80 research outputs found
Room temperature multiferroicity in orthorhombic LuFeO
From the measurement of dielectric, ferroelectric, and magnetic properties we
observe simultaneous ferroelectric and magnetic transitions around 600 K
in orthorhombic LuFeO. We also observe suppression of the remanent
polarization by 95\% under a magnetic field of 15 kOe at room
temperature. The extent of suppression of the polarization under magnetic field
increases monotonically with the field. These results show that even the
orthorhombic LuFeO is a room temperature multiferroic of type-II variety
exhibiting quite a strong coupling between magnetization and polarization.Comment: 5 pages with 5 figures; published in Appl. Phys. Let
Origin of the asymmetric exchange bias in BiFeO3/Bi2Fe4O9 nanocomposite
We show from detailed magnetometry across 2-300 K that the BiFeO3-Bi2Fe4O9 nanocomposite offers a unique spin morphology where superspin glass (SSG) and dilute antiferromagnet in a field (DAFF) coexist at the interface between ferromagnetic Bi2Fe4O9 and antiferromagnetic BiFeO3. The coexisting SSG and DAFF combine to form a local spin texture, which gives rise to a path- dependent exchange bias below the spin freezing temperature (similar to 29 K). The exchange bias varies depending on the protocol or path followed in tracing the hysteresis loop. The exchange bias has been observed below the blocking temperature (T-B) 60 K of the superparamagnetic Bi2Fe4O9. The conventional exchange bias (CEB) increases nonmonotonically as temperature decreases. The magnitude of both exchange bias (H-E) and coercivity (H-C) increase with decrease in temperature and are found to be asymmetric below 20 K depending on the path followed in tracing the hysteresis loop and bias field. The local spin texture at the interface between ferromagnetic and antiferromagnetic particles generates a nonswitchable unidirectional anisotropy along the negative direction of the applied field. The influence of this texture also shows up in " asymmetric" jumps in the hysteresis loop at 2 K, which smears off at higher temperature. The role of the interface spin texture in yielding the path dependency of exchange bias is thus clearly delineated
Maity et al. reply to the comment on “Superspin glass mediated giant spontaneous exchange bias in a nanocomposite of BiFeO3−Bi2Fe4O9”, A. Harres, J. Geshev, and V. Skumryev, Physical Review Letters, 114, 099703 (2015)
In this article we reply to the concerns raised by Harres et al. [Phys. Rev. Lett. 114, 099703 (2015)] about some of the results reported in our original paper [T. Maity et al. Phys. Rev. Lett. 110, 107201 (2013)]. We show that the magnetic hysteresis loops are not minor and both path dependency of exchange bias and presence of superspin glass phase in the nanocomposite are indisputable
Large magnetocapacitance in electronic ferroelectric manganite systems
We have observed a sizable positive magnetocapacitance () in
perovskite PrCaMnO and bilayer
Pr(SrCa)MnO system under 5T magnetic field across
20-100 K below the magnetic transition point T. The magnetodielectric
effect, on the other hand, exhibits a crossover: (a) from positive to negative
for the perovskite system and (b) from negative to positive for the bilayer
system over the same temperature range. The bilayer
Pr(SrCa)MnO system exhibits a sizable anisotropy as
well. We have also noticed the influence of magnetic field on the dielectric
relaxation characteristics of these systems. These systems belong to a class of
improper ferroelectrics and are expected to exhibit charge/orbital order driven
ferroelectric polarization below the transition point T. Large
magnetocapacitance in these systems shows typical multiferroic behavior even
though the ferroelectric polarization is small in comparison to that of other
ferroelectrics.Comment: 6 pages with 5 embedded figures; accepted for publication in J. Appl.
Phy
Superspin Glass Mediated Giant Spontaneous Exchange Bias in a Nanocomposite of BiFeO-BiFeO
We observe an enormous exchange bias (300-600
Oe) - measured in an unmagnetized state following zero-field cooling - in a
nanocomposite of BiFeO (94%)-BiFeO (6%) over a
temperature range 5-300 K. Depending on the path followed in tracing the
hysteresis loop - positive (p) or negative (n) - as well as the maximum field
applied, the exchange bias () varies significantly with
. The temperature dependence of is nonmonotonic. It
increases, initially, till 150 K and then decreases as the blocking
temperature is approched. All these rich features appear to be
originating from the spontaneous symmetry breaking and consequent onset of
unidirectional anisotropy driven by "superinteraction bias coupling" between
ferromagnetic core of BiFeO (of average size 19 nm) and
canted antiferromagnetic structure of BiFeO (of average size 112 nm)
via superspin glass moments at the shell.Comment: 5 pages with 4 figures; published in Phys. Rev. Let
Particle size dependence of magnetization and noncentrosymmetry in nanoscale BiFeO(3)
The saturation magnetization (M(S)), antiferromagnetic transition point (T(N)), and the off-center displacements of Bi and Fe ions have been measured as a function of particle size in nanoscale BiFeO(3). TN decreases down to similar to 550 K for particles of size similar to 5 nm from similar to 653 K in bulk, while MS rises by more than an order of magnitude. Analysis of crystallographic structure from Rietveld refinement of x-ray diffraction patterns shows significant rise in off-center displacements of Bi (delta(Bi)) and Fe (delta(Fe)) ions within a unit cell with the decrease in particle size. The net unit-cell polarization PS too, is found to be larger in nanoscale regime. (c) 2011 American Institute of Physics. [doi: 10.1063/1.3567038
Large structure-dependent room temperature exchange bias in self-assembled BiFeO3 nanoparticles
We studied the magnetic properties of self-assembled aggregates of BiFeO3
nanoparticles (~ 20-40 nm). The aggregates formed two different structures -
one with limited and another with massive cross-linking - via `drying-mediated
self-assembly' process following dispersion of the nanoparticles within
different organic solvents. They exhibit large coercivity H_C (>1000 Oe) and
exchange bias field H_E (~ 350-900 Oe) in comparison to what is observed in
isolated nanoparticles (H_C ~ 250 Oe; H_E ~ 0). The H_E turns out to be
switching from negative to positive depending on the structure of the
aggregates with |H_E| being larger. The magnetic force microscopy reveals the
magnetic domains (extending across 7-10 nanoparticles) as well as the domain
switching characteristics and corroborate the results of magnetic measurements.
Numerical simulation of the `drying-mediated-self-assembly' process shows that
the nanoparticle-solvent interaction plays an important role in forming the
`nanoparticle aggregate structures' observed experimentally. Numerical
simulation of the magnetic hysteresis loops, on the other hand, points out the
importance of spin pinning at the surface of nanoparticles as a result of
surface functionalization of the particles in different suspension media.
Depending on the concentration of pinned spins at the surface pointing
preferably along the easy-axis direction - from greater than 50\% to less than
50% - H_E switches from negative to positive. Quite aside from bulk sample and
isolated nanoparticle, nanoparticle aggregates - resulting from surface
functionalization - therefore, offer remarkable tunability of properties
depending on structures.Comment: 14 pages, 33 pdf figures. Contact authors for the supplementary data
and movie
Micro-Farming Situation Observed through Manual Discriminant Analysis
Micro-farming situation is a relatively homogeneous farming situation conceptualised by the farmers themselves on the basis of certain agro-ecological and socio-economic criteria. These criteria are more holistic in its coverage than those used during identifying conventional recommendation domains. The article outlines the rationale of observing a micro-farming situation, proposes a method to carry on such exercises and points to certain areas of further research. Not only technology positioning, but also a methodological insight can be developed from such exercises. With some modifications this can be used as a participatory research tool during the study of farming systems, especially in the resource-poor CRD agriculture
Large Magnetoelectric Coupling in the Thin Film of Multiferroic CuO
We report observation of large magnetoelectric coupling in an epitaxial thin film of multiferroic CuO grown on the (100)MgO substrate by the pulsed laser deposition technique. The film is characterized by X-ray diffraction, transmission electron microscopy, and Raman spectrometry. The crystallographic structure of the film turns out to be monoclinic (space group C2/c) with 111]CuO parallel to100]MgO ``out-of-plane'' epitaxy and ``in-plane'' domain structure. The lattice misfit strain is found to vary within +/- 1-3%. The dc resistivity, magnetization, dielectric spectroscopy, and remanent ferroeletric polarization have been measured across 80-300 K. The dielectric constant is found to decrease by >20% under a moderate magnetic field of similar to 18 kOe while the remanent ferroelectric polarization, emerging at the onset of magnetic transition (T-N similar to 175 K), decreases by nearly 50% under similar to 18 kOe field. These results could assume importance as the strain-free bulk CuO does not exhibit magnetoelectric coupling within such magnetic field regime. The strain-induced large magnetoelectric coupling in the CuO thin film would generate new possibility of further strain tuning to observe room-temperature magnetoelectric multiferroicity suitable for scores of applications such as memories, sensors, energy-harvesting devices, generators, amplifiers, and so forth
Large magnetoelectric coupling in nanoscale BiFeO from direct electrical measurements
We report the results of direct measurement of remanent hysteresis loops on
nanochains of BiFeO at room temperature under zero and 20 kOe
magnetic field. We noticed a suppression of remanent polarization by nearly
40\% under the magnetic field. The powder neutron diffraction data reveal
significant ion displacements under a magnetic field which seems to be the
origin of the suppression of polarization. The isolated nanoparticles,
comprising the chains, exhibit evolution of ferroelectric domains under dc
electric field and complete 180 switching in switching-spectroscopy
piezoresponse force microscopy. They also exhibit stronger ferromagnetism with
nearly an order of magnitude higher saturation magnetization than that of the
bulk sample. These results show that the nanoscale BiFeO exhibits
coexistence of ferroelectric and ferromagnetic order and a strong
magnetoelectric multiferroic coupling at room temperature comparable to what
some of the type-II multiferroics show at a very low temperature.Comment: 7 pages with 5 figures, published in Phys. Rev.
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