Compositions of the Si(OC2H5)4 (TEOS), H2O, and C2H5OH solutions used in the sol–gel process.
Abstract
Significant experimental effort has been inspected to consider and implement favorable high-k gate dielectrics with magnetodielectric (MD) effect of series of rare earth oxide (RE2O3, RE ~ rare earth ions) nanoparticles (NPs) embedded in sol–gel derived SiO2 glass matrix. Properly calcined RE2O3 NP-glass composite systems (in which RE ~ Sm, Gd and Er) show an intriguing colossal enhancement of dielectric constant along with MD effect near room temperature. The enhancement of dielectric constant is closely related to oxygen vacancy induced dielectric relaxation (or, more correctly, particle size effect from different calcined temperature), reconstructed from extended X-ray absorption fine structure. The MD response is strongly depended on the superparamagnetic property of the rare earth ions. From application point of view, the enhancement of dielectric constant associated with MD response can be achieved by tuning the NPs size through varying annealing temperature and/or increasing the doping concentration of magnetic rare earth oxide, which will be the key guidelines to accomplish the compatibility, performance and reliability requirements for future complementary metal-oxide-semiconductor (CMOS) technology.
Keywords
- Rare earth oxide nanoparticle
- high-k materials
- magnetodielectric effect
- diffuse phase transition
1. Introduction
Tiny electrical components are now unanimously required to be high in functionality and reliability and low priced in response to progress in the high density mounting technology. Continued device scaling for future technology nodes requires reduction in equivalent oxide thickness (EOT) of gate dielectrics to maintain electrostatic control of the charges induced in the channel. The use of amorphous SiO2 as a gate dielectric offers several key advantages in complementary metal-oxide semiconductor (CMOS) processing, including thermal and chemical stability as well as superior electrical isolation properties (high band gap of nearly 9 eV, and a Si–SiO2 potential barrier for electrons of about 3 eV). The continuous miniaturization of Si electronics has imposed severe constraints on the performance of the SiO2 gate oxide, with its thickness now approaching the quantum tunneling limit [1,2]. To continue the downward scaling, dielectrics with a higher dielectric constant (high-
Besides the aforementioned consideration, the superior electrical characteristics of the Si–SiO2 interface in ideal gate dielectric stack compatible with planarization technology has not achieved with any other alternative semiconductor–dielectric combination. Despite several key advantages of SiO2, the continual scaling of CMOS technologies has pushed the Si–SiO2 system in formidable challenge. One promising alternative approach to overcome the scaling limit has been proposed to substitute by silica-based single-valence nanoparticles (NPs) as gate insulator (interface between silicon and NP-oxides embedded silica), where flexibility, compartibility and functionality may be achieved through different NPs sizes/concentrations. Concentrating on the desired NP-oxides, potentially stable rare earth oxides (RE2O3, RE ~ rare earth, a series of elements from La to Lu with stable RE3+) were chosen, which are attractive materials based on good thermodynamic energy considerations with silicon, highly resistive and a high conduction band offset over 2 eV. We have presented extensive results, providing useful insight into the physics of nano-composite high-
2. Sample preparation
The preparation of RE2O3:SiO2 nano-glass composite system (RE ~ La, Nd, Sm, Eu, Gd, Dy, Ho, Er, Tm, Yb and Lu) consists of three consecutive processes: (a) preparation of wet gel in which rare earth ions were doped by sol–gel way, (b) drying of the gel and (c) densification of the dry gel to a dense glass in which RE2O3 NPs embedded by calcining at selective temperatures [15]. The process was based on the hydrolysis of precursors, such as tetraethylorthosilicate {Si(OC2H5)4} (TEOS) and subsequent condensation of hydrolyzed TEOS in a medium containing a hydroalcoholic solution of rare earth salt [16] (Figure 1(a)) having different mol% concentrations following essentially the method developed by Sakka and Kamiya [17]. Water was required for the hydrolysis. The molar ratio of water and TEOS was kept at 20 while that of TEOS and catalyst HCl at 100. Dry ethanol was used for diluting the alkoxide. The following composition of the Si(OC2H5)4 solutions used in the study (Table 1):
|
|
|
|
|
|
169.5 | 292.8 | 37.5 | 20 | 500 | 9.80 |
Table 1.
There are two distinct chemical reactions involved in the sol–gel process, describing Eqn. (1) for hydrolysis of the alcohol groups, Eqns. (2) and (3) for polycondensation of hydroxyl groups.
Hydrolysis:
Condensation (water/alcohol condensation):
Water condensation:
Alcohol condensation:
The clear solutions without any precipitaion are prepared with the mixing of half amount of ethanol in alkoxide and the solution consisting of the specified amount of water with another half of the ethanol containing HCl and dopant. The mixure solutions continued stirring for 2–3 hours at room temperature. The clear solution was kept in pyrex beaker at the atmospheric condition for 7/8 days to form stiff monolithic transparent gel. Further, the gels were allowed to dry for 4–5 weeks at room temperature. The dried (liquid removed by thermal evaporation) monolith is termed as xerogel. The oven–dried gel (temperature range 100–200°C) still contains large concentration of chemisorbed hydroxyls. Heat treatment in the temperature range 500–800°C desorbs the hydroxyls, forming a stabilized gel. At 1000°C, it transformed to a dense glass. Heat treatments of samples were performed according to preselected calcination temperature schedule [16] (Figure 1(b)).
![](http://cdnintech.com/media/chapter/48467/1512345123/media/fig1.png)
Figure 1.
(Color online) (a) Sol–gel process. (b) Gel–glass embedded with rare earth nanoparticle calcination process.
It is relevant to mention here the important findings of Raman spectroscopic studies including measurements of pore size, density and specific surface area on the densification of undoped SiO2 gel as a function of heat treatment up to 900oC [18]. With increasing temperature from 700 to 800oC, the average pore size increases abruptly from 1.0 nm to 2.3 nm, whereas, the specific surface area decreases from 550 m2/g to 160 m2/g and the pore volume/gm decreases from 0.19 cc/g to 0.12 cc/g. The surface energy for a siloxane surface is higher than for a hydroxyl surface. The
3. Experimental details
Powder X-ray diffraction (XRD) of the sample was performed by using Cu-
4. Results and discussion
![](http://cdnintech.com/media/chapter/48467/1512345123/media/fig2.png)
Figure 2.
(Color online) (a) TEM image of Er05-8, upper inset: the particle size distribution histogram and lower inset: the HRTEM image, (b) electron diffraction and (c) XRD patterns of all the Er05-7, Er05-8 and Er05-12 samples.
The XRD patterns of the Er2O3 oxide NPs doped SiO2 matrix calcined at 1200oC (Er05-12) show crystalline nature with quite large Er2O3 NPs. It exhibits clearly in Figure 2(c) the most intense characteristic line of single phase Er2O3 (JCPDF Card No. 43-1007) at 2
Among various rare earth oxides, Er2O3 has been chosen first in the present work as it possesses most appealing properties viz. high resistivity (1012-1015 cm-3), large band gap (
![](http://cdnintech.com/media/chapter/48467/1512345123/media/fig3.png)
Figure 3.
(Color online) (a) The (
4.1. Temperature dependence dielectric response
Figure 3(a) illustrates the relative dielectric constant (
![](http://cdnintech.com/media/chapter/48467/1512345123/media/fig4.png)
Figure 4.
(Color online) (a) Dielectric loss tanδ of Er05-8 at different frequency, (b) representative Arrhenius plot of the relaxation time of Er05-8. The calculated activation energy values (in electron volt (eV)) are illustrated in each case.
4.2. Dielectric relaxation analysis
To shed more light on the relaxation dynamics of rare earth oxide NPs-glass composite systems, temperature dependent dielectric loss tangent (tanδ) are carried out at various frequencies. The appearance of three maxima with strong frequency dispersion located at peak
![](http://cdnintech.com/media/chapter/48467/1512345123/media/fig5.png)
Figure 5.
(Color online) Dielectric hysteresis loop of Er05-8, measured near DPT (275 K) and above room temperature (320 K) using 2.0 and 1.0 kHz polarization frequency.
4.3. Polarization studies
Figure 5 shows the frequency and temperature dependence hysteresis loop (
4.4. Equivalent circuit analysis
Materials exhibiting colossal enhancement of dielectric value are usually adopted to explain by Maxwell–Wagner (MW) mechanism. The present NPs-glass composite system is basically NPs grain of rare earth oxide (uniformly distributed) embedded in more insulating SiO2 matrix. The enhancement of dielectric constant along with DPT behavior might be a signature of the effect of internal barrier layer capacitance depending on the ration of grain size and the grain-boundary thickness. The complex impedance curves in Figure 6 have also been analyzed using an equivalent circuit, consisting of the two inclined semicircular arc (deviation from the ideal Debye response). Thus, the two depressed semi-arc in the Nyquist plot (complex impedance Z″-Z′plane) of the impedance data could be modeled on two parallel resistor–capacitor (RC) networks connected in series, one corresponds to the conducting part in high frequency region assigned to the intrinsic effect of grain (typical Er2O3 NPs) and the other arc in low frequency side corresponds to the more resistive part (SiO2 matrix) of the sample. Interestingly, the entire measured frequency region (20 – 2 × 106 Hz) at the temperature below
![](http://cdnintech.com/media/chapter/48467/1512345123/media/fig6.png)
Figure 6.
(Color online) (a) Complex plane plots, Z″-Z′, of Er05-8 at several temperatures and (b) schematic model of equivalent electrical circuits indicating of two parallel resistor–capacitor (RC) combinations [(
4.5. Magnetodielectric effect
The observation of colossal MD effect is the most interesting finding of Er05-8 system as shown in Figure 7(a) at a specific frequency of 2.5 kHz. The large enhancement of dielectric constant (~2.75 times) is observed around the transition regime 260–300 K under 9 T magnetic field. The inverse of dielectric constant with temperature under magnetic field (upper inset of Figure 7(a)) are also fitted by Curie–Weiss law with Curie constant (C) (3968.82, 6211.29 and 6918.04 K for 0, 5 and 9 T, respectively) and Curie–Weiss temperature (
![](http://cdnintech.com/media/chapter/48467/1512345123/media/image19_w.jpg)
Figure 7.
(Color online) (a) The magnetic field dependence of (
4.6. Micro-structural correlated resistivity analysis
Figure 8 shows the contribution of amorphous NP Er2O3 grain resistance
![](http://cdnintech.com/media/chapter/48467/1512345123/media/image21_w.jpg)
Figure 8.
Color online) Temperature dependence of grain resistance (
![](http://cdnintech.com/media/chapter/48467/1512345123/media/image22_w.jpg)
Figure 9.
(Color online) Temperature dependence of
The magnetoresistive property of magnetic NPs is attributed by spin-polarized tunneling [37]. Although, the observed strong positive magnetoelectric interaction constant (α~ 0.782) has a similar appearance to intrinsic multiferroics, the MD effect can also be achieved through a combination of magnetoresistance and the Maxwell–Wagner effect, as predicted by Catalan [38]. Since the current results suggest that MD behavior is probably a manifestation of magnetoresistance changes, depending on the NP size and separation. Enhancement of MD response (i.e., positive MD effect) through the decreases of NPs Er2O3 resistance under external magnetic field, (i.e., negative magnetoresistance) might imply the possible tunability of the resistive MD effect.
![](http://cdnintech.com/media/chapter/48467/1512345123/media/image23_w.jpg)
Figure 10.
(Color online) (a) The (
![](http://cdnintech.com/media/chapter/48467/1512345123/media/image26_w.jpg)
Figure 11.
(Color online) (a), (b) The (
5. Eu2O3 NPs-glass composite system: Smaller dielectric response and negative MD effect
Typical data is shown for Eu2O3:SiO2 NPs-glass composite system having 0.5 mol% dopant Eu2O3 concentration calcined at different temperatures, namely, 700, 800 and 900oC (henceforth referred as Eu05-7, Eu05-8 and Eu05-9 respectively). Figure 10 represents the temperature dependence of
6. Effect of different rare earth oxides on the dielectric properties
In previous sections, we have presented interesting particle size dependent colossal dielectric response along with MD effect in Er2O3 and Eu2O3 nano-glass composite systems. From the obtained results, there are colossal enhancement of dielectric constant and large MD effect in Er2O3 case [20], while those in Eu2O3 case, smaller responses were observed [39]. Obviously, the different electronic and magnetic properties for Er2O3 and Eu2O3 play a crucial role. However, these results suggest great promise in further systematic investigation to distinguish the mechanisms that contribute to colossal dielectric responses along with MD effect in other RE2O3:SiO2 nano-glass composite systems (RE2O3, RE
Figure 12 illustrates the temperature dependent
![](http://cdnintech.com/media/chapter/48467/1512345123/media/fig12.png)
Figure 12.
(Color online) The
![](http://cdnintech.com/media/chapter/48467/1512345123/media/fig13.png)
Figure 13.
(Color online) (a) Maximum value of dielectric constant, and (b) MDR under 5 T applied field of RE2O3:SiO2 nano-glass composite systems calcined at 700oC with rare earth atomic number.
The amorphous self-organized rare earth oxide nano-glass composite systems may be the promising high-
7. Effect of molar concentration of magnetic NPs on the observed dielectric and MD properties
As discussed in the above section, we have systematically investigated the colossal responses of dielectric behavior along with MD effect in rare earth oxide (RE2O3, RE
|
|
|
LGS1 | 0.150 | 0.000 |
LGS2 | 0.120 | 0 |
LGS3 | 0.090 | 0 |
LGS4 | 0.075 | 0 |
LGS5 | 0.060 | 0 |
LGS6 | 0.000 | 0 |
LGS7 | 0.000 | 0 |
Table 2.
Different doping concentrations of non-magnetic La2O3 and magnetic Gd2O3 (mol%) in SiO2 NP-glass composite systems.
Figure 14 illustrated the
![](http://cdnintech.com/media/chapter/48467/1512345123/media/fig14.png)
Figure 14.
(Color online) The
Figure 15(a) illustrates the
![](http://cdnintech.com/media/chapter/48467/1512345123/media/image27_w.jpg)
Figure 15.
(Color online) (a) Maximum value of dielectric constant, and (b). MDR under 5 T applied field of LGS NP-glass composite systems with different Gd2O3 doping concentrations calcined at 700oC.
8. Extended X-ray Absorption Fine Structure (EXAFS) experiments
Extended X-ray absorption fine structure (EXAFS) experiments were performed at the Gd
|
|
|
||
|
|
|
||
Gd05-7 | First coordination shell (Gd3+–O) |
5.3±0.2 | 2.216±0.012 | 0.016±0.002 |
Gd05-8 | 5.6±0.2 | 2.234±0.011 | 0.015±0.003 | |
Gd05-9 | 5.8±0.3 | 2.248±0.013 | 0.014±0.002 | |
Gd2O3 | 6.0±0.2 | 2.265±0.012 | 0.007±0.003 |
Table 3.
Results of the quantitative analysis of the first coordination shell derived from EXAFS filtered data of Gd2O3:SiO2 nano-glass composite systems at different calcinations temperatures.
![](http://cdnintech.com/media/chapter/48467/1512345123/media/fig16.png)
Figure 16.
(Color online) Gd
Figure 17 depicts the room temperature experimental EXAFS spectra of LGS systems ((La, Gd)2O3:SiO2 NP-glass composite systems) with different doping concentrations (Table II) and particles size (different calcined temperatures). The first coordination peak located at ~1.8 Å (Figures 17(a), (b)) with the interatomic distance of La3+-O/Gd3+-O looks very much the similar without any perceptible shift at different doping concentrations. However, the interatomic distances of the first coordination peak (~1.8 Å) of LGS4 with different calcination temperatures (Figures 17(c), (d)) are shifted significantly even with very low doping concentration of La2O3/Gd2O3. It reveals significantly that the average La3+–O/Gd3+–O interatomic distances of LGS4 samples at lower calcination temperature is shorter, suggesting higher oxygen vacancies around La/Gd ions, supported with our previously reported article [16]. Therefore, the dielectric value decreases by annealing the sample at higher temperatures (or, more correctly, with higher NPs size) with identical molar concentration of dopant element. However, identical particle size (magnetic and/or non-magnetic NPs) with concentration dependence does not affect the oxygen vacancies. In other words, oxygen vacancies depend only on the particle size but not its magnetic phase.
![](http://cdnintech.com/media/chapter/48467/1512345123/media/fig17.png)
Figure 17.
(Color online) Room temperature Fourier transforms moduli radial distribution functions EXAFS spectra of LGS systems at (a) La
9. Magnetic measurements
The
![](http://cdnintech.com/media/chapter/48467/1512345123/media/fig18.png)
Figure 18.
(Color online) ZFC and FC magnetization versus temperature curves of LGS5 sample calcined at 700°C, right axis shows the temperature dependent inverse susceptibility curve. In the inset, the region close to the superparamagnetic transition is highlighted.
![](http://cdnintech.com/media/chapter/48467/1512345123/media/fig19.png)
Figure 19.
(Color online) ZFC and FC magnetization versus temperature curves of LGS4 sample at different calcination temperatures. Applied
The data obtained for the temperature dependence magnetization of LGS4 samples calcined at 700, 800, 900 and 1200°C are graphically depicted in Figure 19. The superparamagnetic blocking temperature cannot be traced in low accuracy (or resolution) of measurement with very low percentage-doping (~ 0.075 mol%) of magnetic Gd2O3. However, from the observed continuous increase in ZFC and FC curves at low temperature indicating the ferromagnetic nature of the LGS4 sample. Magnetic properties with size dependency are also observed for LGS4 samples calcined at different temperatures, related with the uncompensated surface spins present on the Gd2O3 NPs. It is likely that the Gd2O3 NPs with smaller size (i.e., higher surface-to-volume ratio) contain larger proportion of uncompensated surface spins and consequently reveal higher ferromagnetic values than larger NPs (higher calcined temperature). Temperature dependent inverse susceptibility data for LGS4 samples calcined at different temperatures with respect to bulk Gd2O3 can be fitted by the Curie–Weiss law (Figure 20(a)) having different slopes of straight lines. The intersection points of fitted lines with
![](http://cdnintech.com/media/chapter/48467/1512345123/media/fig20.png)
Figure 20.
(Color online) (a) Inverse susceptibility versus temperature curves of LGS4 samples at different calcination temperatures with respect to bulk Gd2O3, (b) the region close to the extrapolated lines intersect with temperature axis is highlighted.
Isothermal magnetization-field sweeps were performed to further investigate the nature of the superparamagnetic state and the ferromagnetism below transition temperature. Figure 21 displays the magnetic field dependence of the magnetization (
![](http://cdnintech.com/media/chapter/48467/1512345123/media/fig21.png)
Figure 21.
(Color online) Hysteresis loop of LGS4 sample calcined at 700°C, lower inset: the region close to the coercive field value is highlighted, upper inset: magnetization vs. H/T of LGS4 sample.
10. Conclusions
We have synthesized self-organized RE2O3 NPs with almost equal size and separation embedded in SiO2 glass matrix by the sol–gel method.
Principal findings may be summarized below:
Presence of superparamagnetic phase occurs in magnetic rare earth oxide NPs doped glass samples.
Properly annealed sol–gel glass (in which RE ~ Sm, Gd and Er) (Fig. 2) shows an interesting colossal response of dielectric constant along with DPT and MD behavior around room temperature.
The experimental facts strongly suggest that the dielectric anomaly with DPT behavior is related to oxygen vacancy-induced dielectric relaxation in the material without ferroelectric phase transition.
The MDR observed in this glassy composite is considered to be associated with the direct consequence of magnetoresistance changes depending on the calcination temperatures (magnetic NPs size).
However, keeping the NPs size constant, the increase in dielectric constant and MDR strongly depends on the magnetic property (superparamagnetism) of the rare earth ions.
Acknowledgments
This research was partially supported by the Ministry of Science and Technology, Taiwan under Grant No. NSC 103-2112-M-110-010-MY3.
References
- 1.
Chau R, Datta S, Doczy M, Doyle B, Kavalieros J, Metz M. High-k/Metal gate stack and its MOSFET characteristics. IEEE Electron Device Lett 2004;25:408–10. - 2.
Lo SH, Buchanan DA, Taur Y, Wang W. Quantum-mechanical modeling of electron tunneling current from the inversion layer of ultra-thin-oxide MOSFETs. IEEE Electron Device Lett 1997;18:209–11. - 3.
Homes CC, Vogt T, Shapiro SM, Wakimoto S, Ramirez AP. Optical response of high-dielectric-constant perovskite-related oxide. Science 2001;293:673–6. - 4.
Liu J, Duan CG, Yin WG, Mei WN, Smith RW, Hardy JR. Large dielectric constant and Maxwell-Wagner relaxation in Bi2/3Cu3Ti4O12. Phys Rev B 2004;70:144106(7). - 5.
Martín SG, Orrantia AM, Aguirre MH, Franco MÁA. Giant barrier layer capacitance effects in the lithium ion conducting material La0.67Li0.25Ti0.75Al0.25O3. Appl Phys Lett 2005;86:043110(3). - 6.
Yang Z, Hou Y, Liu B, Wei L. Structure and electrical properties of Nd2O3-doped 0.82Bi0.5Na0.5TiO3–0.18Bi0.5K0.5TiO3 ceramics. Ceram Int 2009;35:1423–7. - 7.
Wang Z, Chen XM, Ni L, Liu XQ. Dielectric abnormities of complex perovskite Ba(Fe1/2Nb1/2)O3 ceramics over broad temperature and frequency range. Appl Phys Lett 2007;90:022904(3). - 8.
Raevski IP, Prosandeev SA, Bogatin AS, Malitskaya MA, Jastrabik L. High dielectric permittivity in AFe1/2B1/2O3nonferroelectric perovskite ceramics (A=Ba, Sr, Ca; B=Nb, Ta, Sb). J Appl Phys 2003;93:4130–6. - 9.
Wu JB, Nan CW, Lin YH, Deng Y. Giant dielectric permittivity observed in Li and Ti doped NiO. Phys Rev Lett 2002;89:217601(4). - 10.
Pecharromán C, Esteban-Betegón F, Bartolomé JF, López-Esteban S, Moya JS. New percolative BaTiO3–Ni composites with a high and frequency-independent dielectric constant (er ≈ 80000). Adv Mater 2001;13:1541–4. - 11.
Cohn JL, Peterca M, Neumeier JJ. Low-temperature permittivity of insulating perovskite manganites. Phys Rev B 2004;70:214433(6). - 12.
Park T, Nussinov Z, Hazzard KRA, Sidorov VA, Balatsky AV, Sarrao JL, Cheong SW, Hundley MF, Lee JS, Jia QX, Thompson JD. Novel dielectric anomaly in the hole-doped La2Cu1-xLixO4 and La2-xSrxNiO4 insulators: signature of an electronic glassy state. Phys Rev Lett 2005;94:017002(4). - 13.
Rivas J, Rivas-Murias B, Fondado A, Mira J, Señarís-Rodríguez MA. Dielectric response of the charge-ordered two-dimensional nickelateLa1.5Sr0.5NiO4. Appl Phys Lett 2004;85:6224–6. - 14.
Zhu WJ, Tamagawa T, Gibson M, Furukawa T, Ma TP. Effect of Al inclusion in HfO2 on the physical and electrical properties of the dielectrics. IEEE Electron Device Lett 2002;23:649–651. - 15.
Mukherjee S, Pal AK, Bhattacharya S, Raittila J. Magnetism of Mn2O3 nanocrystals dispersed in a silica matrix: Size effects and phase transformations. Phys Rev B 2006;74:104413(10). - 16.
Mukherjee S, Lin YH, Kao TH, Chou CC, Yang HD. Searching for high-k RE2O3 nanoparticles embedded in SiO2 glass matrix. J Appl Phys 2012;111:064103(6). - 17.
Sakka S, Kamiya K. The sol–gel transition in the hydrolysis of metal alkoxides in relation to the formation of glass fibers and films. J Non-Cryst Solids 1982;48:31–46. - 18.
Krol DM, van Lierop JG. The densification of monolithic gels. J Non-Cryst Solids 1984;63:131–44. - 19.
Ankudinov A, Ravel B, Rehr JJ, Newville M. FEFFIT Manual within the FEFF Project (Seattle, WA: University of Washington, USA); 1992–1999. - 20.
Mukherjee S, Chen CH, Chou CC, Tseng KF, Chaudhuri BK, Yang HD. Colossal dielectric and magnetodielectric effect in Er2O3 nanoparticles embedded in a SiO2 glass matrix. Phys Rev B 2010;82:104107(7). - 21.
Afify ND, Dalba G, Kuzmin A. Local structure around Er3+ in SiO2-HfO2glassy waveguides using EXAFS. Phys Rev B 2007;76:024114(8). - 22.
Maqsood A. Phase transformations in Er2Si2O7 ceramics. J Mater Sci Lett 1997;16:837–840. - 23.
Losurdo M, Giangregorio MM, Capezzuto P, Bruno G, Toro RG, Malandrino G, Fragalà IL, Armelao L, Barreca D, Tondello E, Suvorova AA, Yang D, Irene EA. Multifunctional nanocrystalline thin films of Er2O3: interplay between nucleation kinetics and film characteristics. Adv Funct Mater 2007;17:3607–12. - 24.
Chen S, Zhu YY, Xu R, Wu YQ, Yang XJ, Fan YL, Lu F, Jiang ZM, Zou J. Superior electrical properties of crystalline Er2O3 films epitaxially grown on Si substrates. Appl Phys Lett 2006;88:222902(3). - 25.
Rivas J, Mira J, Rivas-Murias B, Fondado A, Dec J, Kleemann W, Señarís-Rodríguez MA. Magnetic-field-dependent dielectric constant in La2/3Ca1/3MnO3. Appl Phys Lett 2006;88:242906(3). - 26.
Jana A, Kundu TK, Pradhan SK, Chakravorty D. Dielectric behavior of Fe-ion-doped BaTiO3 nanoparticles. J Appl Phys 2005;97:044311(6). - 27.
Rivera I, Kumar A, Ortega N, Katiyar RS, Lushnikov S. Divide line between relaxor, diffused ferroelectric, ferroelectric and dielectric. Solid State Commun 2009;149:172–6. - 28.
Lal HB. Low temperature dielectric studies of some rare-earth oxides. J Phys C: Solid State Phys 1980;13:3969–76. - 29.
Yu Z, Ang C, Guo R, Bhalla AS. Ferroelectric-relaxor behavior of Ba(Ti0.7Zr0.3)O3 ceramics. J Appl Phys 2002;92:2655–7. - 30.
Raymond O, Font R, Suárez-Almodovar N, Portelles J, Siqueiros JM. Frequency-temperature response of ferroelectromagnetic Pb(Fe1/2Nb1/2)O3 ceramics obtained by different precursors. Part I. Structural and thermo-electrical characterization. J Appl Phys 2005;97:084107(8). - 31.
Ang C, Yu Z, Cross LE. Oxygen-vacancy-related low-frequency dielectric relaxation and electrical conduction in Bi:SrTiO3. Phys Rev B 2000;62:228–36. - 32.
Samara GA. The relaxational properties of compositionally disordered ABO3 perovskites. J Phys: Condens Matter 2003;15:R367–R411. - 33.
Scott JF. Ferroelectrics go bananas. J Phys: Condens Matter 2008;20:021001(2). - 34.
Pintilie L, Alexe M. Ferroelectric-like hysteresis loop in nonferroelectric systems. Appl Phys Lett 2005;87:112903(3). - 35.
Yáñez-Vilar S, Mira J, Sánchez-Andújar M, Castro-García S, Fondado A, Rivas J, Senarís-Rodríguez MA. Particle size reduction: a way to enhanced dielectric properties of magnetocapacitive La2/3Ca1/3MnO3. Appl Phys Lett 2010;96:162904. - 36.
Kimura T, Kawamoto S, Yamada I, Azuma M, Takano M, Tokura Y. Magnetocapacitance effect in multiferroic BiMnO3. Phys Rev B 2003;67:180401(R)(4). - 37.
Tang J, Feng L, Wiemann JA. Negative magnetoresistance of γ-Fe2O3 observed in γ-Fe2O3/Ag granular nanocomposite. Appl Phys Lett 1999;74:2522–4. - 38.
Catalan G. Magnetocapacitance without magnetoelectric coupling. Appl Phys Lett 2006;88:102902(3). - 39.
Mukherjee S, Chen CH, Chou CC, Yang HD. Anomalous dielectric behavior in nanoparticle Eu2O3:SiO2 glass composite system. Euro Phys Lett 2010;92:57010(4). - 40.
Kao TH, Mukherjee S, Yang HD. Magnetic nanoparticles induced dielectric enhancement in (La,Gd)2O3:SiO2 composite systems. J Magn Magn Mater 2013;346:11–5. - 41.
Lukashev P, Sabirianov RF. Flexomagnetic effect in frustrated triangular magnetic structures. Phys Rev B 2010;82:094417(6). - 42.
Eliseev EA, Glinchuk MD, Khist V, Skorokhod VV, Blinc R, Morozovska AN. Linear magnetoelectric coupling and ferroelectricity induced by the flexomagnetic effect in ferroic. Phys Rev B 2011;84:174112(16). - 43.
Foster AS, Lopez Gejo F, Shluger AL, Nieminen RM. Vacancy and interstitial defects in hafnia. Phys Rev B 2002;65:174117(13). - 44.
Nogami M, Moriya Y. Glass formation through hydrolysis of Si(OC2H5)4 with NH4OH andHCl solution. J Non-Cryst Solids 1980;37:191–201. - 45.
Rocca F, Ferrari M, Kuzmin A, Daldosso N, Duverger C, Monti F. EXAFS studies of the local structure of Er3+ ions in silica xerogel co-doped with aluminium. J Non-Cryst Solids 2001;293–295:112–7. - 46.
Kliava J, Malakhovskii A, Edelman I, Potseluyko A, Petrakovskaja E, Melnikova S, Zarubina T, Petrovskii G, Bruckental Y, YeshurunY. Unusual magnetic transitions and nature of magnetic resonance spectra in oxide glasses containing gadolinium. Phys Rev B 2005;71:104406(9). - 47.
Kliava J, Malakhovskii A, Edelman I, PotseluykoA, Petrakovskaja E, Melnikova S, Zarubina T, Petrovskii G, Bruckental Y, Yeshurun Y. Reply to “Comment on ‘Unusual magnetic transitions and nature of magnetic resonance spectra in oxide glasses containing gadolinium.’” Phys Rev B 2006;74:026404(2). - 48.
Bud’ko SL, Canfield PC. Evaluation of a long-time temperature drift in a commercial quantum design MPMS SQUID magnetometer using Gd2O3 as a standard. J Magn Magn Mater 2006;299:281–7. - 49.
Hadjipanayis G, Sellonyer DJ, Brandt B. Rare-earth-rich metallic glasses. I. Magnetic hysteresis. Phys Rev B 1981;23:3349–54.