Magnetoelectric, magnetodielectric and magneto-impedance couplings in Bi1−xNdxFe0.99Co0.01O3 compounds

In this work Bi1−xNdxFe0.99Co0.01O3 ceramics compositions were synthesized for x = 0.05, 0.20 and, y = 0.01. Structural refinement results show that most of the samples crystallized in a rhombohedral symmetry with R3c. Measurements magnetoelectric coefficient, show that the magnetoelectric coefficients are of second order. The electrical impedance characterization of in function external magnetic fields, has a relative variation of the real dielectric response, the loss tangent and the electrical impedance. The systems, as the DC magnetic field strength increased a gain in both the values of the dielectric constant variation, as well as the variation of the electrical impedance. In other words, the greater the intensity of the magnetic field, the greater your response. There were also significant variations with of the magnetic field AC.


Introduction
Materials that simultaneously exhibit ferroic properties, such as magnetism, ferroelectricity and ferroelasticity are classified multiferroics (Tokura, Seki & Nagosa 2014) (Ramazanoglu et al 2011). The main applications invised these materials is in are sensors, spintronic among others (Bilmes et al 2000) (Wang et al 2003). Bismuth ferrite is a multiferroic because have two orders ferroic being called a magnetoelectric material. Is a promising material because it ferroeletric and magnetic room temperature, i.e. G-type antiferromagnetic order it has a transition of 640 K (Tn), while the ferroelectric order appears at about 1100 K (TC). The BiFeO3 crystallizes in a rhombohedral perovskite structure with R3c (Fischei et al 1931). A of the problems shown by other authors is the appearance of unwanted phases in the process phase of bismuth ferrite (Hasan et al 2016). Some rare earth substitutions at the bismuth site (La3 + , Gd3 + , Tb3 + , Dy3 + ) are reported by as an option to improve the electrical and magnetic properties of BiFeO3   (Fei et al 2015). A of the focus of this study is the dielectric measurements and impedances under action of an external magnetic field, classified as magnetodielectric and magnetoimpedance respectively. These phenomena have resumed the great demand for magnetic field sensitive materials and their range of applications (Phan & Peng 2007). In this work, the Bi1−xNdxFe0.99Co0.01O3 system was processed three samples thickness in the 1.2 mm and 5.4 mm diameter to make the characterizations.

Methodology
This study was carried out in the materials science laboratory and is part of a research on the development of electronic devices capable of electrical and magnetic interaction. The samples were processed under the following conditions: the precursors were weighed and mixed in three stoichiometry. They then went through high energy ball milling at 250 rotation per minute (RPM) for one hour. All samples were pressed and baked for sintering at 890° degrees for 3 minutes with rapid heating and cooling, called quenting (Shvartsman et al 2007). To check if the samples are in proper phases, X-ray diffraction was performed with Shimadzu diffractometer model XRD-7000, with scan rate of 2°/min, from 10° to 130°, in continuous mode at room temperature. From the x-ray diffraction, the refinement was performed using the Le Bail method, finding its network parameters. For dielectric measurements and electrical impedance under the magnetic field, an LCR meter (model E4980A), agilent function generator (model 33210A) and magnetic system (model GMW 5970-80) as shown in the measurement diagram of Figure 1.
The magnetodieletric and magneto-impedance measurements can be defined as x100% and x100% respectively.

Results and Discussion
The results on x-ray diffraction and Le Bail refinement of Figure 2 showed results with the same phase described in the literature (Mincache et al 2016). According to the results of Le Bail refinement has the network parameters changing according to the doping. The sample volume a) has the larger volume then as neodymium increase the volume decreases, thus resulting in a phase change, noting also that noting also that in c) is above a good refinement. in c) is above a good refinement as show a Table 1. Analyzing each diffractogram can see a change in peaks between angles of 31° to 33° degrees. It is possible that a structural change is taking place in the systems phase as already reported in other work (Singh et al 2017).
The phase changes are happening in b) and c) of Figure 2, recent work (Oliveira 2015) has shown that these phases are rhombohedral and orthorobinch.  Bi0.80Nd0.2Fe0.99Co0.01O3.

Source: Authors.
It can be seen from the magnetization (Figure 3) result that the compartment between the two samples is significant.
when we add more neodymium sample with 20 percent becomes almost paramagnetic. A possible explanation for this phenomenon may be lone pair moving from its center of symmetry (Geng et al 2014), in which case the neodymium may be interfering with the magnetization of the system. When a magnetic field is placed under a sample and its response with an electric voltage coefficient, it says that the material has a coupling between electricity and magnetism, so the material is magnetoelectric as shown in Figure 4. The compartment of the two samples is observed to have similar shapes. The value of the magnetoelectric coefficient is low and becomes lower when we add more neodymium. A possible explanation for this effect is that the values of electro-striction and magneto-striction (Shen et al 2013) are not acting on the system in a linear way, but something more complex, such as the nonlinear magnetoelectric effect as reported in the works (Pirc & Blinc 2010).  Source: Authors.
The electrical impedance measurements follow the same scheme as the magnetodielectric measurement ( Figure 6).

Conclusion
With the results of x-ray diffraction and refinement observed in the sample with 5% of neodymium a phase R3c. In the second sample with 20% neodymium it is possible that its structure is changing to another phase, possibly orthorhombic. and when we add more neodymium to the system it becomes more paramagnetic. Magnetoelectric results possibly show a nonlinear effect. Regarding the magnetodielectric and magneto-impedance measurements it can be observed that their nominal values increase when the DC magnetic field is increased, however this happens with the addition of neodymium.