Thin film synthesis, structural analysis, and magnetic properties of novel ternary transition metal nitride MnCoN 2

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Recent high-throughput computational searches have predicted many novel ternary nitride compounds providing new opportunities for materials discovery in underexplored phase spaces. Nevertheless, there are hardly any predictions and/or syntheses that incorporate only transition metals into new ternary nitrides. Here, we report on the synthesis, structure, and properties of <a:math xmlns:a="http://www.w3.org/1998/Math/MathML"> <a:msub> <a:mi>MnCoN</a:mi> <a:mn>2</a:mn> </a:msub> </a:math> , a new ternary nitride material comprising only transition metals and N. We find that crystalline <b:math xmlns:b="http://www.w3.org/1998/Math/MathML"> <b:msub> <b:mi>MnCoN</b:mi> <b:mn>2</b:mn> </b:msub> </b:math> can be stabilized over its competing binaries, and over a tendency of this system to become amorphous, by controlling growth temperature within a narrow window slightly above ambient condition. We find that single-phase <c:math xmlns:c="http://www.w3.org/1998/Math/MathML"> <c:msub> <c:mi>MnCoN</c:mi> <c:mn>2</c:mn> </c:msub> </c:math> thin films form in a cation-disordered rocksalt crystal structure. X-ray photoelectron spectroscopy analysis suggests that <d:math xmlns:d="http://www.w3.org/1998/Math/MathML"> <d:msub> <d:mi>MnCoN</d:mi> <d:mn>2</d:mn> </d:msub> </d:math> is sensitive to oxygen through various oxides and hydroxides binding to cobalt on the surface. X-ray absorption spectroscopy is used to verify that <e:math xmlns:e="http://www.w3.org/1998/Math/MathML"> <e:msup> <e:mrow> <e:mi>Mn</e:mi> </e:mrow> <e:mrow> <e:mn>3</e:mn> <e:mo>+</e:mo> </e:mrow> </e:msup> </e:math> and <f:math xmlns:f="http://www.w3.org/1998/Math/MathML"> <f:msup> <f:mrow> <f:mi>Co</f:mi> </f:mrow> <f:mrow> <f:mn>3</f:mn> <f:mo>+</f:mo> </f:mrow> </f:msup> </f:math> cations exist in an octahedrally coordinated environment, which is distinct from a combination of CoN and MnN binaries and in agreement with the rocksalt-based crystal structure prediction. Magnetic measurements suggest that <g:math xmlns:g="http://www.w3.org/1998/Math/MathML"> <g:msub> <g:mi>MnCoN</g:mi> <g:mn>2</g:mn> </g:msub> </g:math> has a canted antiferromagnetic ground state below 10 K. We extract a Weiss temperature of <h:math xmlns:h="http://www.w3.org/1998/Math/MathML"> <h:mrow> <h:mi>θ</h:mi> <h:mo>=</h:mo> <h:mo>−</h:mo> <h:mn>49.7</h:mn> <h:mspace width="0.16em"/> <h:mi mathvariant="normal">K</h:mi> </h:mrow> </h:math> , highlighting the antiferromagnetic correlations in <k:math xmlns:k="http://www.w3.org/1998/Math/MathML"> <k:msub> <k:mi>MnCoN</k:mi> <k:mn>2</k:mn> </k:msub> </k:math> .