Quasi-two-dimensional magnetism and antiferromagnetic ground state in Li${}_2$FeSiO${}_4$

Abstract

Our experimental (neutron diffraction, Mössbauer spectroscopy, magnetic susceptibility, specific heat) and numerical studies on the evolution of short- and long-range magnetic order in ${\gamma }_{\mathrm{II}}$-Li\(_2\)FeSiO\(_4\) suggest a quasi-two-dimensional (2D) nature of magnetism. The experimental data obtained on single crystals imply long-range antiferromagnetic order below $T_{\mathrm{N}}=17$~K. A broad maximum in magnetic susceptibility $\chi$ at $T_{\mathrm{m}}\simeq 28$~K, observation of magnetic entropy changes up to 100~K and anisotropy in $\chi$ are indicative of low-dimensional magnetism and suggest short-range magnetic correlations up to 200~K. Neutron diffraction shows that long-range antiferromagnetic order is characterised by the propagation vector k=(1/2,0,1/2). The ordered moment $\mu =2.50(2){\mu }_B$ /Fe, at $T=1.5$~K, is along the crystallographic $a$-axis. This is consistent with the observed static hyperfine field of $B_{\mathrm{hyp}}=14.8(3)$\,T by Mössbauer spectroscopy which indicates significant orbital contributions. The temperature dependence of $B_{\mathrm{hyp}}$ yields the critical exponent $\beta =0.116(12)$ which is in the regime of the 2D Ising behaviour. LSDA+U studies exploiting the experimental spin structure suggest dominating magnetic exchange coupling within the $ac$-layers (i.e., $J_3\simeq -6$~K and $J_6\simeq -2$~K) while interlayer coupling is much smaller and partly frustrated. This confirms the 2D nature of magnetism and is in full agreement with the experimental findings.

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Cited by in corpus (1)

• Critical behavior and evidence of dimensional crossover in quasi-two-dimensional Li${}_2$FeSiO${}_4$