperatures. The temperature dependence of this anomalous shift is proportional to the square of the magnetization, a result which is consistent with previous second-order perturbation calculations. Regarding the measurements under pressure, a negative pressure coefficient with a value of $dE/dP=-(59\mathrm{}\pm 2\mathrm{m}\mathrm{e}\mathrm{V}/\mathrm{G}\mathrm{P}\mathrm{a})$ has been found. The Néel temperature is known to increase with pressure in hexagonal MnTe, due to an increment of the exchange interaction, or equivalently, of the sublattice magnetization. Consequently a positive pressure shift could be expected at room temperature, derived from both the antiferromagnetic splitting of Mn $3d$ orbital and second-order electron and hole interaction with fixed Mn spins. The negative pressure coefficient has thus been interpreted as a sum of that positive contribution and a larger negative one derived from an enhanced p-d repulsion which would lead to an upwards shift of the valence-band maximum.

Less than thirty years after the giant magnetoresistance (GMR) effect was described, GMR sensors are the preferred choice in many applications demanding the measurement of low magnetic fields in small volumes. This rapid deployment from theoretical basis to market and state-of-the-art applications can be explained by the combination of excellent inherent properties with the feasibility of fabrication, allowing the real integration with many other standard technologies. In this paper, we present a review focusing on how this capability of integration has allowed the improvement of the inherent capabilities and, therefore, the range of application of GMR sensors. After briefly describing the phenomenological basis, we deal on the benefits of low temperature deposition techniques regarding the integration of GMR sensors with flexible (plastic) substrates and pre-processed CMOS chips. In this way, the limit of detection can be improved by means of bettering the sensitivity or reducing the noise. We also report on novel fields of application of GMR sensors by the recapitulation of a number of cases of success of their integration with different heterogeneous complementary elements. We finally describe three fully functional systems, two of them in the bio-technology world, as the proof of how the integrability has been instrumental in the meteoric development of GMR sensors and their applications.

Full Wheatstone bridge spin-valve-based electrical current sensors at the IC level are presented. Prototypes with different geometrical parameters have been designed, fabricated and fully characterized. DC characterization has been carried out, for measurement of insertion losses, linearity, voltage offset and sensitivity. Current ranges from 10 muA to 100 mA can be covered with these sensors with excellent linearity and sensitivities above 1 mV/(VmiddotmA) . AC characteristics have also been analyzed and bandwidths exceeding 100 kHz are demonstrated. Moreover, the temperature coefficients have been extracted in the range of -20degC to +60degC. In order to highlight the design properties, dependence of the sensor's performance with external magnetic perturbations and self-heating have also been measured and quantified. The associated errors are in the range of 1%-2% of the full scale.

With the expansion in number and requirements of modern wireless communications, the technology related to their associated antennas has been continuously improved. Among other options, printed antennas offer excellent features, such as low weight, profile, and cost, while maintaining good performance characteristics. In addition, their straightforward integration with electronics has opened new fields of application such as smart sensing systems. Printed antennas can be used in different parts of a wireless smart sensor as a radio link, sensing element, or even as energy harvester. In this paper, we present a thorough review of recent advances of printed antennas as regards their use in smart sensing applications.