scholarly journals Thermodynamic and Relaxation Processes near Curie Point in Gadolinium

2014 ◽  
Vol 215 ◽  
pp. 113-118 ◽  
Author(s):  
Alexander P. Kamantsev ◽  
Victor V. Koledov ◽  
Vladimir G. Shavrov ◽  
Irina S. Tereshina
Keyword(s):  
Phase Transition ◽  
Magnetic Susceptibility ◽  
Curie Point ◽  
Abrupt Change ◽  
Kinetic Coefficient ◽  
Magnetic Phase ◽  
Magnetic Phase Transitions ◽  
Specific Power ◽  
Relaxation Processes

An experimental method is suggested for the determination of the rate of magnetic phase transitions. The method is based on the measurement of the change of magnetic susceptibility of a ferromagnetic sample in the vicinity of the phase transition in response to an abrupt change of the sample temperature. This paper describes the measurement of the change of the magnetic susceptibility of a thin gadolinium plates, cooled by water-flow at a temperature below the Curie point (TC=292 K). It was found that the relaxation time of the magnetic susceptibility of gadolinium in the temperature range from 289.9 to 291.3 K can be approximated using the Landau-Khalatnikov equation with a kinetic coefficient value γ = 3.9×10-8cm3/(erg×s). The linear approximation does not fit well in the range from 291.3 to 293.2 K. The fundamental restriction of specific power of the magnetocaloric refrigerator (made by gadolinium plates) was estimated.

Deuterium substitution effects on the structural and magnetic phase transitions of a hydrogen-bonded coordination polymer, bis(glycolato)copper(ii)

2016 ◽  
Vol 45 (42) ◽  
pp. 16774-16778 ◽  
Author(s):  
Shota Yoneyama ◽  
Takeshi Kodama ◽  
Koichi Kikuchi ◽  
Takumi Fujisawa ◽  
Akira Yamaguchi ◽  
...  
Keyword(s):  
Phase Transition ◽  
Phase Transitions ◽  
Transition Temperature ◽  
Magnetic Phase ◽  
Structural Phase ◽  
Magnetic Phase Transitions ◽  
Substitution Effects ◽  
Hydroxyl Groups ◽  
Large Shift ◽  
Deuterium Substitution

Bis(glycolato)copper(ii) [Cu(HOCH2CO2)2] shows a large shift of the structural phase transition temperature by deuterium substitution of the hydroxyl groups in it.

scholarly journals Magnetic phase transitions and magnetic entropy in the XY antiferromagnetic pyrochlores (Er 1− x Y x ) 2 Ti 2 O 7

2014 ◽  
Vol 470 (2171) ◽  
pp. 20140387 ◽  
Author(s):  
John F. Niven ◽  
Michel B. Johnson ◽  
Alex Bourque ◽  
Patrick J. Murray ◽  
David D. James ◽  
...  
Keyword(s):  
Magnetic Field ◽  
Heat Capacity ◽  
Magnetic Phase ◽  
Magnetic Phase Transitions ◽  
Magnetic Contribution ◽  
Magnetic Entropy ◽  
Lattice Contribution ◽  
Lower Temperature ◽  
Very High

We present the results of experimental determination of the heat capacity of the pyrochlore Er 2 Ti 2 O 7 as a function of temperature (0.35–300 K) and magnetic field (up to 9 T), and for magnetically diluted solid solutions of the general formula (Er 1− x Y x ) 2 Ti 2 O 7 ( x ≤0.471). On either doping or increase of magnetic field, or both, the Néel temperature first shifts to lower temperature until a critical point above which there is no well-defined transition but a Schottky-like anomaly associated with the splitting of the ground state Kramers doublet. By taking into account details of the lattice contribution to the heat capacity, we accurately isolate the magnetic contribution to the heat capacity and hence to the entropy. For pure Er 2 Ti 2 O 7 and for (Er 1− x Y x ) 2 Ti 2 O 7 , the magnetic entropy as a function of temperature evolves with two plateaus: the first at R ln ⁡ 2 , and the other at R ln ⁡ 16 . When a very high magnetic field is applied, the first plateau is washed out. The influence of dilution at low values is similar to the increase of magnetic field, as we show by examination of the critical temperature versus critical field curve in reduced terms.

Structure of the clinopyroxene-type compound CaCuGe2O6 between 15 and 800 K

2005 ◽  
Vol 61 (4) ◽  
pp. 367-380 ◽  
Author(s):  
Günther J. Redhammer ◽  
Gerold Tippelt ◽  
Michael Merz ◽  
Georg Roth ◽  
Werner Treutmann ◽  
...  
Keyword(s):  
Phase Transition ◽  
Magnetic Susceptibility ◽  
Magnetic Phase ◽  
Metal Layer ◽  
Lattice Parameters ◽  
Zigzag Chain ◽  
Two Dimensional ◽  
Teller Distortion ◽  
Jahn Teller ◽  
Jahn Teller Distortion

CaCuGe2O6 shows a strongly distorted clinopyroxene-type structure with P21/c symmetry at 298 K. The Cu2+ ion at the M1 site is coordinated by six O atoms forming an octahedron, which deviates significantly from ideal geometry. Individual M1 sites are connected via common edges to form an infinite zigzag chain parallel to the crystallographic c axis. The Ca2+ ion at M2 shows a sevenfold coordination. M2 sites are connected to the M1 chain via three common edges, thereby forming a metal layer within the bc plane. Besides the strong Jahn–Teller distortion of the Cu site, the structure of the title compound differs from `normal' clinopyroxenes by a distortion of alternate layers of Ge sites. While the Ge(A) site is fourfold coordinated by O atoms, forming infinite chains of corner-sharing chains parallel to the c axis, the Ge(B) site exhibits a fivefold coordination, thereby forming a true two-dimensional layer of edge-sharing GeO5 bipyramids. Decreasing the temperature causes a magnetic phase transition at 40 K, as monitored by a broad maximum in the magnetic susceptibility and by discontinuities in the lattice parameters. Increasing the temperature causes variations in bond lengths, edge lengths and bond angles. Most prominent is the increase of one bond length of the Ge(B) site and the increase of the tetrahedral bridging angle of the Ge(A) site. At 660 K a crystallographic phase transition is observed where the symmetry changes from P21/c to C2/c. The transition is accompanied by large changes in the lattice parameters which are indicative of distinct topological changes of several structural building units. The high-temperature C2/c structure is similar to that of the germanate clinopyroxene CaMgGe2O6.

Studies on the interaction between two correlated electronic bands. I. Phase transition in NiS

1980 ◽  
Vol 373 (1753) ◽  
pp. 253-268 ◽  
Keyword(s):  
Phase Transition ◽  
Phase Transitions ◽  
Density Of States ◽  
Magnetic Phase ◽  
Magnetic Phase Transitions ◽  
Temperature Dependent ◽  
Interacting Electrons

An expression for the density of states of two electronic bands with intraand inter-band correlations has been derived. The consequences of the inter-band interaction on Mott-Hubbard split bands are discussed. The model is applied to explain the metal, semi-metal and magnetic phase transitions in NiS by using a semi-elliptical form for the density of states of non-interacting electrons. It is shown that the temperature-dependent overlap and hybridization parameters between d- and p-bands can provoke both the phase transitions in NiS as pointed out earlier by White & Mott (1971)

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