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Spintronics and Metamaterials



CISS develops sensors based on thin films and artificial materials. In the field of spintronics the spin of electrons is facilitated to develop performance-enhanced magnetic field sensors. In the field of metamaterials optical properties of materials are specifically engineered.


Spintronics, meaning "spin transport electronics", exploits the intrinsic spin of electrons, in addition to their electronic charge, in solid-state devices like sensors.

Multilayered film systems of ferromagnetic and non-magnetic metals show a distinct magnetoresistive effect, the Giant Magneto Resistance (GMR). “Giant” is meant in comparison to the anisotropic magnetoresistance (AMR) effect. The GMR effect is based on the spin-dependent scattering at the layer boundaries (intrinsic effect) and at impurities (extrinsic effect). In addition, the nonmagnetic interlayer may show an interlayer exchange coupling mediated by spin-polarized conduction electrons of this layer. This quantum-mechanical phenomenon (RKKY) provides anti- and ferromagnetic alignment of the adjacent ferromagnetic layers and is oscillating with the interlayer thickness. Resistance changes ΔR/R up to 100 percent can be measured at room temperature. For practical sensors, however, which already operate at small magnetic fields of 1-10 mT, the signal amplitude is in the range between 5 and 15 percent. Optimized GMR film stacks are gaining a growing technical importance. An effect similar to the GMR is the tunnel magnetoresistance (TMR) effect. Here, the layer stacks consist of ferromagnetic metals and insulators. The electric current flows perpendicular to the layers. The magnetoresistance change is caused by spin-dependent tunnel probabilities of the different spin states through the thin insulator. This tunnel barrier acts as a spin filter. The effect can amount to several 100 percent of resistance change at fields of 1 to 10 mT at room temperature.


Hall effect sensor ICs and switches largely dominate the silicon magnetic sensor IC market. Ferromagnetic AMR sensors can be placed further away from the object and their signal-to-noise ratio can be better than for Hall sensors. GMR and TMR are used for high-performance applications and are among the key next generation development in magnetic sensors. Added to this, new applications opening up and the market perspectives for magnetic sensors look very attractive bright in future, e.g. in medical diagnostics and treatment.


CISS utilizes simulation models (micromagnetic modeling, extended Stoner-Wohlfarth model, COMSOL) to optimize the sensors which are fabricated by thin film and lithographic technologies. In general, research efforts target sensor parameters like sensitivity, size, full range, linearity, bandwidth, power consumption and resolution. Level of integration is becoming important for magnetic sensor manufacturers to differentiate their product and to target various new applications. New physical modalities like non-local spin transport, spin Seebeck effect, and spin Hall effect are worldwide under actual research.



CISS concentrates its research on so-called Perfect Metamaterial Absorbers (PMA). It uses numerical models in COMSOL and effective medium calculations to design appropriate composite materials and structures which are fabricated by thin film and lithographic techniques.

Metamaterials are artificial materials consisting of periodic or non-periodic unit cell structures which exhibit unusual electromagnetic properties, not readily found in nature. Metamaterials derive their properties from both, the compositional properties of the base materials and their exactingly-designed unit cell structures. The incorporated structural elements are of sub-wavelength sizes.

A metamaterial absorber utilizes the effective medium design of metamaterials and the loss components of electric permittivity and magnetic permeability to create a material that has a high ratio of electromagnetic radiation absorption. PMA is simply a near 100 percent absorber. The imaginary loss terms can be engineered to create high attenuation and correspondingly large absorption. By independently manipulating resonances in ε and µ, it is possible to absorb both the incident electric and magnetic field. Additionally, a metamaterial can be impedance-matched to free space by engineering its permittivity and permeability, minimizing reflectivity. Thus, it becomes a highly capable absorber.



Photo: ZISS
Photo: ZISS
Photo: ZISS