Investigation of the monopole magneto-chemical potential in spin ices using capacitive torque magnetometry*

Geometrically frustrated systems have an inherent incompatibility between the lattice geometry and the magnetic interactions, resulting in macroscopically degenerate ground-state manifolds. The single-ion anisotropy and magnetic interactions in spin-ice systems give rise to unusual non-collinear spin textures, such as Pauling states and emergent quasiparticle excitations equivalent to magnetic monopoles. The effective spin correlation strength (J_eff) determines the relative energies of the different spin-ice states and the magneto-chemical potential (MCP) associated with monopole formation. Capacitive torque magnetometry is used as a unique tool to characterize the transitions between noncollinear spin textures in spin-ice samples, which allows extraction of J_eff and the MCP of monopole formation [1]. We build a magnetic phase diagram of Ho₂Ti₂O₇, from which we determine that the field-induced magnetic phase transitions cannot be described by a single value of J_eff. Rather, the MCP depends on the spin sublattice (α or β), i.e., the Pauling state, involved in the transition. There is an enticing potential of using these monopoles for the development of new quantum information applications, which requires thin films. Thin films grown on yttria-stabilized zirconia substrates show modified spin ice physics [2] depending on the growth conditions.