This article aims to investigate the possibility to turn the multiferroic orders and magnetocapacitance effect close to/above room temperature in nanosized GaFeO 3 ceramics by a sol-gel preparation method and substitution with non-magnetic Zn atoms. Therefore, in this work, we have synthesized a series of nanocrystalline Ga1-xZnxFeO3(GZFO, x = 0, 0.01, 0.05 and 0.1) ceramic samples and study the effect of Zn substitution on their structural, magnetic, and electric properties. All the GZFO samples have an orthorhombic structure with Pc21n space group and the value of lattice parameters increase systematically with increasing Zn concentration. Interestingly, it shows that magnetic and electric properties are strongly dependent on the Zn substitution concentration. Based on the results of temperature-dependent magnetizations, M(T), it is observed that with increasing Zn-content up to 0.10, the ferrimagnetic transition temperature (TC) increases from 306 to 320 K. It is also found that the nanocrystalline Zn-doped GaFeO3 (GFO) samples exhibit the characteristics of ferroelectricity at room temperature. Furthermore, the magnetization, ferroelectric polarization and magnetocapacitance of Zn-doped GFO nanosized ceramics are enhanced compared to those of the pristine sample of GFO ferrite. These results open wide perspectives for the applications of room temperature multiferroic devices.
Recently, multiferroic and magnetoelectric (ME) materials opened new avenues for the development of novel devices based on new functionalities such as control of the magnetic properties by means of electrical fields and vice versa [
The nanosized ceramic samples of Ga1−xZnxFeO3 (GZFO, x = 0, 0.01, 0.05 and 0.1) were prepared through a sol-gel method using nitrates as metal precursors. First, gallium nitrate [Ga(NO3)3×xH2O], iron nitrate [Fe(NO3)3×9H2O] and zinc nitrate [Zn(NO3)2×6H2O] in stoichiometric proportions were dissolved in distilled water. Citric acid (C6H8O7) in 1:1 molar ratio with respect to the metal nitrates was added to the solution as a complexant. The clear solution was dried at 120˚C to form a gel, and then the obtain gel was burned until the combustion process was completed. After that, the precursory powders were reground and sintered at 800˚C for 12 h.
The crystalline structure and the phase purity of the obtained samples were characterized with a typical X-ray diffraction (XRD), acquired by a Bruker D8 Advance X-ray diffractometer Cu Kα1 radiation. The XRD data were fit using the General Structure Analysis System (GSAS) Rietveld refinement program. Micrographs of the samples were analyzed using a field emission transmission electron microscope (TEM) operated at 120 kV. The temperature- and field-dependent magnetizations were measured with a Quantum Design superconducting quantum interference device (SQUID) magnetometer. For the magnetocapacitance (MC) measurements, the powders were pressed into the disk (5 mm in diameter and 0.5 mm in thickness) under a pressure of 1.5 GPa and then coated with 100 nm thick silver layers on both the top and the bottom sides of the disk as electrodes. A capacitance bridge (Agilent E4980A Precision LCR meter) hooked to a probe station with a closed-cycle low temperature system was used. Room temperature ferroelectric measurements were performed using a Sawyer-Tower circuit and a commercial FE test system (TF Analyzer, aixACCT Co.).
The RT XRD patterns of the Ga1−xZnxFeO3 samples with x = 0, 0.01, 0.05, and 0.1 are given in
GZFO1 | GZFO2 | GZFO3 | GZFO4 | |
---|---|---|---|---|
a (Å) | 8.7622(1) | 8.7645(3) | 8.7678(2) | 8.7715(4) |
b (Å) | 9.4135(5) | 9.4164(2) | 9.4183(2) | 9.4216(1) |
c (Å) | 5.0876(2) | 5.0901(5) | 5.0927(3) | 5.0955(1) |
c/a | 0.58063 | 0.58076 | 0.58084 | 0.58091 |
2 c/b | 0.76432 | 0.76446 | 0.76470 | 0.76485 |
According to the calculation using a Debye-Scherrer equation [
The temperature dependence of magnetization, M(T), was measured in a magnetic field of 1000 Oe under the condition of field-cooled (FC).
228 K in bulk GFO [
The field-dependent magnetization M(H) curves of all the GZFO samples measured at 5 K are presented in
To investigate the presence of spontaneous polarization, the ferroelectric polarization-electric field (P-E) loops for the Zn-doped GFO samples were measured at RT are shown in
of saturation increase with the increase of Zn concentration. From the P-E loops, we see that the values of the maximum polarization of GZFO2, GZFO3 and GZFO4 samples are 0.08, 0.16 and 0.23 μC/cm2, respectively. The enhancement of electric polarization may be ascribed to the increase in distortion of the crystal lattice due to the substitution of Zn2+-cations in place of Ga3+-cations in the doped samples.
In order to know the coupling between the magnetic and ferroelectric orderings, we have measured the dielectric constant of the GZFO samples in presence of an externally applied magnetic field. The change in dielectric constant with the applied magnetic field is one of the important ways to study the coupling effect [
In summary, we have studied the effect of Zn doping on the multiferroic properties of nanocrystalline GZFO samples prepared by a sol-gel method. It shows that magnetic and electric properties are strongly dependent on the Zn-doping. The magnetic characterization indicates that with an increase in the Zn-content, the FM transition temperature increases from 306 to 320 K. It is also found that
the Zn-doped GFO samples exhibit the characteristics of ferroelectricity at RT. Based on the overall data, one can suggest that the Zn-substitution in GFO introduces structural distortion and modifies magnetic exchange interaction, which affects both FM and ferroelectric orderings and MC effect. Furthermore, the simultaneous enhancement of magnetization and electric polarization together with the enhanced values of MC in Zn-doped samples are prominent candidates for the applications of multiferroic devices.
This research was financially supported by Ministry of Science and Technology of Taiwan, under Grant no. MOST-107-2112-M-390-003 and 105-2112-M-390-001.
The authors declare no conflicts of interest regarding the publication of this paper.
Han, T.-C., Yen, C., Chung, Y.-D. and Wu, M.-L. (2018) Effect of Zn Substitution on the Magnetic and Magnetocapacitance Properties of Nanosized Multiferroic GaFeO3 Ceramics. New Journal of Glass and Ceramics, 8, 55-63. https://doi.org/10.4236/njgc.2018.84005