Tunable magnetic properties in van der Waals crystals (Fe${}_{1-x}$Co${}_x$)${}_5$GeTe${}_2$

Abstract

We report the doping effects of cobalt on van der Waals (vdW) magnet Fe${}_5$GeTe${}_2$. A series of (Fe${}_{1-x}$Co${}_x$)${}_5$GeTe${}_2$ (0$\le$x$\le$0.44) single crystals have been successfully grown, their structural, magnetic and transport properties are investigated. For x=0.20, The Curie temperature $T_C$ increases from 276~K to 337~K. Moreover, the magnetic easy-axis is reoriented to the $ab$-plane from the $c$-axis in undoped Fe${}_5$GeTe${}_2$ with largely enhanced magnetic anisotropy. These magnetic properties would make (Fe${}_{0.8}$Co${}_{0.2}$)${}_5$GeTe${}_2$ more effective in stabilizing magnetic order in the two-dimensional limit. A complex magnetic phase diagram is identified on the higher doping side. The x=0.44 crystal first orders ferromagnetically at $T_C$=363~K then undergoes an antiferromagnetic transition at $T_N$=335~K. Furthermore magnetic-field-induced spin-flop transitions are observed for the AFM ground state. Our work reveals (Fe${}_{1-x}$Co${}_x$)${}_5$GeTe${}_2$ as promising candidates for developing new spin-related applications and proposes a method to engineer the magnetic properties of vdW magnet.

5 pages, 5 figures