Is There an Optimum Price-Performance Metric for Permanent Magnet Materials?

John Ormerod, Principal and Founder, JOC LLC

Attend any magnetics conference or seminar and I can guarantee a slide will appear in someoneís presentation showing something along the lines of the year of introduction of a permanent magnet material versus the corresponding (BH)max. I know when I am presenting I always use a variant of the figure shown below.

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Courtesy of Magnet Applications, Inc.

The one thing I always point out is that itís now been 35 years since the last significant new material was announced by Sumitomo Special Metals and General Motors; namely materials based on the Nd2Fe14B tetragonal compound. This despite untold hours and $ís spent on a search for the next big thing in permanent magnets.

So why the fascination/obsession with (BH)max? Well it is an useful and practical index of permanent magnet performance since to a first approximation the higher the (BH)max value the smaller the volume of magnet required to generate a given flux density in an air gap. Of course itís a bit more complicated than that but this is intended to be a short article not a textbook so I will refrain from reproducing tedious equations.

There are a lot of other criteria to consider when either selecting the right magnet for an application or understanding the degree of commercial success of a particular material in the market. Some of the considerations are shown below.

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However, it occurs to me that there is some price-performance sweet spot that determines the degree of market success that is not expressed in the above list of criteria. This magic index is the subject of this article.

Today, there are four major classes of basic magnet material in commercial production; alnico, NdFeB, SmCo and ferrite. In addition there is a subset of products known as bonded magnets that combine these basic magnetic material powders in a non-magnetic binder. Most commonly used magnetic powders are ferrite and isotropic NdFeB. Itís become standard to think of all these material options as providing a continuum of (BH)max performance from 1 MGOe (isotropic ferrite) to 55 MGOe or higher (sintered NdFeB) except for a small gap between 12 MGOe (bonded NdFeB) and 18 MGOe (SmCo5). However, typically the relative market shares of these materials are not included in these discussion and hence no weighting is given to the relative commercial significance of the material options. The table below gives my estimate/guess of the global markets for these materials.

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As can be seen two materials (sintered NdFeB and ferrite) account for over 90 percent of the market. The rest are all less than 5 percent; by my arbitrary definition they are niche materials. The two mass market (again by my arbitrary definition) magnets are ferrite and sintered NdFeB and yet they have dramatically different properties and performance characteristics. So if you are developing a magnet for the mass market I argue the performance gap is actually between 5.5 MGOe and 35 MGOe; a much larger gap than is typically discussed.

So I started wondering is there a metric that might indicate whether a material is destined to be a niche player or mass market behemoth. In the table below I simply divided the average price per kg by the typical (BH)max of the material to give a number with the ugly units of $.MGOe/kg. Interestingly the two mass market materials have similar values; the niche materials have values that are higher by at least 60 percent. My theory is that if the price-performance ratio is optimum then the market will figure out a way to fix or design around the disadvantages of the material e.g. low temperature demagnetization of ferrite, poor corrosion resistance of NdFeB. If the price-performance ratio is not optimum than the material remains a niche product since the market is less inclined to find a solution to the limitations.

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Let me finish by saying I am only a mere metallurgist and not an economist so this is a very simplistic analysis (thatís probably an understatement) which I doubt will ever be considered by the HBR! However, I look forward to hearing your thoughts and comments. You can email me at John@jocllc.com or visit www.jocllc.com.

This article is based on a blog originally posted on LinkedIn by the author.

Dr. John Ormerod is principal and founder of JOC LLC a consultancy to the Global Magnetics and Metals Industries.† John graduated from the University of Manchester, UK with a B.Sc., M.Sc. and Ph.D. in Metallurgy. He has over twenty years of research, product development, and manufacturing experience in the area of magnetics. John has published and presented numerous papers in the field of permanent magnet materials. He has experience in Europe working for Phillips and in the USA with Arnold Engineering (now Arnold Magnetic Technologies). Dr. Ormerod has provided expert testimony on issues of invalidity during the rare earth magnet ITC investigation No. 337-TA-855 and is currently a technical consultant evaluating prior art for the Rare Earth Permanent Magnet Industry Alliance.† In 2015 John founded JOC LLC, a consultancy specializing in the magnetics and metals-related industries.

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