32 research outputs found
Cooperative Jahn-Teller transition and resonant x-ray scattering in thin film
Epitaxial thin films of stoichiometric were grown on substrates using the pulsed laser deposition technique. From the
high resolution x-ray diffraction measurements, the lattice parameters were
determined as a function of temperature and the cooperative Jahn-Teller
transition was found to occur at =573.0 K. Also measured was resonant
x-ray scattering intensity of the orthorhombic (100) peak of
near the Mn K edge from low temperatures to above . We demonstrate that
the integrated intensity of the (100) peak is proportional to the 3/2 power of
the orthorhombic strain at all temperatures, and thus provide an experimental
evidence that the resonant scattering near the Mn K edge in is
largely due to the Jahn-Teller effect.Comment: 13 pages, 4 figure
Average Lattice Symmetry and Nanoscale Structural Correlations in Magnetoresistive Manganites
We report x-ray scattering studies of nanoscale structural correlations in
the paramagnetic phases of the perovskite manganites
La(CaSr)MnO,
LaSrMnO, and NdSrMnO. We find
that these correlations are present in the orthorhombic phase in
La(CaSr)MnO, but they disappear
abruptly at the orthorhombic-to-rhombohedral transition in this compound. The
orthorhombic phase exhibits increased electrical resistivity and reduced
ferromagnetic coupling, in agreement with the association of the nanoscale
correlations with insulating regions. In contrast, the correlations were not
detected in the two other compounds, which exhibit rhombohedral and tetragonal
phases. Based on these results, as well as on previously published work, we
propose that the local structure of the paramagnetic phase correlates strongly
with the average lattice symmetry, and that the nanoscale correlations are an
important factor distinguishing the insulating and the metallic phases in these
compounds.Comment: a note on recent experimental work, and a new reference adde
Persistent magnetoresistive memory in phase separated manganites
We have studied magnetic and transport properties on different manganese
oxide based compounds exhibiting phase separation: polycrystalline
La5/8-yPryCa3/8MnO3 (y=0.3) and La1/2Ca1/2Mn1-zFezO3 (z = 0.05), and single
crystals of La5/8-yPryCa3/8MnO3 (y=0.35). Time dependent effects indicate that
the fractions of the coexisting phases are dynamically changing in a definite
temperature range. We found that in this range the ferromagnetic fraction f can
be easily tuned by application of low magnetic fields (< 1 T). The effect is
persistent after the field is turned off, thus the field remains imprinted in
the actual value of f and can be recovered through transport measurements. This
effect is due both to the existence of a true phase separated equilibrium state
with definite equilibrium fraction f0, and to the slow growth dynamics. The
fact that the same global features were found on different compounds and in
polycrystalline and single crystalline samples, suggests that the effect is a
general feature of some phase separated media.Comment: Proceedings of the MISM-2002 Moscow International Symposium on
Magnetism, Moscow, 20-24 June 2002. To appear in Journal of Magnetism and
Magnetic Material
Universal Static and Dynamic Properties of the Structural Transition in Pb(Zn1/3Nb2/3)O3
The relaxors Pb(ZnNb)O (PZN) and
Pb(MgNb)O (PMN) have very similar properties based on the
dielectric response around the critical temperature (defined by the
structural transition under the application of an electric field). It has been
widely believed that these materials are quite different below with the
unit cell of PMN remaining cubic while in PZN the low temperature unit cell is
rhombohedral in shape. However, this has been clarified by recent high-energy
x-ray studies which have shown that PZN is rhombohedral only in the skin while
the shape of the unit cell in the bulk is nearly cubic. In this study we have
performed both neutron elastic and inelastic scattering to show that the
temperature dependence of both the diffuse and phonon scattering in PZN and PMN
is very similar. Both compounds show a nearly identical recovery of the soft
optic mode and a broadening of the acoustic mode below . The diffuse
scattering in PZN is suggestive of an onset at the high temperature Burns
temperature similar to that in PMN. In contrast to PMN, we observe a broadening
of the Bragg peaks in both the longitudinal and transverse directions below
. We reconcile this additional broadening, not observed in PMN, in terms
of structural inhomogeneity in PZN. Based on the strong similarities between
PMN and PZN, we suggest that both materials belong to the same universality
class and discuss the relaxor transition in terms of the three-dimensional
Heisenberg model with cubic anisotropy in a random field.Comment: 11 pages, 10 figures. Updated version after helpful referee comment
Modelling of strain effects in manganite films
Thickness dependence and strain effects in films of
perovskites are analyzed in the colossal magnetoresistance regime. The
calculations are based on a generalization of a variational approach previously
proposed for the study of manganite bulk. It is found that a reduction in the
thickness of the film causes a decrease of critical temperature and
magnetization, and an increase of resistivity at low temperatures. The strain
is introduced through the modifications of in-plane and out-of-plane electron
hopping amplitudes due to substrate-induced distortions of the film unit cell.
The strain effects on the transition temperature and transport properties are
in good agreement with experimental data only if the dependence of the hopping
matrix elements on the bond angle is properly taken into account.
Finally variations of the electron-phonon coupling linked to the presence of
strain turn out important in influencing the balance of coexisting phases in
the filmComment: 7 figures. To be published on Physical Review
Efficacy and Safety of Nivolumab Plus Ipilimumab in Patients With Advanced Hepatocellular Carcinoma Previously Treated With Sorafenib The CheckMate 040 Randomized Clinical Trial
IMPORTANCE Most patients with hepatocellular carcinoma (HCC) are diagnosed with
advanced disease not eligible for potentially curative therapies; therefore, new treatment
options are needed. Combining nivolumab with ipilimumab may improve clinical outcomes
compared with nivolumab monotherapy.
OBJECTIVE To assess efficacy and safety of nivolumab plus ipilimumab in patients with
advanced HCC who were previously treated with sorafenib.
DESIGN, SETTING, AND PARTICIPANTS CheckMate 040 is a multicenter, open-label,
multicohort, phase 1/2 study. In the nivolumab plus ipilimumab cohort, patients were
randomized between January 4 and September 26, 2016. Treatment group information was
blinded after randomization. Median follow-up was 30.7 months. Data cutoff for this analysis
was January 2019. Patients were recruited at 31 centers in 10 countries/territories in Asia,
Europe, and North America. Eligible patients had advanced HCC (with/without hepatitis B or
C) previously treated with sorafenib. A total of 148 patients were randomized (50 to arm A
and 49 each to arms B and C).
INTERVENTIONS Patients were randomized 1:1:1 to either nivolumab 1 mg/kg plus ipilimumab 3
mg/kg, administered every 3 weeks (4 doses), followed by nivolumab 240 mg every 2 weeks
(arm A); nivolumab 3 mg/kg plus ipilimumab 1 mg/kg, administered every 3 weeks (4 doses),
followed by nivolumab 240 mg every 2 weeks (arm B); or nivolumab 3 mg/kg every 2 weeks
plus ipilimumab 1 mg/kg every 6 weeks (arm C).
MAIN OUTCOMES AND MEASURES Coprimary end points were safety, tolerability, and objective
response rate. Duration of response was also measured (investigator assessed with the
Response Evaluation Criteria in Solid Tumors v1.1).
RESULTS Of 148 total participants, 120 were male (81%). Median (IQR) age was 60
(52.5-66.5). At data cutoff (January 2019), the median follow-up was 30.7 months (IQR,
29.9-34.7). Investigator-assessed objective response rate was 32% (95% CI, 20%-47%) in
arm A, 27% (95% CI, 15%-41%) in arm B, and 29% (95% CI, 17%-43%) in arm C. Median
(range) duration of response was not reached (8.3-33.7+) in arm A and was 15.2 months
(4.2-29.9+) in arm B and 21.7 months (2.8-32.7+) in arm C. Any-grade treatment-related
adverse events were reported in 46 of 49 patients (94%) in arm A, 35 of 49 patients (71%) in
arm B, and 38 of 48 patients (79%) in arm C; there was 1 treatment-related death (arm A;
grade 5 pneumonitis).
CONCLUSIONS AND RELEVANCE In this randomized clinical trial, nivolumab plus ipilimumab
had manageable safety, promising objective response rate, and durable responses. The arm A
regimen (4 doses nivolumab 1 mg/kg plus ipilimumab 3 mg/kg every 3 weeks then nivolumab
240 mg every 2 weeks) received accelerated approval in the US based on the results of this
study.
TRIAL REGISTRATION ClinicalTrials.gov Identifier: NCT0165887