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NaOsO3 has recently attracted significant attention for the strong coupling between its electronic band structure and magnetic ordering. Here, we used time-resolved magnetic x-ray diffraction to determine the timescale of the photoinduced antiferromagnetic dynamics in NaOsO3. Our measurements are consistent with a sub-100 fs melting of the antiferromagnetic long-range order that occurs significantly faster than the lattice dynamics as monitored by the transient change in intensity of selected Bragg structural reflections, which instead show a decrease of intensity on a timescale of several ps.

Orthorhombic $\mathrm{HoMn}{\mathrm{O}}_{3}$ is a multiferroic in which Mn antiferromagnetic order induces ferroelectricity. A second transition occurs within the multiferroic phase, in which a strong enhancement of the ferroelectric polarization occurs concomitantly to antiferromagnetic ordering of Ho $4f$ magnetic moments. Using the element selectivity of resonant x-ray diffraction, we study the magnetic order of the Mn $3d$ and Ho $4f$ moments. We explicitly show that the Mn magnetic order is affected by the Ho $4f$ magnetic ordering transition. Based on the azimuthal dependence of the $(0\phantom{\rule{0.16em}{0ex}}q\phantom{\rule{0.16em}{0ex}}0)$ and $(0\phantom{\rule{0.16em}{0ex}}1\ensuremath{-}q\phantom{\rule{0.16em}{0ex}}0)$ magnetic reflections, we suggest that the Ho $4f$ order resembles an $ac$ cycloid. Using nonresonant diffraction, we show that the magnetically induced polar lattice distortion is unaffected by the Ho ordering, suggesting a mechanism through which the Ho order affects ferroelectric polarization without affecting the lattice in the same manner as the Mn order.

Time-resolved x-ray diffraction experiments on the half-doped single-layered manganite $\mathrm{P}{\mathrm{r}}_{0.5}\mathrm{C}{\mathrm{a}}_{1.5}\mathrm{Mn}{\mathrm{O}}_{4}$ are used to monitor the ultrafast photoinduced dynamics of the structural distortion associated with the charge and orbital ordering (CO/OO). As in the nonlayered three-dimensional counterpart, the ordered phase melts in less than 100 fs after 800-nm photoexcitation and subsequently partially recovers due to thermal equilibration of electronic and vibrational systems. Photoexciting $\mathrm{P}{\mathrm{r}}_{0.5}\mathrm{C}{\mathrm{a}}_{1.5}\mathrm{Mn}{\mathrm{O}}_{4}$ below the transition temperature of a second structural phase transition that occurs around 146 K (deep inside the CO/OO phase) releases this structural transition, but progresses on a much slower timescale. This additional reduction of crystal symmetry, which we ascribe to a further tilt of the oxygen octahedra, can thus be considered to be only weakly coupled to CO/OO. Furthermore, static hard-x-ray and resonant soft-x-ray diffraction at the $\mathrm{Mn}\phantom{\rule{0.16em}{0ex}}{L}_{2,3}$ edges experiments identify correlations between structural distortions and electronic order in thermal equilibrium.

We use femtosecond x-ray diffraction to study the structural response of charge and orbitally ordered ${\mathrm{Pr}}_{1\ensuremath{-}x}{\mathrm{Ca}}_{x}{\mathrm{MnO}}_{3}$ thin films across a phase transition induced by 800 nm laser pulses. By investigating the dynamics of both superlattice reflections and regular Bragg peaks, we disentangle the different structural contributions and analyze their relevant timescales. The dynamics of the structural and charge order response are qualitatively different when excited above and below a critical fluence ${f}_{c}$. For excitations below ${f}_{c}$ the charge order and the superlattice is only partially suppressed and the ground state recovers within a few tens of nanosecond via diffusive cooling. When exciting above the critical fluence the superlattice vanishes within approximately half a picosecond followed by a change of the unit cell parameters on a 10 picoseconds timescale. At this point all memory from the symmetry breaking is lost and the recovery time increases by many order of magnitudes due to the first order character of the structural phase transition.

X-ray magnetic circular dichroism (XMCD) and x-ray magnetic linear dichroism (XMLD) have been used to investigate the Fe magnetic response during the spin-reorientation transition (SRT) in $\mathrm{TmFe}{\mathrm{O}}_{3}$. Comparing the Fe XMLD results with neutron-diffraction and magnetization measurements on the same sample indicates that the SRT has an enhanced temperature range in the near surface region of approximately 82 to 120 K compared to approximately 82 to 92 K in bulk. This view is supported by complementary resonant soft x-ray-diffraction experiments at the Tm ${M}_{5}$ edge. These measurements find an induced magnetic moment on the Tm sites, which is well described by a dipolar mean-field model originating from the Fe moments. Even though such a model can describe the $4f$ response in the experiments, it is insufficient to describe the SRT even when considering a change in the $4f$ anisotropy. Moreover, the results of the Fe XMCD show a different temperature evolution through the SRT, the interpretation of which is hampered by additional spectral shape changes of the XCMD signal.

Using resonant soft x-ray techniques we follow the magnetic behavior of a strained epitaxial film of $\mathrm{CoC}{\mathrm{r}}_{2}{\mathrm{O}}_{4}$, a type-II multiferroic. The film is [110] oriented, such that both the ferroelectric and ferromagnetic moments can coexist in-plane. X-ray magnetic circular dichroism (XMCD) is used in scattering and in transmission modes to probe the magnetization of Co and Cr separately. The transmission measurements utilized x-ray excited optical luminescence from the substrate. Resonant soft x-ray diffraction (RXD) was used to study the magnetic order of the low temperature phase. The XMCD signals of Co and Cr appear at the same ordering temperature ${T}_{C}\ensuremath{\approx}90\phantom{\rule{4pt}{0ex}}\mathrm{K}$, and are always opposite in sign. The coercive field of the Co and of Cr moments is the same, and is approximately two orders of magnitude higher than in bulk. Through sum rules analysis an enlarged $\mathrm{C}{\mathrm{o}}^{2+}$ orbital moment (${m}_{L}$) is found, which can explain this hardening. The RXD signal of the (q q 0) reflection appears below ${T}_{S}$, the same ordering temperature as the conical magnetic structure in bulk, indicating that this phase remains multiferroic under strain. To describe the azimuthal dependence of this reflection, a slight modification is required to the spin model proposed by the conventional Lyons-Kaplan-Dwight-Menyuk theory for magnetic spinels.

Chiral multiferroic langasites have attracted attention due to their doubly chiral magnetic ground state within an enantiomorphic crystal. We report on a detailed resonant soft x-ray diffraction study of the multiferroic ${\mathrm{Ba}}_{3}{\mathrm{TaFe}}_{3}{\mathrm{Si}}_{2}{\mathrm{O}}_{14}$ at the Fe ${L}_{2,3}$ and oxygen $K$ edges. Below ${T}_{N}$ ($\ensuremath{\approx}27K$) we observe the satellite reflections $(0,0,\ensuremath{\tau}), (0,0,2\ensuremath{\tau}), (0,0,3\ensuremath{\tau})$, and $(0,0,1\ensuremath{-}3\ensuremath{\tau})$ where $\ensuremath{\tau}\ensuremath{\approx}0.140\ifmmode\pm\else\textpm\fi{}0.001$. The dependence of the scattering intensity on x-ray polarization and azimuthal angle indicate that the odd harmonics are dominated by the out-of-plane ($\stackrel{\ifmmode \hat{}\else \^{}\fi{}}{\mathbf{c}}$ axis) magnetic dipole while the $(0,0,2\ensuremath{\tau})$ originates from the electron density distortions accompanying magnetic order. We observe dissimilar energy dependencies of the diffraction intensity of the purely magnetic odd-harmonic satellites at the Fe ${L}_{3}$ edge. Utilizing first-principles calculations, we show that this is a consequence of the loss of threefold crystal symmetry in the multiferroic phase.

The dressing of quasiparticles in solids is investigated by changes in the electronic structure $E$($k$) driven by femtosecond laser pulses. Employing time- and angle-resolved photoemission on an optimally doped cuprate above ${T}_{\mathrm{c}}$, we observe two effects with different characteristic temporal evolutions and, therefore, different microscopic origins. First, a marked change in the effective mass due to the 70-meV kink in $E$($k$) is found to occur during the experiment's 100-fs temporal resolution and is assigned to laser-driven perturbation of an electronic interaction dressing the bare band. Second, a change in ${k}_{\mathrm{F}}$ is explained by effective photodoping due to particle-hole asymmetry and offers opportunities for ultrafast optoelectronic switches based on an optically driven insulator-superconductor transition.

Understanding strongly correlated rare-earth intermetallic compounds requires knowledge of the nature of the fermionic quasiparticles in states near the Fermi level ${E}_{\mathrm{F}}$. We report on a pump-probe experiment using femtosecond time- and angle-resolved photoemission spectroscopy to determine lifetimes of hot quasiparticles in the heavy-fermion compound YbRh${}_{2}$Si${}_{2}$. An unoccupied band with electronlike dispersion and a band bottom 0.2 eV above ${E}_{\mathrm{F}}$ was identified at $\overline{\ensuremath{\Gamma}}$, in agreement with band structure calculations for the subsurface region. Hot quasiparticle lifetimes from 30 to 80 fs were found for energies between 0.4 and $0.1$ eV above ${E}_{\mathrm{F}}$. These lifetimes generally follow the typical monotonous increase towards ${E}_{\mathrm{F}}$, in agreement with earlier studies on Yb and Rh elemental metals. However, at normal emission the lifetimes at around 0.2 eV exceed this trend by about $+20$ fs. This difference decreases with increasing photoemission angle and can be assigned to the particular band that is probed in YbRh${}_{2}$Si${}_{2}$. Potential microscopic scenarios are discussed.

We performed ultrafast time resolved near infrared pump resonant soft x ray diffraction probe measurements to investigate the coupling between the photoexcited electronic system and the spin cycloid magnetic order in multiferroic TbMnO3 at low temperatures. We observe melting of the long range antiferromagnetic order at low excitation fluences with a decay time constant of 22.3 ± 1.1 ps which is much slower than the ~1 ps melting times previously observed in other systems. To explain the data we propose a simple model of the melting process where the pump laser pulse directly excites the electronic system which then leads to an increase in the effective temperature of the spin system via a slower relaxation mechanism. Despite this apparent increase in the effective spin temperature we do not observe changes in the wave vector q of the antiferromagnetic spin order that would typically correlate with an increase in temperature under equilibrium conditions.We suggest that this behavior results from the extremely low magnon group velocity that hinders a change in the spin spiral wave vector on these time scales. DOI: 10.1103/PhysRevB.92.184429