Electrical and thermal transport in van der Waals magnets <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML"><mml:mrow><mml:mn>2</mml:mn><mml:mi mathvariant="normal">H</mml:mi><mml:mtext>−</mml:mtext><mml:msub><mml:mi mathvariant="normal">M</mml:mi><mml:mi>x</mml:mi></mml:msub><mml:msub><mml:mi>TaS</mml:mi><mml:mn>2</mml:mn></mml:msub><mml:mo> </mml:mo><mml:mo>(</mml:mo><mml:mi mathvariant="normal">M</mml:mi><mml:mo>=</mml:mo><mml:mi>Mn</mml:mi><mml:mo>,</mml:mo><mml:mo> </mml:mo><mml:mi>Co</mml:mi><mml:mo>)</mml:mo></mml:mrow></mml:math>

Abstract

We report a detailed study of electrical and thermal transport properties in $2\mathrm{H}\text{\ensuremath{-}}{\mathrm{M}}_{x}{\mathrm{TaS}}_{2} (\mathrm{M}=\mathrm{Mn}, \mathrm{Co})$ magnets where M atoms are intercalated in the van der Waals gap. The intercalation induces ferromagnetism (FM) with an easy-plane anisotropy in $2\mathrm{H}\text{\ensuremath{-}}{\mathrm{Mn}}_{x}{\mathrm{TaS}}_{2}$, but FM with a strong uniaxial anisotropy in $2\mathrm{H}\text{\ensuremath{-}}{\mathrm{Co}}_{0.22}{\mathrm{TaS}}_{2}$, which finally evolves into a three-dimensional antiferromagnetism (AFM) in $2\mathrm{H}\text{\ensuremath{-}}{\mathrm{Co}}_{0.34}{\mathrm{TaS}}_{2}$. Temperature-dependent electrical resistivity shows metallic behavior for all samples. Thermopower is negative in the whole temperature range for $2\mathrm{H}\text{\ensuremath{-}}{\mathrm{Co}}_{x}{\mathrm{TaS}}_{2}$, whereas the sign changes from negative to positive with increasing Mn for $2\mathrm{H}\text{\ensuremath{-}}{\mathrm{Mn}}_{x}{\mathrm{TaS}}_{2}$. The diffusive thermoelectric response dominates in both high- and low-temperature ranges for all samples. A clear kink in electrical resistivity, a weak anomaly in thermal conductivity, as well as a slope change in thermopower were observed at the magnetic transitions for $2\mathrm{H}\text{\ensuremath{-}}{\mathrm{Mn}}_{0.28}{\mathrm{TaS}}_{2}$ (${T}_{\text{c}}\phantom{\rule{4pt}{0ex}}\ensuremath{\approx}$ 82 K) and $2\mathrm{H}\text{\ensuremath{-}}{\mathrm{Co}}_{0.34}{\mathrm{TaS}}_{2}$ (${T}_{\text{N}}\phantom{\rule{4pt}{0ex}}\ensuremath{\approx}$ 36 K), respectively, albeit weaker for lower $x$ crystals. Co-intercalation promoted FM to AFM transition is further confirmed by Hall resistivity; the sign change of the ordinary Hall coefficient indicates a multiband behavior in $2\mathrm{H}\text{\ensuremath{-}}{\mathrm{Co}}_{x}{\mathrm{TaS}}_{2}$.

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