researchers at the fraunhofer institute for applied solid state physics iaf in freiburg, germany have partnered with scientists at the max planck institute for solid state research in stuttgart, germany to develop a quantum sensor that can measure the nanoscale magnetic fields that are expected to be in the next generation of hard drives.

ultra-pure diamonds produced at fraunhofer iaf for quantum applications. (fraunhofer iaf)

according to an announcement from fraunhofer, the sensor is only slightly larger than the size of a nitrogen atom and uses synthetic diamond as a substrate.

“diamond has a variety of advantages quite apart from its considerable mechanical and chemical stability,” the announcement explained. “for instance, one can implant foreign atoms such as boron or phosphorus, thereby turning the crystals into semiconductors. diamond is also the perfect material for optical circuits. but perhaps its greatest attribute is its impressive thermal conductivity, with the strength of the carbon atom bonds ensuring that heat is rapidly dissipated.”

fraunhofer has been developing systems for producing diamonds for decades using a plasma reactor that heats gas to 800-900°c to form diamond crystals that are then polished by a laser. to make sure that the diamond being used for the sensor is pure, the scientists first use a zirconium filter for the methane gas and ensure the gas is isotopically pure.

“the hydrogen also undergoes a purification process,” fraunhofer added. “the final result is an extremely fine diamond tip that resembles that of an atomic force microscope. the key to the whole design is the added nitrogen atom together with a neighboring vacancy in the crystal structure.”

the article continued, “this combined nitrogen-vacancy center acts as the actual sensor, emitting light when it is exposed to a laser and microwaves. if there is a magnet nearby, it will vary in its light emission. experts call this electron spin resonance spectroscopy. not only can this technique detect magnetic fields with nanometer accuracy, it can determine their force as well, opening up an extraordinary range of applications.”

the sensor can be used to measure hard drive quality, identify data segments that need to be excluded from the disc reading and writing process to reduce the defect rate.

thanks to the thermal conductivity of diamond, which avoids the need for using the sensor in liquid nitrogen, the sensor can be used at room temperature without the need for cooling.