Tuning the room temperature ferromagnetism in Fe₅GeTe₂by arsenic substitution

In order to tune the magnetic properties of the cleavable high-Curie temperature ferromagnet Fe 5-x GeTe2, the effect of increasing the electron count through arsenic substitution has been investigated. Small additions of arsenic (2.5% and 5%) seemingly enhance ferromagnetic order in polycrystalline samples by quenching fluctuations on one of the three magnetic sublattices, whereas larger As concentrations decrease the ferromagnetic Curie temperature (T C) and saturation magnetization. This work also describes the growth and characterization of Fe4.8AsTe2 single crystals that are structurally analogous to Fe 5-x GeTe2 but with some phase stability complications. Magnetization measurements reveal dominant antiferromagnetic behavior in Fe4.8AsTe2 with a Néel temperature of T N 42 K. A field-induced spin-flop below T N results in a switch from negative to positive magnetoresistance, with significant hysteresis causing butterfly-shaped resistance loops. In addition to reporting the properties of Fe4.8AsTe2, this work shows the importance of manipulating the individual magnetic sublattices in Fe 5-x GeTe2 and motivates further efforts to control the magnetic properties in related materials by fine tuning of the Fermi energy or crystal chemistry.