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Register a new userPhysical properties of CeIrSi with trillium-lattice frustrated magnetism
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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, $mu_{rm eff}approx 2.46mu_B$, 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
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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.
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.
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 $T_{mathrm {SR}} approx$ 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.
We show that pharmacosiderite is a novel cluster antiferromagnet comprising frustrated regular tetrahedra made of spin-5/2 Fe3+ ions that are arranged in the primitive cubic lattice. The connectivity of the tetrahedra and the inter-cluster interaction of 2.9 K, which is significantly large compared with the intra-cluster interaction of 10.6 K, gives a unique playground for frustration physics. An unconventional antiferromagnetic order is observed below TN ~ 6 K, which is accompanied by a weak ferromagnetic moment and a large fluctuation as evidenced by Mossbauer spectroscopy. A q = 0 magnetic order with the total S = 0 for the tetrahedral cluster is proposed based on the irreducible representation analysis, which may explain the origin of the weak ferromagnetism and fluctuation.
We study the spin-1 honeycomb lattice magnets with frustrated exchange interactions. The proposed microscopic spin model contains first and second neighbor Heisenberg interactions as well as the single-ion anisotropy. We establish a rich phase diagram that includes a featureless quantum paramagnet and various spin spiral states induced by the mechanism of order by quantum disorder. Although the quantum paramagnet is dubbed featureless, it is shown that, the magnetic excitations develop a contour degeneracy in the reciprocal space at the band minima. These contour degenerate excitations are responsible for the frustrated criticality from the quantum paramagnet to the ordered phases. This work illustrates the effects of magnetic frustration on both magnetic orderings and the magnetic excitations. We discuss the experimental relevance to various Ni-based honeycomb lattice magnets.
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