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Register a new userHyperfine field assessment of the magnetic structure of ZrZn2
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Alexander Nikolaev Dr.
Publication date
2014
fields
Physics
and research's language is
English
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Time differential perturbed angular gamma-gamma-correlation (TDPAC) method on 111Cd nuclei probes inserted in ZrZn1.9 is used to measure the magnetic hyperfine fields (MHF) at Zr and Zn sites and the electric field gradient (EFG) Vzz at Zn sites as a function of temperature at various pressures and as a function of pressure at the temperature 4 K. Our data indicate that the local magnetic moment of Zr in the magnetically ordered state is substantially larger than its value obtained from the macroscopic measurements and that there is also an induced magnetic moment at the Zn site. We conclude that ZrZn2 is not a simple ferromagnet and discuss a possible type of its magnetic ordering.
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The magnetic structure of honeycomb iridate Na$_2$IrO$_3$ is of paramount importance to its exotic properties. The magnetic order is established experimentally to be zigzag antiferromagnetic. However, the previous assignment of ordered moment to the $bm{a}$-axis is tentative. We examine the magnetic structure of Na$_{2}$IrO$_{3}$ using first-principles methods. Our calculations reveal that total energy is minimized when the zigzag antiferromagnetic order is magnetized along $bm{g}approxbm{a}+bm{c}$. Such a magnetic configuration is explained by adding anisotropic interactions to the nearest-neighbor Kitaev-Heisenberg model. Spin-wave spectrum is also calculated, where the calculated spin gap of $10.4$ meV can in principle be measured by future inelastic neutron scattering experiments. Finally we emphasize that our proposal is consistent with all known experimental evidence, including the most relevant resonant x-ray magnetic scattering measurements [X. Liu emph{et al.} {Phys. Rev. B} textbf{83}, 220403(R) (2011)].
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We report on NMR studies of the quasi--1D antiferromagnetic $S=1/2$ chain cuprate LiCuVO$_4$, focusing on the high--field spin--modulated phase observed recently in applied magnetic fields $H > H_{rm c2}$ ($mu_0H_{rm c2} approx 7.5$ T). The NMR spectra of $^7$Li and $^{51}$V around the transition from the ordered to the paramagnetic state were measured. It is shown that the spin--modulated magnetic structure forms with ferromagnetic interactions between spins of neighboring chains within the {bf ab}--plane at low temperatures 0.6 K $ < T < T_{rm N}$. The best fit provides evidence that the mutual orientation between spins of neighboring {bf ab}--planes is random. For elevated temperatures $T_{rm N} < T lesssim 15$ K, short--range magnetic order occurs at least on the characteristic time scale of the NMR experiment.
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