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Chapter 20: Problem 15

Briefly explain why the magnitude of the saturation magnetization decreases with increasing temperature for ferromagnetic materials, and why ferromagnetic behavior ceases above the Curie temperature.

Short Answer

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Answer: The saturation magnetization of ferromagnetic materials decreases with increasing temperature because the increased thermal energy causes the magnetic moments within the material to become less aligned, leading to weaker overall magnetization. Ferromagnetic behavior ceases above the Curie temperature because the thermal energy becomes so high that it prevents the magnetic moments from maintaining their alignment, causing the material to lose its ability to maintain a strong magnetic field and transition to a weaker, temperature-dependent paramagnetic state.

Step by step solution

01

Understand Ferromagnetic Materials and Saturation Magnetization

Ferromagnetic materials are substances that exhibit strong magnetic properties when aligned. These materials have magnetic domains, which are microscopic regions where the magnetic moments (tiny magnetic fields) of atoms and molecules are aligned in the same direction. When a ferromagnetic material is magnetized, these magnetic domains rearrange and align themselves to create a strong and uniform magnetic field. The saturation magnetization refers to the maximum magnetization that a ferromagnetic material can achieve when all its magnetic domains are aligned.
02

Understand the Effect of Temperature on Magnetic Moments

At higher temperatures, the thermal energy of the atoms increases. This increased thermal energy tends to randomize the magnetic moments within the material, causing the magnetic moments of neighboring atoms to become less aligned. As a result, the net magnetization of the material will decrease.
03

Explain the Decrease in Saturation Magnetization with Temperature

As the temperature of a ferromagnetic material increases, the thermal energy of the atoms will force the magnetic moments to misalign. This misalignment reduces the effectiveness of the magnetic domains in aligning with one another, leading to a weaker overall magnetization. Hence, the saturation magnetization of a ferromagnetic material decreases as the temperature increases.
04

Understand Curie Temperature

The Curie temperature (Tc) is a specific temperature for ferromagnetic materials at which the material undergoes a phase transition. When a ferromagnetic material is heated above its Curie temperature, the thermal energy becomes so high that the magnetic moments can no longer maintain their alignment. At this point, the ferromagnetic material loses its ability to maintain a strong, uniform magnetic field and becomes paramagnetic, a weaker and temperature-dependent magnetic state.
05

Explain Why Ferromagnetic Behavior Ceases Above Curie Temperature

When the temperature of a ferromagnetic material is raised above its Curie temperature, the thermal energy becomes so high that it prevents the magnetic moments from maintaining their aligned state within the magnetic domains. The material's net magnetization essentially drops to zero as the magnetic moments become randomly oriented. Therefore, the ferromagnetic behavior of the material ceases above the Curie temperature, and the material transitions to a paramagnetic state.

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Most popular questions from this chapter

The following data are for a plain carbon steel alloy: \begin{tabular}{cccc} \hline \(\boldsymbol{H}(\boldsymbol{A} / \mathrm{m})\) & \(\boldsymbol{B}(\) tesla \()\) & \(\boldsymbol{H} \mathbf{( A / m )}\) & \(\boldsymbol{B}\) (tesla) \\ \hline 0 & 0 & 80 & \(0.90\) \\ \hline 15 & \(0.007\) & 100 & \(1.14\) \\ \hline 30 & \(0.033\) & 150 & \(1.34\) \\ \hline 50 & \(0.10\) & 200 & \(1.41\) \\ \hline 60 & \(0.30\) & 300 & \(1.48\) \\ \hline 70 & \(0.63\) & & \\ \hline \end{tabular} (a) Construct a graph of \(B\) versus \(H\). (b) What are the values of the initial permeability and initial relative permeability? (c) What is the value of the maximum permeability? (d) At about what \(H\) field does this maximum permeability occur? (e) To what magnetic susceptibility does this maximum permeability correspond?

A coil of wire \(0.5 \mathrm{~m}\) long and having 20 turns carries a current of \(1.0 \mathrm{~A}\). (a) Compute the flux density if the coil is within a vacuum. (b) A bar of an iron-silicon alloy, the \(B-H\) behavior for which is shown in Figure \(20.29\), is positioned within the coil. What is the flux density within this bar? (c) Suppose that a bar of molybdenum is now situated within the coil. What current must be used to produce the same \(B\) field in the Mo as was produced in the iron-silicon alloy (part b) using \(1.0 \mathrm{~A}\) ?

Cite the differences between type I and type II superconductors.

Cite the differences between hard and soft magnetic materials in terms of both hysteresis behavior and typical applications.

(a) Explain the two sources of magnetic moments for electrons. (b) Do all electrons have a net magnetic moment? Why or why not? (c) Do all atoms have a net magnetic moment? Why or why not?
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