25 research outputs found
Neutron scattering study of magnetic phase separation in nanocrystalline LaCaMnO
We demonstrate that magnetic phase separation and competing spin order in the
colossal magnetoresistive (CMR) manganites can be directly explored via tuning
strain in bulk samples of nanocrystalline LaCaMnO. Our results
show that strain can be reversibly frozen into the lattice in order to
stabilize coexisting antiferromagnetic domains within the nominally
ferromagnetic metallic state of LaCaMnO. The measurement of
tunable phase separation via magnetic neutron powder diffraction presents a
direct route of exploring the correlated spin properties of phase separated
charge/magnetic order in highly strained CMR materials and opens a potential
avenue for realizing intergrain spin tunnel junction networks with enhanced CMR
behavior in a chemically homogeneous material.Comment: 6 pages, 4 figures. New figure and text added to manuscrip
Magnetic order and the electronic ground state in the pyrochlore iridate Nd2Ir2O7
We report a combined muon spin relaxation/rotation, bulk magnetization,
neutron scattering, and transport study of the electronic properties of the
pyrochlore iridate Nd2Ir2O7. We observe the onset of strongly hysteretic
behavior in the temperature dependent magnetization below 120 K, and an abrupt
increase in the temperature dependent resistivity below 8 K. Zero field muon
spin relaxation measurements show that the hysteretic magnetization is driven
by a transition to a magnetically disordered state, and that below 8 K a
complex magnetically ordered ground state sets in, as evidenced by the onset of
heavily damped spontaneous muon precession. Our measurements point toward the
absence of a true metal-to-insulator phase transition in this material and
suggest that Nd2Ir2O7 lies either within or on the metallic side of the
boundary of the Dirac semimetal regime within its topological phase diagram.Comment: 21 pages, 7 figure
First-order magnetic and structural phase transitions in FeSeTe
We use bulk magnetic susceptibility, electronic specific heat, and neutron
scattering to study structural and magnetic phase transitions in FeSe%
Te. FeTe exhibits a first order phase transition near 67
K with a tetragonal to monoclinic structural transition and simultaneously
develops a collinear antiferromagnetic (AF) order responsible for the entropy
change across the transition. Systematic studies of FeSeTe system
reveal that the AF structure and lattice distortion in these materials are
different from those of FeAs-based pnictides. These results call into question
the conclusions of present density functional calculations, where
FeSeTe and FeAs-based pnictides are expected to have similar Fermi
surfaces and therefore the same spin-density-wave AF order.Comment: 5 pages, 3 figure
Magnetic quantum oscillations in YBaCuO and YBaCuO in fields of up to 85 T; patching the hole in the roof of the superconducting dome
We measure magnetic quantum oscillations in the underdoped cuprates
YBaCuO with , 0.69, using fields of up to 85 T. The
quantum-oscillation frequencies and effective masses obtained suggest that the
Fermi energy in the cuprates has a maximum at . On either
side, the effective mass may diverge, possibly due to phase transitions
associated with the T=0 limit of the metal-insulator crossover (low- side),
and the postulated topological transition from small to large Fermi surface
close to optimal doping (high side)
Spin ordering and electronic texture in the bilayer iridate SrIrO
Through a neutron scattering, charge transport, and magnetization study, the
correlated ground state in the bilayer iridium oxide SrIrO is
explored. Our combined results resolve scattering consistent with a high
temperature magnetic phase that persists above 600 K, reorients at the
previously defined K, and coexists with an electronic ground state
whose phase behavior suggests the formation of a fluctuating charge or orbital
phase that freezes below K. Our study provides a window into
the emergence of multiple electronic order parameters near the boundary of the
metal to insulator phase transition of the 5d Mott phase.Comment: Revised text and figures. 4 pages, 4 figure
Magnetic Order in the Pyrochlore Iridates A2Ir2O7 (A = Y, Yb)
We present results from muon spin relaxation/rotation, magnetization, neutron
scattering and transport measurements on polycrystalline samples of the
pyrochlore iridates Y2Ir2O7 (Y-227) and Yb2Ir2O7 (Yb-227). Well-defined
spontaneous oscillations of the muon asymmetry are observed together with
hysteretic behavior in magnetization below 130 K in Yb-227, indicative of
commensurate long-range magnetic order. Similar oscillations are observed in
Y-227 below 150 K; however the onset of hysteretic magnetization at T = 190 K
indicates a transition to an intermediate state lacking long-range order as
observed in Nd-227. Our results also show that insulating members of the
iridate family have nearly identical magnetic ground states, and that the
presence of magnetic A-site species does not play any significant role in
altering the ground state properties