Magnetic orders and spin-flop transitions in the cobalt doped multiferroic $\rm Mn_{1-x}Co_{x}WO_4$

TL;DR

This study investigates how cobalt doping influences magnetic orders and spin-flop transitions in MnWO4, revealing complex magnetic phase evolution driven by magnetic frustration and Co ion anisotropy.

Contribution

It provides the first comprehensive neutron diffraction analysis of Mn_{1-x}Co_{x}WO_4 across a range of Co concentrations, uncovering multiple spin-flop transitions and coexistence of magnetic phases.

Findings

Spin structure transitions from elliptical spiral to spin-flop phases.

Identification of a coexistence of commensurate and incommensurate magnetic orders.

Complex phase diagram distinct from other transition metal doped MnWO4 compounds.

Abstract

We present a comprehensive single crystal neutron diffraction investigation of the $\rm Mn_{1-x}Co_{x}WO_4$ with $0.02\leq x \leq0.30$. At lower concentration $x \leq 0.05$, the system is quickly driven into the multiferroic phase with spin structure forming an elliptical spiral order similar to the parent compound. The reduction of electric polarization is ascribed to the tilting of the spiral plane. For $x\sim 0.075$, the magnetic structure undergoes a spin flop transition that is characterized by a sudden rotation of the spin helix envelope into the $ac$ plane. This spin structure persists for concentration up to $x=0.15$, where additional competing magnetic orders appear at low temperature. For $0.17 \leq x \leq 0.30$, the system experiences another spin flop transition and recovers the low-$x$ spiral spin configuration. A simple commensurate spin structure with $\vec{q}=(0.5,0,0)$ is found to coexist with the incommensurate spiral order. The complex evolution of magnetic structure in Co doped $\rm MnWO_4$ contrasts sharply with other transition metal ion doped $\rm Mn_{1-x}A_xWO_4$ (A=Zn, Mg, Fe) where the chemical substitutions stabilize only one type of magnetic structure. The rich phase diagram of $\rm Mn_{1-x}Co_{x}WO_4 $ results from the interplay between magnetic frustration and spin anisotropy of the Co ions.