Tham khảo tài liệu 'physics of magnetism magnetic materials 2011 part 6', kỹ thuật - công nghệ, cơ khí - chế tạo máy phục vụ nhu cầu học tập, nghiên cứu và làm việc hiệu quả | CHAPTER 8. SOME BASIC CONCEPTS AND UNITS 83 Table . Maxwell s and related equations. E electric field p electric polarization H magnetic field B magnetic flux density M magnetization Xm Xe magnetic or electric susceptibility p permeability g permittivity curl Ê -dB dt curl H J dD dt div D p div B 0 D eÊ eoer qE p B p i P0PrH Po Ẩ M Sr 1 Xe Pr 1 Xm B is produced by both the conduction and the Amperian atomic currents while w has its source exclusively in external conduction currents. Hence the analogy considered-Under point ii appears to be more general. It is clear that those advocating the primacy of B have an excellent viewpoint although historically they are at a disadvantage because the magnetic pole approach has traditionally been used in magnetostatics by analogy with electrostatics. In fact for the characterization of magnetic materials the traditional approach is usually preferred because the desired quantity is M H T . The relevant field H in a magnetized sample is the internal field Hint .which originates not only from the external field Text t but also from the stray- or self-field of the magnetized body. Thus ổext has to be corrected by the demagnetizing field Hd NdM where Nd is the demagnetizing factor and depends on the sample geometry as shown in Table . A more detailed discussion regarding these matters can be found in articles written by Cohen and Giacomo 1987 Goldfarb 1992 and Hilscher 2001 . References Cohen E. R. and Giacomo P. 1987 Symbols units nomenclature and fundamental constants in physics Physica A 146 1. Goldfarb R. B. 1992 Demagnetizing factors in J. Evetts Ed. Concise encyclopedia of magnetic and superconducting materials Oxford Pergamon p. 103-104. Hilscher G. 2001 in Encyclopedia of materials science and technology Amsterdam Elsevier Science. This page intentionally left blank 9 Measurement Techniques . THE SUSCEPTIBILITY BALANCE Commonly for measuring the magnetic susceptibility of samples having the shape of long prismatic
