Berlin 2018 – scientific programme

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MA: Fachverband Magnetismus

MA 7: Focus Session: Magnetism in Materials Science: Thermodynamics, Kinetics and Defects I (joint session MM/MA)

MA 7.5: Topical Talk

Monday, March 12, 2018, 11:45–12:15, TC 010

We need perfect defects - challenging the Brown’s paradox in permanent magnetism — •Oliver Gutfleisch — TU Darmstadt, Materialwissenschaft

It is common understanding that among the intermetallic phases used for high performance permanent magnets, practically none can fully realize its potential based on the intrinsic magnetic properties. Even if the grain size of the fully-dense magnet is close to the single domain size, the coercivity Hc is usually one order of magnitude smaller than the anisotropy field Ha - this situation is known as Brown’s paradox. The presence of crystallographic defects of various kinds, of secondary phases, of surface imperfections as well as magnetic inhomogeneities leads to local magnetic softening. On the other hand, a perfect single crystal shows ’no’ coercivity whatsoever. Looking at nucleation-type NdFeB (1,2) and pinning type SmCo (3) magnets we will revisit the Brown’s paradox and discuss possible ways of overcoming it.
1 Helbig et al., Experimental and Computational Analysis of Magnetization Reversal in (Nd,Dy)-Fe-B Core Shell Sintered Magnets, Acta Materialia 127 (2017) 498.
2 Loewe et al., Grain boundary diffusion of different rare earth elements in Nd-Fe-B sintered magnets by experiment and FEM simulation, Acta Materialia 124 (2017) 421.
3 Duerrschnabel et al., Atomic structure and domain wall pinning in samarium -cobalt based permanent magnets, Nature Communications 8:54 (2017).