Multiferroic magnetoelectric nanostructures for novel device applications
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Multiferroic magnetoelectric nanostructures Many of today’s technological challenges require integration of two or more monolithic material components. Much attention has therefore been paid to the study of interfacial coupling between individual components in composite material systems,1,2 where new functionalities can arise from coupling among different variables (order parameters) across the interfaces (see the Introductory article in this issue). In particular, in composite nanostructures with relatively large numbers of interfaces, one can utilize these new functionalities to achieve ultimate performance in a device. One good example is multiferroic magnetoelectric nanostructures, with magnetic and ferroelectric materials integrated at the nanoscale. Figure 1 shows a nanostructure with juxtaposed magnetic and ferroelectric layers. Across the interface, electric polarization in the ferroelectric layer can be coupled to the magnetization in the magnet, based on the interplay among the lattice, charge, spin, and orbit degrees of freedom achieved typically through the exchange of certain type(s) of potential energy, such as mechanical, electric, and magnetic. Such coupled polarization and magnetization further enable an electrically tunable magnetization or a magnetically tunable polarization, known as converse and direct magnetoelectric coupling, respectively. In this article,
we review several novel device prototypes based on interfacebased magnetoelectric coupling and provide a brief outlook. Details of recent progress in multiferroic magnetoelectric nanostructures can be found in existing review articles (e.g., References 3–6).
Ultrahigh-density magnetic memories Based on converse magnetoelectric coupling in multiferroic magnetoelectric nanostructures, the magnetization is switched with an electric field (via, strain7–12 or exchange bias13–18 across the interface) rather than a current. This property can be exploited to lift the obstacles now limiting the storage densities of magnetic memories.
Ultrahigh-density hard disk drive The density limit for a hard disk drive (HDD) is set by the thermal stability of one storage unit that consists of a number of magnetic grains (typically 50–100) in a granular recording medium.19 This density limit is about 1 Tb in–2 for stateof-the-art perpendicular recording technology, where the bit information (i.e., 0 and 1) is represented by the polarity of a magnetization aligning perpendicularly to the plane of the recording medium.20 To achieve higher area density, the thermal stability of one storage unit, expressed as KuVm/kBT
Jia-Mian Hu, The Pennsylvania State University, USA; [email protected] Tianxiang Nan, Northeastern University, USA; [email protected] Nian X. Sun, Northeastern University, USA; [email protected] Long-Qing Chen, The Pennsylvania State University, USA; [email protected] DOI: 10.1557/mrs.2015.195
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MRS BULLETIN • VOLUME 40 • SEPTEMBER 2015 • www.mrs.org/bulletin
© 2015 Materials Research Society
MULTIFERROIC MAGNETOELECTRIC NANOSTRUCTURES FOR NOVEL DEVICE A
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