اشترك بالحزمة الذهبية واحصل على وصول غير محدود شمرا أكاديميا
تسجيل مستخدم جديدTime-resolving magnetic scattering on rare-earth ferrimagnets with a bright soft-X-ray high-harmonic source
216
0
0.0
(
0
)
اسأل ChatGPT حول البحث
ﻻ يوجد ملخص باللغة العربية
We demonstrate the first time-resolved X-ray resonant magnetic scattering (tr-XRMS) experiment at the N edge of Tb at 155 eV performed using a tabletop high-brightness high-harmonic generation (HHG) source. In contrast to static X-ray imaging applications, such optical-pump X-ray-probe studies pose a different set of challenges for the ultrafast driver laser because a high photon flux of X-rays resonant with the N edge must be attained at a low repetition rate to avoid thermal damage of the sample. This laboratory-scale X-ray magnetic diffractometer is enabled by directly driving HHG in helium with terawatt-level 1 um laser fields, which are obtained through pulse compression after a high-energy kHz-repetition-rate Yb:CaF2 amplifier. The high peak power of the driving fields allows us to reach the fully phase-matching conditions in helium, which yields the highest photon flux (>2x10^9 photons/s/1% bandwidth) in the 100-220 eV spectral range, to the best of our knowledge. Our proof-of-concept tr-XRMS measurements clearly resolve the spatio-temporal evolution of magnetic domains in Co/Tb ferrimagnetic alloys with femtosecond and nanometer resolution. In addition to the ultrafast demagnetization, we observe magnetic domain expansion with a domain wall velocity similar to that induced by spin transfer torque. The demonstrated method opens up new opportunities for time-space-resolved magnetic scattering with elemental specificity on various magnetic, orbital and electronic orderings in condensed matter systems.
قيم البحث
اقرأ أيضاً
The extreme nonlinear optical process of high-harmonic generation (HHG) makes it possible to map the properties of a laser beam onto a radiating electron wavefunction, and in turn, onto the emitted x-ray light. Bright HHG beams typically emerge from
a longitudinal phased distribution of atomic-scale quantum antennae. Here, we form a transverse necklace-shaped phased array of HHG emitters, where orbital angular momentum conservation allows us to tune the line spacing and divergence properties of extreme-ultraviolet and soft X-ray high harmonic combs. The on-axis HHG emission has extremely low divergence, well below that obtained when using Gaussian driving beams, which further decreases with harmonic order. This work provides a new degree of freedom for the design of harmonic combs, particularly in the soft X-ray regime, where very limited options are available. Such harmonic beams can enable more sensitive probes of the fastest correlated charge and spin dynamics in molecules, nanoparticles and materials.
Magnetocrystalline anisotropy, the microscopic origin of permanent magnetism, is often explained in terms of ferromagnets. However, the best performing permanent magnets based on rare earths and transition metals (RE-TM) are in fact ferrimagnets, con
sisting of a number of magnetic sublattices. Here we show how a naive calculation of the magnetocrystalline anisotropy of the classic RE-TM ferrimagnet GdCo$_5$ gives numbers which are too large at 0 K and exhibit the wrong temperature dependence. We solve this problem by introducing a first-principles approach to calculate temperature-dependent magnetization vs. field (FPMVB) curves, mirroring the experiments actually used to determine the anisotropy. We pair our calculations with measurements on a recently-grown single crystal of GdCo$_5$, and find excellent agreement. The FPMVB approach demonstrates a new level of sophistication in the use of first-principles calculations to understand RE-TM magnets.
Hard x-ray scattering (HXS) experiments with a photon energy of 100keV were performed as a function of temperature and applied magnetic field on selected compounds of the RFe$_3$(BO$_3$)$_4$ family. The results show the presence of several unexpected
diffraction features, in particular non-resonant magnetic reflections in the magnetically ordered phase, and structural reflections that violate the diffraction conditions for the low temperature phase $P3_121$ of the rare-earth iron borates. The temperature and field dependence of the magnetic superlattice reflections corroborate the magnetic structures of the borate compounds obtained by neutron diffraction. The detailed analysis of the intensity and scattering cross section of the magnetic reflection reveals details of the magnetic structure of these materials such as the spin domain structure of NdFe$_3$(BO$_3$)$_4$ and GdFe$_3$(BO$_3$)$_4$. Furthermore we find that the correlation length of the magnetic domains is around 100 AA{} for all the compounds and that the Fe moments are rotated $53^circpm3^circ$ off from the hexagonal basal plane in GdFe$_3$(BO$_3$)$_4$
We present an experimental technique for realizing a specific absorption spectral pattern in a rare-earth-doped crystal at cryogenic temperatures. This pattern is subsequently probed on two spectral channels simultaneously, thereby producing an error
signal allowing frequency locking of a laser on the said spectral pattern. Appropriate combination of the two channels leads to a substantial reduction of the detection noise, paving the way to realizing an ultra-stable laser for which the detection noise can be made arbitrarily low when using multiple channels. We use such technique to realize a laser with a frequency instability of $1.7times 10^{-15}$ at 1 second, not limited by the detection noise but by environmental perturbation of the crystal. This is comparable with the lowest instability demonstrated at 1 second to date for rare-earth doped crystal stabilized lasers.
Electroactive polymer thin films undergo repeated reversible structural change during operation in electrochemical applications. While synchrotron X-ray scattering is powerful for the characterization of stand-alone and ex-situ organic thin films, in
situ structural characterization has been underutilized--in large part due to complications arising from supporting electrolyte scattering. This has greatly hampered the development of application relevant structure property relationships. Therefore, we have developed a new methodology for in situ and operando X-ray characterization that separates the incident and scattered X-ray beam path from the electrolyte. As a proof of concept, we demonstrate the in situ structural changes of weakly-scattering, organic mixed ionic-electronic conductor thin films in an aqueous electrolyte environment, enabling access to previously unexplored changes in the pi-pi peak and diffuse scatter in situ, while capturing the solvent swollen thin film structure which was inaccessible in previous ex situ studies. These in situ measurements improve the sensitivity to structural changes, capturing minute changes not possible ex situ, and have multimodal potential such as combined Raman measurements that also serve to validate the true in situ/operando conditions of the cell. Finally, we examine new directions enabled by this operando cell design and compare state of the art measurements.
سجل دخول لتتمكن من نشر تعليقات
التعليقات
جاري جلب التعليقات
سجل دخول لتتمكن من متابعة معايير البحث التي قمت باختيارها
