# Curie point for ferromagnetic materials

by Low-Q
Tags: curie, ferromagnetic, materials, point
 PF Patron P: 244 Hi, I have searched the web for a graph that shows the ferromagnetic properties of a metal like iron or nickel as they warms up to the Curie temperature - when the metals becomes non-ferromagnetic. I cannot find any good images or graphs that shows this very clear. I have been told that the Curie point is very sharp, meaning that at temperatures slightly under or over the Curie temperature makes the metal ferromegnetic or not. Can someone please help to explain this to me? Br. Vidar
 P: 1,626 There is a sketch of the magnetization versus temperature for a ferromagnetic material here: http://www.irm.umn.edu/hg2m/hg2m_b/hg2m_b.html Scroll down a little, to get to ferromagnetism. An experimental image cuve for nickel is contained in this graph: http://media.web.britannica.com/eb-m...4-A2511D3C.gif The Curie point is "sharp" in the sense that is the point of a phase transition. It is somewhat similar to the melting point. Above it the material is liquid, below it it's solid. Here it is the ferro- to para- magnetic phase transition. However this is a so called "second order" phase transition whereas the melting is "first order". It means (between other things) that the order parameter (magnetization) does not have a jump over the transition point. It goes to zero when temperature is increased towards Tc and remains zero on the high temperature side of the transition.
 PF Patron P: 244 Thanks for the reply. Is it possible to make a relatively high efficient motor of ferromagnetic materials if the material is close to its Curier temperature so just small changes in temperature (which require "small" energy input) will make a "Curier engine" to work? Say the engine is inside an insolated box where the temperature is possible to be kept high. I am not talking about over unity, but another way to make an engine. br. Vidar
P: 1,626

## Curie point for ferromagnetic materials

 Quote by Low-Q Thanks for the reply. Is it possible to make a relatively high efficient motor of ferromagnetic materials if the material is close to its Curier temperature so just small changes in temperature (which require "small" energy input) will make a "Curier engine" to work? Say the engine is inside an insolated box where the temperature is possible to be kept high. I am not talking about over unity, but another way to make an engine. br. Vidar
The "high" temperature is not really a problem. There are ferromagnetic materials with low Curie temperature. Not very common I guess as the interest is in having it high enough to avoid demagnetization. Gadolinium is an example (TC less than 300 K).
Regarding the motor, I don't know, there are many things to consider.