[Pw_forum] Doubt in Curie temperature value

[Cyrille Barreteau]

Dear Padmaja Patnaik

There are several things wrong or at least approximative in your
reasoning.

-First your estimation of J_0 is quite crude at least for itinerant
magnetism. A better estimate of J_0 would require a spin spiral
calculation (not available within pwscf) and then a fit with Heisenberg
model.
-Second you only include first neighbors  while it is well known that
next nearest neighbors are very important especially for Iron.
-last but not least: your estimation of T_c is based on mean field
approximation which is known to overestimate the transition
temperature..

Cyrille

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On Tue, 2011-03-22 at 04:57 +0000, Padmaja Patnaik wrote:
> Hi
> 
> I am calculating the Curie Temperature for Iron. The experimental
> value for this is  1043 K. I am getting the value as 2398.97 K. I am
> using the following way to calculate.
> Find out the ferromagnetic and anti-ferromagnetic energy of Fe. The
> difference between these two gives the value of J_0. Then,
> T_c = [2/3] [J_0/K_B]
> 
> Please suggest me what is wrong? Why am I getting such a high value.
> On the other hand I am getting very low value for Ni, whose
> experimental Curie temperature is 627K and I am getting 315K. 
> Thanking you in advance,
> regards
> Padmaja Patnaik
> Research Scholar
> Dept of Physics
> IIT Bombay
> Mumbai, India
> 
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