CHAPTER 18

MAGNETIC PROPERTIES

LEARNING OBJECTIVES

  1. Describe a magnetic dipole.
  1. Calculate the magnetic field strength within a coil of wire given the number of wire turns, the length of the coil, and the magnitude of the current.
  1. Determine the magnetic flux density for a specified field strength

(a)in a vacuum given the permeability of a vacuum, and

(b)within some solid material given its permeability.

  1. Compute the relative permeability for some material given its permeability, and the permeability of a vacuum.
  1. Calculate the magnetic susceptibility of some material given the value of its relative permeability.
  1. Determine the magnetization of some material given the magnitude of the applied magnetic field strength and, in addition, its magnetic susceptibility.
  1. From an electronic perspective note and briefly explain the two sources for magnetic moments in materials.
  1. For a specific electron, given its spin orientation as well as its magnetic quantum number, and, in addition, the magnitude of the Bohr magneton, compute orbital and spin contributions to its overall magnetic moment.
  1. Briefly explain why some atoms will possess no net magnetic moment.
  1. (a) Briefly explain the nature and source of diamagnetism.

(b) Note the order-of-magnitude value for the volume susceptibility of diamagnetic materials.

  1. (a) Briefly explain the nature and source of paramagnetism.

(b) Note the order-of-magnitude value range for the volume susceptibility of paramagnetic materials.

  1. (a) Briefly explain the nature and source of ferromagnetism.

(b)For a ferromagnetic material, compute the maximum saturation magnetization, given the number of Bohr magnetons per atom, the value of the Bohr magneton, Avogadro's number, and the density and atomic weight of the material.

  1. Briefly explain the nature and source of antiferromagnetism.
  1. (a) In terms of the crystal structure of cubic ferrites, explain the source of ferrimagnetism.

(b)Calculate the saturation magnetism for a cubic ferrite given its composition, the number of Bohr magnetons associated with each cation type, the value of the Bohr magneton, and the unit cell edge length.

  1. (a) Define Curie temperature.

(b)Briefly explain why saturation magnetization diminishes with increasing temperature for ferromagnetic and ferrimagnetic materials.

  1. Describe the natures of (a) a domain, and (b) a domain wall.
  1. (a) Describe magnetic hysteresis.

(b)Explain why ferromagnetic and ferrimagnetic materials experience magnetic hysteresis.

(c)In terms of magnetic hysteresis, explain why these materials may be permanent magnets.

  1. Given the complete hysteresis loop for a ferromagnetic or ferrimagnetic material, determine:

(a)the initial permeability,

(b)the remanence, and

(c)the coercivity.

  1. In terms of magnetic anisotropy, describe what is meant by a direction of easy magnetization.
  1. Briefly describe the technique that is used to minimize energy losses in transformer cores made of sheets of a polycrystalline 97 wt% Fe-3 wt% Si alloy.
  1. (a) Define soft magnetic material.

(b)Cite the characteristics that are required in order for a ferromagnetic or ferrimagnetic material to be magnetically soft.

  1. (a) Define hard magnetic material.

(b)Cite the characteristics that are required in order for a ferromagnetic or ferrimagnetic material to be magnetically hard.

  1. Briefly explain how information is stored on and retrieved from a magnetic medium using a recording head.
  1. (a) Describe the characteristics of particulate and thin film magnetic storage media.

(b)For each medium type, briefly explain the mechanism of magnetic storage.

  1. Describe the phenomenon ofsuperconductivity.
  1. Define the superconductive (a) critical temperature, (b) critical magnetic field, and (c) critical current density.
  1. In terms of magnetic response, describe the characteristics of types I and II superconductors.
  1. Briefly describe the Meissner effect.