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Register a new userMagnetic order and spin dynamics in the helical magnetic system Fe$_3$PO$_4$O$_3$
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The 3$d$-electronic spin dynamics and the magnetic order in Fe$_3$PO$_4$O$_3$ were investigated by muon spin rotation and relaxation ($mu$SR) and $^{57}$Fe Mossbauer spectroscopy. Zero-field (ZF)-$mu$SR and $^{57}$Fe Mossbauer studies confirm static long range magnetic ordering below $T_{mathrm{N}}$ $approx$ 164,K. Both transverse-field (TF) and ZF-$mu$SR results evidence 100% magnetic volume fraction in the ordered state. The ZF-$mu$SR time spectra can be best described by a Bessel function, which is consistent with the helical magnetic structure proposed by neutron scattering experiments. The Mossbauer spectra are described in detail by considering the specific angular distribution of the local hyperfine field $B_{mathrm{hyp}}$ with respect to the local electric field gradient. The $mu$SR spin-lattice relaxation rate exhibits two peaks: One at the magnetic ordering temperature related to critical magnetic fluctuations and another peak at 35,K signaling the presence of a secondary low energy scale in Fe$_3$PO$_4$O$_3$.
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Magnetic frustration in Fe$_3$PO$_4$O$_3$ has been shown to produce to an unusual magnetic state below T$_N = 163$ K, where incommensurate antiferromagnetic order is restricted to nanosized needle-like domains, as inferred from neutron powder diffraction. Here we show using single-crystal neutron diffraction that Fe$_3$PO$_4$O$_3$ does not exhibit a preferred ordering wavevector direction in the $ab$ plane despite having a well-defined ordering wavevector length. This results in the observation of continuous rings of scattering rather than satellite Bragg peaks. The lack of a preferred incommensurate ordering wavevector direction can be understood in terms of an antiferromagnetic Heisenberg model with nearest-neighbor ($J_1$) and second-neighbor ($J_2$) interactions, which produces a quasi-degenerate manifold of ordering wavevectors. This state appears to be similar to the partially ordered phase of MnSi, but in Fe$_3$PO$_4$O$_3$ arises in a frustrated antiferromagnet rather than a chiral ferromagnet.
The insulating magnetic material Fe3PO4O3 features a non-centrosymmetric lattice composed of Fe^{3+} triangular units. Frustration, due to competing near neighbor ($J_1$) and next nearest neighbor ($J_2$) antiferromagnetic interactions, was recently suggested to be the origin of an antiferromagnetic helical ground state with unusual needle-like nanoscale magnetic domains in Fe3PO4O3. Magnetic dilution is shown here to tune the ratio of these magnetic interactions, thus providing deeper insight into this unconventional antiferromagnet. Dilution of the Fe^{3+} lattice in Fe3PO4O3 was accomplished by substituting non-magnetic Ga^{3+} to form the solid solution series Fe_{3-x}Ga_xPO4O3 with $x = 0.012, 0.06, 0.25, 0.5, 1.0, 1.5$. Magnetic susceptibility and neutron powder diffraction data from this series are presented. A continuous decrease of the both the helical pitch length and the domain size is observed with increasing dilution up to at least $x = 0.25$, while for $x ge 0.5$, the compounds lack long range magnetic order entirely. The decrease in the helical pitch length with increasing $x$ can be qualitatively understood by reduction of the ratio of $J_2/J_1$ in the Heisenberg model, consistent with mean field considerations. Intriguingly, the magnetic correlation length in the $ab$ plane remains nearly equal to the pitch length for each value of $x le 0.25$, showing that the two quantities are intrinsically connected in this unusual antiferromagnet.
We investigate the low temperature magnetic properties of a $S=frac{5}{2}$ Heisenberg kagome antiferromagnet, the layered monodiphosphate Li$_9$Fe$_3$(P$_2$O$_7$)$_3$(PO$_4$)$_2$, using magnetization measurements and $^{31}$P nuclear magnetic resonance. An antiferromagnetic-type order sets in at $T_{rm N}=1.3$ K and a characteristic magnetization plateau is observed at 1/3 of the saturation magnetization below $T^* sim 5$ K. A moderate $^{31}$P NMR line broadening reveals the development of anisotropic short-range correlations within the plateau phase concomitantly with a gapless spin-lattice relaxation time $T_1 sim k_B T / hbar S$, which both point to the presence of a semiclassical nematic spin liquid state predicted for the Heisenberg kagome antiferromagnetic model.
We report a neutron diffraction study of the magnetic phase transitions in the charge-density-wave (CDW) TbTe$_3$ compound. We discover that in the paramagnetic phase there are strong 2D-like magnetic correlations, consistent with the pronounced anisotropy of the chemical structure. A long-range incommensurate magnetic order emerges in TbTe$_3$ at $T_{mag1}$ = 5.78 K as a result of continuous phase transitions. We observe that near the temperature $T_{mag1}$ the magnetic Bragg peaks appear around the position (0,0,0.24) (or its rational multiples), that is fairly close to the propagation vector $(0,0,0.29)$ associated with the CDW phase transition in TbTe$_3$. This suggests that correlations leading to the long-range magnetic order in TbTe$_3$ are linked to the modulations that occur in the CDW state.
The dynamical properties of free and bound domain-wall excitations in Ising-chain materials have recently become the focus of intense research interest. New materials and spectrometers have made it possible to control the environment of coupled Ising chains by both effective internal and applied external fields, which can be both longitudinal and transverse, and thus to demonstrate how the resulting magnetic phase transitions and the nature of the associated excited states obey fundamental symmetry properties. In RbCoCl$_3$, the weakly coupled Ising chains form a triangular lattice whose frustrated geometry and magnetic ordering transitions at low temperature open new possibilities for the Ising-chain environment. We have investigated the structure and magnetism in RbCoCl$_3$ by high-resolution x-ray diffraction and neutron scattering measurements on powder and single crystal samples between 1.5 K and 300 K. Upon cooling, the Co$^{2+}$ spins develop one-dimensional antiferromagnetic correlations along the chain axis ($c$-axis) below 90 K. Below the first Neel temperature, $T_{N1}$ = 28 K, a partial 3D magnetic order sets in, with propagation vector ${vec k}_1$ = (1/3,1/3,1), the moments aligned along the $c$-axis and every third chain uncorrelated from its neighbours. Only below a second magnetic phase transition at $T_{N2}$ = 13 K does the system achieve a fully ordered state, with two additional propagation vectors: ${vec k}_2$ = (0,0,1) establishes a honeycomb $c$-axis order, in which 1/3 of the chains are subject to a strong effective mean field due to their neighbours whereas 2/3 experience no net field, while ${vec k}_3$ = (1/2,0,1) governs a small, staggered in-plane ordered moment. We conclude that RbCoCl$_3$ is an excellent material to study the physics of Ising chains in a wide variety of temperature-controlled environments.
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