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Interplay of ferroic properties in multiferroics (adapted from Ref. 7)
Multiferroics are materials that combine at least two of the primary ferroic properties: ferroelectricity, ferromagnetism and ferroelasticity.
The early years of multiferroics were mostly linked to the magnetoelectric (ME) effect: the interplay between magnetic and electric dipole moments. However, the magnetoelectric family of materials is much broader than what nowadays we came to know and understand as multiferroics.
But let us see at first how it all started. Surprisingly enough, for more than a century since the first report of magnetoelectric effect by Röntgen in 1888,8 both magnetoelectricity and multiferroicity were neglected by the scientific community. Only a few isolated reports of magnetoelectrics or multiferroics appeared during the years, until the so-called “Revival of the magnetoelectric effect” in 2000s.1,9,10
But let us see at first how it all started. Surprisingly enough, for more than a century since the first report of magnetoelectric effect by Röntgen in 1888,8 both magnetoelectricity and multiferroicity were neglected by the scientific community. Only a few isolated reports of magnetoelectrics or multiferroics appeared during the years, until the so-called “Revival of the magnetoelectric effect” in 2000s.1,9,10
The first reported study related to the magnetoelectric effect was, as mentioned above, by Röntgen in 1888, who observed magnetization emergence in a moving dielectric at the presence of external electrical field.8 A few years later, in 1894, Pierre Curie predicted the possible existence of magnetoelectric effect in crystals, by the use of symmetry considerations.11 The reverse magnetoelectric effect, or else the polarization emergence in a moving dielectric at the presence of external magnetic field, was published in 1905 by Wilson.12 However, only in 1926 the term “magnetoelectric effect” was stated for the first time by Debye.13 The essential turn though occurred with the introduction of the broken space- and time-reversal symmetry by Dzyaloshinskii in 1959, as a prerequisite for the manifestation of the magnetoelectric effect.14 In the latter publication, he predicted the occurrence of the magnetoelectric effect in antiferromagnets (AFM), namely Cr2O3, for which a year later was experimentally demonstrated by Astrov.15
Before we continue with the facts that led to what nowadays is understood as multiferroicity, it would be helpful to understand what was meant by the term “ferroic” property or material. The prefix “ferro-“, meaning “iron” in latin, was initially used in “ferromagnets”, materials that present spontaneous magnetic moment, as a courtesy to iron.16 By spontaneous, it is meant that the magnetization appears in the material intrinsically, at the absence of an external magnetic field. Switching of the magnetic moments can occur at the presence of an external 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.17 During the 1960s, Aizu - the first to use the term “ferroic” - in a series of publications, presented all possible ferroelectric,18,19 ferroelastic20 and ferromagnetic21 species, based on crystal symmetry analysis, as well as the possible coexistence of those three different ferroic properties.21 Newnham et al.22,23 further on, classified ferroics, considering as primary ferroic properties: ferromagnetism, ferroelectricity and ferroelasticity. Finally, the first experimental observation of electric field-induced magnetization rotation by 90° was achieved by Ascher et al. in 1966, who studied the boracite Ni3B7O17I.24Unfortunately, in spite of all the significant advances during 1960s and 1970s, the possibility of combined ferroic properties was left aside till 1990s. The main reason was that the family of perovskites, one of the main crystal structures studied among ferroic materials, only seldom share simultaneously magnetic and ferroelectric (FE) properties.6
The reappraisal of the matter was done by Schmid in 1994, who introduced the term “multiferroics”, as “those having two or more primary ferroic properties in the same phase”25 (figure above), followed by Spaldin (as Hill at that time)9 in 2000 and Khomskii10 in 2001, both pointing out the reasons for the existence of so few single-phase magnetoelectric multiferroics.
During the coming years, significant contributions in the microscopic quantum level, as well as experimental breakthrough in various techniques, led to numerous discoveries of multiferroic materials. In 2007, Cheong and Mostovoy reintroduced the classification of ferroelectrics in proper and improper,26 and their role in the wider family of multiferroics. Finally, Khomskii in 2009 established the classification of multiferroics in Type I and II, depending on the origin and/or the microscopic mechanisms of the magnetoelectric coupling.27
Before we continue with the facts that led to what nowadays is understood as multiferroicity, it would be helpful to understand what was meant by the term “ferroic” property or material. The prefix “ferro-“, meaning “iron” in latin, was initially used in “ferromagnets”, materials that present spontaneous magnetic moment, as a courtesy to iron.16 By spontaneous, it is meant that the magnetization appears in the material intrinsically, at the absence of an external magnetic field. Switching of the magnetic moments can occur at the presence of an external 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.17 During the 1960s, Aizu - the first to use the term “ferroic” - in a series of publications, presented all possible ferroelectric,18,19 ferroelastic20 and ferromagnetic21 species, based on crystal symmetry analysis, as well as the possible coexistence of those three different ferroic properties.21 Newnham et al.22,23 further on, classified ferroics, considering as primary ferroic properties: ferromagnetism, ferroelectricity and ferroelasticity. Finally, the first experimental observation of electric field-induced magnetization rotation by 90° was achieved by Ascher et al. in 1966, who studied the boracite Ni3B7O17I.24Unfortunately, in spite of all the significant advances during 1960s and 1970s, the possibility of combined ferroic properties was left aside till 1990s. The main reason was that the family of perovskites, one of the main crystal structures studied among ferroic materials, only seldom share simultaneously magnetic and ferroelectric (FE) properties.6
The reappraisal of the matter was done by Schmid in 1994, who introduced the term “multiferroics”, as “those having two or more primary ferroic properties in the same phase”25 (figure above), followed by Spaldin (as Hill at that time)9 in 2000 and Khomskii10 in 2001, both pointing out the reasons for the existence of so few single-phase magnetoelectric multiferroics.
During the coming years, significant contributions in the microscopic quantum level, as well as experimental breakthrough in various techniques, led to numerous discoveries of multiferroic materials. In 2007, Cheong and Mostovoy reintroduced the classification of ferroelectrics in proper and improper,26 and their role in the wider family of multiferroics. Finally, Khomskii in 2009 established the classification of multiferroics in Type I and II, depending on the origin and/or the microscopic mechanisms of the magnetoelectric coupling.27
1 M. Fiebig, J. Phys. D. Appl. Phys. 38, R123 (2005).2 W. Eerenstein, N.D. Mathur, and J.F. Scott, Nature 442, 759 (2006).3 R. Ramesh and N.A. Spaldin, Nat. Mater. 6, 21 (2007).4 K.F. Wang, J.-M. Liu, and Z.F. Ren, Adv. Phys. 58, 321 (2009).5 S. Dong, J.-M. Liu, S.-W. Cheong, and Z. Ren, Adv. Phys. 64, 519 (2015).6 D.I. Khomskii, in Multiferroic Mater. Prop. Tech. Appl., edited by J. Wang (Taylor & Francis, 2017), pp. 3–4.7 N.A. Spaldin and M. Fiebig, Science 309, 391 (2005).8 W.C. Röntgen, Ann. Phys. 35, 264 (1888).9 N.A. Hill, J. Phys. Chem. B 104, 6694 (2000).10 D.I. Khomskii, in Proc. Am. Phys. Soc. (Seattle, 2001).11 P. Curie, J. Phys. Théorique Appliquée 3, 393 (1894).12 H.A. Wilson, Philos. Trans. R. Soc. London A Math. Phys. Eng. Sci. 204, (1905).13 P. Debye, Zeitschrift Für Phys. 36, 300 (1926).14 I.E. Dzyaloshinskii, Sov. Phys. JETP 10, 628 (1960).15 D.N. Astrov, JETP 11, 708 (1960).16 R.M. Bozorth, Ferromagnetism (Van Nostrand, New York, 1951).17 E. Schrödinger, Sitzungsberichte Der Kais. Akad. Der Wissenschaften Wien. Math. Klasse 121, 1937 (1912).18 K. Aizu, Phys. Rev. 146, 423 (1966).19 K. Aizu, J. Phys. Soc. Japan 23, 794 (1967).20 K. Aizu, J. Phys. Soc. Japan 27, 387 (1969).21 K. Aizu, Phys. Rev. B 2, 754 (1970).22 R.E. Newnham, Am. Mineral. 59, 906 (1974).23 R.E. Newnham and L.E. Cross, Ferroelectrics 10, 269 (1976).24 E. Ascher, H. Rieder, H. Schmid, and H. Stössel, J. Appl. Phys. 37, 1404 (1966).25 H. Schmid, Ferroelectrics 162, 317 (1994).26 S.-W. Cheong and M. Mostovoy, Nat. Mater. 6, 13 (2007).27 D. Khomskii, Physics (College. Park. Md). 2, 20 (2009).
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