Coercivity of 99.8% pure iron is 1 oe but that of 99.95% pure iron is 0.05 oe.Why such difference while both have same retentivity?

Edit: I mean to say if both have same amount of residual magnetism after removal of magnetic field then shouldn't they need same amount of coercive field to make residual magnetism zero?

Edit 2: Link for this data https://www.google.com/url?sa=t&source=web&rct=j&url=http://depts.washington.edu/mictech/optics/sensors/week2.pdf&ved=2ahUKEwji2vKH57HhAhXCAnIKHSqkA44QFjAKegQIBRAB&usg=AOvVaw0p-7rhJW0Cc6tldttgnl_C

  • $\begingroup$ Coercivity depends on many other metallurgical factors, like the size of crystal grains. $\endgroup$ – Pieter Apr 2 '19 at 14:17
  • $\begingroup$ Can you indicate the source of your data? $\endgroup$ – nasu Apr 2 '19 at 15:52
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    $\begingroup$ It is the annealing in hydrogen that makes the big difference. $\endgroup$ – Pieter Apr 2 '19 at 17:38

Coercivity and Retentivity are separate properties of a material. They are not even particularly closely related to each other, given that they both describe the material’s reaction to magnetic fields. You can easily look up their definitions on Wikipedia, but the analogy to physical properties that I use is that low vs high coercivity is like soft vs hard while low vs high retentivity is like elastic vs inelastic or springy vs plastic.

It is obviously very possible to have soft springs as well as hard springs, and soft plastics as well as hard plastics. To continue our physical properties analogy, it is actually a recurring theme in metallurgy that pure metals are much softer than impure metals (steel gets harder as you add small amounts of carbon, gold gets harder as you add small amounts of silver, copper gets harder as you add small amounts of tin...etc). In both the physical and the magnetic case, this is related to crystal/grain structure. Both the size of crystals and the properties of the molecular glue between the crystals are strongly dependent on the impurities present. I am not a materials scientist and can’t offer a very good story to explain the details of that dependency. I suspect it is complex and difficult to summarize.

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  • $\begingroup$ I think it does, not answer, what OP has actually ask. $\endgroup$ – Yuvraj Nov 22 '19 at 5:21

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