Question

3. Saturation Magnetization of Magnetite Fe O The temperature dependence of the spontaneous magnetization of magnetite (lodestone) Fe O, as measured by Pierre Weiss is given in the following table: M/M, 0.92 0.88 0.83 0.77 068 058 043 0.32 0.22 0.03 T/Tc 0.23 0.33 0.43 0.54 066 0.78 0.89 0.94 0.95 0.98 0.8 0.6 olron i-…-쇼Niekel , l...- - xCobalt 0.2 0.4 0.6 0.2 0.8 Include the spontaneous magnetizations into the plot and compare with curve (a) which is the result for the spontaneous magnetization curve predicted from Langevin-theory i.e. J-).One feels tempted to conclude that Fe,Os is a ferromagnet, is this true?

Answer 1

Spontaneous magnetization depends on temperature as follows:

....(1)

Spontaneous magnetization depends on temperature as follows: M = M_0 [1 - (T/T_c)^3/2 ....(1) Where M_0 is the spontaneous magnetization at T = 0. Equation (1) can also be written as: M/M_0 = 1 - (T/T_c)^3/2 ....(2) Curve (c) corresponds to J = 1/2 and represents the spontaneous magnetization curve for Iron, Nickel and Cobalt. Curve (b) corresponds to J = 5/2 Curve (a) corresponds to J = infinity. There is a huge difference between curve (a) and curve (c). Fe_3O_4 is Ferrimagnetic at room temperature.

Where M_o is the spontaneous magnetization at T = 0.

Equation (1) can also be written as:

....(2)
Curve (c) corresponds to J = 1/2 and represents the spontaneous magnetization curve for Iron, Nickel and Cobalt.

Curve (b) corresponds to J = 5/2

Curve (a) corresponds to J = $\infty$ .

There is a huge difference between curve (a) and curve (c).

Fe₃O₄ is Ferrimagnetic at room temperature.