Classical and exotic magnetism: recent advances and perspectives

Motivated by the pioneering studies of Eremenko of magneto-optical effects in antiferromagnetic crystals, we describe an expansion of the horizons of classical magnetism to include study of Earth's magnetic field and natural environments. We also review briefly examples of exotic magnetism not...

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Опубліковано в: :Физика низких температур
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Автори: Kivshar, Y., Roberts, A.P.
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Опубліковано: Фізико-технічний інститут низьких температур ім. Б.І. Вєркіна НАН України 2017
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Цитувати:Classical and exotic magnetism: recent advances and perspectives / Y. Kivshar, A.P. Roberts // Физика низких температур. — 2017. — Т. 43, № 8. — С. 1119-1125. — Бібліогр.: 29 назв. — англ.

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Digital Library of Periodicals of National Academy of Sciences of Ukraine
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author Kivshar, Y.
Roberts, A.P.
author_facet Kivshar, Y.
Roberts, A.P.
citation_txt Classical and exotic magnetism: recent advances and perspectives / Y. Kivshar, A.P. Roberts // Физика низких температур. — 2017. — Т. 43, № 8. — С. 1119-1125. — Бібліогр.: 29 назв. — англ.
collection DSpace DC
container_title Физика низких температур
description Motivated by the pioneering studies of Eremenko of magneto-optical effects in antiferromagnetic crystals, we describe an expansion of the horizons of classical magnetism to include study of Earth's magnetic field and natural environments. We also review briefly examples of exotic magnetism not directly associated with alignment of quantum spins in traditional ferromagnetic and antiferromagnetic crystalline structures. While many such cases have long been known, recent breakthroughs are associated with so-called optical magnetism that became a reality due to development of the field of metamaterials.
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fulltext Low Temperature Physics/Fizika Nizkikh Temperatur, 2017, v. 43, No. 8, pp. 1119–1125 Classical and exotic magnetism: recent advances and perspectives Yuri Kivshar Nonlinear Physics Center, Research School of Physics and Engineering, Australian National University Canberra ACT 2601, Australia E-mail: Yuri.Kivshar@anu.edu.au, ysk@internode.on.net Andrew P. Roberts Research School of Earth Sciences, Australian National University, Canberra ACT 2601, Australia Received February 6, 2017, published online June 26, 2017 Motivated by the pioneering studies of V. Eremenko of magneto-optical effects in antiferromagnetic crystals, we describe an expansion of the horizons of classical magnetism to include study of Earth’s magnetic field and natural environments. We also review briefly examples of exotic magnetism not directly associated with align- ment of quantum spins in traditional ferromagnetic and antiferromagnetic crystalline structures. While many such cases have long been known, recent breakthroughs are associated with so-called optical magnetism that be- came a reality due to development of the field of metamaterials. PACS: 75.10.–b General theory and models of magnetic ordering. Keywords: paleomagnetism, environmental magnetism, optical magnetism. 1. Introduction The phenomenon of magnetism is usually associated with specific states of crystalline solids in which electron spins within the material align in a specific direction. This classical approach was followed by V. Eremenko who more than 30 years ago undertook experimental studies of mag- neto-optical effects in antiferromagnetically ordered crys- tals [1]. The extended zoo of magnetism also houses some inte- resting species in which classical magnetic systems have varying origins and applications. In recent years we have witnessed a renewed interest in the study of magnetic phe- nomena at different scales, ranging from the remarkable magnetar stars [2] with the strongest magnetic fields in the Universe (typically 1010–1011 T), to nanoscale objects where the effective magnetic properties are induced by incoming laser radiation. Magnetic phenomena have become more complex or unusual, with spins arranged in compli- cated geometries or with magnetic responses created by optical fields through resonances that lead to unusual phe- nomena such as optical magnetism. In this brief review paper, we describe some examples of classical and exotic magnetic systems, mainly from our recent research activi- ties, that we consider relevant to celebrating the pioneering research contributions of V. Eremenko into the physics of magnetic systems summarized by his colleagues and friends in this special issue. First, we discuss aspects of classical magnetism associ- ated with antiferromagnetic order, particularly in relation to deviations from perfect antiferromagnetism, in the fields of paleomagnetism [3] and environmental magnetism [4,5]. These applications involve the study of rock and mineral magnetism to understand how magnetic rock-forming min- erals record information about past variations in Earth’s magnetic field or about changing natural environments. Next, we address the recent and still somewhat contro- versial issue of so-called optical magnetism. It is well es- tablished that in the optical regime natural materials do not exhibit magnetic properties so that their magnetic permea- bility µ can be set to unity, i.e. = 1µ , as described in the famous textbook of Landau and Lifshitz [6]. We argue that the use of metamaterials and engineered artificial meta- atoms and metadevices [7] allows any value of µ to be pro- duced to give a strong magnetic response by achieving resonances in structured systems made of nonmagnetic ma- terials [8]. Although magnetism in its conventional sense is not available at mid-IR and optical frequencies, it is pos- sible to engineer the spatial dispersion and nonlocal elec- tric effects so as to induce a strong magnetic dipole mo- © Yuri Kivshar and Andrew P. Roberts, 2017 mailto:Yuri.Kivshar@anu.edu.au Yuri Kivshar and Andrew P. Roberts ment without other higher-order contributions, even though the materials involved do not have a microscopic magneti- zation and their magnetic permeability is strictly unitary [9]. Finally, we demonstrate that some of the exotic magnetic structures produced by optically induced magnetic moments can possess antiferromagnetic order. This provides a direct all-optical analog to the crystalline antiferromagnetic com- pounds studied by V. Eremenko and his colleagues almost 30 years ago [1]. 2. Paleomagnetism and environmental magnetism Magnetic signal recording in minerals. In paleomagnet- ism and environmental magnetism, we measure magnetic signals recorded by magnetically ordered rock-forming mi- nerals to address research questions in geology, geophysics, and environmental science. In his Nobel Prize winning work on the magnetic structure of antiferromagnetic materials, Louis Néel [10] postulated the existence of magnetic sub- lattices, which was later proven by neutron diffraction, where neighboring electron spins have a mutually antiparal- lel alignment so that their magnetic moments cancel com- pletely (Fig. 1). True antiferromagnetism is common in rock- forming minerals, but the zero net spontaneous magnetiza- tion does not provide signals of interest in paleomagnetism and environmental magnetism. Furthermore, true ferromag- netism (Fig. 1) does not exist in rock-forming minerals at Earth’s surface. The magnetizations of interest in paleomag- netism and environmental magnetism arise due to ferrimag- netism, which is a sub-category of antiferromagnetism in which the magnetic moments of the two magnetic sub- lattices are antiparallel but of unequal magnitude. Ferrimag- nets behave macroscopically like ferromagnets, so they are often treated as equivalent, but the main difference is that ferrimagnets have a weaker net magnetization because of partial cancellation associated with the opposite but un- equal sub-lattice magnetizations associated with the basic antiferromagnetic structure (Fig. 1). Ferrimagnetic order was invoked by Néel [10] to explain the magnetization of fer- rites, the best-known example of which among magnetic minerals is magnetite (Fe3O4) where the magnetic mo- ments of an equivalent number of Fe3+ ions are aligned antiparallel so that the net magnetization arises from the magnetic moments of uncompensated Fe2+ ions (Fig. 1). Magnetizations of interest also arise due to other variations on the antiferromagnetic theme: where defects or vacancies in a crystal lattice give rise to incomplete cancellation of sub-lattice magnetic moments (defect antiferromagnetism) or where non-zero net magnetizations are achieved due to slight spin canting (canted antiferromagnetism; Fig. 1). The common magnetic iron oxide mineral hematite (α-Fe2O3) is a canted antiferromagnet. Magnetic signals due to devia- tions from classical antiferromagnetic order, thus, provide information that can be exploited to understand variations Fig. 1. Schematic two-dimensional representations of the main types of exchange-coupled magnetic spin structures. In a ferromagnetic structure, all magnetic moments are aligned, while in antiferromagnetic metal oxides nearest neighbor cations have antiparallel spin vectors and the spin structure consists of two equal and opposite magnetic sub-lattices with zero net moment. In ferrimagnetic metal oxides, as illustrated for the magnetic mineral magnetite, cations on non-equivalent sites are bonded with oxygen to produce a spin structure with two antiparallel but unequal magnetic sub-lattices that give rise to a net moment due to octahedrally coordinated Fe2+ . Weak net magnetizations can also arise in imperfect antiferromagnetic structures due to lattice defects such as cation site vacancies (not illustrated), or due to canting of spins (e.g. in hematite). The degree of spin canting shown is 5°. Net magnetizations have been reported in materials with spin-canting of < 1°. The net magnetizations are small but measurable. Ferrimagnetism Ferromagnetism Antiferromagnetism Canted antiferromagnetism 1120 Low Temperature Physics/Fizika Nizkikh Temperatur, 2017, v. 43, No. 8 Classical and exotic magnetism: recent advances and perspectives in Earth’s magnetic field throughout most of our planet’s history and to address wide-ranging environmental research questions as discussed briefly below. Paleomagnetism. Earth’s magnetic field is dominantly dipolar (Fig. 2), so that as early as 1600 AD, the personal physician of Queen Elizabeth I, William Gilbert, made the empirical deduction that Earth’s magnetic field resembles that of a great magnet (he used lodestone (magnetite ore) in his experiments). This simple dipolar field geometry means that, when averaged over time, the inclination of the geo- magnetic field is a simple function of latitude. When mag- netic minerals record the orientation of the geomagnetic field at the time that their host rock formed, they provide a fossilized record of the ancient magnetic field. When rocks of varying ages are subjected to paleomagnetic analysis, the results do not provide a simple record of the inclination of the present day dipole field. Instead, for progressively older rocks from any continent, the pole calculated for a dipolar field will often lie far from geographic north. Calculated ancient pole positions are not random; they lie along coherent so-called apparent polar wander paths. The term apparent is used because the pole did not move; ra- ther, it is the continent that has moved with respect to the pole. The paleomagnetic record represented by the appar- ent polar wander path for a continent, thus, documents past movements of that continent. This information provided key evidence to confirm the theory of Continental Drift. It is not an overstatement to say that paleomagnetism has revolutionized our understanding of the Earth. It has been instrumental in establishing the plate tectonic paradigm, which provides a unifying theory for Earth science. Paleo- magnetism has also been used to demonstrate that the geo- magnetic field has reversed polarity hundreds of times in Earth history (Fig. 3). Unlike the frequent and regular re- versal of the sun’s magnetic field (every 11 years), the pro- cess responsible for this flipping of geomagnetic polarity is stochastic. The randomly varying time intervals between successive reversals provides a bar-code-like pattern that has made it possible to develop a geomagnetic polarity timescale [11] that is used to calibrate geological time by identifying magnetic polarity reversal patterns (Fig. 3) in geological sequences of lava flows or sedimentary rocks. A fundamental aspect of paleomagnetism is that it pro- vides an understanding of Earth’s magnetic field and the processes that generate the field through a dynamo mecha- nism in which turbulent convection of an iron-nickel alloy in Earth’s molten outer core produces a self-sustaining field (Fig. 2). Geomagnetic variations through geological time provide knowledge of a diverse range of field beha- viors with variable time constants, including polarity re- versals and excursions (thousands of years), and secular Fig. 2. (Color online) Cut-away cartoon of Earth’s interior with a view of the solid inner core (gray) and fluid outer core (yellow) from which geomagnetic flux lines emerge. The helical lines represent magnetic flux emerging from columnar convection cells that occur within the larger scale fluid flow in the outer core that drives the geodynamo. These cells transfer heat from the inner core-outer core boundary to the core-mantle boundary. The over- all field is symmetrical about Earth’s rotation axis. Over time, the field averages to a geocentric axial dipole, which is exploited in paleomagnetism to reconstruct the former positions of conti- nental landmasses. Fig. 3. Geomagnetic polarity timescale for the last 170 million years (age is in million years ago, Ma) [11]. Blue = normal po- larity (i.e. like the present-day field); tan = reversed polarity (i.e. opposite to the present-day field). Reversal frequency has varied considerably over time; the field remained largely in a normal polarity configuration through the Cretaceous Normal Superchron (126 Ma to 93 Ma), but generally reverses polarity several times per million years. Low Temperature Physics/Fizika Nizkikh Temperatur, 2017, v. 43, No. 8 1121 Yuri Kivshar and Andrew P. Roberts variations (years to millennia). The time interval between geomagnetic reversals generally ranges from hundreds of thousands of years to so-called “superchrons” when the field did not reverse polarity for tens of millions of years (Fig. 3). This indicates that phenomena with longer time constants also affect the field. The geomagnetic field shields Earth from harmful cos- mic radiation. Development of the early geomagnetic field is argued to have contributed to conditions that allowed evo- lution of life on, or at least contributed to the habitability of, our planet [12]. All of this information about the Earth is the result of painstaking efforts by paleomagnetists to do- cument information recorded by magnetic minerals. Mag- netic fields are ubiquitous in the cosmos, yet field varia- tions through time, and the valuable information they provide about cosmic evolution, are difficult to study be- cause of the small and incomplete record provided by me- teoritic materials. In contrast, Earth is a natural laboratory for analyzing the magnetic history of a planet through pa- leomagnetic analysis. Space limitations prevent us from elucidating the details of many fascinating phenomena dis- covered through paleomagnetic analysis of terrestrial and meteoritic materials. Readers who are interested in further details are referred to an excellent recent text that is avail- able online [3]. Environmental magnetism. In addition to their capacity to record information about ancient magnetic fields, mag- netic minerals are responsive to changing environmental conditions. Environmental magnetism [4,5] exploits the sen- sitivity of magnetic minerals to chemical reduction-oxid- ation processes at Earth’s surface, which drive transforma- tion of Fe2+ to Fe3+, and vice versa, in magnetic minerals that facilitates understanding of environmental processes. Wide-ranging processes are explored using environmental magnetism, which contributes to understanding the driving forces of environmental change. Instead of describing en- vironmental magnetism in detail, we provide below a par- ticularly clear example of its use in understanding climate variability. Larrasoaña et al. [13] used meteorological, satellite, and geochemical data to identify the eastern Sahara Desert north of the central Saharan watershed at 21°N as the source of windblown dust that accumulates in the Eastern Mediterra- nean Sea. In the hyper-arid Sahara, hematite forms though progressive dehydration and oxidation of other iron-bear- ing minerals. Regional aridity changes have driven varia- tions in dust delivery from the northeastern Sahara to the Eastern Mediterranean Sea over millions of years in re- sponse to African monsoon variations, for which hematite is an excellent proxy. Hematite-based environmental mag- netic records of Saharan dust deposition into the Eastern Mediterranean Sea, therefore, provide important insights into the long-term functioning of the African monsoon and the history of the Sahara Desert [13]. Monsoons are con- trolled by variations in Earth’s orbit that drive cyclical va- riations in the amount of incident solar radiation at Earth’s surface. This magnetic record of dust inputs indicates that long-term African monsoon variations have driven cyclical climatic variations in North Africa, which undergoes large- scale changes from hyper-arid desert conditions to green Sahara episodes [13,14]. Green Sahara episodes would have provided a much broader landscape that was suitable for hominin habitation and would have opened a migration path- way for our ancestors between Africa and Eurasia in con- trast to modern hyper-arid conditions that provide a hostile environment for habitation and a major biogeographic bar- rier to migration [14]. Orbital control of the monsoon is most clearly evident when the hematite dust record is sub- jected to band-pass filtering (Fig. 4). An inverse relation- ship exists between dust and orbital control because maxi- mum dust production occurs during monsoon minima and vice versa. Age uncertainties for the sediment record mean that it is safest to undertake bandpass filtering over an age band for each orbital period. Dust variations occur in lock step with orbital variations (Fig. 4) and are statistically coherent with each other at the 99% significance level [13]. While many examples of the use of magnetism for under- standing environmental processes could be cited, such an immediate environmental response to Earth’s orbital forc- ing of climate makes it clear that the magnetic properties of minerals can provide powerful information about envi- ronmental processes such as climate variability, monsoons, Fig. 4. (Color online) Illustration of environmental magnetic analysis of windblown Saharan dust to understand climate forcing of dust deposition in marine sediments. The band-pass filtered dust record (blue; period bands are in thousands of years) of Larrasoaña et al. [13] reflects an immediate response to insola- tion-driven African monsoon forcing at all major orbital periods (including precession, obliquity, and long and short eccentricity). The astronomical solution of Laskar et al. [15] was band-pass filtered (red) using the same band as the dust record, and is nor- malized by the respective standard deviation. The band-pass- filtered dust signal is scaled identically for all period bands to conserve relative amplitude ratios between the signal compo- nents, and is multiplied by –1 because the insolation-driven mon- soon response anticorrelates with dust production. Ages are in thousands of years before present (ka). 1122 Low Temperature Physics/Fizika Nizkikh Temperatur, 2017, v. 43, No. 8 Classical and exotic magnetism: recent advances and perspectives and desertification. The environmental magnetic record de- scribed here is due to canted antiferromagnetism in hema- tite, and gives an example of the diversity of applications that exploit antiferromagnetic structures. 3. Optical magnetism Mie resonances and magnetic responses. We now move from classical to more exotic manifestations and applica- tions of magnetism. Natural materials exhibit negligible mag- netism at mid-IR and optical frequencies because the direct effects of optical magnetic fields on matter are much weak- er than electric ones. However, in recent decades many re- searchers have sought to overcome this natural limitation by designing artificial subwavelength structures that allow a strong magnetic response, even if such structures are made of nonmagnetic materials. This progress has been possible due to advances in the field of metamaterials, which are com- posed of subwavelength elements that are often referred to as meta-atoms and the exotic states that they can support. One of the first examples of a meta-atom was the metal- lic split-ring resonator (Fig. 5(a)) where electrons oscillate in two parallel arms in the opposite direction to create an ef- ficient magnetic response. Split-ring resonators were first introduced at microwave frequencies to realize artificial mag- netic inclusions with subwavelength footprint, and were translated to optics by exploiting the plasmonic features of metallic nanoparticles. Such magnetic structures have now been realized in many nonmagnetic plasmonic structures ranging from nanobars [16,17] and nanoparticle complexes, which are often called oligomers [18,19], to split-ring-bas- ed structures [20–22], and more complicated multilayered structures such as fishnet metamaterials with both elliptic and hyperbolic types of dispersion [23]. For many years, subwavelength localization of light in nanophotonics was associated with free electrons and elec- tromagnetic waves at metallic interfaces. However, recent developments in the physics of high-refractive-index di- electric nanoparticles [9] suggest an alternative mechanism of light localization via low-order dipole and multipole Mie resonances that may generate strong magnetic res- ponses [24] (Fig. 5(b)). The physics of Mie resonances is usually associated with Rayleigh scattering and the colors of colloidal solutions with gold nanoparticles. However, a more recent understanding is that optical resonances of dielectric nanoparticles with high refractive index can also facilitate light manipulation below the free-space diffrac- tion limit [9]. To illustrate the properties of light scattering by nanoparticles, we consider a small nanodisk illuminated by a plane wave. Scattering by such a nanoparticle gives rise to strong resonances (Fig. 6). Importantly, for dielectric particles we can observe both electric and magnetic responses of comparable strengths. A strong magnetic dipole resonance appears due to coupl- ing of incoming light to the circular displacement currents of the electric field, owing to field penetration and phase retardation inside the particle. This occurs when the wave- length inside the particle becomes comparable to its spatial dimension such as radius, 2 /R n≈ λ , where n is the refrac- tive index of the particle material, R is the nanoparticle radius, and λ is the wavelength of light. First, this type of geometric resonance suggests that a nanoparticle should have a relatively large refractive index in order to have resonances in visible and infrared spectral regions. Second, at the wavelength of a magnetic resonance, the excited magnetic dipole mode of a dielectric nanoparticle may be- come comparable or even stronger than the electric dipole response and make a major contribution to the scattering efficiency. Importantly, the electric and magnetic dipoles are often perpendicular to each other (Fig. 6). The term “displacement current” was considered for many years a mathematical curiosity introduced by J.C. Maxwell Fig. 5. (Color online) Examples of optically induced magnetic dipole moments in metallic split-ring resonators (a) and dielectric nanoparticles with high refractive index (b). Green arrows indi- cate the direction of the electronic current and displacement cur- rent, respectively (courtesy of A. Miroshnichenko). Fig. 6. (Color online) (Color online) Scattering efficiency for a silicon nanodisk with contributions from electric dipole (ED) and magnetic dipole (MD) Mie resonances, shown with the radia- tion patterns of two dipolar modes (adopted from Ref. 8). Low Temperature Physics/Fizika Nizkikh Temperatur, 2017, v. 43, No. 8 1123 Yuri Kivshar and Andrew P. Roberts into his famous equations to provide continuity of current lines in nonconducting media, where the induction D chang- es in time. Now, with resonant all-dielectric photonics driv- en by strong electric and magnetic dipole and multipole Mie resonances, the displacement current becomes a pow- erful tool of nanoscale photonics, and it helps to realize optical magnetism in low-loss, high-efficiency photonic structures. The spectral position of the magnetic dipole resonance of a spherical particle is approximately defined via a geometric resonance where the internal wavelength scales with the refractive index. Therefore, larger refractive indices are desirable from the point of view of metadevice dimensions and visible wavelength operation. The field enhancement and Q-factor of Mie resonances also benefit from large refractive indices of particles, with smaller radi- ation leakage. These considerations motivate the quest for materials with large refractive index. In the visible and near-infrared spectral ranges, large permittivity is known to occur for semiconductors such as Si, Ge, AlGaAs, and others (Fig. 6). In the neighboring mid-infrared range, which is also of great interest in nano- photonics, narrow-band semiconductors (Te and PbTe) and polar crystals such as SiC have been used in all-dielectric metadevices operating with Mie resonances. A pioneering milestone in optical magnetism was the experimental ob- servation of a strong magnetic response in visible and in- frared bands reported for spherical Si nanoparticles [25]. This opened a way to study many interesting phenomena with high-refractive-index dielectric structures employed as building blocks for metadevices with inspiration from century-old studies of light scattering. Optical antiferromagnetism. To reduce the interaction energy of atoms in magnetic solids, the spins of magnetic atoms can align in the opposite direction to that of their neighbors in some structures to give rise to the familiar antiferromagnetic order (Fig. 1). As discussed above, many compounds and oxides are antiferromagnetic, including CoCO3, DyFe3, and Dy3Al5O12, which were studied by V. Eremenko and co-authors [1]. Antiferromagnetism is also associated with the expanding field of high-temperature superconductivity [26]. Thus, the magnetic properties of antiferromagnetic structures remain of great scientific in- terest. When meta-atoms that support optical magnetic dipoles are combined to create metamaterials or metasurfaces, the overall structure of the induced magnetic moments resemb- les ferromagnetic order (Fig. 1), as illustrated by two cases in Fig. 7. This is valid for both illustrated types of electro- magnetic metasurfaces, where it is either induced in metal- lic meta-atoms by oscillation of free electrons or by a dis- placement current in dielectric meta-atoms with high re- fractive index. However, if we assemble hybrid structures with dissimilar elements with magnetic dipole moments of different origin (see Fig. 7), we expect that such hybrid meta-molecules with strong coupling of individual mo- ments can create antiferromagnetic ordering of magnetic moments, as has been suggested recently from theoretical considerations [27]. Experimental demonstration of antiferromagnetic order- ing for a single meta-molecule and for metasurfaces has been reported recently, which establishes a new type of opti- cally induced magnetism that resembles the staggered struc- ture of spins in antiferromagnetically ordered materials [28]. This demonstration was enabled by creating hybrid electro- magnetic metasurfaces by assembling hybrid meta-atoms formed by metallic split-ring resonators and dielectric par- ticles with high refractive index, both of which support opti- cally induced magnetic dipole resonances of different origin. Each pair (or meta-molecule) is characterized by two inter- acting magnetic dipole moments with the distance-depend- ent magnetization resembling the spin exchange interaction in magnetic materials. By mapping directly the structure of the electromagnetic fields, it was demonstrated experimen- tally that strong coupling between optically induced mag- netic moments of different origin can flip the magnetization orientation in a meta-molecule to create an antiferromag- netic lattice of staggered magnetic moments in hybrid me- tasurfaces [28]. Such an approach can be further extended to achieve fine control of magnetic interaction with spec- tral tuning of multipolar coupling of different modes. Thus, hybrid metamaterials offer new opportunities to achieve unprecedented control of light-matter interactions. 4. Conclusions and outlook Magnetism has changed our lives by giving us com- passes that allow navigation. It lies behind many useful practical devices that help us to record sound and music, Fig. 7. (Color online) Schematic illustration of magnetic dipole ordering in electromagnetic metasurfaces. A metasurface com- posed of identical elements (meta-atoms) resembles ferromagnet- ic ordering (Fig. 1) when magnetic dipole moments are induced (upper two cases). When combined, the two dissimilar types of meta-atoms with ferromagnetic ordering can create antiferromag- netic ordering (Fig. 1) with a staggered structure of optically in- duced magnetic dipole moments. The structure is one of several possible realizations of antiferromagnetic order (adopted from Ref. 28). 1124 Low Temperature Physics/Fizika Nizkikh Temperatur, 2017, v. 43, No. 8 Classical and exotic magnetism: recent advances and perspectives and allows us to store information. We believe that the im- portance of magnetism and magnetic phenomena will only grow, and will continue to bring new surprises in science and life. Paleomagnetism has made paradigm-changing contri- butions to our understanding of Earth and its changing ge- ography through time. Many interesting problems remain to be solved such as documenting the earliest geomagnetic fields and their potential relationship to early life on Earth. Likewise, paleomagnetic analysis of extraterrestrial mate- rials is currently booming and is providing new insights into the workings of the early solar system and beyond. Environmental magnetic analysis is providing insights into wide-ranging environmental processes, which are import- ant in understanding modern and ancient environmental change in response to natural and anthropogenic forcing. On a different scene and scales, recent demonstrations of optical magnetism in many types of nanoscale structures are associated with new advances in nanotechnology, bio- technology, and the new field of meta-optics. More import- antly, the study of optical magnetism with resonant high- index dielectric nanoparticles has emerged as a new direc- tion in modern photonics. It originates from century-old studies of light scattering, and it brings various optically induced electric and magnetic dipole and multipole reso- nances into modern studies of metadevices driven by opti- cal magnetic responses. Importantly, this also motivates the recently emerged field of multipolar nonlinear nano- photonics [29]. These recent developments suggest intri- guing opportunities for design of nonlinear subwavelength light sources with reconfigurable radiation characteristics and for engineering large effective optical nonlinearities at the nanoscale, which could have important implications for novel nonlinear photonic devices operating beyond the dif- fraction limit. High-refractive-index nanophotonics is expected to com- plement or even substitute for different plasmonic compo- nents in a range of applications. All-dielectric resonant struc- tures have many advantages, including resonant behavior and low energy dissipation into heat. Importantly, the ex- istence of strong electric and magnetic dipole and multi- pole resonances can result in constructive or destructive interferences with unusual beam shaping, and may also lead to resonant enhancement of magnetic fields in dielectric nanoparticles that bring many novel functionalities for both linear and nonlinear regimes. We expect that many nano- photonic effects can be enhanced by magnetic resonances, including Raman scattering, magneto-optical responses, and nonlinear parametric interactions. Acknowledgements Y.K. acknowledges useful collaboration and discus- sions with Dr. Andrey Miroshnichenko and his help with the figures. This work was supported by the Australian Research Council. 1. V.V. Eremenko and N.F. Kharchenko, Phys. Rep. 155, 379 (1987). 2. L. Kruesi, Phys. World 28, 36 (2015). 3. L. Tauxe, Essentials of Paleomagnetism, Univ. Calif. Press (2010). Available online at: https://earthref.org/MagIC/books/Tauxe/Essentials/ 4. R. Thompson and F. 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id nasplib_isofts_kiev_ua-123456789-174599
institution Digital Library of Periodicals of National Academy of Sciences of Ukraine
issn 0132-6414
language English
last_indexed 2025-12-07T16:50:29Z
publishDate 2017
publisher Фізико-технічний інститут низьких температур ім. Б.І. Вєркіна НАН України
record_format dspace
spelling Kivshar, Y.
Roberts, A.P.
2021-01-25T12:20:40Z
2021-01-25T12:20:40Z
2017
Classical and exotic magnetism: recent advances and perspectives / Y. Kivshar, A.P. Roberts // Физика низких температур. — 2017. — Т. 43, № 8. — С. 1119-1125. — Бібліогр.: 29 назв. — англ.
0132-6414
PACS: 75.10.–b
https://nasplib.isofts.kiev.ua/handle/123456789/174599
Motivated by the pioneering studies of Eremenko of magneto-optical effects in antiferromagnetic crystals, we describe an expansion of the horizons of classical magnetism to include study of Earth's magnetic field and natural environments. We also review briefly examples of exotic magnetism not directly associated with alignment of quantum spins in traditional ferromagnetic and antiferromagnetic crystalline structures. While many such cases have long been known, recent breakthroughs are associated with so-called optical magnetism that became a reality due to development of the field of metamaterials.
Y.K. acknowledges useful collaboration and discussions with Dr. Andrey Miroshnichenko and his help with the figures. This work was supported by the Australian Research Council.
en
Фізико-технічний інститут низьких температур ім. Б.І. Вєркіна НАН України
Физика низких температур
Low dimensionality and inhomogeneity effects in quantum matter
Classical and exotic magnetism: recent advances and perspectives
Article
published earlier
spellingShingle Classical and exotic magnetism: recent advances and perspectives
Kivshar, Y.
Roberts, A.P.
Low dimensionality and inhomogeneity effects in quantum matter
title Classical and exotic magnetism: recent advances and perspectives
title_full Classical and exotic magnetism: recent advances and perspectives
title_fullStr Classical and exotic magnetism: recent advances and perspectives
title_full_unstemmed Classical and exotic magnetism: recent advances and perspectives
title_short Classical and exotic magnetism: recent advances and perspectives
title_sort classical and exotic magnetism: recent advances and perspectives
topic Low dimensionality and inhomogeneity effects in quantum matter
topic_facet Low dimensionality and inhomogeneity effects in quantum matter
url https://nasplib.isofts.kiev.ua/handle/123456789/174599
work_keys_str_mv AT kivshary classicalandexoticmagnetismrecentadvancesandperspectives
AT robertsap classicalandexoticmagnetismrecentadvancesandperspectives