82 research outputs found
Current-driven magnetization decrease in single crystalline ferromagnetic manganese oxide
The electrical and magnetic response to a bias current has been investigated
in a singlecrystalline ferromagnetic manganese oxide
CaMnO . A significant decrease of the magnetization is
observed at the same threshold current where a non-linearity of V-I
characteristics appears. Such a behavior cannot be understood in the framework
of the filamentary picture usually invoked for the non linearity of the other
manganese oxides. Instead, an analogy with spintronic features might be useful
and experimental signatures seem to be in agreement with excitations of spin
waves by an electric current. This provides an example of a bulk system in
which the spin polarized current induces a macroscopic change in the
magnetization.Comment: 3 pages, 4 figure
Microphase separation in Pr0.67Ca0.33MnO3 by small angle neutron scattering
We have evidenced by small angle neutron scattering at low temperature the
coexistence of ferromagnetism (F) and antiferromagnetism (AF) in
Pr0.67Ca0.33MnO3. The results are compared to those obtained in
Pr0.80Ca0.20MnO3 and Pr0.63Ca0.37MnO3, which are F and AF respectively.
Quantitative analysis shows that the small angle scattering is not due to a
mesoscopic mixing but to a nanoscopic electronic and magnetic ''red cabbage''
structure, in which the ferromagnetic phase exists in form of thin layers in
the AF matrix (stripes or 2D ''sheets'').Comment: 4 figure
Field dependence of the electronic phase separation in Pr0.67Ca0.33MnO3 by small angle magnetic neutron scattering
We have studied by small angle neutron scattering the evolution induced by
the application of magnetic field of the coexistence of ferromagnetism (F) and
antiferromagnetism (AF) in a crystal of PrCaMnO. The
results are compared to magnetic measurements which provide the evolution of
the ferromagnetic fraction. These results show that the growth of the
ferromagnetic phase corresponds to an increase of the thickness of the
ferromagnetic ''cabbage'' sheets
Non-linear electrical response in a charge/orbital ordered CaMnO crystal : the charge density wave analogy
Non-linear conduction in a charge-ordered manganese oxide
PrCaMnO is reported. To interpret such a feature, it is
usually proposed that a breakdown of the charge or orbitally ordered state is
induced by the current. The system behaves in such a way that the bias current
may generate metallic paths giving rise to resistivity drop. One can describe
this feature by considering the coexistence of localized and delocalized
electron states with independent paths of conduction. This situation is
reminiscent of what occurs in charge density wave systems where a similar
non-linear conduction is also observed. In the light of recent experimental
results suggesting the development of charge density waves in charge and
orbitally ordered manganese oxides, a phenomenological model for charge density
waves motion is used to describe the non-linear conduction in
PrCaMnO. In such a framework, the non-linear conduction
arises from the motion of the charge density waves condensate which carries a
net electrical current.Comment: 13 pages, 6 figure
Non-linear electrical response in a non-charge-ordered manganite: Pr0.8Ca0.2MnO3
Up to now, electric field induced non-linear conduction in the Pr(1-x)CaxMnO3
system has been ascribed to a current-induced destabilization of the charge
ordered phase. However, for x<0.25, a ferromagnetic insulator state is observed
and charge-ordering is absent whatever the temperature. A systematic
investigation of the non-linear transport in the ferromagnetic insulator
Pr0.8Ca0.2MnO3 shows rather similar results to those obtained in charge ordered
systems. However, the experimental features observed in Pr0.8Ca0.2MnO3 are
distinct in that the collapse of the CO energy gap can not be invoked as
usually done in the other members of the PCMO system. We propose
interpretations in which the effectiveness of the DE is restored upon
application of electric field.Comment: 6 pages, 5 figure
Anomaly in the dielectric response at the charge orbital ordering transition of crystalline Pr0.67Ca0.33MnO3
The complex impedance of a Pr0.67Ca0.33MnO3 crystal has been measured. The
frequency dependence is studied for a wide range of temperatures (50K-403K) and
is found to be characteristic of relaxation process with a single Debye time
relaxation constant, which is interpreted as a dielectric constant of the
material. A strong peak is observed in this dielectric constant (up to two
millions) at the charge ordering transition suggesting an interpretation in
terms of ordering of electric dipoles at TCO or in term of phase separation.
Comparison with Pr0.63Ca0.37MnO3 - in which the phase separation is much
smaller and the peak in the dielectric constant is absent - suggests an
interpretation in term of phase separation between insulating and metallic
states.Comment: pdf fil
Colossal dielectric constants in transition-metal oxides
Many transition-metal oxides show very large ("colossal") magnitudes of the
dielectric constant and thus have immense potential for applications in modern
microelectronics and for the development of new capacitance-based
energy-storage devices. In the present work, we thoroughly discuss the
mechanisms that can lead to colossal values of the dielectric constant,
especially emphasising effects generated by external and internal interfaces,
including electronic phase separation. In addition, we provide a detailed
overview and discussion of the dielectric properties of CaCu3Ti4O12 and related
systems, which is today's most investigated material with colossal dielectric
constant. Also a variety of further transition-metal oxides with large
dielectric constants are treated in detail, among them the system La2-xSrxNiO4
where electronic phase separation may play a role in the generation of a
colossal dielectric constant.Comment: 31 pages, 18 figures, submitted to Eur. Phys. J. for publication in
the Special Topics volume "Cooperative Phenomena in Solids: Metal-Insulator
Transitions and Ordering of Microscopic Degrees of Freedom
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