22 research outputs found
Circularly polarized resonant soft x-ray diffraction study of helical magnetism in hexaferrite
Magnetic spiral structures can exhibit ferroelectric moments as recently
demonstrated in various multiferroic materials. In such cases the helicity of
the magnetic spiral is directly correlated with the direction of the
ferroelectric moment and measurement of the helicity of magnetic structures is
of current interest. Soft x-ray resonant diffraction is particularly
advantageous because it combines element selectivity with a large magnetic
cross-section. We calculate the polarization dependence of the resonant
magnetic x-ray cross-section (electric dipole transition) for the basal plane
magnetic spiral in hexaferrite Ba0.8Sr1.2Zn2Fe12O22 and deduce its domain
population using circular polarized incident radiation. We demonstrate there is
a direct correlation between the diffracted radiation and the helicity of the
magnetic spiral.Comment: 4 pages, 4 figure
Melting of chiral order in terbium manganate (TbMnO3) observed with resonant x-ray Bragg diffraction
Resonant Bragg diffraction of soft, circularly polarized x-rays has been used
to observe directly the temperature dependence of chiral-order melting in a
motif of Mn ions in terbium manganate. The underlying mechanism uses the b-axis
component of a cycloid, which vanishes outside the polar phase. Melting is
witnessed by the first and second harmonics of a cycloid, and we explain why
the observed temperature dependence is different in the two harmonics. Our
direct observation of melting is supported by a solid foundation of evidence,
derived from extensive studies of the azimuthal-angle dependence of intensities
with both linear and circular polarization
Origin of the large polarization in multiferroic YMnO thin films revealed by soft and hard x-ray diffraction
We investigated the magnetic structure of an orthorhombic YMnO3 thin film by
resonant soft x-ray and hard x-ray diffraction. We observed a
temperature-dependent incommensurate magnetic reflection below 45 K and a
commensurate lattice-distortion reflection below 35 K. These results
demonstrate that the ground state is composed of coexisting E-type and
cycloidal states. Their different ordering temperatures clarify the origin of
the large polarization to be caused by the E-type antiferromagnetic states in
the orthorhombic YMnO3 thin film.Comment: 4 pages, 6 figure
A Real Space Description of Magnetic Field Induced Melting in the Charge Ordered Manganites: I. The Clean Limit
We study the melting of charge order in the half doped manganites using a
model that incorporates double exchange, antiferromagnetic superexchange, and
Jahn-Teller coupling between electrons and phonons. We primarily use a real
space Monte Carlo technique to study the phase diagram in terms of applied
field and temperature , exploring the melting of charge order with
increasing and its recovery on decreasing . We observe hysteresis in
this response, and discover that the `field melted' high conductance state can
be spatially inhomogeneous even without extrinsic disorder. The hysteretic
response plays out in the background of field driven equilibrium phase
separation. Our results, exploring , , and the electronic parameter
space, are backed up by analysis of simpler limiting cases and a Landau
framework for the field response. This paper focuses on our results in the
`clean' systems, a companion paper studies the effect of cation disorder on the
melting phenomena.Comment: 16 pages, pdflatex, 11 png fig