109 research outputs found
Anisotropic magnetic properties and giant magnetocaloric effect in antiferromagnetic MnO crystals (=Dy, Tb, Ho and Yb)
We have systematically investigated the magnetic properties and
magnetocaloric effect (MCE) in MnO (Dy, Tb, Ho and Yb) single
crystals. Above a critical value of applied field (), MnO undergo a
first-order antiferromagnetic (AFM) to ferromagnetic (FM) transition below the
ordering temperature () of moment and a second-order FM to
paramagnetic (PM) transition above . Both and dependence of
shows that the system is highly anisotropic in the FM as well as PM states
and, as a result, the magnetic entropy change () is extremely
sensitive to the direction of applied field and can be negative (normal MCE) or
positive (inverse MCE). For hexagonal HoMnO and YbMnO systems, a very
small inverse MCE is observed only for parallel to c axis and it decreases
with increasing and crosses over to normal one above . On the other
hand, for orthorhombic DyMnO and TbMnO, though the inverse MCE
disappears above along easy-axis of magnetization, it increases rapidly
with along hard-axis of magnetization for . Except for
YbMnO, the values of , relative cooling power and adiabatic
temperature change along easy-axis of magnetization are quite large in the
field-induced FM state for a moderate field strength. The large values of these
parameters, together with negligible hysteresis, suggest that the multiferroic
manganites could be potential materials for magnetic refrigeration in the
low-temperature region.Comment: 10 pages, 11 figure
Cooling and heating by adiabatic magnetization in the NiMnIn magnetic shape memory alloy
We report on measurements of the adiabatic temperature change in the inverse
magnetocaloric NiMnIn alloy. It is shown that this alloy
heats up with the application of a magnetic field around the Curie point due to
the conventional magnetocaloric effect. In contrast, the inverse magnetocaloric
effect associated with the martensitic transition results in the unusual
decrease of temperature by adiabatic magnetization. We also provide
magnetization and specific heat data which enable to compare the measured
temperature changes to the values indirectly computed from thermodynamic
relationships. Good agreement is obtained for the conventional effect at the
second-order paramagnetic-ferromagnetic phase transition. However, at the first
order structural transition the measured values at high fields are lower than
the computed ones. Irreversible thermodynamics arguments are given to show that
such a discrepancy is due to the irreversibility of the first-order martensitic
transition.Comment: 5 pages, 4 figures. Accepted for publication in the Physical Review
Crystallographic analysis of rock grain orientation at meso- and microscale levels
This paper studies the results of electron backscatter diffraction analysis of naturally deformedpolycrystalline olivine. It also defines the dependence of lattice-preferred orientations of grains on their microstructural position and size. The authors detect the basic mechanisms, consequence and thermal dynamic modes of deformation. They also show that the development of a polycrystalline structure is determined by the following consecutive activation of sliding systems (010)[100] → {0kl}[100] → (100)[010] → {100}[001] → {110}[001], when dislocation sliding and diffusion creep change under the temperature decrease from 1000°C to 650°C
The integrated exploration of Raifa lake sediments and dendrochronological analysis of Raifa forestry pines
© 2006-2017 Asian Research Publishing Network (ARPN). All rights reserved.The article presents some results of comprehensive research on the properties of Raifa lake bottom sediments and dendrochronological study of Raifa forestry pines (Russia). A preliminary seismic acoustic investigations have been carried out, which allowed to select the sampling site (E 48 ° 43'40.6" N 55 ° 54'21.7"). The length of core sample was 32 cm. Laboratory studies of the core, including the study of the elemental composition, magneto-mineralogical and carcinologic analysis revealed the features of sedimentation mass formation
Magnetism, FeS colloids, and Origins of Life
A number of features of living systems: reversible interactions and weak
bonds underlying motor-dynamics; gel-sol transitions; cellular connected
fractal organization; asymmetry in interactions and organization; quantum
coherent phenomena; to name some, can have a natural accounting via
interactions, which we therefore seek to incorporate by expanding the horizons
of `chemistry-only' approaches to the origins of life. It is suggested that the
magnetic 'face' of the minerals from the inorganic world, recognized to have
played a pivotal role in initiating Life, may throw light on some of these
issues. A magnetic environment in the form of rocks in the Hadean Ocean could
have enabled the accretion and therefore an ordered confinement of
super-paramagnetic colloids within a structured phase. A moderate H-field can
help magnetic nano-particles to not only overcome thermal fluctuations but also
harness them. Such controlled dynamics brings in the possibility of accessing
quantum effects, which together with frustrations in magnetic ordering and
hysteresis (a natural mechanism for a primitive memory) could throw light on
the birth of biological information which, as Abel argues, requires a
combination of order and complexity. This scenario gains strength from
observations of scale-free framboidal forms of the greigite mineral, with a
magnetic basis of assembly. And greigite's metabolic potential plays a key role
in the mound scenario of Russell and coworkers-an expansion of which is
suggested for including magnetism.Comment: 42 pages, 5 figures, to be published in A.R. Memorial volume, Ed
Krishnaswami Alladi, Springer 201
Magnetism, entropy, and the first nano-machines
The efficiency of bio-molecular motors stems from reversible interactions
; weak bonds stabilizing intermediate states (enabling
conversion of chemical into mechanical energy). For their (unknown) origins, we
suggest that a magnetically structured phase (MSP) formed via accretion of
super-paramagnetic particles (S-PPs) by magnetic rocks on the Hadean Ocean
floor had hosted motor-like diffusion of ligand-bound S-PPs through its
template-layers; its ramifications range from optical activity to quantum
coherence. A gentle flux gradient offers both detailed-balance breaking
non-equilibrium and to a magnetic dipole, undergoing infinitesimal
spin-alignment changes. Periodic perturbation of this background by local
H-fields of template-partners can lead to periodic high and low-template
affinity states, due to the dipole's magnetic degree of freedom. An
accompanying magnetocaloric effect allows interchange between system-entropy
and bath temperature. We speculate on a magnetic reproducer in a setting close
to the mound-scenario of Russell and coworkers that could evolve bio- ratchets.Comment: 17 pages, 1 figur
Cs2NaAl1-xCrxF6: A family of compounds presenting magnetocaloric effect
In this paper we explore the magnetocaloric effect (MCE) of chromium-doped elpasolite Cs2NaAl1-x,CrxF6 (x = 0.01 and 0.62) single crystals. Magnetization and heat capacity data show the magnetocaloric potentials to be comparable to those of garnets, perovskites, and other fluorides, producing magnetic entropy changes of 0.5 J/kg K (x = 0.01) and 11 J/kg K (x = 0.62), and corresponding adiabatic temperature changes of 4 and 8 K, respectively. These values are for a magnetic field change of 50 kOe at a temperature around 3 K. A clear Schottky anomaly below 10 K, which becomes more apparent when an external magnetic field is applied, was observed and related to the splitting of the Cr3+ energy levels. These results hint at a new family of materials with potential wide use in cryorefrigeration
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