23/12/2016
The magnetics community is notorious for the inconsistent use of quantities and units. Even though the SI system is now 56 years old, a brand new magnetometer still has a Gauss scale. Of the latest three JMMM publications, two are based on CGS. Here is a pledge for a consistent an unambiguous use of SI units.
The magnetics community is notorious for the inconsistent use of quantities and units. Even though the SI system is now 56 years old, a brand new magnetometer still has a Gauss scale. Of the latest three JMMM publications, two are based on CGS. If you are working with cgs-Gauss units in spintronics, did you ever think of the physical meaning when comparing the mobility of domain walls under spin-polarized current density j versus magnetic field H, which is an obscure Oe.cm2/A?.. However appears to be a length in SI! How are we supposed to train students in such an environment?
Those of you who use SI and therefore think you are on the right side of history, think again! There are at least three definitions used in the literature to link magnetization, magnetic field and induction:
These reflect different views of authors how to best interpret M, H and B in physical terms, and all are in principle fine, as well as using cgs-Gauss only would be fine. Thus, if you make any choice and stick to it, you are safe. However, by doing so, they introduce an extreme confusion because any formula involving H or M cannot be used stand-alone, unless one tracks back the definition used by the author. Like for all areas of physics and engineering, standardization is a key to quality and efficiency.
A safe and recommended way is therefore to stick to standards agreed on by international bodies in charge of such standardization procedures, in the present case the Bureau International des Poids et Mesures for the SI units. In the official SI units, B (magnetic induction or magnetic flux density), H (magnetic field) and M (magnetization) are linked through:
B=μ0(H+M)
If you like to express magnetic fields in tesla, then label them μ0H. If you like to express M in tesla, label them μ0M or J (also called magnetic polarization, for example used in Hubert and Schäfer’s book on domain theory). Below are some references of interest.
[1] Bureau International des Poids et Mesures, in charge of the definition and maintenance of the SI system. Comprehensive and pedagogical documents can be downloaded on dimensions and units, choices, conversions, recommended ways to write them.
[2] A. S. Arrott, J. A. C. Bland, & B. Heinrich (Eds.), Ultrathin Magnetic Structures I, Chapter 1.2 “Magnetism in SI Units and Gaussian Units”, Springer, 7-9, (1994). DOI 10.1007/b138789.
[3] P.C. Scholten “Which SI?” J. Magn. Magn. Mater. 149, 57-59 (1995). Doi:10.1016/0304-8853(95)00337-1. Be aware however, that this author labels M instead of mu M, which is confusing.
[4] Practical on units and how to derive conversions, taken from the European School on Magnetism: questions and answers.
[5] LaTeX package SIunits, useful for typesetting, coming with a comprehensive documentation on dimensions and units.
Proposed and discussed by L. Abelmann, O. Fruchart, B. Hillebrands.