NHMFL Research Report (DOC)

Document Sample
NHMFL Research Report (DOC) Powered By Docstoc
					                                 NATIONAL HIGH MAGNETIC FIELD LABORATORY
                                          2010 RESEARCH REPORT

Tailoring the Magnetic Characteristics of Nanocrystalline BiFeO3 by Ce Doping

B. Bhushan (UGC-DAE CSR, Kolkata Centre, India); Z. Wang, J. van Tol, N. S. Dalal (FSU, Chem. & NHMFL);
D. Das (UGC-DAE CSR, Kolkata Centre, India)

Multiferroics are materials in which two or more of the primary ferroic properties are united in the same phase.
These materials have large spectrum of applications in the field of multiple state memory devices, spin valves,
actuators, transducers etc. [1]. Doping is employed to improve the properties of these materials. We have
synthesized pure phase and substrate-free Ce-doped BFO nanoparticles (NPs). We employed a sol-gel route to
prepare Bi1-xCexFeO3 NPs with x = 0, 0.01, 0.03 and 0.05 hence designated as BFO, BCFO1, BCFO3 and
BCFO5 respectively. In this report, HF-EPR was utilized to detect the oxidation state of Fe ion and probe the
differences among the four samples.

High Frequency EPR measurements were performed
on a home-built homodyne instrument at the National
High Field Magnetic Laboratory, Tallahassee, FL.

Results and Discussion
All the samples exhibited EPR spectra at g ~ 2 that are
attributable to the Fe ions, in agreement with
Mössbauer spectroscopy results [2]. As shown in Fig.
1, there is a pronounced effect of Ce doping on the
EPR spectra of these particles. The pristine BFO NPs
exhibit an asymmetric lineshape, characteristic of
samples having magnetic anisotropy. While for all four
samples the linewidth tends to increase with frequency,
the dependence is not linear with field, and it is clear
that the anisotropy in the spectra cannot be explained         Figure 1 HF-EPR spectra of four samples. The
on the basis of g-anisotropy alone. There is a striking        central field values at B = 0 T correspond to the
change in the spectrum of 5% Ce-doped sample, where            resonance fields for a g-value of 2.
the absorption splits into two distinct peaks, which
indicates a substantial change in the magnetic environment for the unpaired electrons in Fe. Clustering is likely
the origin of this effect. The samples with 1% and 3% doping levels have the lineshape that mostly resembles a
single Lorentzian with a slight increase in width with frequency. These concentration correspond to a maximum in
magnetization which appear to correlate to a minimum of anisotropy in the EPR spectrum[2]. This is consistent
with increased exchange narrowing concomitant with increase in the concentration of the added paramagnetic
ions. These spectra show very little temperature depndence from 5-290 K.
The EPR data confirmed the oxidation state of Fe as 3+, which is consistent with Mössbauer measurements.
Multifrequency HF-EPR spectroscopy further revealed the presence of magnetic anisotropy, which was found to
be maximum for the pristine sample and minimum for the 3% Ce-doped sample.

B.B. thanks CSIR, Govt. of India, for the award of Senior Research Fellowship. NHMFL thanks NSF for support.

[1] Fiebig, M. et al., Nature, 419, 818 (2002).
[2] Bhushan, B. et al., manuscript submitted.

Shared By: