# Multiple phases with tricritical point and Lifshitz point in skyrmion host Cu$_2$OSeO$_3$

## TL;DR

This study explores the complex magnetic phase diagram of Cu$_2$OSeO$_3$, revealing multiple phase transitions, tricritical and Lifshitz points, and the role of fluctuations in skyrmion phase formation, advancing understanding of magnetic phenomena in chiral magnets.

## Contribution

It uncovers the presence of multiple multicritical points, including tricritical and Lifshitz points, and details the nature of phase transitions in Cu$_2$OSeO$_3$, a unique insulating chiral helimagnet.

## Key findings

- Identification of at least two multicritical points.
- Evidence of fluctuation-induced first order transition near skyrmion phase.
- Detection of coexisting commensurate and incommensurate phases.

## Abstract

Magnetic skyrmions, a topologically stable spin swirling object, have attracted a great interest due to their potential applications in future spintronics and ultra high dense magnetic memory devices. Cu$_2$OSeO$_3$ is only known insulating chiral helimagnet with multiple phases including skyrmion phase. Existence of skyrmion phase as well as first and second order phase transitions make Cu$_2$OSeO$_3$ a promissing candidate for investigating complex magnetic phenomena. Here, we report that both first and second order magnetic phase transitions are responsible in determining the phase diagram with atleast two multicritical point in Cu$_2$OSeO$_3$. Fluctuation-induced first order transition is realized as a precursor for skyrmion phase over a small window of temperature of magnetic field. The evolution of field dependent entropy at the phase transition provides the evidence for tricritical point. Furthermore, existence of commensurate and incommensurate phases, alongwith co-existence of three second order phase transitions provide evidence for the existence of Lifshitz point.