Soft magnetic materials, from statics to radiofrequencies - PowerPoint PPT Presentation

Soft magnetic materials, from statics to radiofrequencies Victorino Franco Sevilla University. Spain

Current trends in Confirmed invited speakers Magnetic Refrigeration J. I. Betancourt Reyes (UNAM);  E.H. Bruck (Delft University of Technology);  Magnetocaloric materials:  G.P. Carman (UCLA);  A. Fujita (Tohoku University);  – Giant magnetocaloric materials Z.W. Liu (South China University of Technology);  – Second order phase transition materials V.K. Pecharsky (Ames Laboratory);  – Nanostructured materials M.H. Phan (University of South Florida);  – Multiphase materials and composites A. Rowe (University of Victoria);  Modeling the magnetocaloric effect  J. L. Sánchez Llamazares (IPICYT);  K. Skokov (Technische Universität Darmstadt);  Experimental techniques for the  K. G. Suresh (IIT Bombay).  characterization of magnetocaloric materials Magnetic refrigeration devices  Related topics on thermomagnetic energy  http://www.mrs.org/imrc-2013-cfp-7b/ harvesting Victorino Franco. European School of Magnetism. Cargèse (France) 2013

 Introduction – 5 key questions in a nutshell: What, which, where, when, why  Optimization of soft magnetic properties – Coercivity: disorder is not a bad quality all the time. – Frequency response: losses – Do we always need the highest permeability?: high frequency power conversion  Example of sensor application: GMI Victorino Franco. European School of Magnetism. Cargèse (France) 2013

Soft magnets in the global market JMD Coey, J. Alloy. Compd. 326 (2001) 2 Victorino Franco. European School of Magnetism. Cargèse (France) 2013

Where are they used?  Magnetic shielding (passive)  Flux concentrators  Sensors, anti-theft systems  Power conversion – Transformers, inductors – Motors, generators Tesla car; induction motor Victorino Franco. European School of Magnetism. Cargèse (France) 2013

What we need  High saturation magnetization – composition  Low coercivity – microstructure  High Curie temperature  High permeability (most of the times)  Frequency response  low losses Victorino Franco. European School of Magnetism. Cargèse (France) 2013

Evolution of soft magnetic materials M.A. Willard, M. Daniil, K.E. Kniping, Scripta Mater. 67 (2012) 554 JMD Coey, Magnetism and Magnetic Materials, Cambridge University Press, 2010 Victorino Franco. European School of Magnetism. Cargèse (France) 2013

M.E. McHenry, M.A. Willard, D.E. Laughlin, Prog Mater Sci 44 (1999) 291 Victorino Franco. European School of Magnetism. Cargèse (France) 2013

Warning: The importance of the demagnetizing field   H H H appl demag  H NM demag Measurement: Material: Applied field Internal field Apparent susceptibility “intrinsic” susceptibility     M H M H a appl             H ( H NM ) ( H N H ) H (1 N ) a appl a a a      a (1 N )   1 N If N or the susceptibility are large, a Victorino Franco. European School of Magnetism. Cargèse (France) 2013

 Small applied fields for samples with high permeability      1 N   a (1 ) N a      H H NM H N (1 N H ) 0 appl appl appl 30 25 20 field (Oe):  M(T) for different 1 M (memu) 15 10 100 1000 10 5000 applied fields 10000 3 2 1 0 150 200 250 300 350 T (ºC) Victorino Franco. European School of Magnetism. Cargèse (France) 2013

OPTI MI ZATI ON OF COERCI VI TY Victorino Franco. European School of Magnetism. Cargèse (France) 2013

Domain wall pinning and defects Potential energy E of the  wall (per area unit): – Random function of position Local stresses • Defects • 180º domain wall of area A  moving a distance x – Magnetization change from -M to M   – Energy change 2 H Mx 0 i Equilibrium:  R.C. O’Handley, “Modern magnetic materials: principles   d E ( 2 H Mx )  0 i 0 and applications”. John Wiley and Sons, 1999 dx dE   2 H M 0 i dx Victorino Franco. European School of Magnetism. Cargèse (France) 2013

Grain size and coercivity Reduce defects to decrease coercivity G. Herzer, J. Magn. Magn. Mater. 112 (1992) 258 Victorino Franco. European School of Magnetism. Cargèse (France) 2013

Grain size and coercivity G. Herzer, J. Magn. Magn. Mater. 112 (1992) 258 Victorino Franco. European School of Magnetism. Cargèse (France) 2013

SI MPLE ANALOGI ES TO EXPLAI N THE SMALL CRYSTAL SI ZE RANGE (AKA: understanding the random anisotropy model without formulae) Victorino Franco. European School of Magnetism. Cargèse (France) 2013

Who will feel the irregularities? Floor of Colegiata de Santa María de Arbas, León (Spain) The key is the different length scale (irregularities vs. shoes) Victorino Franco. European School of Magnetism. Cargèse (France) 2013

Refrigerator magnets Domains Field lines Victorino Franco. European School of Magnetism. Cargèse (France) 2013 Front (decorated side) Reverse side Side view

Refrigerator magnets Side view Field lines Reverse side Front (decorated side) Domains Victorino Franco. European School of Magnetism. Cargèse (France) 2013

Characteristic lengths  Two characteristic lengths along the direction of movement: – Substrate (separation between stripes) – Mobile piece  Parallel orientations: – L substr. ~ separation between stripes – L mobile ~ L substr. – Movement significantly alters the energy of the system  Perpendicular orientations: – L mobile ~ size of the mobile piece – L substr. < < L mobile – We cannot detect, macroscopically, energy differences Victorino Franco. European School of Magnetism. Cargèse (France) 2013

Two different correlation lengths Correlation lengths structural magnetic Victorino Franco. European School of Magnetism. Cargèse (France) 2013

Let’s quantify  Select randomly the orientation of particles 0.09 1.0 0.08 0.07  Choose magnetic 0.8 0.06 correlated areas of E max -E min (a.u.) 0.05 0.6 different sizes 0.04 0.03 0.4  Displace the correlated area thoughout the 1000 10000 0.2 “sample” 0.0 0 2 4 6 8 10  Measure the dispersion # of correlated particles (x1000) in energy 1  Average multiple times  N Victorino Franco. European School of Magnetism. Cargèse (France) 2013

Random anisotropy model K  * K N 3   L    N   l  * 4 6 *3 K K l / A G. Herzer, J. Magn. Magn. Mater. 112 K. Suzuki, in Handbook of Advanced Magnetic (1992) 258 Materials, Springer, 2006, pp. 339-373 Victorino Franco. European School of Magnetism. Cargèse (France) 2013

Finemet alloy Composition: Fe 73.5 Si 13.5 B 9 Cu 1 Nb 3  Magnetically softer after nanocrystallization  – Two phase nature – Influence of the addition of Cu & Nb 25 nm Segregation of Cu-rich clusters • Rejection of Nb at the crystal interfaces • Importance  – Technological applications (magnetic sensors, anti-theft systems, etc.) – Fundamental studies in magnetism Victorino Franco. European School of Magnetism. Cargèse (France) 2013

Production of amorphous alloys I : melt spinning Video courtesy of Joseph F . Huth III MAGNETICS, div. of SPANG & CO. Victorino Franco. European School of Magnetism. Cargèse (France) 2013

Crystallization behavior  Devitrification takes place in two main stages – 1 st exotherm:  -Fe,Si dH/dt ( kW / kg ) 0.1 – 2 nd exotherm: Fe 2 B, ... 0.0  Compositional effects – Substitution of Fe by Cr or Mo 700 800 900 1000 T ( K ) • Enhancement of the stability of the amorphous Fe 76 Si 10.5 B 9.5 Cu 1 Nb 3 phase Victorino Franco. European School of Magnetism. Cargèse (France) 2013

Microstructure Amorphous 25 nm 40 60 80 100 2  (º) Nanocrystalline 25 nm 40 60 80 100 2  (º) Fully crystallized 350 nm 40 60 80 100 2  (º) Victorino Franco. European School of Magnetism. Cargèse (France) 2013

Thermomagnetic measurements 140 140 140  As cast sample (a): 120 120 120 – T c (Amorphous) – Onset of Crystallization 100 100 100 – T c (Fe,Si) 80 80 80  Nanocrystalline (b,c): M ( a. u. ) M ( a. u. ) M ( a. u. ) 60 60 60 – T c (residual amorphous) a a a b b c c d – T c (Fe,Si) 40 40 40  Fully crystallized (d): 20 20 20 – T c (Fe,Si) (change in % Si) 0 0 0 – T c (Fe 2 B) 400 400 400 600 600 600 800 800 800 1000 1000 1000 – T c (boride type phase) T ( K ) T ( K ) T ( K ) V . Franco, C.F . Conde, and A. Conde, J. Magn. Magn. Mater. 185 (1998) 353 Victorino Franco. European School of Magnetism. Cargèse (France) 2013

Coercivity 2 nd crystallization stage Nanocrystallization onset 4000 2000 H C ( A / m ) 40 30 20 10 0 400 600 800 1000 T a ( K ) Stress relaxation Averaging of anisotropy V . Franco, C.F . Conde, A. Conde, L.F . Kiss, J. Magn. Magn. Mater. 215 (2000) 400 Victorino Franco. European School of Magnetism. Cargèse (France) 2013