ARTICLE IN PRESS
A.Ye. Yermakov et al. / Journal of Magnetism and Magnetic Materials 272–276 (2004) 2445–2447
2446
External magnetic field was applied and then removed at
RT to the Cu NP before the chemical reaction. The
reference Cu NP was not subjected to magnetic field.
For definiteness, the magnetic field strength and the
duration of exposure were fixed to be 2 kOe and 1 min,
respectively. Copper NP containing copper oxides were
prepared using gas-condensation and electrical wire
explosion methods. Control over the course of the
reaction and characterization of phthalocyanine pro-
ducts was carried out by the electron absorption
spectroscopy (EAS), IR, elemental, X-ray phase analysis
and others.
content of Cu oxides B9 wt%) the rate of PcCu
formation is increased by 7–8 times (see Fig. 1, a-
100 nm). The PcCu yield for the Cu-100 nm after
applying of magnetic field was more than 90%. At the
same time the concentration of PcCu for NP Cu-30 nm
was twice less (Fig. 1, b-30 nm). The results obtained
from the ratio of intensity absorption lines and weighing
of the final solid products (PcCu) for NP Cu (30 and
100 nm) well agreed with each other. Doping nano-Cu
with iron completely (see Fig. 1) suppresses the magnetic
field effect.
The most consistent approach applicable for the
explanation of magnetic field-controlled reactivity could
be a model of strongly correlated polar pseudo-Jahn–
Teller (PJT)-centers [3]. The existence of the (PJT)-
centers (hole [CuO45À] and electron [CuO74À] centers) can
be caused by the appearance of charge carriers due to
non-stoichiometry of nano-CuO. In fact, the optical
absorption spectra in infra-red range (up to 3 eV) display
the essential increase of the numbers of the hole and
electron centers in the nanocrystalline cupric oxide.
The existence and quantum behavior of the specific
tunnel paramagnetic centers with special valence and
hysteresis spin states enables to qualitatively understand
the reactivity change of CuO nanopowders under
applying of magnetic field [6].
3. Results and discussion
In the absence of magnetic field at any combinations
(AII + NP + solvent) the rate of the reaction of PcCu
formation was approximately constant.
A very clear chemical response (acceleration of
chemical reaction rate) as a result of the magnetic field
influence on the oxidized Cu NP was registered. It is an
outstanding experimental fact that a short-term applica-
tion and then removal of a magnetic field is sufficient to
initiate the reaction. The required time to complete the
reaction (PcCu yield X90%) after magnetic treatment
depends on the phase composition and size particles.
In the Fig. 1 the ratio of intensities of the EAS lines
measured for final solid products (PcCu) of reaction
using the gas-condensation NP samples (30 and 100 nm)
under the field and without it (Fig. 1c) are given.
Intensity of the absorption lines is proportional to
concentration of PcCu (b-phase). After magnetic field
treatment of copper NP (average size 100 nm and
Many problems are yet left to be solved, which might
help to both understand and clarify the fundamental
nature of the new effect and to ensure their successful
application. The magnetic phase diagram of non-
stoichiometric CuO oxide in the wide-temperature range
is not fully understood and it is not clear how it will be
modified for nanoscaled particles. Evidently the detailed
physical and chemical mechanisms that are responsible
for the changing of reactivity of nanocrystalline cuprates
(or other strong correlated systems) require more deep
investigation in further.
8
6
4
2
0
a-100 nm
Acknowledgements
The authors would like to express gratitude to
V.S. Gaviko, N.N. Shchegoleva, A.V. Korolyov, A.V.
Vosmerikov for their assistance in carrying out ex-
periments and to A.S. Moskvin, Yu.P. Sukhorukov,
B.A. Gizhevskii, A.I. Ponomarev, A. Ignatenkov, N.N.
Loshkareva for fruitful and useful discussions.
This work was carried out with support by the
Russian Foundation for Basic Research (Project 01-03-
96521-p2001ural).
b-30 nm
catalysis
c-H=0
0.0
Inhibition
0.5
1.0 1.5
2.0
2.5
3.0
%, Fe
Fig. 1. The ratio of line intensities for typical of wave length of
PcCu (626 nm) in EAS spectra for the ended products (in
130 days) for magnetized (a, b) and non-magnetized (c—dotted
line) of oxidized Cu powders (30 and 100 nm) versus Fe content
in copper.
References
[1] E.L. Nagaev, Usp. Fiz. Nauk. 38 (5) (1995) 497.
[2] J. Zaanen, O. Gunnarsson, Phys. Rev. B 40 (1989) 7391.
Yermakov
