Chapter 8
Electric and Magnetic Phenomena
This chapter treats the responses of bulk matter to constant external electric
and magnetic fields. The concepts of electric and magnetic dipole moments are
reviewed, modifications to thermodynamics needed to accommodate field effects,
and the statistical mechanical descriptions of polarizable media in the presence
of applied fields are developed. The canonical ensemble for dipolar molecules is
employed to obtain an expression for the dielectric constant of a polar gas. The main
focus for magnetizable media is on paramagnetism: the statistical mechanics of
nuclear spin systems is employed to obtain a statistical thermodynamic expression
for the Curie susceptibility of ground level atoms or ions, which is then applied
to the lanthanide tripositive ions that play important roles in modern electronic
devices. The chapter finishes with a brief consideration of ferromagnetism and the
one-dimensional Ising model.
8.1 Responses of Matter to Electric and Magnetic Fields
The response of a material system to an electric and/or magnetic field derives from
the responses of the individual constituent atoms or molecules that make up the
system under consideration. In principle, electric or magnetic fields will be deemed
to be external (or applied) fields if they originate outside the system and will be
deemed internal if they are the result of interactions amongst constituents of the
system itself. Although, in principle, an applied may either be constant (in time)
or oscillatory, we shall focus in the main upon the response of matter to constant
external fields.
Two types of electric dipole moment, referred to as either (a) a permanent, or (b)
an induced, dipole moment, may be encountered at the atomic/molecular level.
© Springer Nature Switzerland AG 2021
F. R. W. McCourt, Statistical Thermodynamics for Pure and Applied Sciences,
https://doi.org/10.1007/978-3-030-52006-9_8
411
Electric and Magnetic Phenomena
This chapter treats the responses of bulk matter to constant external electric
and magnetic fields. The concepts of electric and magnetic dipole moments are
reviewed, modifications to thermodynamics needed to accommodate field effects,
and the statistical mechanical descriptions of polarizable media in the presence
of applied fields are developed. The canonical ensemble for dipolar molecules is
employed to obtain an expression for the dielectric constant of a polar gas. The main
focus for magnetizable media is on paramagnetism: the statistical mechanics of
nuclear spin systems is employed to obtain a statistical thermodynamic expression
for the Curie susceptibility of ground level atoms or ions, which is then applied
to the lanthanide tripositive ions that play important roles in modern electronic
devices. The chapter finishes with a brief consideration of ferromagnetism and the
one-dimensional Ising model.
8.1 Responses of Matter to Electric and Magnetic Fields
The response of a material system to an electric and/or magnetic field derives from
the responses of the individual constituent atoms or molecules that make up the
system under consideration. In principle, electric or magnetic fields will be deemed
to be external (or applied) fields if they originate outside the system and will be
deemed internal if they are the result of interactions amongst constituents of the
system itself. Although, in principle, an applied may either be constant (in time)
or oscillatory, we shall focus in the main upon the response of matter to constant
external fields.
Two types of electric dipole moment, referred to as either (a) a permanent, or (b)
an induced, dipole moment, may be encountered at the atomic/molecular level.
© Springer Nature Switzerland AG 2021
F. R. W. McCourt, Statistical Thermodynamics for Pure and Applied Sciences,
https://doi.org/10.1007/978-3-030-52006-9_8
411