Tính chất từ dị thường của multiferroics BaTiO3 pha tạp Fe

Nguyễn Văn Đăng và Đtg Tạp chí KHOA HỌC & CÔNG NGHỆ 96(08): 49 - 54

49

ABNORMAL MAGNETIC PROPERTY IN Fe-DOPED BaTiO3

MULTIFERROICS

Nguyen Van Dang1*, Nguyen Thi Dung1

,

Nguyen Van Khien1

, To Manh Kien2

, Nguyen Khac Hung1

1College of Science - TNU, 2Xuan Mai High School – Hanoi City

SUMMARY

Samples of multiferroic BaTi1-xFexO3 material (x = 0.0, 0.07, 0.08, 0.09, 0.10, 0.11, 0.12, 0.2 and

0.3) were synthesized by using the solid-state reaction method. The influence of Fe substitution for

Ti on the crystalline structure and the magnetic property of BaTi1-xFexO3 samples were

investigated. The obtained X-ray diffraction patterns showed that the structure of the material

sensitively depends on Fe dopant content, x, and transforms gradually from the tetragonal (P4mm)

phase to the hexagonal (P63/mmc) one with increasing x. All of the samples exhibit both

ferroelectricity and ferromagnetism at room temperature. The result of magnetization

measurements showed that the magnetization at a magnetic field as high as 1 T abnormally

depends on x, increases with increasing x to a maximum at x=0.1 then decreases monotonously

afterward. There are possibilities to account for this anomalous magnetic behavior such as the

Fe3+-to-Fe4+ and/or Ti4+-to-Ti3+ change(s) induced by oxygen vacancies. The substitution of Fe

into Ti sites also changes the conductivity of the material and impurity (acceptor) levels in the

band gap, which can be evident from the absorption spectra, electric impedance, and time￾dependent leakage current measured at room temperature.

Key words: Multiferroics, XRD, UV - visible spectra, magnetization, model for ferromagnetism

INTRODUCTION*

BaTiO3 has been well known for its

ferroelectricity at room temperature, high

permittivity, wide band gap, and numerous

dielectric-based applications. It has also

attracted great attention of basic research due

to its different polymorphs, which exist at

various temperature ranges: rhombohedral (T

< -90 0C), orthorhombic (-90 0C < T < 5 0C),

tetragonal (0 oC < T < 130 oC), cubic (130 oC

< T < 1460 0C), and hexagonal (T > 1460 0C).

Nevertheless, partially doping Fe or Mn with

high content, for instance, may stabilize the

hexagonal polymorph at room temperature [1-

5]. Moreover, Ren [6] reported a giant

electrostrain effect (about 0.75% at 200

V/mm) in Fe-doped BaTiO3 single crystals

based on a new mechanism of the symmetry of

point defects, in which defect dipole moments

yield internal storing forces for recovering the

reversibility of domain switching.

*

Tel: 0983 009975, Email: [email protected]

Increasing attention has been also paid to

studying the Fe-doped BaTiO3 material

because of its interesting magneto-optical

properties [7,8]. Most importantly, the Fe￾doped BaTiO3 material is currently addressed

to investigate as a multiferroic material, in

which magnetism and ferroelectricity coexist

in a structurally-single phase system at room

temperature [1,2,9], which is of importance in

the development of multifunctional materials

for spintronic devices [8-10]. In this report,

we present our experimental results for BaTi1-

xFexO3 ceramic samples. The influence of the

Fe doping on the crystalline structure is

investigated using X-ray diffraction patterns

and Raman scattering spectra, and on the

band structure via UV absorption spectra and

electric impedance and leakage current

measurements. Most importantly, we report

an abnormal behavior of the magnetization

with respect to the doping content of Fe ions.