Electric Field Eect on Skyrmion phase in Chiral lattice Ferrimagnet Cu2OSeO3

Naman Agarwal
2016
Student project

Abstract

Insulator materials are the recent research interest in Spintronics because of the absence of joule heating. There has been continued interest in insulator material Cu2OSeO3 because it possesses the novel Skyrmion phase [1], specific type of spin vortices in the lattice, characterized by quantized topological number, near the paramagnetic phase boundary [2]. This Skyrmion phase can be harnessed for the switching applications in the data storage devices [3–6]. We study the effect of positive or negative DC electric field on the Skyrmion phase boundary of this material by magnetoelectric susceptibility(dM/dE)measurements, which is a sensitive technique for scanning phase boundary [7,8]. We scan out the phase diagram for positive, negative and zero DC electric fields and find that electric field effect is maximum at the phase boundaries and decreases inside the phase There is no cut-off for the electric field effect. Also, the electric field effect is maximum at upper skyrmion boundary compared to other phase boundaries. We also show the small expansion(contraction) of Skyrmion phase along temperature axis with the application of positive(negative) DC electric field.

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Electric Field Effects in the Skyrmion Lattice Hosting Magnet Cu2OSeO3

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Magnetic skyrmions have garnered much attention in recent years because of their non trivial topology and potential to be used in next generation memory devices. They may exist individually or as a lattice of skyrmions(SkL). A number of investigations have been done on SkL in metallic samples, but recently a few magnetoelectric insulators have also begun to attract a lot of attention. The magnetoelectric nature of these materials presents a possibility to make prototype memory devices where skyrmions form a storage bit and can be controlled with only electric fields without the losses caused by Joule heating. We focus here on the material Cu2OSeO3, for which interesting electric field effects have been seen like the control of size of the region in the phase diagram where SkL is stable, creation of metastable skyrmions and the use of magnetolectric susceptibility to map the phase diagram. We use the magnetoelectric susceptibility to explore the above mentioned effects of electric fields, attempting to confirm previous reports of such effects using different techniques like neutron scattering and AC susceptibility. We also propose a new design to create metastable SkL state at low temperatures and confirm its existence using magnetoelectric susceptibility. We also attempt to measure the change in polarization between the SkL phase and the trivial phase on application of DC electric fields, which in principle could lead to electrical readout of skyrmions in a prototype skyrmion based memory device.

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Thermopower as a Unique Tool to Probe Quantum Phase Transitions

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EPFL2012

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