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Statics and dynamics of an incommensurate spin order in a geometrically frustrated antiferromagnet CdCr$_2$O$_4$

J. -H. Chung·M. Matsuda·S. -H. Lee·K. Kakurai·H. Ueda·T. J. Sato·H. Takagi·K. -P. Hong·S. Park
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Abstract

Using elastic and inelastic neutron scattering we show that a cubic spinel, CdCr$_2$O$_4$, undergoes an elongation along the c-axis ($c > a = b$) at its spin-Peierls-like phase transition at $T_N$ = 7.8 K. The Néel phase ($T < T_N$) has an incommesurate spin structure with a characteristic wave vector \textbf{Q}$_M$ = (0,$δ$,1) with $δ\sim$ 0.09 and with spins lying on the $ac$-plane. This is in stark contrast to another well-known Cr-based spinel, ZnCr$_2$O$_4$, that undergoes a c-axis contraction and a commensurate spin order. The magnetic excitations of the incommensurate Néel state has a weak anisotropy gap of 0.6 meV and it consists of at least three bands extending up to 5 meV.

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J. -H. Chung, M. Matsuda, S. -H. Lee, K. Kakurai, H. Ueda, T. J. Sato, H. Takagi, K. -P. Hong, S. Park. 2005-10-13. Statics and dynamics of an incommensurate spin order in a geometrically frustrated antiferromagnet CdCr$_2$O$_4$. https://doi.org/10.1103/physrevlett.95.247204

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