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Computer evolution from the 60’s up to the 00’s, with decreasing cost and dimensions and increasing capacity and velocity
(adapted from reference [12])
If 60 years took us to get from the room-sized computer of the 1960’s to the extremely powerful smartphones of the 2020s, we are just on the threshold of the era of electrically controllable nanoscale storage, which will lead to thinner, lighter and flexible devices, with significantly high and sustainable energetic efficiencies and huge capacities.
The limitations of Moore’s law,1 which predicted the exponential increase over time of the number of components in integrated circuits, have led to a high demand for alternatives in the field of microelectronics. The combination of the miniaturization of the components (Moore’s law) and the use of novel material architectures (“More than Moore”) makes possible the integration of digital and non-digital functionalities into compact systems. Within this context multiferroic materials hold great promise.
Schematic representation of a Magnetolectric Random Access Memory (MERAM) [13].
Data storage, probably the most crucial battlefield of the tough and consuming expedition for miniaturization, is mainly focused on the development of Ferroelectric and Magnetic Random Access Memories (FeRAMs and MRAMs respectively), which have limited efficiencies.5 The use of MFs can provide electrically written and magnetically read devices, thus faster, low-energy consumption and with a non-destructive magnetic read operation.
Particularly for the case of spintronics memories, the presence of the ME effect in MFs may increase the number of logic states from 2 to 4 (or 8), due to the additional binary state emerging from such multifunctionality.6 Most importantly, the ability to manipulate the magnetization by electric fields leads to simple, cost-effective and energetically sustainable technological strategies.
An even more promising route to design efficient future hybrid devices is the use of the dynamical ME effect, where the order parameters of magnetization and polarization are not static, but oscillatory. Very often, in this dynamical regime, elementary excitations called electromagnons emerge, as “carriers” of such dynamical ME coupling. These spin excitations can be tuned by external magnetic and/or electric fields, thus promoting the modulation of the index of refraction by both static fields and electromagnetic radiation.7,8
The understanding of the underlying quantum-level microscopic mechanisms that lead to ME coupling is essential for the engineering of novel single-phase ME MFs, since only a limited number of them is known in nature.
EMAGICS project aims at a clearer understanding of the magnetoelectric (ME) multiferroic (MF) properties of novel materials, from the macroscopic to the quantum microscopic level, encompassing a series of advanced experimental and computational techniques.
The acronym “EMAGICS” stands for “Electromagnonics”, a field that studies the dynamical coupling between the electronic and magnetic properties of ME materials.
Merging theory and experiment is the optimal approach for achieving a better understanding of such exotic and sophisticated physical concepts. EMAGICS has employed a combination of first principles calculations and atomistic spin dynamics, together with experimental spectroscopic investigation, for a series of new ME MF materials.
The field of Density Functional Theory (DFT) ranks among the top 10 cited papers of all times.9 Highly accurate and fast electronic structure calculations can be performed by an approximation of the electron correlation and exchange interaction with a functional of the electron density.10,11 The versatility of DFT is based on the fact that by calculating the electronic structure of materials we can study a range of microscopic and macroscopic properties of matter, such as: electronic band structure, band gap, magnetic ordering, magnetization, spin and orbital magnetic moments, crystal structure, magnetocrystalline anisotropy, lattice vibrations, electric polarization, exchange interactions.
Motivation and strategy of the project
Multiferroics (MFs) are materials that can combine at least two primary ferroic properties: ferromagnetism, ferroelectricity and ferroelasticity. In the case of magnetoelectric (ME) MFs, coupling between ferroelectricity and ferromagnetism occurs.2
The prefix “ferro-“, meaning “iron” in Latin, was initially used in “ferromagnets”, materials that present spontaneous magnetic moment, as a courtesy to iron.3 By spontaneous, it is meant that the magnetization appears in the material intrinsically, at the absence of an external magnetic field. As an analogy to the spontaneous magnetization in ferromagnets, the term “ferroelectrics” was used for the first time by Schrödinger in 1912, for materials that present spontaneous polarization.4 Schmid introduced the term “multiferroics” in 1994, as “those having two or more primary ferroic properties in the same phase”.2
Currently, the field of multiferroics has attracted more and more researchers, from both fundamental theoretical and experimental physics, as well as the radiant world of applications. New exotic physics concepts have been introduced, such as monopoles, vortices, skyrmions and electromagnons, the latter being one of the main subjects of this project.
The main research objectives of EMAGICS are:
(RO1) to address the origin of the ME coupling in the polar antiferromagnets (AFM) Ni-based tellurates,
(RO2) to propose new spin-induced ME MF systems, and
(RO3) to synthesize and experimentally investigate the static and dynamical ME effects in these new compounds.
References
Moore, G. E. Cramming More Components Onto Integrated Circuits. Proceedings of the IEEE 86, 82 (1998).
Schmid, H. Multi-ferroic magnetoelectrics. Ferroelectrics 162, 317–338 (1994).
Bozorth, R. M. Ferromagnetism. (Van Nostrand, 1951).
Schrödinger, E. Studien über Kinetik der Dielektrika, den Schmelzpunkt, Pyro- und Piezoelektrizität. Sitzungsberichte der Kais. Akad. der Wissenschaften Wien. Math. Klasse 121, 1937–1972 (1912).
Scott, J. F. A comparison of magnetic random access memories (MRAMs) and ferroelectric random access memories (FRAMs). in Ferro- and Antiferroelectricity: Order/Disorder Versus Displacive (eds. Dalal, N. S. & BussmannHolder, A.) 124, 199 (Springer-Verlag Berlin, 2007).
Vopson, M. M. & M., M. Fundamentals of Multiferroic Materials and Their Possible Applications. Crit. Rev. Solid State Mater. Sci. 40, 223–250 (2015).
Pimenov, A. et al. Possible evidence for electromagnons in multiferroic manganites. Nat Phys 2, 97–100 (2006).
Rovillain, P. et al. Electric-field control of spin waves at room temperature in multiferroic BiFeO3. Nat Mater 9, 975–979 (2010).
Van Noorden, R., Maher, B. & Nuzzo, R. The top 100 papers. Nature 514, 550–553 (2014).
Kohn, W. & Sham, L. J. Self-Consistent Equations Including Exchange and Correlation Effects. Phys. Rev. 140, A1133–A1138 (1965).
Hohenberg, P. & Kohn, W. Inhomogeneous Electron Gas. Phys. Rev. 136, B864–B871 (1964).
http://www.pocketables.com/2011/08/whats-the-next-step-in-the-evolution-of-the-computer.html, 2013.
Kleemann W., American Physical Society 2009, 2, 105.
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