Magnetic Cluster Excitations

Abstract

Magnetic clusters, i.e., assemblies of a finite number (between two or three and several hundred) of interacting spin centers which are magnetically decoupled from their environment, can be found in many materials ranging from inorganic compounds, magnetic molecules, artificial metal structures formed on surfaces to metalloproteins. The magnetic excitation spectra in them are determined by the nature of the spin centers, the nature of the magnetic interactions, and the particular arrangement of the mutual interaction paths between the spin centers. Small clusters of up to four magnetic ions are ideal model systems to examine the fundamental magnetic interactions which are usually dominated by Heisenberg exchange, but often complemented by anisotropic and/or higher-order interactions. In large magnetic clusters which may potentially deal with a dozen or more spin centers, the possibility of novel many-body quantum states and quantum phenomena are in focus. In this review the necessary theoretical concepts and experimental techniques to study the magnetic cluster excitations and the resulting characteristic magnetic properties are introduced, followed by examples of small clusters demonstrating the enormous amount of detailed physical information which can be retrieved. The current understanding of the excitations and their physical interpretation in the molecular nanomagnets which represent large magnetic clusters is then presented, with an own section devoted to the subclass of the singlemolecule magnets which are distinguished by displaying quantum tunneling of the magnetization. Finally, some quantum many-body states are summarized which evolve in magnetic insulators characterized by built-in or field-induced magnetic clusters. The review concludes addressing future perspectives in the field of magnetic cluster excitations.

Spin–orbit coupled molecular quantum magnetism realized in inorganic solid

“…2c. The obtained I ( Q ) is obviously well explained by the molecular model rather than the ionic model35, supporting the presence of molecular quantum magnetism in Ba 3 Yb 2 Zn 5 O 11 . The Q integrated intensities I ( ω ) presented in Fig.…”

“…To explore magnetic excitations in this novel quantum magnet, we performed INS measurements2021223536. Figure 2a shows the intensities I ( Q , ω ) as a function of momentum and energy transfer obtained from the measurements at T =200 mK and at the zero magnetic field.…”

Single-ion versus two-ion anisotropy in magnetic compounds: A neutron scattering study

“…The anisotropy of the magnetic interactions in CsMn x Mg 1-x Br 3 was unravelled in a comprehensive neutron spectroscopic study of low-lying Mn 2+ dimer and 13 tetramer excitations. The observed anisotropy was shown to be predominantly of a single-ion origin due to the axial ligand field with an anisotropy parameter D=0.0183(16) meV, which is considerably larger than the value D=0.012 (1) meV determined from the analysis of the spin-wave dispersion [8].…”

Magnetic Excitations in the Trimeric Compounds A3Cu3(PO4)4(A = Ca, Sr, Pb)

“…1. In addition, for the compound Ca 3 Cu 3 (PO 4 ) 4 we have c 2 13 = −0.32 (8) and J ≈ 4.741 meV based on INS data at T = 1.5 K [7,13] . Table 1: The values of the coupling constants and the quantities c 1 13 , c 2 13 for our model applied to A 3 Cu 3 (PO 4 ) 4 (A = Ca, Sr, Pb) obtained by taking into account the experimental data in Ref.…”

“…It is cumbersome to apply a general approach with a unique set of parameters that can describe all possible magnetic effects and in addition to distinguish between inter-molecular and intra-molecular features. Usually, one starts with bilinear spin microscopic models, such as the Heisenberg Hamiltonian [13] and depending on the exhibited magnetic features different interaction terms are included [14] .…”