Doping-induced quantum cross-over in Er2_2Ti2−x_{2-x}Snx_xO7_7

We present the results of the investigation of magnetic properties of the Er$_2$Ti$_{2-x}$Sn$_x$O$_7$ series. For small doping values the ordering temperature decreases linearly with $x$ while the moment configuration remains the same as in the $x = 0$ parent compound. Around $x = 1.7$ doping level we observe a change in the behavior, where the ordering temperature starts to increase and new magnetic Bragg peaks appear. For the first time we present evidence of a long-range order (LRO) in Er$_2$Sn$_2$O$_7$ ($x = 2.0$) below $T_N = 130$ mK. It is revealed that the moment configuration corresponds to a Palmer-Chalker type with a value of the magnetic moment significantly renormalized compared to $x = 0$. We discuss our results in the framework of a possible quantum phase transition occurring close to $x = 1.7$.Comment: accepted in PRB Rapi

Magnetic structure and dynamics of a strongly one-dimensional cobaltII^{II} metal-organic framework

We investigate the magnetism of the Co$^{II}_4$(OH)$_2$(C$_1$$_0$H$_1$$_6$O$_4$)$_3$ metal-organic framework which displays complex inorganic chains separated from each other by distances of 1 to 2 nm, and which orders at ~5.4 K. The zero-field magnetic structure is determined using neutron powder diffraction: it is mainly antiferromagnetic but posseses a ferromagnetic component along the $\textbf{c}$-axis. This magnetic structure persists in presence of a magnetic field. Ac susceptibility measurements confirm the existence of a single thermally activated regime over 7 decades in frequency ($E/k_B\approx64 K$) whereas time-dependent relaxation of the magnetization after saturation in an external field leads to a two times smaller energy barrier. These experiments probe the slow dynamics of domain walls within the chains: we propose that the ac measurements are sensitive to the motion of existing domain walls within the chains, while the magnetization measurements are governed by the creation of domain walls.Comment: 12 pages, 14 figure

A high temperature neutron diffraction study of the double perovskite Ba 2 154SmMoO 6

Acknowledgments We acknowledge STFC for beam time provision and the University of Aberdeen for provision of a studentship (TKW)Peer reviewedPublisher PD

Variable Temperature Neutron Diffraction Study of the Oxide Ion Conductor Ba3VWO8.5

Acknowledgements We thank the UK Science and Technology Facilities Council (STFC) for provision of neutron beamtime at the ILL. This research was supported by the Leverhulme trust (RPG-2017-351 and DS-2017-073). DNT, a Leverhulme Trust Doctoral Scholar, is part of the 15 PhD scholarships of the “Leverhulme Centre for Doctoral Training in Sustainable Production of Chemicals and Materials” at the University of Aberdeen (Scotland, United Kingdom). AG is supported by the Commonwealth Scholarship CommissionPeer reviewedPostprin

(CuCl)LaTa2O7 and quantum phase transition in the (CuX)LaM2O7 family (X = Cl, Br; M = Nb, Ta)

We apply neutron diffraction, high-resolution synchrotron x-ray diffraction, magnetization measurements, electronic structure calculations, and quantum Monte-Carlo simulations to unravel the structure and magnetism of (CuCl)LaTa2O7. Despite the pseudo-tetragonal crystallographic unit cell, this compound features an orthorhombic superstructure, similar to the Nb-containing (CuX)LaNb2O7 with X = Cl and Br. The spin lattice entails dimers formed by the antiferromagnetic fourth-neighbor coupling J4, as well as a large number of nonequivalent interdimer couplings quantified by an effective exchange parameter Jeff. In (CuCl)LaTa2O7, the interdimer couplings are sufficiently strong to induce the long-range magnetic order with the Neel temperature TN~7 K and the ordered magnetic moment of 0.53 mu_B, as measured with neutron diffraction. This magnetic behavior can be accounted for by Jeff/J4~1.6 and J4~16 K. We further propose a general magnetic phase diagram for the (CuCl)LaNb2O7-type compounds, and explain the transition from the gapped spin-singlet (dimer) ground state in (CuCl)LaNb2O7 to the long-range antiferromagnetic order in (CuCl)LaTa2O7 and (CuBr)LaNb2O7 by an increase in the magnitude of the interdimer couplings Jeff/J_4, with the (CuCl)LaM2O7 (M = Nb, Ta) compounds lying on different sides of the quantum critical point that separates the singlet and long-range-ordered magnetic ground states.Comment: 13 pages, 13 figures, 4 tables + Supplementary informatio

Magnetic Phase Separation in the Oxypnictide Sr2Cr1.85 Mn1.15As2O2

The authors thank the U.K. Science and Technology Facilities Council (STFC) for provision of neutron beamtime at the ILL under the experiment code 5-31-2665. Data are available from ILL at DOI:10.5291/ILL-DATA.5-31-2665.Peer reviewedPublisher PD

A Variable Temperature Neutron Diffraction Study of Dual Ion Conducting Sr3V2O8

This research was supported by the Leverhulme Trust (RF-2020-295\4 and DS-2017-073). DNT, a Leverhulme Trust Doctoral Scholar, is part of the 15 PhD scholarships of the “Leverhulme Centre for Doctoral Training in Sustainable Production of Chemicals and Materials” at the University of Aberdeen (Scotland, United Kingdom). We acknowledge the UK Science and Technology Facilities Council (STFC) for provision of neutron beamtime at the ILL.Peer reviewedPublisher PD

Chemical Pressure Effect on the Magnetic Order of the La1.4Sr1.6Mn2O7 Bilayered Manganite

In this Communication is it shown the role of Ca-doping in stabilizing the A-type AFM structure of the optimally doped La1.4Sr1.6Mn2O7 bilayered manganite.Comment: 10 pages, 4 figure

Hydration and Ionic Conduction Mechanisms of Hexagonal Perovskite Derivatives

ACKNOWLEDGMENT S.F. and A.C.M. acknowledge STFC-GB for provision of beamtime at ISIS (DOI: 10.5286/ISIS.E.RB1920006) and the ILL. J.A.D. gratefully acknowledges the EPSRC and the MCC/Archer consortium (EP/L000202/1) for computational resources. J.A.D. also gratefully acknowledges Newcastle University for funding through a Newcastle Academic Track (NUAcT) Fellowship Funding Sources This research was supported by the Leverhulme-Trust (RPG2017-351).Peer reviewedPostprin