77 research outputs found
Magnetic Phase Transitions in NdCoAsO
Magnetization measurements reveal that NdCoAsO undergoes three magnetic phase
transitions below room temperature. The crystal and magnetic structures of
NdCoAsO have been determined by powder neutron diffraction, and the effects of
the phase transitions on physical properties are reported. Near 69 K a
ferromagnetic state emerges with a small saturation moment of about 0.2 Bohr
magnetons, likely on Co atoms. At 14 K the material enters an antiferromagnetic
state with propagation vector (0 0 1/2) and small ordered moments (~0.4 Bohr
magnetons) on Co and Nd. Near 3.5 K a third transition is observed, and
corresponds to the antiferromagnetic ordering, with the same propagation
vector, of larger moments on Nd reaching 1.30(2) Bohr magnetons at 1.4 K. In
addition, transport properties and heat capacity results are presented, and
show anomalies at all three phase transitions.Comment: Some minor changes made, and lower temperature neutron diffraction
results are included. Accepted for publication in Physical Review
Synthesis, Structure and Properties of Tetragonal Sr2M3As2O2 (M3 = Mn3, Mn2Cu and MnZn2) Compounds Containing Alternating CuO2-Type and FeAs-Type Layers
Polycrystalline samples of Sr2Mn2CuAs2O2, Sr2Mn3As2O2, and Sr2Zn2MnAs2O2 were
synthesized. Their temperature- and applied magnetic field-dependent
structural, transport, thermal, and magnetic properties were characterized by
means of x-ray and neutron diffraction, electrical resistivity rho, heat
capacity, magnetization and magnetic susceptibility measurements. These
compounds have a body-centered-tetragonal crystal structure (space group
I4/mmm) that consists of MO2 (M = Zn and/or Mn) oxide layers similar to the
CuO2 layers in high superconducting transition temperature Tc cuprate
superconductors, and intermetallic MAs (M = Cu and/or Mn) layers similar to the
FeAs layers in high-Tc pnictides. These two types of layers alternate along the
crystallographic c-axis and are separated by Sr atoms. The site occupancies of
Mn, Cu and Zn were studied using Rietveld refinements of x-ray and neutron
powder diffraction data. The temperature dependences of rho suggest metallic
character for Sr2Mn2CuAs2O2 and semiconducting character for Sr2Mn3As2O2 and
Sr2Zn2MnAs2O2. Sr2Mn2CuAs2O2 is inferred to be a ferrimagnet with a Curie
temperature TC = 95(1) K. Remarkably, we find that the magnetic ground state
structure changes from a G-type antiferromagnetic structure in Sr2Mn3As2O2 to
an A-type ferrimagnetic structure in Sr2Mn2CuAs2O2 in which the Mn ions in each
layer are ferromagnetically aligned, but are antiferromagnetically aligned
between layers.Comment: 18 pages, 16 figures, 6 tables; submitted to Phys. Rev.
Inhomogeneous magnetism in the doped kagome lattice of LaCuO2.66
The hole-doped kagome lattice of Cu2+ ions in LaCuO2.66 was investigated by
nuclear quadrupole resonance (NQR), electron spin resonance (ESR), electrical
resistivity, bulk magnetization and specific heat measurements. For
temperatures above ~180 K, the spin and charge properties show an activated
behavior suggestive of a narrow-gap semiconductor. At lower temperatures, the
results indicate an insulating ground state which may or may not be charge
ordered. While the frustrated spins in remaining patches of the original kagome
lattice might not be directly detected here, the observation of coexisting
non-magnetic sites, free spins and frozen moments reveals an intrinsically
inhomogeneous magnetism. Numerical simulations of a 1/3-diluted kagome lattice
rationalize this magnetic state in terms of a heterogeneous distribution of
cluster sizes and morphologies near the site-percolation threshold
Disorder from order among anisotropic next-nearest-neighbor Ising spin chains in SrHoO
We describe why Ising spin chains with competing interactions in segregate into ordered and disordered ensembles at low temperatures
(). Using elastic neutron scattering, magnetization, and specific heat
measurements, the two distinct spin chains are inferred to have N\'eel
() and double-N\'eel
() ground states respectively. Below
~K, the N\'eel chains develop three dimensional (3D) long
range order (LRO), which arrests further thermal equilibration of the
double-N\'eel chains so they remain in a disordered incommensurate state for
below ~K. distills an important
feature of incommensurate low dimensional magnetism: kinetically trapped
topological defects in a quasidimensional spin system can preclude order
in dimensions.Comment: 10 pages, 10 figure
Neutron scattering study of TbPtIn intermetallic compound
Neutron diffraction techniques have been used to study the magnetic properties of a TbPtIn single-crystal as a function of temperature and magnetic field. In the absence of an externally applied magnetic field, the compound orders, below approximately 47 K, in an antiferromagnetic structure with propagation vector k=(12,0,12); the magnetic moments were found to be parallel to the [12Ì„0] direction. Measurements at 4.2 K, with a magnetic field applied along the [12Ì„0] direction, revealed metamagnetic transitions at approximately 20 kG and 40 kG
Neutron diffraction studies of the magnetoelastic compounds Tb5SixGe4−x (x=2.2 and 2.5)
We report the results of a neutron diffraction study, carried out on both single crystalline and polycrystalline samples of Tb5Si2.2Ge1.8 and polycrystalline Tb5Si2.5Ge1.5. On cooling, at approximately 120 K, the Tb5Si2.2Ge1.8 system undergoes a magnetoelastic transition from a high-temperature monoclinic-paramagnetic to a low-temperature orthorhombic-ferromagnetic structure. Between 120 K and 75 K, the magnetic structure has a net ferromagnetic component along the a axis direction. The moments are slightly canted with respect to the a axis, while the components along the b and c axes are ordered antiferromagnetically. A second magnetic transition occurs at approximately 75 K. Below this temperature, the magnetic structure consists of ferromagnetically aligned μx and μz projections of the magnetic moments and an antiferromagnetic arrangement of theμy moment components. Magnetic structures of Tb5Si2.5Ge1.5 are nearly identical to those of Tb5Si2.2Ge1.8
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