# High-pressure optical floating-zone growth of Li(Mn,Fe)PO$_4$ single crystals

## TL;DR

This study demonstrates high-pressure optical floating-zone growth of large, stoichiometric Li(Mn,Fe)PO$_4$ single crystals with tunable magnetic properties, optimizing growth conditions for different compositions and analyzing their structural and magnetic characteristics.

## Contribution

It introduces a high-pressure floating-zone method for growing large Li(Mn,Fe)PO$_4$ single crystals with optimized conditions across doping levels, and provides detailed structural and magnetic property analysis.

## Key findings

- Large single crystals grown successfully at 30 bar Argon pressure.
- Lattice parameters vary linearly with Mn:Fe ratio.
- Néel temperature increases from 32.5 K to 49.5 K with Fe doping.

## Abstract

Mm-sized LiMn$_{1-x}$Fe$_x$PO$_4$ single crystals with $0\leq x \leq 1$ were grown by means of the traveling floating-zone technique at elevated Argon pressure of 30~bar. For the various doping levels, the growth process was optimized with respect to the composition-dependant effective light absorption and transparency of the materials. A convex crystal/melt interface, determined by the angle of incident light, was identified to be particularly crucial for a successful growth. The resulting large single crystalline grains are stoichiometric. Structure refinement shows that lattice parameters as well as the atomic positions and bond lengths linearly depend on the Mn:Fe-ratio. Oriented cuboidal samples with several mm$^3$ of volume were used for magnetic studies which imply an antiferromagnetic ground state for all compositions. The N\'eel-temperature changes from $T_N$ = 32.5(5) K in LiMnPO$_4$ to 49.5(5) K in LiFePO$_4$ while the easy magnetic axis in the ordered phase flips from the crystallographic $a$- to the $b$-axis upon Fe-doping of $x<0.2$.