Magnetic field sensors can enhance applications that require efficient power management. Improving the magnetic field sensor below the picoTesla range can use a technique to measure brain activity at room temperature, the millisecond resolution - called the magnetic brain map - without the superconducting quantum interference device (SQUID) technology, which requires low temperature operation.

A team of researchers from the National Institute of Materials Science and the LG Japan Laboratory at the University of Tsukuba in Japan explored the use of semi-metals to increase the magnetoresistance ratio in current vertical plane giant magnetoresistance (CPP-GMR) devices. Heusler CoFeAl0.5Si0.5 (CFAS) alloy. The alloy has 100% spin-polarized conduction electrons, which makes the spin asymmetry of electron scattering very high and results in a large magnetoresistance ratio. They reported their findings in the Journal of Applied Physics at AIP Press.

Magnetoresistance - Resistance change in response to an externally applied magnetic field - is important for all magnetic field sensor applications. In order to increase the sensitivity of the magnetic field sensors, they must first increase their magnetoresistance ratio (defined as the value of the resistance change against magnetic fields or magnetization).

“By manufacturing CFAS and silver (Ag) multilayer stacks, we are able to further increase the magnetoresistance ratio,” said Yuya Sakuraba, head of NIMS Magnet Materials Group. "By precisely controlling the interface roughness of the multilayer film, we obtained an anti-parallel interlayer exchange coupling between each CFAS layer, up to a maximum of six, and achieved not only a high magnetoresistance ratio but also a magnetic field. High resistance linearity changes."

Previous studies have shown that semi-metallic Heusler alloys are well suited to increase the magnetoresistance ratio of CPP-GMR devices. "Heusler-based alloys are expected to be the next generation of readheads for hard disk drives with high surface recording densities of over 2TB/in 2", Sakuraba said.

“Our work has proven that the magnetoresistance ratio can be further increased by creating multilayer structures, and now the potential of Heusler-based CPP-GMR for high-sensitivity magnetic field sensor applications is truly open,” Sakuraba explained.

The researchers fabricated a fully epitaxial device on a single crystal magnesium oxide (MgO) substrate. If a similar characteristic can be obtained in a polycrystalline device, it can be a candidate for a new magnetic field sensor with higher sensitivity than a conventional Hall sensor or a tunnel magnetoresistive sensor.

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