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تسجيل مستخدم جديدFrustrated Magnetism in Fluoride and Chalcogenide Pyrochlore Lattice Materials
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Pyrochlore lattices, which are found in two important classes of materials -- the $A_2B_2X_7$ pyrochlore family and the $AB_2X_4$ spinel family -- are the quintessential 3-dimensional frustrated lattice architecture. While historically oxides ($X =$~O) have played the starring role in this field, the past decade has seen materials synthesis breakthroughs that have lead to the emergence of fluoride ($X =$~F) and chalcogenide ($X =$~S, Se) pyrochlore lattice materials. In this Research Update, we summarize recent progress in understanding the magnetically frustrated ground states in three families of non-oxide pyrochlore lattice materials: (i) $3d$-transition metal fluoride pyrochlores, (ii) rare earth chalcogenide spinels, and (iii) chromium chalcogenide spinels with a breathing pyrochlore lattice. We highlight how the change of anion can modify the single ion spin anisotropy due to crystal electric field effects, stabilize the incorporation of new magnetic elements, and dramatically alter the exchange pathways and thereby lead to new magnetic ground states. We also consider a range of future directions -- materials with the potential to define the next decade of research in frustrated magnetism.
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Muon spin relaxation experiments have been performed in the pyrochlore iridate Pr_2Ir_2O_7 for temperatures in the range 0.025-250 K. Kubo-Toyabe relaxation functions are observed up to > 200 K, indicating static magnetism over this temperature range
. The T -> 0 static muon spin relaxation rate Delta(0) ~ 8 mus^-1 implies a weak quasistatic moment (~0.1 mu_B). The temperature dependence of Delta is highly non-mean-field-like, decreasing smoothly by orders of magnitude but remaining nonzero below ~150 K. The data rule out ordering of the full Pr^3+ CEF ground-state moment (3.0 mu_B) down to 0.025 K. The weak static magnetism is most likely due to hyperfine-enhanced ^141Pr nuclear magnetism. The dynamic relaxation rate lambda increases markedly below ~20 K, probably due to slowing down of spin fluctuations in the spin-liquid state. At low temperatures lambda is strong and temperature-independent, indicative of a high density of low-lying spin excitations as is common in frustrated antiferromagnets.
Strong spin-lattice coupling and prominent frustration effects observed in the 50$%$ Fe-doped frustrated hexagonal ($h$)LuMnO$_3$ are reported. A N{e}el transition at $T_{mathrm N} approx$ 112~K and a possible spin re-orientation transition at $T_{ma
thrm {SR}} approx$ 55~K are observed in the magnetization data. From neutron powder diffraction data, the nuclear structure at and below 300~K was refined in polar $P6_3cm$ space group. While the magnetic structure of LuMnO$_3$ belongs to the $Gamma_4$ ($P6_3cm$) representation, that of LuFe$_{0.5}$Mn$_{0.5}$O$_3$ belongs to $Gamma_1$ ($P6_3cm$) which is supported by the strong intensity for the $mathbf{(100)}$ reflection and also judging by the presence of spin-lattice coupling. The refined atomic positions for Lu and Mn/Fe indicate significant atomic displacements at $T_{mathrm N}$ and $T_{mathrm {SR}}$ which confirms strong spin-lattice coupling. Our results complement the discovery of room temperature multiferroicity in thin films of $h$LuFeO$_3$ and would give impetus to study LuFe$_{1-x}$Mn$_x$O$_3$ systems as potential multiferroics where electric polarization is linked to giant atomic displacements.
Magnetic ($chi$), transport ($rho$) and heat capacity ($C_m$)properties of CeIrSi are investigated to elucidate the effect of geometric frustration in this compound with trillium type structure because, notwithstanding its robust effective moment, $m
u_{rm eff}approx 2.46mu_B$, this Ce-lattice compound does not undergo a magnetic transition. In spite of that it shows broad $C_m(T)/T$ and $chi(T)$ maxima centered at $T_{max}approx 1.5$,K, while a $rho propto T^2$ thermal dependence, characteristic of electronic spin coherent fluctuations, is observed below $T_{coh} approx 2.5$,K. Magnetic field does not affect significantly the position of the mentioned maxima up to $approx 1$,T, though $chi(T)$ shows an incipient structure that completely vanishes at $mu_0 H approx 1$,T. Concerning the $rho propto T^2$ dependence, it is practically not affected by magnetic field up to $mu_0 H = 9$,T, with the residual resistivity $rho_0(H)$ slightly decreasing and $T_{coh}(H)$ increasing. These results are compared with the physical properties observed in other frustrated intermetallic compounds
We report neutron scattering studies of the spin correlations of the geometrically frustrated pyrochlore Tb2Mo2O7 using single crystal samples. This material undergoes a spin-freezing transition below Tg~24 K, similar to Y2Mo2O7, and has little appar
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