Chapter 1
Introduction
It has long been known that a magnet cannot be broken down to its simplest
constituents—the north and south poles. This is reflected in the asymmetry of
Maxwell’s equations with respect to electric and magnetic fields. While the electric
monopole is very much present and is the foundational basis of modern electronics,
the magnetic monopole charge is conspicuous by its absence. The search for the
fundamental magnetic monopole [1] has proven to be quite elusive till date, but
condensed matter physics has provided a few candidates [2, 3]. This chapter reviews
one such class of candidate materials, namely the Dipolar Spin Ices: Dysprosium
Titanate and Holmium Titanate.
Lanthanide pyrochlore oxides are a class of materials wherein the rare-earth
(RE) ions resides on corners of a tetrahedral network (Fig. 1.1) and the RE spins
are usually frustrated. Magnetically frustrated systems [4] refer to conflict within
different couplings between spins in a lattice. A simple illustration of frustration is
a triangular lattice with Ising spins coupled antiferromagnetically. The attribute of
frustration leads itself to the existence of a multitude of exotic magnetic states such
as spin ices [5], spin slush [6] and candidates for quantum spin liquids [7]. One such
member of this class presents itself as a candidate for housing magnetic monopoles,
namely dipolar spin ice which is a geometrically frustrated magnet. Dysprosium
Titanate (Dy 2 Ti 2 O 7 ) and Holmium Titanate (Ho 2 Ti 2 O 7 ) both belong to this subclass of dipolar Spin Ices. Theorists predict that elementary spin excitations in these
compounds behave like magnetic charges [8] that are deconfined to move about the
lattice freely [3].
1.1 Spin Ices
The structure of (Dy/Ho) 2 Ti 2 O 7 is made up of a cubic unit cell (lattice parameter
10.12Å) with two sublattices—pyrochlore lattice of Dy ions (Fig. 1.1) with O at
© Springer Nature Switzerland AG 2021
R. Dusad, Magnetic Monopole Noise, Springer Theses,
https://doi.org/10.1007/978-3-030-58193-0_1
1
Introduction
It has long been known that a magnet cannot be broken down to its simplest
constituents—the north and south poles. This is reflected in the asymmetry of
Maxwell’s equations with respect to electric and magnetic fields. While the electric
monopole is very much present and is the foundational basis of modern electronics,
the magnetic monopole charge is conspicuous by its absence. The search for the
fundamental magnetic monopole [1] has proven to be quite elusive till date, but
condensed matter physics has provided a few candidates [2, 3]. This chapter reviews
one such class of candidate materials, namely the Dipolar Spin Ices: Dysprosium
Titanate and Holmium Titanate.
Lanthanide pyrochlore oxides are a class of materials wherein the rare-earth
(RE) ions resides on corners of a tetrahedral network (Fig. 1.1) and the RE spins
are usually frustrated. Magnetically frustrated systems [4] refer to conflict within
different couplings between spins in a lattice. A simple illustration of frustration is
a triangular lattice with Ising spins coupled antiferromagnetically. The attribute of
frustration leads itself to the existence of a multitude of exotic magnetic states such
as spin ices [5], spin slush [6] and candidates for quantum spin liquids [7]. One such
member of this class presents itself as a candidate for housing magnetic monopoles,
namely dipolar spin ice which is a geometrically frustrated magnet. Dysprosium
Titanate (Dy 2 Ti 2 O 7 ) and Holmium Titanate (Ho 2 Ti 2 O 7 ) both belong to this subclass of dipolar Spin Ices. Theorists predict that elementary spin excitations in these
compounds behave like magnetic charges [8] that are deconfined to move about the
lattice freely [3].
1.1 Spin Ices
The structure of (Dy/Ho) 2 Ti 2 O 7 is made up of a cubic unit cell (lattice parameter
10.12Å) with two sublattices—pyrochlore lattice of Dy ions (Fig. 1.1) with O at
© Springer Nature Switzerland AG 2021
R. Dusad, Magnetic Monopole Noise, Springer Theses,
https://doi.org/10.1007/978-3-030-58193-0_1
1