scholarly journals Spin Structures in Magnetic Nanoparticles

2013 ◽  
Vol 2013 ◽  
pp. 1-8 ◽  
Author(s):  
Steen Mørup ◽  
Erik Brok ◽  
Cathrine Frandsen
Keyword(s):  
Low Temperatures ◽  
Particle Surface ◽  
Exchange Interactions ◽  
Short Review ◽  
Spin Reorientation ◽  
Spin States ◽  
Anomalous Temperature ◽  
Spin Structures ◽  
Canted Spin ◽  
Temperature Dependences

Spin structures in nanoparticles of ferrimagnetic materials may deviate locally in a nontrivial way from ideal collinear spin structures. For instance, magnetic frustration due to the reduced numbers of magnetic neighbors at the particle surface or around defects in the interior can lead to spin canting and hence a reduced magnetization. Moreover, relaxation between almost degenerate canted spin states can lead to anomalous temperature dependences of the magnetization at low temperatures. In ensembles of nanoparticles, interparticle exchange interactions can also result in spin reorientation. Here, we give a short review of anomalous spin structures in nanoparticles.

scholarly journals Anomalous Temperature and Field Behaviors of Magnetization in Cubic Lattice Frustrated Ferromagnets

2015 ◽  
Vol 233-234 ◽  
pp. 3-7
Author(s):  
A.N. Ignatenko ◽  
Andrey A. Katanin ◽  
Valentin Yu. Irkhin
Keyword(s):  
Experimental Data ◽  
Monte Carlo Simulation ◽  
Low Temperatures ◽  
Strong Field ◽  
Wave Spectrum ◽  
Exchange Interactions ◽  
Thermal Fluctuations ◽  
Anomalous Temperature ◽  
Cubic Lattice ◽  
Spin Wave Spectrum

Thermodynamic properties of cubic Heisenberg ferromagnets with competing exchange interactions are considered near the frustration point where the coefficient D in the spin-wave spectrum Ek ~ Dk2vanishes. Within the Dyson-Maleev formalism it is found that at low temperatures thermal fluctuations stabilize ferromagnetism by increasing the value of D. For not too strong frustration this leads to an unusual "concave" shape of the temperature dependence of magnetization, which is in agreement with experimental data on the europium chalcogenides. Anomalous temperature behavior of magnetization is confirmed by Monte Carlo simulation. Strong field dependence of magnetization (paraprocess) at finite temperature is found near the frustration point.

Spontaneous and Field-Induced Magnetic Phase Transitions in Tb1-xRxMn6Sn6 (R = Gd, Y) Compounds

2009 ◽  
Vol 152-153 ◽  
pp. 37-40 ◽  
Author(s):  
N.V. Mushnikov ◽  
P.B. Terent’ev ◽  
V.S. Gaviko ◽  
E.G. Gerasimov ◽  
E.V. Rosenfeld ◽  
...  
Keyword(s):  
Magnetic Phase ◽  
Exchange Interactions ◽  
Spin Reorientation ◽  
Magnetic Phase Transitions ◽  
Critical Fields ◽  
Concentration Dependences ◽  
Temperature Dependences ◽  
Powder Samples ◽  
Spiral Magnetic Structure ◽  
Ferrimagnetic Ordering

Magnetization curves and magnetic susceptibility of Tb1 xRxMn6Sn6 (R = Gd, Y) compounds have been measured for aligned powder samples. Concentration dependences of the spin-reorientation transition temperature and temperature dependences of critical fields of the field-induced magnetic transitions have been determined. For the compound Tb0.1Y0.9Mn6Sn6 with the spiral magnetic structure, we found that application of hydrostatic pressure facilitates the ferrimagnetic ordering. This unusual feature is supported by the observation of a large negative spontaneous volume magnetostriction for TbMn6Sn6. The obtained results are discussed in a model considering three different interlayer Mn-Mn exchange interactions in these compounds.

scholarly journals Exchange interactions and high-energy spin states inMn12-acetate

2004 ◽  
Vol 70 (10) ◽  
Author(s):  
G. Chaboussant ◽  
A. Sieber ◽  
S. Ochsenbein ◽  
H.-U. Güdel ◽  
M. Murrie ◽  
...  
Keyword(s):  
Exchange Interactions ◽  
High Energy ◽  
Spin States

FEATURES OF THE MAGNETIC STATE IN AMORPHOUS RE–TM AND RE–TM–B MAGNETS (review)

2021 ◽  
pp. 43-58
Author(s):  
R.B. Morgunov ◽  
◽  
D.V. Korolev ◽  
R.A. Valeev ◽  
V.P. Piskorskiy ◽  
...  
Keyword(s):  
Rare Earth ◽  
Amorphous Alloys ◽  
Magnetic State ◽  
Rare Earth Metals ◽  
Earth Metal ◽  
Spin Reorientation ◽  
Heavy Rare Earth ◽  
Temperature Dependences ◽  
Magnetic States ◽  
Amorphous Magnets

Provides an overview of the magnetism features of amorphous magnets of the RE–TM and RE–TM–B alloys (RE – rare earth metal, TM – transition metal, B – boron). Magnetic states in amorphous alloys, the effect of the single-ionic anisotropy of heavy rare-earth metals on local disorder and spin frustrations in an amorphous body, and some spin-reorientation transitions observed in such compounds are presented. It is shown that the identification of the spin-glass state can be achieved by detecting specific features on the field and temperature dependences of the magnetic moment and magnetic susceptibility of the sample.

Composites

2015 ◽  
Author(s):  
James E. Mark ◽  
Dale W. Schaefer ◽  
Gui Lin
Keyword(s):  
Low Temperatures ◽  
Powder Processing ◽  
Porous Ceramic ◽  
Sol Gel ◽  
Particle Surface ◽  
Average Diameter ◽  
Ceramic Coatings ◽  
Silica Nanocomposites ◽  
Silica Microparticles ◽  
Hydrolysis Of

A relatively new area that involves silicon-containing materials is the synthesis of “ultrastructure” materials (i.e., materials in which structure can be controlled at the level of 100 Å). An example is the “sol-gel” hydrolysis of alkoxysilanes (organosilicates) to give silica, SiO2. The reaction is complicated, involving polymerization and branching, but the overall reaction may be written . . . Si(OR4 + 2H2O → SiO2 + 4ROH (9.1) . . . where the Si(OR)4 organometallic species is typically tetraethoxysilane such as tetraethylorthosilicate (TEOS, with R being C2H5). In this application, the precursor compound is hydrolyzed and then condensed to yield branched polymers. Eventually a continuous swollen gel is formed. The gel is dried at moderately low temperatures to remove volatile species, and then it is fired into a porous ceramic object that can then be densified and machined into a final ceramic part. The production of ceramics by this novel route triggered interest in the ceramics community because of advantages over the conventional powder-processing approach to ceramics. Advantages include (i) the higher purity of the starting materials, (ii) the relatively low temperatures required, (iii) the possibility of controlling the ultrastructure to reduce the microscopic flaws that lead to failure, (iv) the ease with which ceramic coatings can be formed, and (v) the ease with which ceramic alloys can be prepared (e.g., by hydrolyzing solutions of both silicates and titanates). The sol-gel approach has been used to form ceramic-like phases in a variety of polymers. Poly(dimethylsiloxane) (PDMS) is the most popular. PDMS is relatively weak and stands to benefit most from reinforcement. PDMS is easily absorbs the precursor materials generally used in the solgel process. Nearly monodisperse silica microparticles can be obtained using siloxane elastomer mixtures. In some cases, the PDMS has been part of a copolymer, with ureas, imides, amideimides, and dianilines. In other approaches, the particle surface is modified, for example, with a polysiloxane. Siloxane/silica nanocomposites have also been used as “culture-stone-protective materials.” Sol-gel hydrolysis and condensation can be carried out within a polymeric matrix to generate particles of the ceramic material, typically with an average diameter of a few hundred angstroms.

scholarly journals Spin reorientation inα-Fe2O3nanoparticles induced by interparticle exchange interactions inα-Fe2O3/NiO nanocomposites

2011 ◽  
Vol 84 (21) ◽  
Author(s):  
C. Frandsen ◽  
K. Lefmann ◽  
B. Lebech ◽  
C. R. H. Bahl ◽  
E. Brok ◽  
...  
Keyword(s):  
Exchange Interactions ◽  
Spin Reorientation

Temperature evolution of frustrated spin states in the system with competing exchange interactions. Fe0.65Ni0.35)1−x Mnx (x=0, 0.024, 0.034)

1998 ◽  
Vol 40 (9) ◽  
pp. 1500-1505
Author(s):  
N. N. Delyagin ◽  
A. L. Erzinkyan ◽  
V. P. Parfenova ◽  
S. I. Reiman ◽  
G. M. Gurevich ◽  
...  
Keyword(s):  
Exchange Interactions ◽  
Temperature Evolution ◽  
Spin States ◽  
Frustrated Spin
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