Ferroelectric Switching in Multiferroic Magnetite (Fe<sub>3</sub>O<sub>4</sub>) Thin Films

Alexe, Marin; Ziese, M.; Hesse, D.; Esquinazi, P.; Yamauchi, Kunihiko; Fukushima, Tetsuya; Picozzi, Silvia; Gösele, U.

doi:10.1002/adma.200901381

Cited by 163 publications

(129 citation statements)

References 42 publications

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“…At low temperature it becomes ferroelectric, and thus, multiferroic. 5,6 A bad metal at room temperature (RT), but predicted to be a half-metal with only the minority-spin band crossing the Fermi level, 7 it has been considered a promising material for spintronic applications as an spin-injector 8,9 or as part of a spin-valve.10,11 For such purposes, it is often desired to obtain highly perfect magnetite films on different oxide substrates. In particular, SrTiO 3 is a very attractive material in the microelectronics industry and can be doped to provide either an insulating or metallic substrate.…”

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confidence: 99%

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Room temperature in-plane ⟨100⟩ magnetic easy axis for Fe3O4/SrTiO3(001):Nb grown by infrared pulsed laser deposition

Monti¹,

Sanz²,

Oujja³

et al. 2013

Journal of Applied Physics

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We examine the magnetic easy-axis directions of stoichiometric magnetite films grown on SrTiO 3 :Nb by infrared pulsed-laser deposition. Spin-polarized low-energy electron microscopy reveals that the individual magnetic domains are magnetized along the in-plane h100i film directions. Magneto-optical Kerr effect measurements show that the maxima of the remanence and coercivity are also along in-plane h100i film directions. This easy-axis orientation differs from bulk magnetite and films prepared by other techniques, establishing that the magnetic anisotropy can be tuned by film growth. 2 It is a highly correlated electron material that presents a prototypical metal-insulator transition close to 120 K (the Verwey transition 3,4 ). At low temperature it becomes ferroelectric, and thus, multiferroic. 5,6 A bad metal at room temperature (RT), but predicted to be a half-metal with only the minority-spin band crossing the Fermi level, 7 it has been considered a promising material for spintronic applications as an spin-injector 8,9 or as part of a spin-valve.10,11 For such purposes, it is often desired to obtain highly perfect magnetite films on different oxide substrates. In particular, SrTiO 3 is a very attractive material in the microelectronics industry and can be doped to provide either an insulating or metallic substrate. In consequence, there is interest in the magnetic and transport properties of magnetite films grown on SrTiO 3 , both Nb-doped 12-16 and undoped, 17-23 by using techniques such as molecular beam epitaxy or pulsed-laser deposition (PLD).The magnetization bulk easy-axis directions of Fe 3 O 4 at RT are the cubic h111i ones. The first order anisotropy constant changes sign upon cooling to 130 K, temperature below which the easy axis are the h100i directions, [24][25][26] down to Verwey transition at $120 K where the structure changes from cubic to monoclinic. Thus, in the (001) surface of bulk samples, the magnetization is expected to lie along the projection of the bulk h111i on the (001) surface, i.e., the in-plane h110i directions, 27 an expectation confirmed by spin-polarized low-energy electron microscopy observations (SPLEEM). 28 Most magnetic studies of thin films on SrTiO 3 are performed by techniques such as magneto-optical Kerr effect (MOKE), and SQUID or vibrating-sample magnetometry (VSM), all of which average over the full thickness of the magnetite film. 16,17,19,20,23 In most cases, h110i in-plane directions are reported for the easy-axis, 17,29,30 although some works indicate in-plane isotropic films. 20 There are several reports of real-space imaging of the surface domains by magnetic-force microscopy (MFM), 16,19,23 showing domains of about 60-100 nm in size, similar to the observed grain size, but they do not identify the local domain magnetization direction. On other (100) substrates, h110i easy-axis directions are also usually reported. 31,32 Although attempts have been made to modify the easy axis orientation by the use of piezoelectric substrates 29 or through growth on ste...

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confidence: 99%

Room temperature in-plane ⟨100⟩ magnetic easy axis for Fe3O4/SrTiO3(001):Nb grown by infrared pulsed laser deposition

Monti¹,

Sanz²,

Oujja³

et al. 2013

Journal of Applied Physics

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“…3 The material, historically referred to as lodestone, is currently a promising candidate for spintronic applications. 4 Bulk magnetite (Fe 3 O 4 ) is a ferrimagnet with a 850 K Curie temperature 5 and becomes multiferroic at low temperatures, 6,7 allowing electrical control of magnetic domains. The prediction of half-metal character, 8 which implies that the conduction electrons are 100% spin-polarized, led to its use as a spin injector.…”

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Magnetism in nanometer-thick magnetite

et al. 2012

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The oldest known magnetic material, magnetite, is of current interest for use in spintronics as a thin film. An open question is how thin can magnetite films be and still retain the robust ferrimagnetism required for many applications. We have grown 1-nm-thick magnetite crystals and characterized them in situ by electron and photoelectron microscopies including selected-area x-ray circular dichroism. Well-defined magnetic patterns are observed in individual nanocrystals up to at least 520 K, establishing the retention of ferrimagnetism in magnetite two unit cells thick.

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“…These compounds, however, have antiferromagnetic order, which makes their application strongly limited because of zero magnetization (and therefore uncontrollability), and what is worse, they have quite small electric polarization (≤0.1 µC/cm 2 ). On the other hand, it was found from first-principles and experiments that, in some ferrites including magnetite Fe 3 O 4 [21][22][23] and rare earth ferrites RFe 2 O 4 (R = Y, Yb or Lu) [20,[25][26][27], charge ordering or spin-charge ordering induces a spontaneous polarization of remarkably large value: up to 5 µC/cm 2 in monoclinic Fe 3 O 4 [23] and even tens of µC/cm 2 in hexagonal LuFe 2 O 4 [26], comparable to those of conventional perovskite ABO 3 -type ferroelectrics as well as proper multiferroics. In these ferrites, moreover, the charge and spin degrees of freedom of electrons can be controlled simultaneously, because they have ferrimagnetic order and thus may have non-zero magnetization.…”

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First-principles study of ferroelectricity induced by p–d hybridization in ferrimagnetic NiFe 2 O 4

Jong¹,

Yu²,

Park³

et al. 2016

Physics Letters A

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We investigate the ferrimagnetism and ferroelectricity of bulk NiFe2O4 with tetragonal P 4122 symmetry by means of density functional calculations using generalized gradient approximation + Hubbard U approach. Special attention is paid to finding the most energetically favorable configuration on magnetic ordering and further calculating the reliable spontaneous electric polarization. With the fully optimized crystalline structure of the most stable configuration, the spontaneous polarization is obtained to be 23 µC/cm 2 along the z direction, which originates from the hybridization between the 3d states of the Fe 3+ cation and the 2p states of oxygen induced by Jahn-Teller effect.PACS numbers: 41.20. Gz, 75.85.+t,Magnetic ferroelectrics that possess ferroelectricity together with some form of magnetic order like ferromagnetic, antiferromagnetic, or ferrimagnetic property in the same crystalline phase have attracted much interest due to their fundamental physics and a great promise for applications in future information technology [2][3][4][5][6][7][8]. In particular, improper multiferroics in which a ferroelectric polarization is induced by electronic correlation effects such as non-centrosymmetric spin, charge, and orbital ordering, is currently under intensive study [9][10][11][12]. This is related to the suggestion that a magneto-electric (ME) coupling in improper multiferroics is expected to be stronger than in proper case, because both dipolar and magnetic orderings share the same physical origin and occur at the same temperature [9].In the early days of searching improper multiferroics, spin ordering was accepted to be a main driving force for the manifestation of ferroelectric polarization; examples include rare earth manganites RMnO 3 [13][14][15][16] [10] are typical compounds belonged to this materials class. These materials have weak ferromagnetism and thus a significant ME coupling is expected. Despite the great progress in the field of improper multiferroics, the effort to find new mechanism and design new materials is being continued.In this letter, we present that spinel-type nickel ferrite NiFe 2 O 4 (NFO) is a promising candidate for improper multiferroics with finite magnetization and considerably large polarization, based on the first-principles density functional theory (DFT) calculations. In fact, spinels exhibit several unusual features including magnetoelectricity and multiferroicity [9]. From the experiment, it was established that the bulk NFO shows soft ferrimagnetic ordering below relatively high transition temperature of 850 K with a magnetization of 2 µ B per formula unit (f.u.) [30]. In the recent experiment [31], moreover, high dielectric permitivity was observed in NFO nanoparticles to be ranged from 60 to 600 at different frequencies and temperatures. This is comparable with the conventional ferroelectrics and therefore implies the presence of spontaneous polarization in the bulk NFO. However, the ferroelectricity of bulk NFO has neither been calculated nor measured yet, though ...

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Ferroelectric Switching in Multiferroic Magnetite (Fe₃O₄) Thin Films

Cited by 163 publications

References 42 publications

Room temperature in-plane ⟨100⟩ magnetic easy axis for Fe3O4/SrTiO3(001):Nb grown by infrared pulsed laser deposition

Room temperature in-plane ⟨100⟩ magnetic easy axis for Fe3O4/SrTiO3(001):Nb grown by infrared pulsed laser deposition

Magnetism in nanometer-thick magnetite

First-principles study of ferroelectricity induced by p–d hybridization in ferrimagnetic NiFe 2 O 4

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Ferroelectric Switching in Multiferroic Magnetite (Fe3O4) Thin Films

Cited by 163 publications

References 42 publications

Room temperature in-plane ⟨100⟩ magnetic easy axis for Fe3O4/SrTiO3(001):Nb grown by infrared pulsed laser deposition

Room temperature in-plane ⟨100⟩ magnetic easy axis for Fe3O4/SrTiO3(001):Nb grown by infrared pulsed laser deposition

Magnetism in nanometer-thick magnetite

First-principles study of ferroelectricity induced by p–d hybridization in ferrimagnetic NiFe 2 O 4

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Ferroelectric Switching in Multiferroic Magnetite (Fe₃O₄) Thin Films