Posted by Ali on April 9, 2013, 7:07 pm
As in my previous question, I am confused about something from the 2011 condensed matter paper, question 8 this time. In the last paragraph of the question, you are asked to estimate the value of the mean field B_e, which is given earlier as: B_e = mu_0 * lambda * M Where M is the magnetization. A value for lambda has already been estimated in this question but I'm not so sure about M. In the solutions from the physics website [http://www.physics.ox.ac.uk/expapers/ExamSolutions_for%20Students/20122013/B3%20V.pdf.pdf], the value for M used is n*g*mu_B*J. I'm presuming that this is taken from the original magnetization formula in the limit for B_J(x) when x>>1? If so, why is this approximation valid? Any help is appreciated. 
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