253 research outputs found
Observation of superspin glass state in magnetically textured ferrofluid (gamma-Fe2O3)
Magnetic properties in a magnetically textured ferrofluid made out of
interacting maghemite (gamma-Fe2O3) nanoparticles suspended in glycerin have
been investigated. Despite the loss of uniform distribution of anisotropy axes,
a superspin glass state exists at low temperature in a concentrated, textured
ferrofluid as in the case of its non-textured counterpart. The onset of
superspin glass state was verified from the sample's AC susceptibility. The
influence of the anisotropy axis orientation on the aging behavior in the
glassy states is also discussed
Nondestructive Testing Using Magnetic Field Visualization Technique
This paper describes a new technique to detect cracks or flaws in conducting or ferromagnetic materials using a magnetic field visualization system. In this system there are two sources for magnetic field generation, i.e. electrical current and magnetization. And the magnetic field generated by the source could give us useful information on cracks or flaws included in the material. Thus, visualization of magnetic field would enable us to identify the shape and size of cracks. We developed a preliminary system to verify the validity of the speculation and applied it to both ferromagnetic and conducting materials with flaws. The applicability of magnetic visualization has been confirmed to be an effective method in NDE and diagnosis of magnetic equipments in the present experiment. Furthermore, combination of this method with numerical prediction could demonstrate more potential capability in the field of NDE</p
Intrinsic Low Temperature Paramagnetism in B-DNA
We present experimental study of magnetization in -DNA in
conjunction with structural measurements. The results show the surprising
interplay between the molecular structures and their magnetic property. In the
B-DNA state, -DNA exhibits paramagnetic behaviour below 20 K that is
non-linear in applied magnetic field whereas in the A-DNA state, remains
diamagnetic down to 2 K. We propose orbital paramagnetism as the origin of the
observed phenomena and discuss its relation to the existence of long range
coherent transport in B-DNA at low temperature.Comment: 5 pages, 4 figures, submitted to Physical Review Letters October 200
Noise Measurement of Interacting Ferromagnetic Particles with High Resolution Hall Microprobes
We present our first experimental determination of the magnetic noise of a
superspinglass made of < 1 pico-liter frozen ferrofluid. The measurements were
performed with a local magnetic field sensor based on Hall microprobes operated
with the spinning current technique. The results obtained, though preliminary,
qualitatively agree with the theoretical predictions of Fluctuation-Dissipation
theorem (FDT) violation [1].Comment: 4pages, 2 figure
Growth of a dynamical correlation length in an aging superspin glass
We report on zero field cooled magnetization relaxation experiments on a
concen- trated frozen ferrofluid exhibiting a low temperature superspin glass
transition. With a method initially developed for spin glasses, we investigate
the field dependence of the relaxations that take place after different aging
times. We extract the typical number of correlated spins involved in the aging
dynamics. This brings important insights into the dynamical correlation length
and its time growth. Our results, consistent with expressions obtained for spin
glasses, extend the generality of these behaviours to the class of superspin
glasses. Since the typical flipping time is much larger for superspins than for
atomic spins, our experiments probe a time regime much closer to that of
numerical simulations
Superspin glass aging behavior in textured and nontextured frozen ferrofluid
The effect of magnetic anisotropy-axis alignment of individual nanoparticles
on the collective aging behavior in the superspin glass state of a frozen
ferrofluid has been investigated. The ferrofluid studied here consists of
maghemite nanoparticles (\gamma-Fe2O3, mean diameter = 8.6 nm) dispersed in
glycerin at a volume fraction of ~15%. The low temperature aging behavior has
been explored through 'zero-field cooled magnetization' (ZFCM) relaxation
measurements using SQUID magnetometry. The ZFCM response functions were found
to scale with effective age of the system in both textured and non-textured
superspin glass states, but with markedly different scaling exponents, \mu. The
value of {\mu} was found to shift from ~0.9 in non-textured case to ~ 0.6 in
the textured case, despite the identical cooling protocol used in both
experiments
Non-generality of the Kadowaki-Woods ratio in correlated oxides
An explicit expression for the Kadowaki-Woods ratio in correlated metals is
derived by invoking saturation of the (high-frequency) Fermi-liquid scattering
rate at the Mott-Ioffe-Regel limit. Significant deviations observed in a number
of oxides are quantitatively explained due to variations in carrier density,
dimensionality, unit cell volume and the number of individual sheets in the
Brillouin zone. A generic re-scaling of the original Kadowaki-Woods plot is
also presented.Comment: 9 pages of text, 1 table, 2 figure
Anisotropy-axis orientation effect on the magnetization of {\gamma}-Fe2O3 frozen ferrofluid
The effect of magnetic anisotropy-axis alignment on the superparamagnetic
(SPM) and superspin glass (SSG) states in a frozen ferrofluid has been
investigated. The ferrofluid studied here consists of maghemite nanoparticles
(\gamma-Fe2O3, mean diameter = 8.6 nm) dispersed in glycerine at a volume
fraction of ~15%. In the high temperature SPM state, the magnetization of
aligned ferrofluid increased by a factor varying between 2 and 4 with respect
to that in the randomly oriented state. The negative interaction energy
obtained from the Curie-Weiss fit to the high temperature susceptibility in the
SPM states as well as the SSG phase onset temperature determined from the
linear magnetization curves were found to be rather insensitive to the
anisotropy axis alignment. The low temperature aging behaviour, explored via
"zero-field cooled magnetization" (ZFCM) relaxation measurements, however, show
distinct difference in the aging dynamics in the anisotropy-axis aligned and
randomly oriented SSG states.Comment: to appear in Journal of Physics D: Applied Physic
- …