Search

We report the magnetic properties of the layered heavy fermion antiferromagnet CePdGa$_{6}$, and their evolution upon tuning with the application of magnetic field and pressure. CePdGa$_{6}$ orders antiferromagnetically below $T\rm_{N}$ = 5.2 K, where there is evidence for heavy fermion behavior from an enhanced Sommerfeld coefficient. Our results are best explained by a magnetic ground state of ferromagnetically coupled layers of Ce $4f$-moments orientated along the $c$-axis, with antiferromagnetic coupling between layers. At low temperatures we observe two metamagnetic transitions for fields applied along the $c$-axis corresponding to spin-flip transitions, where the lower transition is to a different magnetic phase with a magnetization one-third of the saturated value. From our analysis of the magnetic susceptibility, we propose a CEF level scheme which accounts for the Ising anisotropy at low temperatures, and we find that the evolution of the magnetic ground state can be explained considering both antiferromagnetic exchange between nearest neighbor and next nearest neighbor layers, indicating the influence of long-range interactions. Meanwhile we find little change of $T\rm_{N}$ upon applying hydrostatic pressures up to 2.2 GPa, suggesting that significantly higher pressures are required to examine for possible quantum critical behaviors., Comment: 9 pages, 9 figures

Despite being one of the most thoroughly characterised molecular crystals, hexamethylenetetramine (HMT) and its deuterated counterpart (DHMT), are still not fully understood, especially regarding anharmonic and nuclear quantum effects. In this work, an unprecedented combination of experimental techniques, including neutron and x-ray diffraction, inelastic neutron scattering, neutron transmission, and Compton scattering, all augmented ab initio by harmonic lattice dynamics calculations, was applied. The main question that motivated the presented work was the interplay between the phonon anharmonicity and isotope and nuclear quantum effects related to the zero-point energies of proton and deuteron. Signatures of the combined effects of isotopic substitution, temperature, anharmonicity and nuclear quantum effects were found in data from all experimental methods. In the case of neutron and x-ray diffraction, these signatures manifested as systematic discrepancies between the structural and atomic displacement parameters and thermal diffuse scattering obtained from harmonic lattice calculations and their experimental counterparts. To this end, an important effect was found that could not have been explained by the harmonic lattice modelling; the reverse Ubbelohde effect, i.e. the observation that deuteration decreases hydrogen bond length in HMT. In the case of neutron transmission, further discrepancies between theoretical predictions and experimental data were found at cryogenic temperatures. Finally, applying the diabatic theory of the local potential of the intermolecular hydrogen bond in HMT, it was possible to elucidate the degree of anharmonicity of the C–H···N bonds by relating it to the magnitude of the vibrational isotope effect for the C–H bond stretching observed in inelastic and neutron Compton scattering experiments. It was found that the combined nuclear quantum and anharmonic effects of the protons (deuterons) in hydrogen bonds in HMT (DHMT) manifest as systematic discrepancies between the ab initio predictions for the widths of nuclear momentum distributions and the experimental values.

Pressure plays a key role in the study of quantum materials. Its application in angle resolved photoemission (ARPES) studies, however, has so far been limited. Here, we report the evolution of the k-space electronic structure of bulk Ca2RuO4, lightly doped with Pr, under uniaxial strain. Using ultrathin plate-like crystals, we achieve uniaxial strain levels up to −4.1%, sufficient to suppress the insulating Mott phase and access the previously unexplored electronic structure of the metallic state at low temperature. ARPES experiments performed while tuning the uniaxial strain reveal that metallicity emerges from a marked redistribution of charge within the Ru t2g shell, accompanied by a sudden collapse of the spectral weight in the lower Hubbard band and the emergence of a well-defined Fermi surface which is devoid of pseudogaps. Our results highlight the profound roles of lattice energetics and of the multiorbital nature of Ca2RuO4 in this archetypal Mott transition and open new perspectives for spectroscopic measurements., The role of the lattice in the correlated metal-insulator transition of Ca2RuO4 has led to significant interest but experiments that are at the same time sensitive to crystal and electronic structure are difficult. Riccò et al. successfully combine ARPES measurements with in situ strain tuning across the Mott transition.

We have synthesized a single-crystalline sample of ${\mathrm{Mn}}_{2}{\mathrm{V}}_{2}{\mathrm{O}}_{7}$ using the floating zone technique, and we investigated the ground state using magnetic susceptibility, heat capacity, and neutron diffraction. Our magnetic susceptibility and heat capacity reveal two successive magnetic transitions at ${T}_{N1}=17\phantom{\rule{4pt}{0ex}}\mathrm{K}$ and ${T}_{N2}=11.8\phantom{\rule{4pt}{0ex}}\mathrm{K}$ indicating two distinct magnetically ordered phases. The single-crystal neutron diffraction study shows that in the temperature ($T$) range $11.8\ensuremath{\le}T\ensuremath{\le}17\phantom{\rule{4pt}{0ex}}\mathrm{K}$ the magnetic structure is commensurate with propagation vector ${k}_{1}=(0,0.5,0)$, while upon lowering temperature below ${T}_{N2}=11.8\phantom{\rule{4pt}{0ex}}\mathrm{K}$ an incommensurate magnetic order emerges with ${k}_{2}=(0.38,0.48,0.5)$ and the magnetic structure can be represented by cycloidal modulation of the Mn spin in the $ac$ plane. We discuss the role of magnetic exchange interactions and spin-orbital coupling on the stability of the observed magnetic phase transitions.

Pyrochlore systems are ideally suited to the exploration of geometrical frustration in three dimensions, and their rich phenomenology encompasses topological order and fractional excitations. Classical spin ices provide the first context in which it is possible to control emergent magnetic monopoles, and anisotropic exchange leads to even richer behaviour associated with large quantum fluctuations. Whether the magnetic ground state of Yb2Ti2O7 is a quantum spin liquid or a ferromagnetic phase induced by a Higgs transition appears to be sample dependent. Here we have determined the role of structural defects on the magnetic ground state via the diffuse scattering of neutrons. We find that oxygen vacancies stabilise the spin liquid phase and the stuffing of Ti sites by Yb suppresses it. Samples in which the oxygen vacancies have been eliminated by annealing in oxygen exhibit a transition to a ferromagnetic phase, and this is the true magnetic ground state., Exploring the role of structural defect is essential to understand the exotic quantum spin phenoma in rare earth pyrochlores. Here the authors show oxygen vacancies can stabilise the spin liquid phase and reveal the ferromagnetic ground state when oxygen vacancies are eliminated in Yb2Ti2O7.

The chemical and magnetic structures of the series of compounds ${\mathrm{Ca}}_{2\ensuremath{-}x}{\mathrm{La}}_{x}{\mathrm{RuO}}_{4}$ $[x=0$, 0.05(1), 0.07(1), 0.12(1)] have been investigated using neutron diffraction and resonant elastic x-ray scattering. Upon La doping, the low-temperature S-$Pbca$ space group of the parent compound is retained in all insulating samples $[x\ensuremath{\le}0.07(1)]$, but with significant changes to the atomic positions within the unit cell. These changes can be characterized in terms of the local ${\mathrm{RuO}}_{6}$ octahedral coordination: with increasing doping, the structure, crudely speaking, evolves from an orthorhombic unit cell with compressed octahedra to a quasitetragonal unit cell with elongated ones. The magnetic structure on the other hand, is found to be robust, with the basic $\mathbf{k}=(0,0,0)$, $\mathbf{b}$-axis antiferromagnetic order of the parent compound preserved below the critical La doping concentration of $x\ensuremath{\approx}0.11$. The only effects of La doping on the magnetic structure are to suppress the A-centred mode, favoring the B mode instead, and to reduce the N\'eel temperature somewhat. Our results are discussed with reference to previous experimental reports on the effects of cation substitution on the ${d}^{4}$ Mott insulator ${\mathrm{Ca}}_{2}{\mathrm{RuO}}_{4}$, as well as with regard to theoretical studies on the evolution of its electronic and magnetic structure. In particular, our results rule out the presence of a proposed ferromagnetic phase, and suggest that the structural effects associated with La substitution play an important role in the physics of the system.

Magnetic materials are a cornerstone for developing spintronic devices for the transport of information via magnetic excitations. To date, relatively few materials have been investigated for the purpose of spin transport, mostly due to the paucity of suitable candidates as these materials are often chemically complex and difficult to synthesize. We present the crystal growth and a structure solution on the high-temperature crystal structure of the layered, polar ferrimagnet ${\mathrm{CaBaFe}}_{4}{\mathrm{O}}_{7}$, which is a possible new contender for spintronics research. The space group is identified as $P3$ by refinement of single crystal and powder neutron diffraction data. At 400 K, the trigonal lattice parameters are $a=11.0114(11)\phantom{\rule{4pt}{0ex}}\AA{}$ and $c=10.330(3)\phantom{\rule{4pt}{0ex}}\AA{}$. The structure is similar to the low-temperature phase with alternating layers of triangular and Kagome-arranged Fe-O tetrahedra. We also present details of the crystal growth by traveling solvent method.

Single crystal neutron diffraction is combined with synchrotron x-ray scattering to identify the different superlattice phases present in ${\text{Cs}}_{0.8}{\text{Fe}}_{1.6}{\text{Se}}_{2}$. A combination of single crystal refinements and first principles modeling are used to provide structural solutions for the $\sqrt{5}\ifmmode\times\else\texttimes\fi{}\sqrt{5}$ and $\sqrt{2}\ifmmode\times\else\texttimes\fi{}\sqrt{2}$ superlattice phases. The $\sqrt{5}\ifmmode\times\else\texttimes\fi{}\sqrt{5}$ superlattice structure is predominantly composed of ordered Fe vacancies and Fe distortions, whereas the $\sqrt{2}\ifmmode\times\else\texttimes\fi{}\sqrt{2}$ superlattice is composed of ordered Cs vacancies. The Cs vacancies only order within the plane, causing Bragg rods in reciprocal space. By mapping x-ray diffraction measurements with narrow spatial resolution over the surface of the sample, the structural domain pattern was determined, consistent with the notion of a majority antiferromagnetic $\sqrt{5}\ifmmode\times\else\texttimes\fi{}\sqrt{5}$ phase and a superconducting $\sqrt{2}\ifmmode\times\else\texttimes\fi{}\sqrt{2}$ phase.

The idea of magnetic monopoles in spin ice has enjoyed much success at intermediate temperatures, but at low temperatures a description in terms of monopole dynamics alone is insufficient. Recently, numerical simulations were used to argue that magnetic impurities account for this discrepancy by introducing a magnetic equivalent of residual resistance in the system. Here we propose that oxygen deficiency is the leading cause of magnetic impurities in as-grown samples, and we determine the defect structure and magnetism in Y2Ti2O(7-\delta) using diffuse neutron scattering and magnetization measurements. These defects are eliminated by oxygen annealing. The introduction of oxygen vacancies causes Ti4+ to transform to magnetic Ti3+ with quenched orbital magnetism, but the concentration is anomalously low. In the spin-ice material Dy2Ti2O7 we find that the same oxygen-vacancy defects suppress moments on neighbouring rare-earth sites, and that these magnetic distortions dramatically slow down the long-time monopole dynamics at sub-Kelvin temperatures., Comment: (12 pages, 5 figures; Supplementary Information available from the journal website)

We have studied the magnetostructural phase diagram of multiferroic TbMn2O5 as a function of temperature and magnetic field by neutron diffraction. Dielectric and magnetic anomalies are found to be associated with steps in the magnetic propagation vector, including a rare example of a commensurate-incommensurate transition on cooling below 24 K, and in the structural parameters. The geometrically frustrated magnetic structure is stabilized by "canted antiferroelectric" displacements of the Mn3+ ions, an example of the magnetic Jahn-Teller effect. The Tb moments order ferromagnetically at low temperatures in an applied field, while the Mn magnetic structure is largely unchanged.

To the Editor:— During the past months I have been variously interrogated whether I had any knowledge of allergic reactions after typhoid or T. A. B. vaccination. So far I have always given a negative answer. In numerous cases fainting was allegedly observed a few hours after the injections. In 1 case it was reported that a dangerous collapse had taken place. When asked why an allergic case should be suggested, physicians based their diagnosis on Theodore J. Curphey's paper "Fatal Allergic Reaction Due to Influenza Vaccine" (The Journal, April 12, p. 1062). In that report a previous paper of V. E. Roth is cited: "Thus Roth reported 9 cases of allergic reactions to typhoid vaccines, in only 4 of which the patient gave a reliable history of allergy to egg protein." As typhoid vaccine is not prepared with any egg products I supposed a misprint. Roth's paper in the

To the Editor:— Referring to the interesting paper inThe Journalby Blumstein and Johnson (Gastrointestinal Allergy Simulating Regional Enteritis, 147 :1441 [Dec. 8] 1951), I would like to mention an article I wrote in 1933 entitled "Allergic Symptoms Due to Foodstuffs ( Deut. med. Wchnschr. 59 :1281, 1933). This case has also found its way into textbooks. Urbach in his allergy text (New York, Grune & Stratton, Inc., 1943) writes: "Gutmann's case is especially striking: the patient underwent seven laparotomies within six years because of very severe intestinal spasm simulating an ileus, the true cause of the condition was finally found to be hypersensitivity to yeast in beer." The finding of an allergy to yeast as the cause of the last attack saved the patient from another operation after the spasm had been relieved with epinephrine and ephedrine.

As a rule auscultation in cases of bronchial asthma does not present any particular difficulty, there being a prolonged expiration with normal inspiration heard uniformly over all parts of the lungs, as stated by the classical school. Actually, however, there is "prolongation of both phases of the respiratory cycle and in particular that of the expiratory phase is noteworthy." The typical musical rales, sibilant and sonorous, are more accentuated during expiration and frequently altogether inaudible during inspiration. As to the differentiation from other pathological conditions causative of prolonged expiration, diagnosis will depend on the character of the breath sounds. Thus, as R. A. Cooke justly states, "The diagnosis of asthma during the active stage is not as a rule very hard to make but the diagnosis of the existence of the asthmatic state or asthmatic predisposition is by no means easy. The necessity for some measure of diagnostic technic is