236 research outputs found
Cluster formation in quantum critical systems
The presence of magnetic clusters has been verified in both antiferromagnetic
and ferromagnetic quantum critical systems. We review some of the strongest
evidence for strongly doped quantum critical systems
(Ce(RuFe)Ge) and we discuss the implications for the
response of the system when cluster formation is combined with finite size
effects. In particular, we discuss the change of universality class that is
observed close to the order-disorder transition. We detail the conditions under
which clustering effects will play a significant role also in the response of
stoichiometric systems and their experimental signature.Comment: 5 pages; 2 figures; Internation Conference on Strongly Correlated
Electron System
Magnetic excitations in the spinel compound Li[MnLi]O (x= 0.2, 0.6, 0.8, 1.0): how a classical system can mimic quantum critical scaling
We present neutron scattering results on the magnetic excitations in the
spinel compounds Li[MnLi]O (x= 0.2, 0.6, 0.8, 1.0).
We show that the dominant excitations below T ~ 70 K are determined by clusters
of Mn^4+ ions, and that these excitations mimic the E/T-scaling found in
quantum critical systems that also harbor magnetic clusters, such as
CeRuFeGe. We argue that our results for this classical
spinel compound show that the unusual response at low temperatures as observed
in quantum critical systems is (at least) partially the result of the
fragmentation of the magnetic lattice into smaller units. This fragmentation in
quantum critical systems is the direct and unavoidable result of intrinsic
disorder.Comment: 8 pages, 8 figures; to be submitted to PR
Ba{1-x}KxMn2As2: An Antiferromagnetic Local-Moment Metal
The compound BaMn2As2 with the tetragonal ThCr2Si2 structure is a
local-moment antiferromagnetic insulator with a Neel temperature TN = 625 K and
a large ordered moment mu = 3.9 mu_B/Mn. We demonstrate that this compound can
be driven metallic by partial substitution of Ba by K, while retaining the same
crystal and antiferromagnetic structures together with nearly the same high TN
and large mu. Ba_{1-x}K_xMn2As2 is thus the first metallic ThCr2Si2-type
MAs-based system containing local 3d transition metal M magnetic moments, with
consequences for the ongoing debate about the local moment versus itinerant
pictures of the FeAs-based superconductors and parent compounds. The
Ba_{1-x}K_xMn2As2 class of compounds also forms a bridge between the layered
iron pnictides and cuprates and may be useful to test theories of high Tc
superconductivity.Comment: 5 two-column typeset pages, 5 figures, 20 references; v2: minor
revisions, 4 new references, published versio
Genotoxicity evaluation of the insecticide ethion in root of Allium cepa L.
In this study, the genotoxic effects of ethion were investigated in the mitotic cell division of Allium cepa. Primary roots of A. cepa were treated with various concentrations (25, 50, 75, and 100%) of ethion solutions for different duration of time. The result revealed that increase in the concentration and duration of treatment decreases the mitotic indices. 24 h treatment at 100% concentration of ethion induced lowest mitotic index (20.08%) than that of the control (36.37%). The percentage of chromosomal abnormalities in different mitotic stages was significantly generally higher than that of the control in all the treatment period and concentrations. These abnormalities appeared in various degrees depending on the treatment duration and concentrations of ethion. The abnormalities in dividing cell reached a maximum value of 11.30% after 12 h of treatment at 75% concentration. The type of abnormalitiesproduced were scattered prophase, non-synchronized condensation of chromosome, disturbed prophase, equatorial plate shifting, sticky chromosomes, C-metaphase and sticky metaphase. Overall, it can be concluded that ethion has a potential genotoxic effects on mitotic divisions in A. cepa root tip cells. So, it will be necessary to test the mutagenic potential of ethion on a more intensive and extensive basis especially on non-target systems before it is recommended for wider use in agriculturalfield
Magnetic Ordering in the Rare Earth Intermetallic Compound Tb₂Ti₃Ge₄: Magnetization and Neutron Diffraction Studies
Magnetization and neutron diffraction studies on a polycrystalline Tb2Ti3Ge4 sample (orthorhombic Sm5Ge4-type structure, space group Pnma, No. 62) have been carried out. This compound is found to order antiferromagnetically at ~18 K (TN). The magnetization (M) versus field (H) isotherms obtained at 2, 3, 5, and 10 K indicate a field-induced antiferromagnetic to ferromagnetic transition in fields of the order of 0.5 T. The saturation magnetization value at 2.5 K (M extrapolated to 1/H--\u3e0) is only ~5.6µB/Tb3+, suggesting the possible presence of crystal field effects with or without a persisting antiferromagnetic component. Neutron powder diffraction data at 10 K confirm the existence of a magnetic long range order. Modeling of the magnetic scattering reveals a complex and incommensurate antiferromagnetic spin structure below TN
Observation of spin glass state in weakly ferromagnetic SrFeCoO double perovskite
We report the observation of spin glass state in the double perovskite oxide
SrFeCoO prepared through sol-gel technique. Initial structural
studies using x rays reveal that the compound crystallizes in tetragonal structure with lattice parameters, = 5.4609(2) \AA and = 7.7113(7)
\AA. The temperature dependent powder x ray studies reveal no structural phase
transition in the temperature range 10 -- 300 K. However, the unit cell volume
shows an anomaly coinciding with the magnetic transition temperature thereby
suggesting a close connection between lattice and magnetism. Neutron
diffraction studies and subsequent bond valence sums analysis show that in
SrFeCoO, the site is randomly occupied by Fe and Co in the
mixed valence states of Fe/Fe and Co/Co. The random
occupancy and mixed valence sets the stage for inhomogeneous magnetic exchange
interactions and in turn, for the spin glass like state in this double
perovskite which is observed as an irreversibility in temperature dependent dc
magnetization at 75 K. Thermal hysteresis observed in the
magnetization profile of SrFeCoO is indicative of the mixed
magnetic phases present. The dynamic magnetic susceptibility displays
characteristic frequency dependence and confirms the spin glass nature of this
material. Dynamical scaling analysis of yields a critical
temperature = 75.14(8) K and an exponent = 6.2(2) typical for
spin glasses. The signature of presence of mixed magnetic interactions is
obtained from the thermal hysteresis in magnetization of SrFeCoO.
Combining the neutron and magnetization results of SrFeCoO, we deduce
the spin states of Fe to be in low spin while that of Co to be in low spin and
intermediate spin.Comment: 23 pages, 6 figures, accepted in J. Appl. Phy
Persistence of local-moment antiferromagnetic order in Ba(1-x)KxMn2As2
BaMn2As2 is a local-moment antiferromagnetic insulator with a N\'eel
temperature of 625 K and a large ordered moment of 3.9 Bohr magneton per Mn.
Remarkably, this compound can be driven metallic by the substitution of as
little as 1.6% K for Ba while retaining essentially the same ordered magnetic
moment and N\'eel temperature, as previously reported. Here, using both powder
and single crystal neutron diffraction we show that the local moment
antiferromagnetic order in Ba(1-x)KxMn2As2 remains robust up to x = 0.4. The
ordered moment is nearly independent of x for 0 < x < 0.4 and the N\'eel
transition temperature decreases to 480 K at x = 0.4.Comment: 5 pages, 5 figure
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