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Colors and Magnetism03:02

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Color in Coordination Complexes
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Coordination compounds and complexes exhibit different colors, geometries, and magnetic behavior, depending on the metal atom/ion and ligands from which they are composed. In an attempt to explain the bonding and structure of coordination complexes, Linus Pauling proposed the valence bond theory, or VBT, using the concepts of hybridization and the overlapping of the atomic orbitals. According to VBT, the central metal atom or ion (Lewis acid) hybridizes to provide empty orbitals of suitable...
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Materials like iron, nickel, and cobalt consist of magnetic domains, within which the magnetic dipoles are arranged parallel to each other. The magnetic dipoles are rigidly aligned in the same direction within a domain by quantum mechanical coupling among the atoms. This coupling is so strong that even thermal agitation at room temperature cannot break it. The result is that each domain has a net dipole moment. However, some materials have weaker coupling, and are ferromagnetic at lower...
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Paramagnets are materials with unpaired electrons that possess a finite magnetic moment. In the absence of a magnetic field, these moments are randomly oriented, and thus the net moment is zero. Under an external field, a torque acting on the moments tends to align them along the field's direction. However, the random thermal motion of electrons produces a torque opposite to the external field and tries to disorient the moments. These two competing effects align only a few moments along the...
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Quadrupolar ordering and exotic magnetocaloric effect in RB4 (R = Dy, Ho).

M S Song1, K K Cho1, B Y Kang1

  • 1School of Materials Science and Engineering, Gwangju Institute of Science and Technology (GIST), Gwangju, 61005, Korea.

Scientific Reports
|January 23, 2020
PubMed
Summary
This summary is machine-generated.

Researchers discovered a new mechanism for giant inverse magnetocaloric effect (MCE) in rare-earth tetraborides. This finding could significantly advance magnetic cooling technologies by enabling efficient cooling with low magnetic fields.

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Area of Science:

  • Condensed Matter Physics
  • Materials Science

Background:

  • The magnetocaloric effect (MCE) is crucial for magnetic cooling applications.
  • Interplay of charge, spin, orbital, and lattice degrees of freedom influences MCE.
  • Rare-earth tetraborides are promising materials for MCE.

Purpose of the Study:

  • To propose and investigate a new mechanism for large entropy change in rare-earth tetraborides.
  • To explore the magnetocaloric properties of Ho$_{1-x}$Dy$_{x}$B$_{4}$ compounds.
  • To understand the correlation between entropy change, magnetic field, temperature, and magnetic transitions.

Main Methods:

  • Experimental synthesis and characterization of Ho$_{1-x}$Dy$_{x}$B$_{4}$ (x = 0.0, 0.5, 1.0).
  • Measurement of magnetic entropy changes under varying magnetic fields and temperatures.
  • Analysis using Landau theory to explain the observed phenomena.

Main Results:

  • Giant inverse MCE observed in Ho$_{1-x}$Dy$_{x}$B$_{4}$ with maximum entropy changes of 22.7 J/kgK (x=0.0), 19.6 J/kgK (x=0.5), and 19.0 J/kgK (x=1.0).
  • Critical fields for these transitions were determined (25 kOe, 40 kOe, 50 kOe, respectively).
  • Correlation established between entropy changes and consecutive double transitions (magnetic dipolar and quadrupolar ordering).

Conclusions:

  • The observed giant inverse MCE is attributed to strong coupling between magnetic dipoles and quadrupoles, influenced by spin-orbit coupling and geometric frustration.
  • This mechanism offers new insights for developing advanced magnetic cooling systems.
  • The study highlights the potential of rare-earth tetraborides for practical MCE applications.