2,800 research outputs found
Observation of plastoferrite character and semiconductor to metal transition in soft ferromagnetic Li0.5Mn0.5Fe2O4ferrite
We prepared Li0.5Mn0.5Fe2O4 ferrite through chemical reaction in highly
acidic solution and subsequent sintering of chemical routed powder at
temperatures > 800 0C. Surface morphology showed plastoferrite character for
sintering temperature > 1000 0C. Mechanical softening of metal-oxygen bonds at
higher measurement temperatures stimulated delocalization of charge carriers,
which were strongly localized in A and B sites of the spinel structure at lower
temperatures. The charge delocalization process has activated semiconductor to
metallic transition in ac conductivity curves, obeyed by Jonscher power law and
Drude equation, respectively. Metallic state is also confirmed by the frequency
dependence of dielectric constant curves.Comment: 5 figure
Evidence of Ferrimagnetism in Ferromagnetic La0_{67}Ca0_{33}MnO_3 nanoparticle
The present report is dedicated to show that ferromagnetic La0.67Ca0.33MnO3
(LCMN) particles can be better described in the framework of ferrimagnetic
model. To confirm the ferrimagnetic signature in ferromagnetic LCMN particles,
the temperature dependence of the inverse of magnetic susceptibility in the
paramagnetic state of the samples was taken as a tool of data analysis. The
observed ferrimagnetism is understood as an effect of of the core-shell spin
structure in LCMN particles.Comment: 4 figure
Unconventional relaxation in antiferromagnetic CoRhO nanoparticles
Magnetic relaxation in antiferromagnetic CoRhO nanoparticles is
investigated at 2 K by cooling the sample from a temperature (70 K) well above
the antiferromagnetic ordering temperature at 27 K, following zero field cooled
(ZFC) and field cooled (FC) process. In ZFC process, the sample at 2 K is
subsequently followed by magnetic field on and off sequences, whereas in FC
process the cooling field is made off during measurement of remanent
magnetization as a function of time. The experiments suggest an unconventional
relaxation behaviour in the system, as an effect of increasing surface exchange
anisotropy with decreasing the size of antiferromagnetic nanoparticles
Static magnetic response of clusters in Co_{0.2}Zn_{0.8}Fe_{1.95}Ho_{0.05}O_{4} spinel oxide
Earlier investigation of Co_{0.2}Zn_{0.8}Fe_{1.95}Ho_{0.05}O_{4} spinel has
shown the existence of "super-ferromagnetic " clusters containing Fe^{3+} and
Ho^{3+} ions along with small size clusters of Fe^{3+} ions (Bhowmik et al, J.
Magn. Magn. Mater. {247}, 83 (2002)). Here, We report the static magnetic
response of these clusters. The experimental data suggests some interesting
magnetic features, such as, enhancement of magnetization; re-entrant magnetic
transitions with paramagnetic to ferromagnetic state below 225 K and
ferromagnetic to spin glass state below 120 K; appearance of field induced
ferromagnetism. We also observe an unusual maximum in the thermoremanent
magnetization (TRM) vs temperature data. Our measurements suggest that this
unusuality in TRM is related to the blocking of "super-ferromagnetic" clusters
,out of the ferromagnetic state, along their local anisotropy axis.Comment: LaTex file and 9 ps Figure
Lattice disorder and Ferromagnetism in La0.67Ca0.33MnO3 nanoparticle
We study the ferromagnetism of La0.67Ca0.33MnO3 in bulk polycrystalline,
nanocrystalline and amorphous phase. The structural change from crystalline
phase to amorphous phase exhibited a systematic decrease of TC(paramagnetic to
ferromagnetic transition temperature) and spontaneous magnetization (MS). The
experimental results suggested few more features, e.g., appearance of large
magnetic irreversibility in the temperature dependence of magnetization, lack
of magnetic saturation at high magnetic field, blocking of magnetization below
TB, and enhancement of coercivity. In addition, the magnetic phase transition
near to TC has changed from first order character in bulk sample to second
order character in nanocrystalline and amorphous samples. We understand the
observed magnetic features as the effects of decreasing particle size and
increasing magnetic (spin- lattice) disorder. We noted that magnetic dynamics
of amorphous samples is distinctly different from the nanocrystalline samples.
The ferromagnetism of amorphous samples are comparable with the properties of
reported amorphous ferromagnetic nanoparticles. We also demonstrate the effect
of disorder shell in controlling the dynamics of ferromagnetic cores.Comment: 11 figure
Ferromagnetism in lead graphite-pencils and magnetic composite with CoFe2O4 particles
This work has been initiated with a curiosity to investigate the elemental
composition and magnetic response of different grades of lead pencils (6B, 2B,
HB, 2H, 5H) that people use in daily life. Interestingly, experimental results
landed with a great achievement of observing soft magnetism in lead pencils,
indicating a wide scope of magnetic tuning for room temperature applications. A
novel magnetic composite has been synthesized by mixing different concentration
of CoFe2O4 (CF) nanoparticles in 5H and 6B pencils for studying the magnetic
tailoring aspects using pencils. Our results showed different possibilities of
controlling disorder induced ferromagnetic parameters and a simple approach of
producing sufficiently high coercive magnetic composite using pencils
Physical properties of RIr3 (R = Gd, Tb, Ho) compounds with coexisting polymorphic phases
The binary compounds GdIr3, TbIr3 and HoIr3 are synthesized successfully and
found to form in macroscopic co-existence of two polymorphic phases: C15b and
AuCu3-type. The dc magnetization and heat capacity studies confirm that C15b
phase orders ferromagnetically, whereas the AuCu3 phase remains paramagnetic
down to 2 K. The frequency dependent ac-susceptibility data, time dependent
magnetic relaxation behavior and magnetic memory effect studies suggest that
TbIr3 and HoIr3 are cannonical spin-glass system, but no glassy feature could
be found in GdIr3. The critical behavior of all the three compounds has been
investigated from the magnetization and heat capacity measurements around the
transition temperature (TC). The critical exponents alpha, beta, gamma and
delta have been estimated using different techniques such as Arrott-Noaks plot,
Kouvel-Fisher plot, critical isotherm as well as analysis of specific heat data
and study of magnetocaloric effect. The critical analysis study identifies the
type of universal magnetic class in which the three compounds belong.Comment: 18 pages, 12 figure
Particle size effects in the antiferromagnetic spinel CoRhO
We report the particle size dependent magnetic behaviour in the
antiferromagnetic spinel CoRh2O4. The nanoparticles were obtained by mechanical
milling of bulk material, prepared under sintering method. The XRD spectra show
that the samples are retaining the spinel structure. The particle size
decreases from 70 nm to 16 nm as the milling time increases from 12 hours to 60
hours. The magnetic measurements suggest that the antiferromagnetic ordering at
T 27K exists in bulk as well as in nanoparticle samples. However,
the magnitude of the magnetization below T increases with decreasing
particle size.Comment: 13 pages,7 figure
Structural phase stability and Magnetism in Co2FeO4 spinel oxide
We report a correlation between structural phase stability and magnetic
properties of Co2FeO4 spinel oxide. We employed mechanical alloying and
subsequent annealing to obtain the desired samples. The particle size of the
samples changes from 25 nm to 45 nm. The structural phase separation of
samples, except sample annealed at 9000C, into Co rich and Fe rich spinel phase
has been examined from XRD spectrum, SEM picture, along with EDAX spectrum, and
magnetic measurements. The present study indicated the ferrimagnetic character
of Co2FeO4, irrespective of structural phase stability. The observation of
mixed ferrimagnetic phases, associated with two Curie temperatures at TC1 and
TC2 (>TC1), respectively, provides the additional support of the splitting of
single cubic spinel phase in Co2FeO4 spinel oxide.Comment: 6 figure
Low temperature ferromagnetic properties, magnetic field induced spin order and random spin freezing effect in Ni1.5Fe1.5O4 ferrite; prepared at different pH values and annealing temperatures
We present the low temperature magnetic properties in Ni1.5Fe1.5O4 ferrite as
the function of pH at which the material was prepared by chemical route and
post annealing temperature. The material is a ferri or ferromagnet, but showed
magnetic blocking and random spin freezing process on lowering the measurement
temperature down to 5 K. The sample prepared at pH =12 and annealed at 800 ^C
showed a sharp magnetization peak at 105 K, the superparamagnetic blocking
temperature of the particles. The magnetization peak remained incomplete within
measurement temperature up to 350 K for rest of the samples, although peak
temperature was brought down by increasing applied dc field. The fitting of
temperature dependence of coercivity data according to Kneller law suggested
random orientation of ferromagnetic particles. The fitting of saturation
magnetization according to Bloch law provided the exponent that largely
deviated from 1.5, a typical value for long ranged ferromagnet. An abrupt
increase of saturation magnetization below 50 K suggested the active role of
frozen surface spins in low temperature magnetic properties. AC susceptibility
data elucidated the low temperature spin freezing dynamics and exhibited the
characters of cluster spin glass in the samples depending on pH value and
annealing temperature.Comment: 19 pages, 7 figure
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