Microstructure Analysis in Magnetic Materials
Microstructure Analysis in Magnetic Materials
Microstructure Analysis in Magnetic Materials
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<strong>Microstructure</strong><strong>Analysis</strong> <strong>in</strong><strong>Magnetic</strong> <strong>Materials</strong>Ernesto Estevez RamsInstituto de Materiales y ReactivosUniversidad de la Habana
Topics Permanent magnets Brown Paradox Case Study: NdFeB, , thestrongest magnet Case Study: SmCo, , the magnetfor high temperature Case Study: Hexaferrite, , thecheap alternative.
Magnets
HAµ MBrown Paradox2K= Anisotropy Field0sH = NM Demagnetiz<strong>in</strong>g FieldD sJHtheorC=HN=2Kµ M0s−NMsTheoretical CoerciveFieldJtheorH >>CJHrealC!!!! <strong>Microstructure</strong>
(BH) max[kJ/m 3 ]Permanent Magnets
Permanent MagnetsMaterialBaFe 12 O 19Coercivity Remanence (BB 0/µ 0) max190.360.3625(T)(T)(kJ/m 3 )Alnico IV0.070.610.3Alnico V0.071.3555Alcomax I0.051.227.8MnBi0.370.4844Ce(CuCo) 50.450.792SmCo 51.00.83160Sm 2 Co 170.61.15215Nd 2 FeCo 17Fe 14 B1.21.2260
NdFeBDiscovered <strong>in</strong> 1988 byJapanese and AmericansPros: Best (BH)max product High Magnetization Saturation ValueCons: Sensitive to Corrosion Low Curie Temperature value
NdFeBProduction methods:• S<strong>in</strong>tered• HDDR• Melt spun-Hot Pressed
Alignment of the Gra<strong>in</strong>sGood alignmentimproves the squarnessof the hysteresis loopbut degrades thecoercive field valueHow do we measure alignment ?
Alignment of the gra<strong>in</strong>sKerr Microscopy
Doma<strong>in</strong> ObservationHigh coercivity,High MsLow coercivity,Low Ms
Gra<strong>in</strong> Interaction
Isolation of the Gra<strong>in</strong>s<strong>Magnetic</strong> Isolationof the gra<strong>in</strong>s favorsthe coercive fieldvalue avoid<strong>in</strong>gcollective(avalanche) processof reversion
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