Examine the domain walls in the magnetic nanowires

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a) XAS of the device, with the magnetic field in the direction of the nanowire but with the X-ray beam in the direction of the contact wire. bd) XMCD in the same configuration. With this configuration it is possible to probe the magnetization of the contact. These measurements together with those in Figure 2 allow us to unequivocally define the direction of magnetization in our device. Credit: Advanced material (2023). DOI: 10.1002/adma.202211176

Magnetic domain walls are known to be a source of electrical resistance due to the difficulty for the spins of the carrying electrons to follow their magnetic structure. This phenomenon has the potential for use in spintronic devices, where electrical resistance can vary based on the presence or absence of a domain wall.

A particularly intriguing class of materials are half metals such as La2/3Mr1/3Mno3 (LSMO) that exhibit complete spin polarization, allowing their exploitation in spintronic devices. However the strength of a single domain wall in half metals remained unknown. Now a team from Spain, France and Germany has generated a single-domain wall on an LSMO nanowire and measured 20 times greater resistance changes than on a regular ferromagnet such as cobalt.

The magnetic domain texture inherent in magnetic domain walls holds the potential for spintronic applications. The electrical resistance in ferromagnets depends on whether or not there are domain walls. This binary effect (known as domain wall magnetoresistance) could be used to encode information in spintronic memory devices.

However, their exploitation is hampered by the small resistance changes observed for ordinary ferromagnets. Of particular interest are manganite perovskites such as LSMO. These compounds exhibit only one type of spin (full spin polarization) which could potentially lead to domain wall magnetoresistance effects large enough to be exploited in a new generation of spintronic sensors and injectors.

Despite this promising prospect, large discrepancies exist in the reported values ​​of domain wall magnetoresistance for this system. Scientists from Spain, France and Germany fabricated nanowire-based devices that enable nucleation of individual magnetic domain walls. Magnetic transport measurements in these devices show that the presence of a domain wall leads to an increase in electrical resistance of up to 12%. In absolute terms, the observed resistance change is 20 times greater than that reported for cobalt.

This work is the result of a long-standing collaboration involving film growth and nanofabrication, transport measurements, contact microscopy (MFM) imaging, theoretical simulations, and the use of advanced characterization techniques such as electron microscopy X-ray photoemission. The combination of a wide variety of different techniques provides a comprehensive and multifaceted view of a complex problem that has allowed new insights into a hotly debated open question to be achieved.

The study is published in the journal Advanced material.

More information:
Gloria Orfila et al, Large magnetoresistance of isolated domain walls in LSMO nanowires, Advanced material (2023). DOI: 10.1002/adma.202211176

About the magazine:
Advanced material

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