Magnetoelectric materials, phenomena, and devices Cite as: APL Mater. 9, 050401 (2021); https://doi.org/10.1063/5.0053631 Submitted: 09 April 2021 • Accepted: 11 April 2021 • Published Online: 03 May 2021 Liza Herrera Diez, Robert Kruk, Karin Leistner, et al. COLLECTIONS Paper published as part of the special topic on Magnetoelectric Materials, Phenomena, and Devices ARTICLES YOU MAY BE INTERESTED IN Advances in magneto-ionic materials and perspectives for their application APL Materials 9, 030903 (2021); https://doi.org/10.1063/5.0042544 Opportunities and challenges for magnetoelectric devices APL Materials 7, 080905 (2019); https://doi.org/10.1063/1.5112089 Emerging opportunities for voltage-driven magneto-ionic control in ferroic heterostructures APL Materials 9, 040904 (2021); https://doi.org/10.1063/5.0045820 APL Mater. 9, 050401 (2021); https://doi.org/10.1063/5.0053631 9, 050401 © 2021 Author(s). APL Materials EDITORIAL scitation.org/journal/apm Magnetoelectric materials, phenomena, and devices Cite as: APL Mater. 9, 050401 (2021); doi: 10.1063/5.0053631 Submitted: 9 April 2021 • Published Online: 3 May 2021 Liza Herrera Diez,1,a) Robert Kruk,2,b) Karin Leistner,3,4,c) and Jordi Sort5,6,d) AFFILIATIONS 1 Centre de Nanosciences et de Nanotechnologies, CNRS, Universite Paris-Saclay, 91120 Palaiseau, France 2 Institute of Nanotechnology, Karlsruhe Institute of Technology (KIT), 76344 Eggenstein-Leopoldshafen, Germany 3 Leibniz IFW Dresden, Helmholtzstrasse 20, Dresden 01069, Germany 4 Faculty of Natural Sciences, Institute of Chemistry, Chemnitz University of Technology, Straße der Nationen 62, 09111 Chemnitz, Germany 5 Departament de Física, Universitat Autònoma de Barcelona, E-08193 Cerdanyola del Vallès, Spain 6 Institució Catalana de Recerca i Estudis Avançats (ICREA), Pg. Lluís Companys 23, E-08010 Barcelona, Spain Note: This paper is part of the Special Topic on Magnetoelectric Materials, Phenomena, and Devices. a) Author to whom correspondence should be addressed: liza.herrera-diez@c2n.upsaclay.fr b) Electronic mail: robert.kruk@kit.edu c) Electronic mail: K.Leistner@ifw-dresden.de d) Electronic mail: Jordi.Sort@uab.cat https://doi.org/10.1063/5.0053631 Progress in information and communication technologies (i) using single-phase multiferroics, where various types of ferroic largely relies on an optimized utilization of electric power. Nano- orders (e.g., ferromagnetic and ferroelectric) intrinsically coexist magnetism and spintronics have largely contributed to the dig- in the material; (ii) surface charging or carrier density modula- ital revolution by drastically increasing hard disk capacity and tion, which can modify the electronic band structure of ultra-thin data processing speeds. Innovative energy-saving solutions are also metallic layers or semiconductors; (iii) magneto-ionics, which refers sought in magnetic actuation technologies, which are at the heart of to the voltage-driven ion motion typically across layers in con- micro/nano-electro-mechanical systems (MEMS/NEMS) and many tact with liquid electrolytes or ionic conductors (e.g., Gd2 O3 or other engineering applications. However, in both cases, either to HfO2 ); (iv) electrochemical redox reactions; and (v) strain-mediated write magnetic bits of data or to operate small-sized magnetic sys- coupling in piezoelectric/magnetostrictive heterostructures. Each tems, miniaturized electromagnets are required. The utilization of of these approaches faces some drawbacks: (i) dearth of available electric currents in such electromagnets (or spin-torque effects in single-phase multiferroic materials and limited strength of magneto- spintronics) involves a significant power dissipation due to the Joule electric coupling at room temperature; (ii) limited penetration depth heating effect. This is aggravated at the micro-/nanoscales, where the of electric field inside semiconductors and total electric-field screen- small device dimensions hinder heat conduction and thus effective ing at the surface of metals; (iii) low speed and limited endurance cooling. As a result, roughly half of the electric power reaching large in magneto-ionic systems; (iv) lack of precise control of chemi- data servers is wasted in the form of heat dissipation or in sophisti- cal reactions and their kinetics; and (v) clamping effects with the cated cooling systems.1 In view of enhancing energy efficiency, the substrate and need of good interfaces in strain-mediated compos- last two decades have seen a renaissance of the interest for control- ite multiferroics. Despite these system-specific limitations, all the ling magnetism with electrical voltage. The so-called “converse mag- above mechanisms can be used to modify the properties of fer- netoelectric effect” has emerged as a fundamentally different mag- romagnetic materials (anisotropy, coercivity, saturation magnetiza- netic control and actuation approach, prompting the development tion, Dzyaloshinskii-Moriya interaction, etc.), to a varying extent, of ultralow power consumption devices operated at the nanoscale. with voltage.5 Therefore, further progress is needed to address and Electricity and magnetism have always had an intimate link. overcome the current challenges. An added value to novel technolo- There are various ways to manipulate magnetism with voltage:2–4 gies is expected in piezoelectric/magnetostrictive heterostructures, APL Mater. 9, 050401 (2021); doi: 10.1063/5.0053631 9, 050401-1 © Author(s) 2021 APL Materials EDITORIAL scitation.org/journal/apm where the induced direct magnetoelectric effects (that is, generation coupling and direct magnetoelectric coupling is demonstrated in of electricity by applying magnetic fields) are appealing for energy the CoFe2 O4 /BiFeO3 system,11 which consists of self-assembled harvesting/conversion applications and for wireless neuron/muscle CoFe2 O4 slab-shaped crystals embedded in the BiFeO3 matrix. cell stimulation. This example underscores the highly interdisci- Electric-field-induced non-volatile magnetic switching in a plinary character of magnetoelectric technologies, whose develop- La0.7 Sr0.3 MnO3 (LSMO) thin film is investigated by Wilhelm et al.12 ment has triggered a wealth of new research directions in physics, Detailed photoemission electron microscopy observations are used chemistry, electronics, and engineering, in general. to correlate chemical with magnetic voltage-driven effects in this Recent advances in the understanding of magnetoelectric system. Rouco et al.13 reported on the independent control of ferro- mechanisms and new materials with significant voltage-driven mag- electric and oxygen vacancy switching in multiferroic tunnel junc- netic effects are reported in this Special Topic. State-of-the-art appli- tions with the LSMO bottom electrode, BaTiO3 ferroelectric bar- cations, including antennas, sensors, actuators, or magnetoelectric rier, and Ni top electrode (leading to a controlled inversion of the random-access memories, among others, are also described. Specif- interface spin polarization), an effect that could open interesting ically, the Special Topic contains one Research Update, three Per- new avenues toward neuromorphic devices. The use of novel ion spectives, and eight original research articles covering fundamental species, such as hydrogen or fluorine, surpassing some of the char- and application-oriented aspects of magnetoelectrics. acteristics of oxygen ion migration, is explored in the works by In the Research Update by Liang et al.,6 the authors pro- Goessler et al.14 and Vasala et al.15 The former studied the influence vide an extensive review of the existing magnetoelectric materials of hydrogen intercalation (using aqueous electrolytes) on the mag- and devices, with emphasis on multiferroics, either single-phase netic properties of nanoporous Pd(1-x) Cox , with Co being located or composites, both in bulk and thin-film form. The paper com- in superparamagnetic clusters. Temperature-dependent magneti- pares the magnetoelectric coupling strength for an extensive vari- zation curves show that interstitial hydrogen atoms lead to an ety of materials and lists the values of magnetoelectric constants increase in magnetic anisotropy energy and a concomitant block- in the dynamic regime in a wide range of operational frequencies. ing of their magnetic moments (i.e., tuning the superparamag- The salient features of a range of magnetoelectric devices (anten- netic blocking temperature). In turn, electrochemical fluorination nas, sensors, random-access memories, energy harvesters, induc- of La2 CuO4 , in solid state, offers the possibility of precisely adjust- tors, filters, etc.) are described, and the advantages with respect to ing hole doping and thus tuning of the superdiamagnetic prop- other conventional systems not using magnetoelectric effects are erties (perfect diamagnetic behavior of superconductors) of this emphasized. compound. In their Perspective, Nichterwitz et al.7 put the focus on Finally, included in the Special Topic are two papers magneto-ionics, particularly on the achieved voltage coefficients for dealing with specific applications of magnetoelectric materials. magnetization and coercivity and the demonstrated time scales for Nguyen et al.16 showed the performance of cantilever magnetoelec- magneto-ionic switching. The authors overview the progress in oxy- tric Pb(Zr,Ti)O3 /Tb–Fe–Co resonators for magnetic sensing appli- gen magneto-ionics, using solid and liquid electrolytes, while the use cations. In turn, Spetzler et al.17 studied the influence of the piezo- of other ion species (nitrogen, hydrogen, etc.) is also mentioned. The electric material on the signal and noise of magnetoelectric magnetic challenges of using this type of materials for real applications (in field sensors. terms of switching rates and endurance) are discussed. In conclusion, our Special Topic covers diverse aspects of mag- Voltage-driven magneto-ionic control in ferroic heterostruc- netoelectricity and highlights the recent discoveries in this com- tures using ionic liquids and ionic conductors is also overviewed in pelling research area. We hope that the included manuscripts will the Perspective by Gu et al.8 A particular aspect of this work is that it provide new insights inspiring the development of new magneto- reports on the usefulness of electrostatic and electrochemical meth- electric materials. Moreover, this Special Topic is intended to serve ods in tuning the ferroelectric properties of oxide-containing het- as a forum for students and researchers to further explore new sys- erostructures. The potential of magneto-ionics in tuning the prop- tem designs and devices whose energy efficiency, performance, and erties of skyrmions, van der Waals magnets, and topological Hall functionalities will surpass the current state of the art. effects is also considered, as well as its applicability in healthcare technologies and synaptic devices (i.e., neuromorphics). REFERENCES In the Perspective by Nicolenco et al.,9 the advantageous effects 1 J. Puebla, J. Kim, K. Kondou, and Y. Otani, “Spintronic devices for energy- of “strain gradients” (compared to homogeneous strains) in certain efficient data storage and energy harvesting,” Commun. Mater. 1, 24 (2020). multiferroic heterostructures (such as vertically aligned compos- 2 C. Song, B. Cui, F. Li, X. Zhou, and F. Pan, “Recent progress in voltage control ites or multi-phase porous frameworks) are reviewed. Although this of magnetism: Materials, mechanisms, and performance,” Prog. Mater. 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