Domain Walls in Magnetic Nanowires


Magnetic domain walls are known as a source of electrical resistance due to the difficulty in transporting electron spins to follow their magnetic texture. This phenomenon has potential for use in spintronic devices, where the electrical resistance can vary based on the presence or absence of domain walls. A very interesting class of materials are the half metals such as La2/3Sr1/3MnO3 (LSMO) which provides full spin polarization, which allows its exploitation in spintronic devices. However single domain wall resistance in half metals is still unknown. Now teams from Spain, France and Germany have generated single domain walls on the LSMO nanowires and measured a change in resistance 20 times greater than that of normal ferromagnets such as Cobalt.

Magnetic sensitive PEEM images acquired in HZB: a) XAS images of crossed nanowires. The X-ray beam and magnetic field are aligned along the direction of the nanowire (vertical) (green arrow). bf) XMCD cross images for various applied fields. Image Credit: © HZB

Magnetic domain textures attached to magnetic domain walls have potential for spintronic applications. The electrical resistance in a ferromagnet depends on whether the domain walls are present or not. This binary effect (known as a wall magnetoresistance domain) can be used to encode information in spintronic memory devices. However, its exploitation is hindered due to the small changes in resistance observed for normal ferromagnets. A very interesting class of materials is perovskite manganite such as La2/3Sr1/3MnO3 (LSMO). These compounds present only one type of spin (full spin polarization) which has the potential to cause domain wall magnetoresistance effects large enough to be exploited in new generation spintronic sensors and injectors.

Despite this promising perspective, there are large differences in the reported values ​​of the domain wall magnetoresistance for these systems. Scientists from Spain, France and Germany have created a device based on nanowires that allows the nucleation of individual magnetic domain walls. Magneto transport measurements on this device show that the presence of domain walls causes an increase in electrical resistance of up to 12%. In absolute terms, the resistance changes observed were 20 times greater than those reported for Cobalt.

This work is the result of a long-term collaboration involving film growth and nanofabrication, transport measurements, contact microscopy (MFM) imaging, theoretical simulations and the use of advanced characterization techniques such as X-ray photoemission electron microscopy. The combination of a variety of different techniques provides a comprehensive, multi-faceted view of complex problems allowing to achieve new insights into highly debated open questions.



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