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.

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Magnetic Field Sensors Based on Giant Magnetoresistance (GMR) Technology: Applications in Electrical Current Sensing.

Development of Sensors Based on Giant Magnetoresistance Material

In this work, we report the magnetic properties of sputtered Permalloy (Py: Ni80Fe20)/molybdenum (Mo) multilayer thin films. We show that it is possible to maintain a low coercivity and a high permeability in thick sputtered Py films when reducing the out-of-plane component of the anisotropy by inserting thin film spacers of a non-magnetic material like Mo. For these kind of multilayers, we have found coercivities which are close to those for single layer films with no out-of-plane anisotropy. The coercivity is also dependent on the number of layers exhibiting a minimum value when each single Py layer has a thickness close to the transition thickness between Neel and Bloch domain walls.

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Magnetic properties of sputtered Permalloy/molybdenum multilayers

Microstructural and magnetic properties of thin obliquely deposited films: A simulation approach

In the smart grid, wide-area current measurement system is of great importance to assist with the estimation of the power grid loss and the smart dispatching. However, the limited current sensing techniques have always been an obstacle to realizing such system. Recently, the development of giant magnetoresistance (GMR) based sensors has offered an effective solution to address this issue. The outstanding merits of compact size, high sensitivity and cost-effective price of GMR sensors have made them a perfect choice for widely distributed current measurement and data collection in smart grid. In this paper, with a design of flux guided structure for line current sensing, typical performance characteristics of optimized GMR design are illustrated. The validity of the structure is demonstrated with simulation and experiment. Based on the characteristics of GMR sensors, their prospects for application in smart grid are further discussed.

Current sensors based on GMR effect for smart grid applications

We have studied the influence of the growth conditions on the structural characteristics of sputtered Py(Fe20Ni80)/ Gd/Py(Fe20Ni80) thin films. Auger electron spectroscopy reveals the existence of Ni in the Gd layer. The Ni concentration profile appears asymmetric with a higher concentration close to the top Py layer. This asymmetrical Ni concentration produces a different coercivity of each Py layer. It is possible to reduce the Ni interdiffusion by using multilayers based on Py/Gd bilayers separated by Mo spacers between the Py/Gd bilayers. In these samples we have obtained an enhancement of the structural and magnetic properties.

Improvement of the structural and magnetic properties of Permalloy/Gadolinium multilayers with Mo spacers

The influence of magnetic anisotropy on magnetoresistance has been studied in magnetic-non-magnetic-magnetic sandwiches. A numerical model has been developed considering different anisotropies in each magnetic layer and different exchange couplings between them. Both contributions to the magnetoresistance are evaluated; anisotropic and giant magnetoresistance (GMR). Appropriate magnetic anisotropy configurations allow GMR without antiferromagnetic coupling between the magnetic layers. Sandwiches of permalloy-copper-permalloy have been obtained in a dc magnetron sputtering system with different thickness and different anisotropy distributions in order to make a comparison between the experimental magnetoresistance and the numerical results.

https://iopscience.iop.org/article/10.1088/0957-4484/13/3/330/pdf

The influence of anisotropy on the magnetoresistance of permalloy-copper-permalloy thin films

This work reports the magnetic properties of sputtered permalloy (Ni80Fe20) multilayers grown changing the anisotropy direction 90° in successive layers. Magnetic measurements show how the saturating field can be controlled by the thickness ratio between different anisotropy layers and how the coercive field is reduced increasing the number of layers. The linearity of the hysteresis loop is also improved when increasing the number of layers. Magnetic measurements are compared to simulations based on a Stoner-Wolfarth magnetization rotation mechanism.

Magnetic properties of permalloy multilayers with alternating perpendicular anisotropies

Py/Gd/Py trilayers (Py: :Fe 20 Ni 80 ) have been electrical and magnetically characterized as a function of the temperature. Results show a weak Py-Gd exchange coupling probably due to the Ni interdiffusion into the Gd layer. These results have been compared with magnetic measurements in Py/Gd double bilayers ([Py/Gd/Mo] 2 ). An enhancement of the Py-Gd exchange coupling has been obtained in these samples where the Ni concentration in the Gd layer is almost null.

Effective exchange coupling in permalloy-gadolinium films

We have studied the effect of the homogeneity of hydrogen distribution on magnetic properties of hydrogen charged amorphous samples (Metglass 2826MB: Fe40Ni40Mo4B18). The results suggest that, in high magnetostrictive samples, the induced internal stresses and hence the magnetic anisotropy are related to the hydrogen distribution and not to the total quantity of hydrogen inside the sample. To perform this study, the homogeneity of hydrogen distribution in the sample was improved by using a very low rate of hydrogen charging by means of a pulsed electrolytic current. Furthermore, this pulsed electrolytic current allows us to introduce a high quantity of hydrogen without breaking the sample.

P. Sánchez

Papers

Improvement of the structural and magnetic properties of Permalloy/Gadolinium multilayers with Mo spacers

The influence of anisotropy on the magnetoresistance of permalloy-copper-permalloy thin films

Magnetic properties of permalloy multilayers with alternating perpendicular anisotropies

Effective exchange coupling in permalloy-gadolinium films

Influence of hydrogen distribution on magnetic properties of amorphous samples