Full propagation-vector star antiferromagnetic order in quantum spin trimer system $\mathrm{C}{\mathrm{a}}_3\mathrm{CuN}{\mathrm{i}}_2(\mathrm{P}{\mathrm{O}}_4{)}_4$

Abstract

We show that the antiferromagnetic structure in the quantum spin trimer system $\mathrm{C}{\mathrm{a}}_3\mathrm{CuN}{\mathrm{i}}_2(\mathrm{P}{\mathrm{O}}_4{)}_4$ is based on both arms of propagation vector $\vec{k}$ star $\{[\frac{1}{2},\frac{1}{2},0],[-\frac{1}{2},\frac{1}{2},0]\}$ of the paramagnetic space group $C2/c$. The structure is generated by a symmetric direction of the order parameter of two dimensional irreducible representation of $C2/c$ with one active magnetic mode and corresponds to the Shubnikov magnetic space group $C_{a}2/c$. We reveal the relation between representation analysis in the propagation vector formalism and Shubnikov symmetry. These types of multi-$\vec{k}$ structures are extremely rarely observed experimentally. To further prove the specific magnetic structure we have performed the calculations of the spin expectation values in the isolated Ni${}^{2+}$-Cu${}^{2+}$-Ni${}^{2+}$ trimer with realistic Hamiltonian. The calculated spin values $<S_{\mathrm{Ni}}>=0.9$ and $<S_{\mathrm{Cu}}>=0.3$ are within 10% accuracy in agreement with the experiment, providing strong complimentary argument in favor of multi-arm magnetic structure.

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References in corpus (2)

• Magnetic excitations in the spin-trimer compounds Ca3Cu3-xNix(PO4)4 (x=0,1,2)
• Crystal and magnetic structures of the spin-trimer compounds Ca3 Cu3xNix (PO4)4 (x=0,1,2)