37 research outputs found
Aging dip and cumulative aging in hierarchical successive transition of stage-2 CoCl graphite intercalation compound
Memory and aging behaviors in stage-2 CoCl GIC ( = 8.9 K and
= 6.9 K) have been studied using low frequency ( = 0.1 Hz) AC
magnetic susceptibility ( and ) as well as
thermoremnant magnetization. There occurs a crossover from a cumulative aging
(mainly) with a partial memory effect for the domain-growth in the intermediate
state between and to an aging and memory in a spin glass
phase below . When the system is aged at single or multiple stop and
wait processes at stop temperatures 's below for wait times
, the AC magnetic susceptibility shows single or multiple aging dips at
's on reheating. The depth of the aging dips is logarithmically
proportional to the wait time . Very weak aging dip between and
indicates the existence of a partial memory effect. The sign of the
difference between the reference cooling and reference heating curves changes
from positive to negative on crossing from the high -side. The time
dependence of and below is
described by a scaling function of . its a local maximum at 6.5 K
just below , and drastically decreases with increasing . The nature
of the cumulative aging between and is also examined.Comment: 11 pages. 13 figures, 1 tabl
Ordered spin structures of -MnO (rutile-type) systems with competing exchange interactions: numerical approach using equi-energy contour plot
Using numerical calculations of equi-energy contour plot of the Fourier
transform of the spin Hamiltonian, we study the magnetic phase diagram (
and ) of the rutile type -MnO, where () is
fixed and is the antiferromagnetic interaction along the diagonal direction,
is the interaction along the c axis, and is the interaction
along the a axis. The magnetic phase diagram consists of the multricritical
point (the intersection and ), the
helical order along the c axis, the phase, the helical
order along the a axis, and the phase . The shift of the
location of the magnetic Bragg peak in the reciprocal lattice plane
is examined with the change of and in the phase diagram. The
shift is discontinuous on the first-order phase transition, and is continuous
on the second-order phase transition. The detail of our magnetic phase diagram
is rather different from that reported by Yoshimori.Comment: 16 pages, 20 figure
A proper understanding of the Davisson and Germer experiments for undergraduate modern physics course
The physical interpretation for the Davisson-Germer experiments on nickel
(Ni) single crystals [(111), (100), and (110) surfaces] is presented in terms
of two-dimensional (2D) Bragg scattering. The Ni surface acts as a reflective
diffraction grating when the incident electron beams hits the surface. The 2D
Bragg reflection occurs when the Ewald sphere intersects the Bragg rods arising
from the two-dimension character of the system. Such a concept is essential to
proper understanding of the Davisson-Germer experiment for undergraduate modern
physics course.Comment: 8 pages and 14 figure
Stretched exponential relaxation in three dimensional short-range spin glass CuCoCl-FeCl graphite bi-intercalation compound
CuCoCl-FeCl graphite bi-intercalation compound is
a three-dimensional short-range spin glass with a spin freezing temperature
( K). The time evolution of the zero-field cooled
magnetization has been measured under various combinations of wait
time (), temperature (), temperature-shift (), and magnetic
field (). The relaxation rate [d/d]
shows a peak at a peak time . The shape of in the vicinity
of is well described by stretched exponential relaxation (SER). The
SER exponent and the SER relaxation time are determined as a
function of , , , and . The value of at
is nearly equal to 0.3. There is a correlation between and ,
irrespective of the values of , , , and . These features
can be well explained in terms of a simple relaxation model for glassy
dynamics.Comment: 11 pages, 12 figures; submitted to Physical Review
Observation of a magnetic-field-induced Griffiths phase in three-dimensional Ising random magnet NiMg(OH) from absorption of AC magnetic susceptibility
The nature of the Griffiths phase in three-dimensional Ising random magnet
Ni_{p}Mg_{1-p}(OH)_{2} (p = 0.10, 0.25, 0.315, 0.50, 0.80, and 1) is studied
from the measurements of absorption (the out-of phase in AC magnetic
susceptibility) in the field-cooled (FC) state. The temperature (T) dependence
of absorption is measured in the vicinity of the critical temperature [N\'{e}el
temperature for p = 0.50, 0.80, 1, and the spin glass transition temperature
for p = 0.1, 0.25, 0.315] in the presence of an external magnetic field H. A
broad peak is clearly observed for absorption vs T well above the critical
temperature at H > 20 kOe. This result gives a piece of evidence for the
magnetic-field induced Griffiths phase.Comment: 10 pages, 17 figure
Magnetic Ordering of CoCl_{2}-GIC: a Spin Ceramic -Hierarchical Successive Transitions and the Intermediate Glassy Phase-
Stage-2 CoCl-GIC is a spin ceramic and shows hierarchical successive
transitions at (= 8.9 K) and (= 7.0 K) from the paramagnetic
phase into an intra-cluster (two-dimensional ferromagnetic) order with
inter-cluster disorder and then to an inter-cluster (three-dimensional
antiferromagnetic like) order over the whole system. The nature of the
inter-cluster disorder was suggested to be of spin glass by nonlinear magnetic
response analyses around and by studies on dynamical aspects of
ordering between and . Here, we present a further extensive
examination of a series of time dependence of zero-field cooled magnetization
after the aging protocol below . The time dependence of the
relaxation rates dramatically changes
from the curves of simple spin glass aging effect below to those of
two peaks above . The characteristic relaxation behavior apparently
indicates that there coexist two different kinds of glassy correlated regions
below .Comment: 6 pages, 3 figures, Proceeding of HFM2006, J. Phys.: Condensed Matter
(accepted for publication
Memory and aging effect in hierarchical spin orderings of stage-2 CoCl_{2} graphite intercalation compound
Stage-2 CoCl graphite intercalation compound undergoes two magnetic
phase transitions at (= 7.0 K) and (= 8.9 K). The aging
dynamics of this compound is studied near and . The
intermediate state between and is characterized by a spin
glass phase extending over ferromagnetic islands. A genuine thermoremnant
magnetization (TRM) measurement indicates that the memory of the specific spin
configurations imprinted at temperatures between and during
the field-cooled (FC) aging protocol can be recalled when the system is
re-heated at a constant heating rate. The zero-field cooled (ZFC) and TRM
magnetization is examined in a series of heating and reheating process. The
magnetization shows both characteristic memory and rejuvenation effects. The
time dependence of the relaxation rate
d/d after the ZFC aging protocol with a
wait time , exhibits two peaks at characteristic times and
between and . An aging process is revealed as the
strong dependence of . The observed aging and memory effect is
discussed in terms of the droplet model.Comment: 14 pages, 16 figures; submitted to Phys. Rev.
Successive superconducting transitions and Anderson localization effect in TaSC
A complex carbide TaSC consists of van der Waals (vdw)-bonded
layers with a stacking sequence C-Ta-S-vdw-S-Ta-C- along the c
axis. The magnetic properties of this compound have been studied from DC and AC
magnetic susceptibility. TaSC undergoes successive superconducting
transitions of a hierachical nature at K
[ Oe and kOe] and
K [ kOe]. The
intermediate phase between and , where , is an intra-grain superconductive state
occurring in the Ta-C layers in TaSC. The low temperature phase
below , where clearly appears, is an inter-grain
superconductive state. The magnetic susceptibility at well above
is described by a sum of a diamagnetic susceptibility and a
Curie-like behavior. The latter is due to the localized magnetic moments of
conduction electrons associated with the Anderson localization effect,
occurring in the 1T-TaS type structure in TaSC.Comment: 12 pages, 13 figures; submitted to Phys. Rev.
Magnetic-field induced superconductor-metal-insulator transitions in bismuth metal-graphite
Bismuth-metal graphite (MG) has a unique layered structure where Bi
nanoparticles are encapsulated between adjacent sheets of nanographites. The
superconductivity below (= 2.48 K) is due to Bi nanoparticles. The
Curie-like susceptibility below 30 K is due to conduction electrons localized
near zigzag edges of nanographites. A magnetic-field induced transition from
metallic to semiconductor-like phase is observed in the in-plane resistivity
around ( 25 kOe) for both and
(: c axis). A negative magnetoresistance in for
(03.5 kOe) and a logarithmic divergence in
with decreasing temperature for ( 40 kOe) suggest the
occurrence of two-dimensional weak localization effect.Comment: 9 pages, 9 figures; published in Phys. Rev. B 66, 014533 (2002
Specific heat of stage-2 MnCl graphite intercalation compound: co-existence of spin glass phase and incommensurate short-range spin order
Stage-2 MnCl GIC magnetically behaves like a quasi 2D
antiferromagnet on the triangular lattice. It shows a typical spin glass
behavior below the spin freezing temperature (= 1.1 K). The AC
magnetic susceptibility shows a peak at = at = 0. This peak
shifts to the low temperature side with increasing , according to the de
Almeida-Thouless critical line. We have undertaken an extensive study on the
dependence of specific heat in the absence of an external field and in
the presence of along the plane. The magnetic specific heat
at = 0 shows no anomaly at , but exhibits double broad peaks around
5 K and 41 K. The magnetic specific heat at = 0 is described by
with K,
while at = 10 kOe is proportional to . The entropy due to the
broad peak around 5 K is 1/3 of the total entropy. The residual entropy is 63 %
of the total entropy because of highly frustrated nature of the system. The
magnetic neutron scattering indicates that a short range spin order associated
with the incommensurate wave vector (
at 0.45 K) appears below 5 K and remains unchanged down to 63 mK. The in-plane
spin correlation length is only 18 at 0.45 K. The low temperature phase
below is a kind of reentrant spin glass phase where the spin glass
phase coexists with a short range spin order associated with .Comment: 14 pages, 20 figure