Magnetic materials

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MAGNETIC MATERIALS:GARNETS AND PERVOSKITES

Sujith VargheseM140057CY

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GARNETS Garnets are large family of complex oxides. General formula: A3B2X3O12

A= Y,Sm,Gd,Tb,Dy,Ho,Er,Tm,Yb,Lu. Coordination number=8 in a distorted cubic

environment. B and X are smaller ions which occupy Oh and Td

sites, respectively.

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STRUCTURE

Schematic of the cubic unit cell of Y3Fe5O12 (YIG) garnet structure. 8 formula units per unit cell i.e., 160 atoms in the unit cell. 24 c-sites, 16 a-sites, 24 d-sites, 96 h-sites in a unit cell.Google images.

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A B X COMBINATIONS

Grossular: Ca3Al2Si3O12 Uvarovite: Ca3Cr2Si3O12 Pyrope: Mg3Al2Si3O12

Andradite: Ca3Fe2Si3O12 YIG: Y3Fe5O12 Almandine: Fe3Al2Si3O12

Images adapted from Wikipedia.org

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MAGNETIC PROPERTIES Basic requirement: magnetic cations in d and a sites. d-site cations sublattice are coupled

ferromagnetically. a-site and c-site cations sublattices coupled

ferromagnetically. d-site and a-site cations sublattices coupled

antiferromagnetically. The net magnetic moment,

M=Md-Ma-Mc

•Consider ,Yttrium Iron Garnet (YIG), Y3Fe5O12

Y3+ is a d0 ion, it has no magnetic moment. Fe+3 occupies both 16(a) and 24(d) sites The magnetic moment per YIG molecule, M= 3Fe3+ - 2Fe3+ = 5µB

•YIG and other rare earth garnets are ferrimagnetic with a Tc 548K to578K

•Saturation magnetization of yttrium gadolinium iron garnet (Y3-3xGd3x)Fe2Fe3O12

•Saturation Magnetization of Gd doped YIG < pure YIG

6From Ref. 2

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•Doped YIG crystals show variation in saturation magnetization with temperature.•There is a temperature at which M=0, called Compensation temperature(Tcomp).•Tcomp increases with increased substitution of Gd+3 for Y3+.•Above Tcomp, contribution from c-sublattice diminishes .•With appropriate substitution it is possible to prepare variety of garnet magnetic materials for specific purposes.

From Ref. 2

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APPLICATIONS

microwave YIG filters.  

Solid-state lasers.

Faraday rotators.

Data storage.

Images adapted from Wikipedia.org

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PEROVSKITESThe mineral perovskite (CaTiO3) is named after Russian mineralogist, Count LevAleksevich von Perovski, and was discovered and named by Gustav Rose in 1839 from samples found in the Ural Mountains.

CaTiO3 Perovski Gustav Rose

Images adapted from Wikipedia.org

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•Class of compounds, which have the same type of crystal structure as CaTiO3, known as the perovskites.

•General Formula: ABO3

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A network of corner-sharing BO6 octahedra with a large A-site cation occupying the interstitial position is shown.

Prasanna V. Balachandran et al. Proc. R. Soc. A 2011;467:2271-2290

©2011 by The Royal Society

(a) A network of corner-sharing BO6 octahedra with a large A-site cation occupying the interstitial position is shown. (b) The simplified unit-cell representation of cubic perovskite without showing coordination. (c) The geometry of the building units, AO12 cuboctahedra and BO6 octahedra, with 12-coordinated A-site and 6-coordinated B-site, respectively.

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MAGNETIC PROPERTIES•Perovskites with transition metal ions (TMI) on the B site show an enormous variety of magnetic properties.

Google images.

13From Ref. 3

•LaMnO3 is an insulating, antiferromagnetic (AFM) compound.•La1-xSrxMn+3

1-xMn+4xO3 becomes ferromagnetic with a well-

defined Curie temperature at a finite x, and metallic below TC

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APPLICATIONS

•Perovskite solar cell

•Lasers

•LEDS

•Photoelectrolysis

Google images

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REFERENCES1. Solid State Chemistry and its Applications, 2nd Edition, Student Edition,

Anthony R. West.

2. Microwave Materials edited by V.R.K. Murthy, S. Sundaram, B. Viswanathan, Google Books.

3. Study of the giant electroresistance in epitaxial thin films of La0.9Sr0.1MnO3, Yao, Hui; 2005.

4. Prasanna V. Balachandran et al. Proc. R. Soc. A 2011;467:2271-2290.

5. Wikipedia.org

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