304 research outputs found
Single crystal growth and anisotropy of CeRuPO
We report on the single crystal growth of the ferromagnetic Kondo lattice
system CeRuPO using a Sn flux method. Magnetic susceptibility and electrical
resistivity measurements indicate strong anisotropy of this structurally
layered compound. They evidence that the magnetic moments order
ferromagnetically along the c-direction of the tetragonal unit cell, whereas
the crystal electric field (CEF) anisotropy favors the ab-plane. Therefore,
CeRuPO presents the unusual case within rare earth systems, where the
anisotropy of the interionic exchange interaction overcomes the single ion
anisotropy due to the CEF interaction.Comment: 13 pages, 7 figures, high quality figures:
http://www.cpfs.mpg.de/~krellner
Magnetic anisotropy of YbNi4P2
We report on transport and magnetic measurements between 1.8 and 400 K on
single crystalline YbNi4P2, which was recently reported to be a heavy fermion
system with a low lying ferromagnetic transition at T_C=0.17 K, based on data
from polycrystals. The tetragonal crystal structure of YbNi4P2 presents
quasi-one-dimensional Yb chains along the c direction. Here we show that at
high temperatures, the magnetic anisotropy of YbNi4P2 is dominated by the
crystal electrical field effect with an Ising-type behaviour, which gets more
pronounced towards lower temperatures. The electrical resistivity also reflects
the strong anisotropy of the crystal structure and favours transport along c,
the direction of the Yb chains.Comment: SCES 2011 proceedings, in pres
Single crystal growth and anisotropy of CeRuPO
We report on the single crystal growth of the ferromagnetic Kondo lattice
system CeRuPO using a Sn flux method. Magnetic susceptibility and electrical
resistivity measurements indicate strong anisotropy of this structurally
layered compound. They evidence that the magnetic moments order
ferromagnetically along the c-direction of the tetragonal unit cell, whereas
the crystal electric field (CEF) anisotropy favors the ab-plane. Therefore,
CeRuPO presents the unusual case within rare earth systems, where the
anisotropy of the interionic exchange interaction overcomes the single ion
anisotropy due to the CEF interaction.Comment: 13 pages, 7 figures, high quality figures:
http://www.cpfs.mpg.de/~krellner
Magnetic field dependence of the antiferromagnetic phase transitions in Co-doped YbRh_2Si_2
We present first specific-heat data of the alloy Yb(Rh_(1-x)Co_x)_2Si_2 at
intermediate Co-contents x=0.18, 0.27, and 0.68. The results already point to a
complex magnetic phase diagram as a function of composition. Co-doping of
YbRh_2Si_2 (T_N^{x=0}=72 mK) stabilizes the magnetic phase due to the volume
decrease of the crystallographic unit cell. The magnetic phase transitions are
clearly visible as pronounced anomalies in C^{4f}(T)/T and can be suppressed by
applying a magnetic field. Going from x=0.18 to x=0.27 we observe a change from
two mean-field (MF) like magnetic transitions at T_N^{0.18}=1.1 K and
T_L^{0.18}=0.65 K to one sharp \lambda-type transition at T_N^{0.27}=1.3 K.
Preliminary measurements under magnetic field do not confirm the field-induced
first-order transition suggested in the literature. For x=0.68 we find two
transitions at T_N^{0.68}=1.14 K and T_L^{0.68}=1.06 K.Comment: Accepted for the ICM proceedings 200
Electron Spin Resonance of the Yb 4f moment in Yb(Rh1-xCox)2Si2
[published in Phys. Rev. B 85, 035119 (2012)] The evolution of spin dynamics
from the quantum critical system YbRh2Si2 to the stable trivalent Yb system
YbCo2Si2 was investigated by Electron Spin Resonance (ESR) spectroscopy. While
the Kondo temperature changes by one order of magnitude, all compositions of
the single crystalline series Yb(Rh1-xCox)2Si2 show well defined ESR spectra
with a clear Yb3+ character for temperatures below \approx 20 K. With
increasing Co-content the ESR g-factor along the c-direction strongly increases
indicating a continuous change of the ground state wave function and, thus, a
continuous change of the crystal electric field. The linewidth presents a
complex dependence on the Co-content and is discussed in terms of the Co-doping
dependence of the Kondo interaction, the magnetic anisotropy and the influence
of ferromagnetic correlations between the 4f states. The results provide
evidence that, for low Co-doping, the Kondo interaction allows narrow ESR
spectra despite the presence of a large magnetic anisotropy, whereas at high
Co-concentrations, the linewidth is controlled by ferromagnetic correlations. A
pronounced broadening due to critical correlations at low temperatures is only
observed at the highest Co-content. This might be related to the presence of
incommensurate magnetic fluctuations.Comment: 8 pages, 8 Figure
Structural and magnetic transition in CeFeAsO: separated or connected?
Using an adapted Sn-flux growth technique we obtained comparatively large
CeFeAsO single crystals of better quality than previously reported polycrystals
or single crystals, as evidenced by much sharper anomalies at the structural
and magnetic phase transitions as well as a much higher residual resistivity
ratio of 12. In the magnetically ordered phase we observe a very pronounced
metallic behavior of the in-plane resistivity, which excludes a Mott insulator
regime at low temperature. The separation Delta_T = T_0 - T_N between
structural and magnetic ordering temperatures decreases with increasing sample
quality, from 18 K in the initial reports to 6 K in the present single
crystals, demonstrating that this separation is not an intrinsic property of
the RFeAsO systems. Our results indicate that the coupling between magnetic
ordering and structural distortion is very similar in AFe2As2 and RFeAsO type
of compounds, much more similar than previously thought. The implications of
our experimental results give arguments both in favor and against the nematic
phase model.Comment: published in PRB with the title 'Coupling between the structural and
magnetic transition in CeFeAsO
Weak magnetic anisotropy in GdRhSi studied by magnetic resonance
The antiferromagnetically (AFM) ordered state of GdRhSi which
consists of AFM-stacked ferromagnetic layers is investigated by magnetic
resonance spectroscopy. The almost isotropic Gd paramagnetic resonance
becomes anisotropic in the AFM ordered region below 107 K. The emerging
internal anisotropic exchange-fields are still small enough to allow an
investigation of their magnetization dynamics by using a standard
microwave-frequency magnetic resonance technique. We could characterize this
anisotropy in detail in the ferromagnetic layers of the excitation at 9 and 34
GHz. We derived a resonance condition for the AFM ordered phase to describe the
weak in-plane anisotropic behaviour in combination with a mean-field analysis.Comment: 7 page
Anisotropic electron spin resonance of YbIr2Si2
A series of electron spin resonance (ESR) experiments were performed on a
single crystal of the heavy fermion metal YbIr2Si2 to map out the anisotropy of
the ESR-intensity I_ESR which is governed by the microwave field component of
the g-factor. The temperature dependencies of I_ESR(T) and g(T) were measured
for different orientations and compared within the range 2.6K \le T \le 16K.
The analysis of the intensity dependence on the crystal orientation with
respect to both the direction of the microwave field and the static magnetic
field revealed remarkable features: The intensity variation with respect to the
direction of the microwave field was found to be one order of magnitude smaller
than expected from the g-factor anisotropy. Furthermore, we observed a weak
basal plane anisotropy of the ESR parameters which we interpret to be an
intrinsic sample property.Comment: 10 pages, 5 figure
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