176 research outputs found

### Phase Diagram of the Dzyaloshinskii-Moriya Helimagnet Ba2CuGe2O7 in Canted Magnetic Fields

The evolution of different magnetic structures of non-centrosymmetric
Ba2CuGe2O7 is systematically studied as function of the orientation of the
magnetic field H. Neutron diffraction in combination with measurements of
magnetization and specific heat show a virtually identical behaviour of the
phase diagram of Ba2CuGe2O7 for H confined in both the (1,0,0) and (1,1,0)
plane. The existence of a recently proposed incommensurate double-k AF-cone
phase is confirmed in a narrow range for H close to the tetragonal c-axis. For
large angles enclosed by H and the c-axis a complexely distorted non-sinusoidal
magnetic structure has recently been observed. We show that its critical field
Hc systematically increases for larger canting. Measurements of magnetic
susceptibility and specific heat finally indicate the existence of an
incommensurate/commensurate transition for H /sim 9 T applied in the basal
(a,b)-plane and agree with a non-planar, distorted cycloidal magnetic
structure.Comment: 14 pages, 13 figure

### Cooperative ordering of gapped and gapless spin networks in Cu$_2$Fe$_2$Ge$_4$O$_{13}$

The unusual magnetic properties of a novel low-dimensional quantum
ferrimagnet Cu$_2$Fe$_2$Ge$_4$O$_{13}$ are studied using bulk methods, neutron
diffraction and inelastic neutron scattering. It is shown that this material
can be described in terms of two low-dimensional quantum spin subsystems, one
gapped and the other gapless, characterized by two distinct energy scales.
Long-range magnetic ordering observed at low temperatures is a cooperative
phenomenon caused by weak coupling of these two spin networks.Comment: 4 pages, 4 figure

### Switching of the magnetic order in CeRhIn$_{5-x}$Sn$_{x}$ in the vicinity of its quantum critical point

We report neutron diffraction experiments performed in the tetragonal
antiferromagnetic heavy fermion system CeRhIn$_{5-x}$Sn$_{x}$ in its ($x$, $T$)
phase diagram up to the vicinity of the critical concentration $x_c$ $\approx$
0.40, where long range magnetic order is suppressed. The propagation vector of
the magnetic structure is found to be $\bf{k_{IC}}$=(1/2, 1/2, $k_l$) with
$k_l$ increasing from $k_l$=0.298 to $k_l$=0.410 when $x$ increases from $x$=0
to $x$=0.26. Surprisingly, for $x$=0.30, the order has changed drastically and
a commensurate antiferromagnetism with $\bf{k_{C}}$=(1/2, 1/2, 0) is found.
This concentration is located in the proximity of the quantum critical point
where superconductivity is expected.Comment: 5 pages, 5 figures, submitted to Phys. Rev.

### Magnetic frustration in an iron based Cairo pentagonal lattice

The Fe3+ lattice in the Bi2Fe4O9 compound is found to materialize the first
analogue of a magnetic pentagonal lattice. Due to its odd number of bonds per
elemental brick, this lattice, subject to first neighbor antiferromagnetic
interactions, is prone to geometric frustration. The Bi2Fe4O9 magnetic
properties have been investigated by macroscopic magnetic measurements and
neutron diffraction. The observed non-collinear magnetic arrangement is related
to the one stabilized on a perfect tiling as obtained from a mean field
analysis with direct space magnetic configurations calculations. The
peculiarity of this structure arises from the complex connectivity of the
pentagonal lattice, a novel feature compared to the well-known case of
triangle-based lattices

### Kagom\'{e} ice state in the dipolar spin ice Dy_{2}Ti_{2}O_{7}

We have investigated the kagom\'{e} ice behavior of the dipolar spin-ice
compound Dy_{2}Ti_{2}O_{7} in magnetic field along a [111] direction using
neutron scattering and Monte Carlo simulations. The spin correlations show that
the kagom\'{e} ice behavior predicted for the nearest-neighbor (NN) interacting
model, where the field induces dimensional reduction and spins are frustrated
in each two-dimensional kagom\'{e} lattice, occurs in the dipole interacting
system. The spins freeze at low temperatures within the macroscopically
degenerate ground states of the NN model.Comment: 5 pages, 3 figures, submitted to PR

### Half-ordered state in the anisotropic Haldane-gap antiferromagnet NDMAP

Neutron diffraction experiments performed on the Haldane gap material NDMAP
in high magnetic fields applied at an angle to the principal anisotropy axes
reveal two consecutive field-induced phase transitions. The low-field phase is
the gapped Haldane state, while at high fields the system exhibits
3-dimensional long-range Neel order. In a peculiar phase found at intermediate
fields only half of all the spin chains participate in the long-range ordering,
while the other half remains disordered and gapped.Comment: 4 pages, 2 figures, submitted to Phys. Rev.

### Single domain magnetic helicity and triangular chirality in structurally enantiopure Ba3NbFe3Si2O14

A novel doubly chiral magnetic order is found out in the structurally chiral
langasite compound Ba$_3$NbFe$_3$Si$_2$O$_{14}$. The magnetic moments are
distributed over planar frustrated triangular lattices of triangle units. On
each of these they form the same triangular configuration. This ferro-chiral
arrangement is helically modulated from plane to plane. Unpolarized neutron
scattering on a single crystal associated with spherical neutron polarimetry
proved that a single triangular chirality together with a single helicity is
stabilized in an enantiopure crystal. A mean field analysis allows discerning
the relevance on this selection of a twist in the plane to plane
supersuperexchange paths

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