Spin ice

Summary

A spin ice is a magnetic substance that does not have a single minimal-energy state. It has magnetic moments (i.e. "spin") as elementary degrees of freedom which are subject to frustrated interactions. By their nature, these interactions prevent the moments from exhibiting a periodic pattern in their orientation down to a temperature much below the energy scale set by the said interactions. Spin ices show low-temperature properties, residual entropy in particular, closely related to those of common crystalline water ice. The most prominent compounds with such properties are dysprosium titanate (Dy2Ti2O7) and holmium titanate (Ho2Ti2O7). The orientation of the magnetic moments in spin ice resembles the positional organization of hydrogen atoms (more accurately, ionized hydrogen, or protons) in conventional water ice (see figure 1). Experiments have found evidence for the existence of deconfined magnetic monopoles in these materials, with properties resembling those of the hypothetic

Official source

https://en.wikipedia.org/wiki/Spin_ice

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Evidence from thermodynamic measurements for a singlet crystal-field ground state in pyrochlore Tb2Sn2O7 and Tb2Ti2O7

The magnetic entropy variation for the ordered spin-ice Tb2Sn2O7 and the spin-liquid Tb2Ti2O7 measured up to similar to 20 K shows that the crystal-field ground state for both systems is a singlet split from the first excited level by a thermal energy of similar to 2 K. It is the superexchange interactions between the Tb3+ spins which induce the terbium magnetic moments. Our results are analyzed in terms of a tetragonal perturbation for Tb2Ti2O7 and this perturbation plus a molecular field for Tb2Sn2O7.

2010

Magnon Modes of Microstates and Microwave-Induced Avalanche in Kagome Artificial Spin Ice with Topological Defects

Vinayak Shantaram Bhat, Dirk Grundler

We investigate spin dynamics of microstates in artificial spin ice (ASI) in Ni81Fe19 nanomagnets arranged in an interconnected kagome lattice using microfocus Brillouin light scattering, broadband ferromagnetic resonance, magnetic force microscopy, x-ray photoemission electron microscopy, and simulations. We experimentally reconfigure microstates in ASI using a 2D vector field protocol and apply microwave-assisted switching to intentionally trigger reversal. Our work is key for the creation of avalanches inside the kagome ASI and reprogrammable magnonics based on ASIs.

2020

We report broadband spin-wave spectroscopy on kagome artificial spin ice (ASI) made of large arrays of interconnected Ni 80 Fe 20 nanobars. Spectra taken in saturated and disordered states exhibit a series of resonances with characteristic magnetic field dependencies. Making use of micromagnetic simulations, we identify resonances that reflect the spin-solid-state and monopole-antimonopole pairs on Dirac strings. The latter resonances allow for the generation of highly charged vertices in ASIs via microwave-assisted switching. Our findings open further perspectives for fundamental studies on ASIs and their usage in reprogrammable magnonics

Amer Physical Soc2016