PREPARATION AND MANETIC PROPERTIES OF TiO2 DOPED WITH V, Mn, Co, La

Fig. 1. The XRD pattern of pure TiO2 without anealing and TiO2 : Mn, concentration: 0.2%, 0.6%, 1%, 5%, 9% at 650oC

Nguyen The Khoi, Nguyen Ngoc Hai, Pham Van Vinh Department of Physics, Ha noi National University of Education

136 Xuan Thuy Road, Cau Giay Distr., Hanoi, Vietnam

CONCLUSION

APCTP–ASEAN Workshop on Advanced Materials Science and Nanotechnology (AMSN2008) - Nha Trang, Vietnam – September 15-21, 2008

Fig. 2 SEM images of

TiO2: 0.6% Mn samples

RESULTS AND DISCUSSION

INTRODUCTION

EXPERIMENT

XRD used a Siemens-D5005 diffractometer with Cu Kα radiation. SEM was operated by using a JSM-5600 microscope. Raman spectra were recorded by using T64000 spectrometer (Jobin-Yvon), backscattering geometry and using 514.5 nm line Ar+ laser excitation at the room temperature.The magnetic properties investigated by DMS-VSM ( VNU )

450oC

650oC

850oC

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Lin

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TiO2 - 0% Mn, Not annealed

TiO2 - 0.2% Mn, 650C

TiO2 - 0.6% Mn, 650C

TiO2 - 1% Mn, 650C

TiO2 - 5% Mn, 650C

TiO2 - 9% Mn, 650C

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TiO2- 0% Mn, Not annealed

TiO2- 1% Mn, 450C

TiO2- 1% Mn, 650C

TiO2- 1% Mn, 850C

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nsity

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TiO2 : 0.2% Mn - 650oC TiO2 : 0.6% Mn - 650oC TiO2 : 1% Mn - 650oC

Fig. 2. The XRD pattern of pure TiO2 without anealing and TiO2 : Mn, Concentration: 1% at different annealed temprature

from 450oC to 850oC.

-15000 -10000 -5000 0 5000 10000 15000-0.04

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M (

emu

/ g )

H ( Oe )

0.2 % Mn - 650oC 0.6 % Mn - 650oC 1 % Mn - 650oC 3 % Mn - 650oC 5 % Mn - 650oC 7 % Mn - 650oC 9 % Mn - 650oC

Fig. 8. Magnetic hysteresis loops ( M – H ) at 300K of TiO2 : Mn samples, annealed at 650oC, concentration: 0.2%, 0.6%, 1%, 3%, 5%, 7%, 9%.

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emu

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0.6% Mn - 450oC 0.6% Mn - 650oC 0.6% Mn - 850oC

Fig. 7. Magnetic hysteresis loops ( M – H ) at 300K of TiO2 : 0.6% Mn samples, annealed at different tempratures 450oC, 650oC, 850oC

Fig. 3. The Raman spectrums of TiO2 : Mn samples, concentration: 0.2%, 0.6%, 1%, 5%, 9%

annealed at 650oC.

-15000 -10000 -5000 0 5000 10000 15000-0.04

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M (

emu

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0.2% Mn - 650oC 0.2% V - 650oC 0.2% Co - 650oC 0.2% La - 650oC

Fig. 9. Magnetic hysteresis loops ( M – H ) at 300K of TiO2:Mn, TiO2:V, TiO2:Co, TiO2:La samples, annealed at 650oC, concentration: 0.2 %.

TiCl4 H2O

Stirring

Stirring

Dopant Complex

TiCl4 Solution

NH4NO3 /HCl

Mixed solution

80oC NH3

Precipitate

Drying

TiO2 powder

Washing

The XRD patterns of the TiO2: Mn samples, concentration : 0.2%, 0.6%, 1%, 5%, 9%, annealed at 650oC in air atmospheres shows that : As a common feature, the anatase phase are dominated for all samples sintered at 450oC, with the increase of annealed temperature, anatase phase transforms into rutile phase, and no anatase phase exists when the sintering temperature is 850oC and with the increase in the Mn doping concentration, the diffraction peaks shift to the lower angles, shows that ions Mn2+ may substitute into the TiO2 lattices, revealing that the clusters of the manganese oxide, such as Mn2O3, MnO,MnO2 may exist in the samples. The magnetization hysteresis loops ( M – H ) at 300 K :The samples annealed at low temperature clearly exhibit ferromagnetic behavior. With the increase of annealed temperature, the ferromagnetic component decreases, while the paramagnetic component increases. Magnetization as functions of annealed temperatures.The saturation magnetization of the samples annealed at 450oC is larger than that of the samples at 650oC and 850oC with the highest coercive field Hc and remanent magnetism Mr.

In recent years, oxide-diluted magnetic semiconductors with room temperature ferromagnetism have been studied for the potential spintronic applications. The investigations have been performed on the magnetic properties of TiO2 doped with transition metal and some rear earth elements, such as Mn, Cr, Fe, N, V... Although ferromagnetism at room temperature has been observed in doped TiO2 powder samples, some studies suggested the presence of second phases or precipitated ferromagnetic clusters as the origin of ferromagnetism, while other results seemed to indicate the existence of intrinsic ferromagnetism of transition metal substitution in the Ti lattice. Along with these, in this paper, the structural and magnetic properties of TiO2 powder

doped with V, Mn, Co and La, were was investigated in order to contribute to the understanding of the ferromagnetic mechanism.

With the increase in the annealing temperature and concentration, the ferromagnetism of the samples decreases. For the samples annealed at 650oC with different dopant contents of Mn, V, Co, La ,the ferromagnetism exhibits clearly. The main reason for the ferromagnetism at room can be the substitution of the V5+, Mn2+, Co2+, La3+ ions into the TiO2 latices and the formation of the clusters.Mn, V, Co, La concentrations in TiO2 play the key role in ferromagnetic mechanism but it still remaining the difference in the saturation magnetization Ms, the coervive field Hc and the remanent magnetism Mr in the cases.

Powder samples of TiO2:A, where A is Mn, V, Co and La, with dopant concentration of 0.2 %, 0.6 %, 1 %, 5 % and 9 %, were prepared by hydrothermal technique at temperatures ranging from 450 oC to 850oC.The crystalline structure and phase of the samples were investigated by XRD, Raman scattering and SEM. The magnetic properties were studied by measuring the magnetization loops at room temperature.The structure and lattice parameters are found to depend on the dopant and annealing temperature. All doped samples exhibited ferromagnetism. A comparison between the doped samples with different elements was carried out in order to contribute to the understanding of the ferromagnetic mechanism

ABSTRACT

Schematic diagram of the experimental process