As-prepared, single-crystalline bismuth ferrite nanoparticles show strong size-dependent magnetic properties that correlate with: (a) increased suppression of the known spiral spin structure (period ...length of ∼62 nm) with decreasing nanoparticle size and (b) uncompensated spins and strain anisotropies at the surface. Zero-field-cooled and field-cooled magnetization curves exhibit spin-glass freezing behavior due to a complex interplay between finite size effects, interparticle interactions, and a random distribution of anisotropy axes in our nanoparticle assemblies.
The complex interplay between superconducting and magnetic phases remains poorly understood. Here, we report on the phase separation of doped holes into separate magnetic and superconducting regions ...in superoxygenated La(2-x)Sr(x)CuO(4+y), with various Sr contents. Irrespective of Sr-doping, excess oxygen raises the superconducting onset to 40 K with a coexisting magnetic spin-density wave that also orders near 40 K in each of our samples. The magnetic region is closely related to the anomalous, 1/8-hole-doped magnetic versions of La(2)CuO(4), whereas the superconducting region is optimally doped. The two phases are probably the only truly stable ground states in this region of the phase diagram. This simple two-component system is a candidate for electronic phase separation in cuprate superconductors, and a key to understanding seemingly conflicting experimental observations.
The perovskites Sr2MnRuO6 and LaSrMnRuO6 have been investigated and their properties compared with those of the broader family of A2MRuO6 double perovskites (A=Sr, La; M=Cr, Mn, Fe, Co, Ni). Neutron ...powder diffraction shows that both phases lack long‐range Mn/Ru order. Sr2MnRuO6 exhibits a cooperative Jahn–Teller distortion, conductivity that proceeds via variable‐range hopping, and antiferromagnetic (AFM) order (C‐type structure, TN≅200K, 2.05(1) μB per transition metal). LaSrMnRuO6 exhibits nearly undistorted octahedra, conductivity that proceeds via diffusion‐assisted small‐polaron hopping, and ferromagnetic (FM) order (TC≅220K, 1.60(4) μB transition metal). Band structure calculations show that AFM Mn–O–Ru coupling optimizes polarization of the Ru t2g orbitals, while FM coupling favors delocalization of the Ru t2g electrons. The transition from antiferromagnetism to ferromagnetism is linked to a loss of orbital order and stabilized over competing glassy states by delocalization of Ru t2g electrons.
Lattice parameter, particle size, and thermal expansion results obtained from high‐temperature synchrotron transmission X‐ray diffraction are reported for magnetostructual NiAs‐type MnBi nanorods ...embedded in a Bi matrix. The structural data are consistent with elevated‐temperature magnetic measurements that indicate a first‐order nanorod Curie transition at 520 K, significantly depressed from the bulk MnBi Curie temperature of 633 K. The data suggest that the unit cell volume dependence of the magnetic behavior—also known as the volume exchange striction—of the MnBi compound is the determining factor underlying this phenomenon. The results imply that materials with magnetostructural transitions of technological interest may be altered by strain effects to tailor the interatomic distances towards the critical transition values.
MnBi nanorods embedded in a Bi matrix exhibit a magnetostructural transition at a significantly lower temperature than that found in the bulk compound, as evidenced by magnetization and synchrotron X‐ray diffraction measurements obtained as a function of temperature. These results imply that materials with magnetostructural transitions of technological interest may be tailored by strain.
Single-crystalline, submicron-sized Bi2Fe409 cubes of reproducible shape have been successfully prepared using a facile, large-scale solid-state reaction employing a molten salt technique in the ...presence of a nonionic surfactant. The role of surfactant as well as alterations in the molar ratio of Bi3+ to Fe3+ precursors have been examined under otherwise identical reaction conditions and correlated with the predictive formation of different shapes of Bi2Fe4O9 products. Extensive structural characterization of as-prepared samples has been performed using scanning electron microscopy (SEM), transmission electron microscopy (TEM), high-resolution TEM (HRTEM), energy-dispersive X-ray spectroscopy (EDS), selected area electron diffraction (SAED), Mossbauer spectroscopy, and X-ray diffraction (XRD). Magnetic measurements were obtained using a superconducting quantum interference device (SQUID).
The perovskites Sr2MnRuO6 and LaSrMnRuO6 have been investigated and their properties compared with those of the broader family of A2MRuO6 double perovskites (A=Sr, La; M=Cr, Mn, Fe, Co, Ni). Neutron ...powder diffraction shows that both phases lack long-range Mn-Ru order. Sr2MnRuO6 exhibits a cooperative Jahn-Teller distortion, conductivity that proceeds via variable-range hopping, and antiferromagnetic (AFM) order (C-type structure, TN?200K, 2.05(1) kB per transition metal). LaSrMnRuO6 exhibits nearly undistorted octahedra, conductivity that proceeds via diffusion-assisted small-polaron hopping, and ferromagnetic (FM) order (TC?220K, 1.60(4) kB transition metal). Band structure calculations show that AFM Mn-O-Ru coupling optimizes polarization of the Ru t2g orbitals, while FM coupling favors delocalization of the Ru t2g electrons. The transition from antiferromagnetism to ferromagnetism is linked to a loss of orbital order and stabilized over competing glassy states by delocalization of Ru t2g electrons.
The perovskites Sr
2
MnRuO
6
and LaSrMnRuO
6
have been investigated and their properties compared with those of the broader family of A
2
MRuO
6
double perovskites (A=Sr, La; M=Cr, Mn, Fe, Co, Ni). ...Neutron powder diffraction shows that both phases lack long‐range Mn/Ru order. Sr
2
MnRuO
6
exhibits a cooperative Jahn–Teller distortion, conductivity that proceeds via variable‐range hopping, and antiferromagnetic (AFM) order (C‐type structure,
T
N
≅200K, 2.05(1) μ
B
per transition metal). LaSrMnRuO
6
exhibits nearly undistorted octahedra, conductivity that proceeds via diffusion‐assisted small‐polaron hopping, and ferromagnetic (FM) order (
T
C
≅220K, 1.60(4) μ
B
transition metal). Band structure calculations show that AFM Mn–O–Ru coupling optimizes polarization of the Ru
t
2
g
orbitals, while FM coupling favors delocalization of the Ru
t
2
g
electrons. The transition from antiferromagnetism to ferromagnetism is linked to a loss of orbital order and stabilized over competing glassy states by delocalization of Ru
t
2
g
electrons.
The perovskites ... and ... have been investigated and their properties compared with those of the broader family of ... double perovskites (A=Sr, La; M=Cr, Mn, Fe, Co, Ni). Neutron powder ...diffraction shows that both phases lack long-range Mn/Ru order. ... exhibits a cooperative Jahn-Teller distortion, conductivity that proceeds via variable-range hopping, and antiferromagnetic (AFM) order (C-type structure, T... ...200K, 2.05(1) ... per transition metal). ... exhibits nearly undistorted octahedra, conductivity that proceeds via diffusion-assisted small-polaron hopping, and ferromagnetic (FM) order (T... ...220K, 1.60(4) ... transition metal). Band structure calculations show that AFM Mn-O-Ru coupling optimizes polarization of the Ru ... orbitals, while FM coupling favors delocalization of the Ru ... electrons. The transition from antiferromagnetism to ferromagnetism is linked to a loss of orbital order and stabilized over competing glassy states by delocalization of Ru ... electrons. (ProQuest: ... denotes formulae/symbols omitted.)
