Abstract
The recent discovery of magnetic skyrmion lattices initiated a surge of interest in the scientific community. Several novel phenomena have been shown to emerge from the interaction of conducting electrons with the skyrmion lattice, such as a topological Hall-effect and a spin-transfer torque at ultra-low current densities. In the insulating compound Cu2OSeO3, magneto-electric coupling enables control of the skyrmion lattice via electric fields, promising a dissipation-less route towards novel spintronic devices. One of the outstanding fundamental issues is related to the thermodynamic stability of the skyrmion lattice. To date, the skyrmion lattice in bulk materials has been found only in a narrow temperature region just below the order-disorder transition. If this narrow stability is unavoidable, it would severely limit applications. Here we present the discovery that applying just moderate pressure on Cu2OSeO3 substantially increases the absolute size of the skyrmion pocket. This insight demonstrates directly that tuning the electronic structure can lead to a significant enhancement of the skyrmion lattice stability. We interpret the discovery by extending the previously employed Ginzburg-Landau approach and conclude that change in the anisotropy is the main driver for control of the size of the skyrmion pocket.
Highlights
Skyrmions were first introduced in the context of topologically protected excitations in the field theory of hadrons[1]
In addition to the observed growth, one can notice a qualitative change in the way the phases are arranged in that part of the phase diagram
We can proceed with the discussion of the size of the skyrmion pocket in terms of thermodynamic temperature T
Summary
At the highest pressure (p = 2.3 GPa) the low susceptibility region extends almost to 30 K, indicating that skyrmions exist down to at least half of the ordered phase diagram in the high-magnetic field region. The microscopic parameters J, D and K are related to experimental observables in a simple way: TC ∝ J, BC2 ∝ D2/J (ref.29), while as mentioned previously we assume BC1 ∝ K It has been shown[9] that when thermal fluctuations around the mean-field solution are included, the skyrmion lattice phase becomes stable close to TC. The square-root dependence is preserved across the pressure range investigated in this study
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