Background Art [2] Magnetoelectric material means a material responding sensitively to both a external magnetic field and an external electric field. Accordingly, the materials generate an electric voltage upon being exposed to a magnetic field and are magnetized upon being exposed to an electric field.

[3] Extensive researches have been recently undertaken on magnetic-electric sensors, magnetic sensors, electric sensors, optoelectronic devices, microwave electronic devices, magnetic-electric as well as electric-magnetic transducers, and etc. For successful commercialization of these modern devices, a number of studies have been focused onto the development of the materials having large magnetoelectric effect over room temperature, which is the range of temperature for actual use of the devices.

[4] For realization of large magnetoelectric effect, the magnetoelectric material should have large magnetic moment upon being exposed to a magnetic field. Simultaneously , it should have ferroelectricity or antiferroelectricity, which are properties indicating the induction of large electric voltage in the material upon being exposed to an electric field.

[5] Since the 1890's, great efforts have been directed toward the development of ho- mogeneous magnetoelectric materials exhibiting magnetoelectric effects. As a result, homogeneous magnetoelectric materials, such as Cr O, Pb (Fe Nb) O, BaMeF (Me 2 3 1/2 1/2 3 4 is Mn, Fe, Co or Ni), Cr BeO and BiFeO, have been found to exhibit magnetoelectric 243 effects (G Smolenskii and V A. Ioffe, Colloque International du Magnetisme, Com- munication No. 71,1958 ; G A. Smolenskii and I. E. Chupis, Problems in Solid State Physics (Mir Publishers, Moscow, 1984; 1. H. Ismailzade, V I. Nesternko, F. A.

Mirishli, and P. G Rustamov, Phys. Status Solidi 57,99 (1980)) [6] However, these materials were found to have small magnetoelectric coefficient or to exhibit magnetoelectric effects only in the low temperature range below 0 C. Ac- cordingly, they are not suitable for practical application to electronic devices.

[7] One of the early developed magnetoelectric materials having both large magnetic moment and ferroelectricity is bismuth manganite (BiMnO3) [8] Bismuth manganite has a ferromagnetic phase transition temperature of about 100K and a ferroelectric phase transition temperature (Tc) of about 450K. Accordingly, it has large magnetic moment and ferroelectricity only below the temperature of 100K (N. A. Hill, K. M. Rabe, Physical Review B, vol. 59 pp. 8759 (1999)) [9] This kind of materials cannot be applied to actual electronic devices operated over room temperature due to its lack of magnetoelectric effect over room temperature.

[10] Similarly to bismuth manganite, antiferromagnetic and ferroelectric yttrium manganite (YMnO3) has an antiferromagnetic phase transition temperature of 70#130K and a ferroelectric phase transition temperalture of 570#990K, it has large magnetic moment and ferroelectricity only at a temperature not higher than 70-130K.

Accordingly, yttrium manganite cannot be commercialized into the devices due to the same reason as that of bismuth manganite (A. Filippetti, N. A. Hill, Journal of Magnetism and Magnetic Materials, vol. 236, pp. 176 (2001)) [11] Many research efforts have been made for development of magnetoelectric composite materials having enhanced magnetoelectric effect over room temperature through mixing materials having large magnetic moment and ferrolectricity over room temperature.

[12] A representative magnetoelectric composite material exhibiting large magne- toelectric effects over room temperature is Terfenol (a metal having large magnetic memont) /PZT (a ferroelectric oxide) /Terfenol slabs.

[13] In spite of its large magnetoelectric effects over room temperature, the composite material Terfenol/PZT/Terfenol is problematic due to its complicate structure and manifestation of large magnetoelectric effect only upon specific condition. The composite represents large magnetoelectric effects only upon being exposed to a direct magnetic field over 1,000 gauss. Furthermore, metallic terfenol tend to be easily oxidized in air. This makes a fabrication of the composite material in the form of film, adequate to high-density devices, difficult. (J. G Wan, J. M. Liu, H. L. W. Chand et al.

Journal of Applied Physics, Vol. 93, No. 12, pp. 9916-9919 (2003); Jungho Ryu, Shashank Priya, Kenji Uchino, and Hyoun-Ee Kim, Journal of the American Ceramic Society, Vol. 84, No. 12, pp. 2905-2908 (2001)) [14] Thus, there is an urgent need to develop single-phase materials having i) large magnetoelectric effect originated from large magnetic moment and ferroelectricity over room temperature and ii) capability to be fabricated in the form of film.

Disclosure [15] Therefore, the present invention has been made for resolving the above-mentioned problems in magnetoelectric materials. It is an objective of the present invention to provide single-phase perovskite materials having i) large magnetoelectric effect originated from large magnetic moment and ferroelectricity over room temperature and ii) capability to be fabricated in the form of film.

[16] It is another objective of the present invention to provide electronic devices comprising the single-phase perovskites materials.

[17] In order to accomplish the above objectives of the present invention, magne- toelectric layered perovskite materials having large magnetic moment and ferro- electricity over room temperature are provided. The magnetoelectric layered perovskites are characterized by Formula 1 or 2 below: [18] Formula 1 [19] Bi RTi O 4-x x 3 12 [20] Formula 2 [21] Bi RTi TO 4-x x 3-y y 12 [22] wherein R is a lanthanide series element selected from the group consisting of Nd, Gd, Pr, Pm, Sm, Eu, Er, Tm, Tb, Yb, Dy, Ho, Er, Ce and mixtures thereof; T is a transition element selected from the group consisting of Co, Ni, Fe, Mn, W, V, Nb, Mo, Ta, Zr and mixtures thereof; x is a number of from 0.1 to 4; and y is a number of from 0. 001 to 3.

[23] Hereinafter, the present invention will be described in more detail.

[24] It is known that the ferroelectricity of a bismuth titanate layered perovskites material (Bi Ti O) arises from an octahedral structure consisting of one titanium ion 4 3 12 (Ti) and six oxygen atoms in the crystal lattice.

[25] However, bismuth, titanium, and oxygen ions in the layered perovskites do not endow it with large magnetic moment.

[26] In order to endow the ferroelectric layered perovskites with large magnetic moment, the introduction of a element having or inducing large magnetic moment into the layered perovskites crystal is required.

[27] Thus, the present inventors have adopted lanthanide series elements and transition elements capable of inducing large magnetic moment to the layered perovskites, re- spectively.

[28] In selecting appropriate lanthanide series elements and transition elements, the present inventors considered various physicochemical factors: i) the stability of layered perovskites phase, ii) capability of endowment with large magnetic moment, iii) the enhancement of ferroelectricity of the layered perovskites.

[29] As a result, the present inventors have found that magnetic lanthanide series elements, for example, Nd, Gd, Pr, Pm, Sm, Eu, Er, Tm, Tb, Yb, Dy, Ho, Er, and Ce, have an atomic valence of +3 and ionic radius similar to that of bismuth. These elements can easily substitute bismuth ions in the layered perovskites crystal, resulting in enhancement of its magnetic moment and ferroelectric properties. In addition to this, the present inventors have also found that magnetic transition elements, for example, Co, Ni, Fe, Mn, W, V, Nb, Mo, Ta and Zr, have an ionic radius similar to that of titanium. Similarly to the lanthanide series elements, these elements can easily substitute titanium atoms in the layered perovskites crystal lattice, resulting in en- hancement of its magnetic moment and ferroelectric properties. Based on these findings, the present inventors have developed the materials of Formulae 1 and 2 which exhibit large magnetoelectric effects originating from its large magnetic moment and enhanced ferroelectricity over room temperature.

[30] In Formulae 1 and 2, x is a number of 0. 1-4, preferably 0. 25-3, and more preferably 0. 45-1. 5.

[31] In Formula 2, y is a number of 0. 001-3, preferably 0. 02-3, and more preferably 0. 05-1. 25.

[32] Since the layered perovskites materials of Formula 1 or 2 have large magne- toelectric effects originating from its large magnetic moment and enhanced ferro- electricity over room temperature, it can be utilized as a functional part in various electronic devices requiring magnetoelectric properties, including spintronic devices, ultra-high-density information storage devices, magnetic-electric sensors, magnetic sensors, electric sensors, optoelectronic devices, microwave electronic devices, magnetic-electric transducers, and electric-magnetic transducers, etc.

[33] The present inventors have adopted metal-organic sol decomposition (MOSD) technique for fabrication of capacitors based on the layered perovskites. Using the MOSD technique, the capacitors are typically fabricated by i) desolving inorganic or organic salts of bismuth, a rare earth element, titanium, and optionally those of a transition element in a predetermined mixing ratio to form a sol, ii) coating the sol on a substrate, ill) drying the coated layer, iv) thermal annealing of the coated layer for crystallization, and v) depositing an electrically conductive electrode onto the crystallized layer. However, the present invention is not limited to this fabrication method. The fabrication method can be extended to various available techniques, including pulsed laser vapor deposition, chemical vapor deposition (CVD), sputtering deposition and the like.

[34] Examples of materials for the electrically conductive electrode include gold, platinum, silver, conductive oxides and mixtures thereof.

Description Of Drawings [35] The above and other objectives, features, and other advantages of the present invention will be more clearly understood from the following detailed description taken in conjunction with the accompanying drawings, in which: [36] Figs. la to lc show the layered perovskite crystal structure of Bi R Ti TO 4-x x 3-y y 12 according to the present invention; [37] Fig. 2 shows a synchrotron XRD pattern of a Bi Gd Ti O thin film grown 3. 15 0. 85 3 12 onto STO (strontium titanate) substrate; [38] Fig. 3 shows an XRD pole figure of a Bi Gd Ti O thin film grown onto an 3. 15 0. 85 3 12 STO substrate; [39] Fig. 4 shows a synchrotron X-ray absorption fine structure (XAFS) spectrum of a Bi Gd Ti O thin film grown onto STO substrate; 3. 15 0. 85 3 12 [40] Fig. 5 shows room-temperature ferromagnetic properties of Bi Gd Ti O thin 3. 15 0. 85 3 12 film grown onto STO substrate.

[41] Magnetization behavior of Bi Gd Ti O thin film grown onto STO substrate 3. 15 0. 85 3 12 was measured through a magnetic field-magnetization reversal process. Fig. 5a shows details of a magnetization hysteresis loop of the Bi Gd Ti O thin film at low 3. 15 0. 85 3 12 external magnetic field. Fig. 5b shows the temperature dependence of magnetization in the Bi Gd Ti O thin film; 3. 15 0. 85 3 12 [42] Fig. 6 shows room-temperature diamagnetic properties of a Bi Ti O thin film 4 3 12 grown onto STO substrate Magnetization behavior of Bi Ti O thin film grown onto 4 3 12 STO substrate was measured through a magnetic field-magnetization reversal process; [43] Fig. 7a shows the ferroelectric properties of a Bi R Ti O (R is Gd, and x is 0.85) 4-x x 3 12 capacitor. The ferroelectric properties of it were measured through an electric field- polarization reversal process. Specifically, Fig. 7a compares electric field-polarization curves before and after 4.5 x 10 cycles of polarization reversal. Fig. 7b shows the variation of switching charges and non-switching charges with increasing numbers of switching cycle ; [44] Fig. 8 shows change in the magnetoelectric (ME) coefficient (α) of a Bi Gd Ti 3. 15 0. 85 3 O thin film grown onto Pt/TiO/SiO/Si substrate along the direction and magnitude 12 2 2 of a direct magnetic field superimposed on externally applied alternating sinusoidal magnetic field; a and a are ME coefficients measured upon application of direct 31 33 magnetic field perpendicular and parallel to alternating sinusoidal magnetic field, re- spectively.

Mode for Invention [45] The following examples are provided to assist further understanding of the present invention.

[46] However, these examples are given for the purpose of illustration. Thus, these should not to be interpreted as limiting the scope of the invention.

[47] Example 1: Fabrication of Bi Gd Ti O film-based capacitor 3. 15 0. 85 _ 12 [48] Bi Gd Ti O film-based capacitor was fabricated in accordance with the 3. 15 0. 85 3 12 following procedure for determination of the magnetic properties, ferroelectric charac- tieristics, and magnetoelectric effects of the Gd-substituted layered perovskite, one of the present invention, over room temperature.

[49] First, bismuth acetate, titanium isopropoxide and gadolinium acetate were dissolved into anhydrous acetic acid to form a homogeneous sol in which bismuth, gadolinium and titanium were contained in a molar ratio of 3.15 : 0.85 : 3. The sol was coated onto Pt/TiO/SiO/Si or STO substrates, dried, and crystallized by thermal z z annealing at 700 C for 1 hr in oxygen atmosphere. Finally, a platinum electrode was deposited onto the crystallized film for fabrication of Bi Gd Ti O capacitor.

3. 15 0. 85 3 12 [50] Comparative Example 1: Fabrication of Bi Ti O capacitor 4 3 12 [51] Bismuth acetate and titanium isopropoxide were dissolved in anhydrous acetic acid to form a homogeneous sol in which bismuth and titanium were contained in a molar ratio of 4: 3. The sol was coated onto Pt/TiO/SiO/Si or STO substrates, dried, and 2 2 crystallized by thermal annealing at 700 C for lhr in oxygen atmosphere. Finally, a platinum electrode was deposited onto the crystallized film for fabrication of Bi Ti O 4 3 12 capacitor.

[52] Hereinafter, the present invention will be explained in more detail with reference to the accompanying drawings.

[53] Figs. la to lc show the layered perovskite crystal structure of Bi R Ti TO (x is 4-x x 3-y y 12 a number of 0. 1-4 and y is a number of 0. 001#3) according to the present invention.

[54] In Fig. la, PL represents the perovskite layers, and BOL represents the bismuth oxide layers.

[55] Fig. lb is a projected view of the layered perovskite crystal structure of Bi R Ti 4-x x 3-y TO (x is a number of 0. 1-4 and y is a number of 0. 001-3) onto the a-c plane, and y 12 Fig. lc is a projected view of the perovskite layer onto the a-b plane.

[56] As shown in Figs. la to lc, Bi atoms located in the perovskite layers (PL) are mainly substituted with rare earth elements, and Ti atoms located in the perovskite layers are mainly substituted with transition elements.

[57] The crystallization behavior of the Bi Gd Ti O film on STO substrate was 3. 15 0. 85 3 12 analyzed by using a synchrotron x-ray diffraction technique. As shown in Fig. 2, it was confirmed that Gd ions effectively substitutes Bi ions in the bismuth titanate layered perovskites crystal without a formation of secondary phases.

[58] Fig. 3 shows an XRD pole figure of the Bi Gd Ti O thin film prepared onto 3. 15 0. 85 3 12 STO substrate.

[59] This figure clearly demonstrates that the Bi Gd Ti O thin film has a uniform 3. 15 0. 85 3 12 in-plane orientation on STO substrate.

[60] Fig. 4 shows a synchrotron XAFS spectrum of the Bi Gd Ti O thin film 3. 15 0. 85 3 12 prepared onto STO substrate.

[61] Gd in the Bi Gd Ti O thin film has an atomic valence of +3 as apparent from 3. 15 0. 85 3 12 Fig. 4. This also indicates that the Gd is dissolved into the layered perovskite crystal without a formation of secondary phases.

[62] The magnetic properties of the Bi Gd Ti O thin film were measured through a 3. 15 0. 85 3 12 magnetic field-magnetization reversal process. The results are shown in Figs. 5a and 5b. I t was confirmed from Figs. 5a and 5b that the Bi Gd Ti O thin film shows 3. 15 0. 85 3 12 ferromagnetic behavior over room temperature. This means that substitution of Bi with Gd ions cause a enhancement of magnetic moment of the layered perovskites.

[63] Fig. 5a shows particulars of a magnetization hysteresis loop of the Bi Gd Ti O 3. 15 0. 85 3 12 thin film at low external magnetic field.

[64] Fig. 5b shows the temperature dependence of magnetization in the Bi Gd Ti O 3. 15 0. 85 3 thin film. It was confirmed from Fig. 5b that the ferromagnetic properties of the Bi 12Gd Ti O thin film are maintained over 400K (127°C) or above. In Fig. 5b, ZFC 3. 15 0. 85 3 12 refers to zero field cooling, and FC refers to field cooling.

[65] On the other hand, the room temperature magnetic properties of the Bi Ti O thin 4 3 12 film, fabricated in Comparative Example 1, were measured. The results are shown in Fig. 6. It was confirmed that the Bi Ti O thin film is diamagnetic at room 4 3 12 temperature. This means that Bi Ti O thin film has low magnetic moment.

4 3 12 [66] The room temperature ferroelectric properties of the Bi Gd Ti O capacitor 3. 15 0.85 3 12 were measured through an electric field-polarization reversal process. The results are shown in Figs. 7a and 7b.

[67] Fig. 7a shows the ferroelectric properties of the Bi Gd Ti O capacitor.

3. 15 0. 85 3 12 Specifically, Fig. 7a shows electric field-polarization curves before and after 4.5 x 10 cycles of polarization reversal.

[68] Fig. 7b shows the variation of switching charges and non-switching charges with increasing numbers of switching cycle.

[69] The Bi Gd Ti O thin film shows excellent ferroelectric properties at room 3. 15 0. 85 3 12 temperature as indicated in Figs. 7a and 7b.

[70] As shown in Figs. 5a and 5b, and Figs. 7a and 7b, the Bi Gd Ti O thin film 3. 15 0. 85 3 12 capacitor shows large magnetic moment and good ferroelectric properties at room temperature.

[71] For determination of magnetoelectric effect at room temperature, the magne- toelectric coefficients of the capacitor were measured at room temperature by using al- ternating sinusoidal and direct magnetic fields. The results are shown in Fig. 8.

[72] Fig. 8 shows changes in the room temperature magnetoelectric (ME) coefficients (α) of the Bi Gd Ti O capacitor along the direction and magnitude of a direct 3. 15 0. 85 3 12 magnetic field superimposed onto externally applied alternating sinusoidal magnetic field. a and a are ME coefficients measured upon application of direct magnetic 31 33 field perpendicular and parallel to alternating sinusoidal magnetic field, respectively.

[73] As shown in Fig. 8, when an alternating sinusoidal magnetic field having the amplitude of 50 gauss and a frequency of 30 kHz was applied in the direction (out-of-plane direction) vertical to the Pt/Bi Gd Ti O thin film/Pt capacitor, the 3. 15 0. 85 3 12 Bi Gd Ti O capacitor had a magnetoelectric coefficient (α) of 36.5 V/cm-Oe. On 3. 15 0. 85 3 12 31 the other hand, when an alternating current magnetic field having the amplitude of 50 gauss and a frequency of 30 kHz was applied in the direction (in-plane direction) horizontal to the Pt/Bi Gd Ti O thin film/Pt capacitor, the Bi Gd Ti O 3. 15 0. 85 3 12 3. 15 0. 85 3 12 capacitor had a magnetoelectric coefficient (α) of 2.5 V/cm-Oe.

33 [74] These results indicate that the Pt/Bi Gd Ti O thin film/Pt capacitor has large 3. 15 0. 85 3 12 anisotropic magnetoelectric effects.

[75] In conclusion, the Bi Gd Ti O thin film capacitor fabricated as described in 3. 15 0. 85 3 12 Example 1 shows large magnetoelectric effects over room temperature. It is originated from its large magnetic moment and ferroelectric properties as shown in Figs. 5a and 5b, and Figs. 7a and 7b, as well as Fig. 8.

[76] In contrast to Pt/Bi Gd Ti O thin film/Pt capacitor, the ferroelectric Bi Ti O 3. 15 0. 85 3 12 4 3 12 thin film capacitor shows small magnetic moment, resulting in poor magnetoelectric effects.

[77] Although the foregoinig exmaple of the present invention illustrated only the Bi3.15 Gd TiO capacitor among Bi R Ti T O (x is a number of 1#4 and y is a number 0. 85 3 12 4-x x 3-y y 12 of 0. 001-3) capacitors, it should be understood that the scope of the present invention is not limited to the material wherein R is Gd and x is 0.85.

[78] As described above, bismuth ions can be substituted with a rare earth elements (R is selected from Nd, Gd, Pr, Pm, Sm, Eu, Er, Tm, Tb, Yb, Dy, Ho, Er, Ce, and mixtures thereof) in the Bi R Ti T O materials fabricated as described in Example 4-x x 3-y y 12 1 of the present invention. Simultaneously, titanium ions can be selectively replaced with a transition elements (T is selected from Co, Ni, Fe, Mn, W, V, Nb, Mo, Ta, Zr and mixtures thereof) in it of the present invention. Of course, it will be appreciated by any person skilled in this art that the present invention can be variously modified and altered within the technical concept of the present invention.

[79] As apparent from the above description, the present invention provides the layered perovskites materials Bi R Ti O (x is a number of from 0.1 to 4) and Bi R Ti T O 4-x x 3 12 4-x x 3-y y (x is a number of from 0.1 to 4 and y is a number of from 0. 001 to 3) containing 12 bismuth (Bi), a rare earth element (R) selected from Nd, Gd, Pr, Pm, Sm, Eu, Er, Tm, Tb, Yb, Dy, Ho, Er, Ce, and mixtures thereof, titanium, and optionally a transition element (T) selected from Co, Ni, Fe, Mn, W, V, Nb, Mo, Ta, Zr and mixtures thereof.

Since the layered perovskites materials have large magnetoelectric effects resulting from both large magnetic moment and ferroelectricity over room temperature, they can be utilized as various types of parts in electronic devices, including spintronic devices, ultrahigh-density information storage devices, magnetic-electric sensors, magnetic sensors, electric sensors, optoelectronic devices, microwave electronic devices, transducers, and etc.