135 research outputs found
History dependence of the magnetic properties of single-crystal FeCoSi
We report the magnetization, ac susceptibility, and specific heat of
optically float-zoned single crystals of FeCoSi, . We determine the magnetic phase diagrams for all major
crystallographic directions and cooling histories. After zero-field cooling,
the phase diagrams resemble that of the archetypal stoichiometric cubic chiral
magnet MnSi. Besides the helical and conical state, we observe a pocket of
skyrmion lattice phase just below the helimagnetic ordering temperature. At the
phase boundaries between these states evidence for slow dynamics is observed.
When the sample is cooled in small magnetic fields, the phase pocket of
skyrmion lattice may persist metastably down to lowest temperatures. Taken
together with the large variation of the transition temperatures, transition
fields, and the helix wavelength as a function of composition, this hysteresis
identifies FeCoSi as an ideal material for future experiments
exploring, for instance, the topological unwinding of the skyrmion lattice.Comment: 14 pages, 11 figure
Extending MIEZE spectroscopy towards thermal wavelengths
We propose a Modulation of intensity with zero effort (MIEZE) set-up for
high-resolution neutron spectroscopy at momentum transfers up to
3\AA,energy transfers up to ~ 20 meV, and an energy resolution in the
eV-range using both thermal and cold neutrons. MIEZE has two prominent
advantages compared to classical neutron spin-echo. The first one is the
possibility to investigate spin-depolarizing samples or samples in strong
magnetic fields without loss of signal amplitude and intensity. This allows for
the study of spin fluctuations in ferromagnets, and facilitates the study of
samples with strong spin-incoherent scattering. The second advantage is that
multi-analyzer setups can be implemented with comparatively small effort. The
use of thermal neutrons increases the range of validity of the spin-echo
approximation towards shorter spin-echo times. In turn, the thermal MIEZE
option for greater ranges (TIGER) closes the gap between classical neutron
spin-echo spectroscopy and conventional high-resolution neutron spectroscopy
techniques such as triple-axis, time-of-flight, and back-scattering. To
illustrate the feasibility of TIGER we present the details of an implementation
at the beamline RESEDA at FRM II by means of an additional velocity selector,
polarizer and analyzer
Low-temperature properties of single-crystal CrB
We report the low-temperature properties of B-enriched single-crystal
CrB as prepared from high-purity Cr and B powder by a solid-state
reaction and optical float zoning. The electrical resistivity, ,
Hall effect, , and specific heat, , are characteristic of an
exchange-enhanced Fermi liquid ground state, which develops a slightly
anisotropic spin gap below . This observation is corroborated by the absence of a Curie dependence in
the magnetization for reported in the literature. Comparison of
with , where we infer lattice contributions from
measurements of VB, reveals strong antiferromagnetic spin fluctuations with
a characteristic spin fluctuation temperature
in the paramagnetic state, followed by a pronounced second-order mean-field
transition at , and unusual excitations around . The pronounced anisotropy of above is
characteristic of an easy-plane anisotropy of the spin fluctuations consistent
with the magnetization. The ratio of the Curie-Weiss to the Nel
temperatures, , inferred from the
magnetization, implies strong geometric frustration. All physical properties
are remarkably invariant under applied magnetic fields up to ,
the highest field studied. In contrast to earlier suggestions of local-moment
magnetism our study identifies CrB as a weak itinerant antiferromagnet
par excellence with strong geometric frustration.Comment: 15 pages, 9 figure
Ultra-high vacuum compatible induction-heated rod casting furnace
We report the design of a radio-frequency induction-heated rod casting
furnace that permits the preparation of polycrystalline ingots of intermetallic
compounds under ultra-high vacuum compatible conditions. The central part of
the system is a bespoke water-cooled Hukin crucible supporting a casting mold.
Depending on the choice of mold, typical rods have a diameter between 6 mm and
10 mm and a length up to 90 mm, suitable for single-crystal growth by means of
float-zoning. The setup is all-metal sealed and may be baked out. We find that
the resulting ultra-high vacuum represents an important precondition for
processing compounds with high vapor pressures under a high-purity argon
atmosphere up to 3 bar. Using the rod casting furnace, we succeeded to prepare
large high-quality single crystals of two half-Heusler compounds, namely the
itinerant antiferromagnet CuMnSb and the half-metallic ferromagnet NiMnSb.Comment: 5 pages, 4 figure
Turn-key module for neutron scattering with sub-micro-eV resolution
We report the development of a compact turn-key module that boosts the
resolution in quasi-elastic neutron scattering by several orders of magnitude
down to the low sub-micro-eV range. It is based on a pair of neutron resonance
spin flippers that generate a well defined temporal intensity modulation, also
known as MIEZE (Modulation of IntEnsity by Zero Effort). The module may be used
under versatile conditions, in particular in applied magnetic fields and for
depolarising and incoherently scattering samples. We demonstrate the power of
MIEZE in studies of the helimagnetic order in MnSi under applied magnetic
fields
Sub-Microsecond Time Synchronization for Network-Connected Microcontrollers
This paper presents a bare-metal implementation of the IEEE 1588 Precision Time Protocol (PTP) for network-connected microcontroller edge devices, enabling sub-microsecond time synchronization in automotive networks and multimedia applications. The implementation leverages the hardware timestamping capabilities of the microcontroller (MCU) to implement a two-stage Phase-locked loop (PLL) for offset and drift correction of the hardware clock. Using the MCU platform as a PTP master enables the distribution of a sub-microsecond accurate Global Positioning System (GPS) timing signal over a network. The performance of the system is evaluated using master-slave configurations where the platform is synchronized with a GPS, an embedded platform, and a microcontroller master. Results show that MCU platforms can be synchronized to an external GPS reference over a network with a standard deviation of 40.7 nanoseconds, enabling precise time synchronization for bare-metal microcontroller systems in various applications
Field dependence of non-reciprocal magnons in chiral MnSi
Spin waves in chiral magnetic materials are strongly influenced by the
Dzyaloshinskii-Moriya interaction resulting in intriguing phenomena like
non-reciprocal magnon propagation and magnetochiral dichroism. Here, we study
the non-reciprocal magnon spectrum of the archetypical chiral magnet MnSi and
its evolution as a function of magnetic field covering the field-polarized and
conical helix phase. Using inelastic neutron scattering, the magnon energies
and their spectral weights are determined quantitatively after deconvolution
with the instrumental resolution. In the field-polarized phase the imaginary
part of the dynamical susceptibility is shown to
be asymmetric with respect to wavevectors longitudinal to the applied
magnetic field , which is a hallmark of chiral magnetism. In the
helimagnetic phase, becomes increasingly
symmetric with decreasing due to the formation of helimagnon bands
and the activation of additional spinflip and non-spinflip scattering channels.
The neutron spectra are in excellent quantitative agreement with the low-energy
theory of cubic chiral magnets with a single fitting parameter being the
damping rate of spin waves.Comment: Paper: 10 pages, 5 figures Supplement: 8 pages, 11 figure
High-resolution neutron depolarization microscopy of the ferromagnetic transitions in NiAl and HgCrSe under pressure
We performed neutron imaging of ferromagnetic transitions in NiAl and
HgCrSe crystals. These neutron depolarization measurements revealed
bulk magnetic inhomogeneities in the ferromagnetic transition temperature with
spatial resolution of about 100~m. To obtain such spatial resolution, we
employed a novel neutron microscope equipped with Wolter mirrors as a neutron
image-forming lens and a focusing neutron guide as a neutron condenser lens.
The images of NiAl show that the sample does not homogeneously go through
the ferromagnetic transition; the improved resolution allowed us to identify a
distribution of small grains with slightly off-stoichiometric composition.
Additionally, neutron depolarization imaging experiments on the chrome spinel,
HgCrSe, under pressures up to 15~kbar highlight the advantages of the
new technique especially for small samples or sample environments with
restricted sample space. The improved spatial resolution enables one to observe
domain formation in the sample while decreasing the acquisition time despite
having a bulky pressure cell in the beam
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