We present an optically induced remanent photostriction in BiFeO 3 , resulting from the photovoltaic effect, which is used to modify the ferromagnetism of Ni film in a hybrid BiFeO 3 =Ni structure. The 75% change in coercivity in the Ni film is achieved via optical and nonvolatile control. This photoferromagnetic effect can be reversed by static or ac electric depolarization of BiFeO 3 . Hence, the strain dependent changes in magnetic properties are written optically, and erased electrically. Light-mediated straintronics is therefore a possible approach for low-power multistate control of magnetic elements relevant for memory and spintronic applications.

We present a nanostructured device that functions as photoacoustic hard x-ray switch. The device is triggered by femtosecond laser pulses and allows for temporal gating of hard x-rays on picosecond (ps) timescales. It may be used for pulse picking or even pulse shortening in 3rd generation synchrotron sources. Previous approaches mainly suffered from insufficient switching contrasts due to excitation-induced thermal distortions. We present a new approach where thermal distortions are spatially separated from the functional switching layers in the structure. Our measurements yield a switching contrast of 14, which is sufficient for efficient hard x-ray pulse shortening. The optimized structure also allows for utilizing the switch at high repetition rates of up to 208 kHz.

Monitoring structural changes in ferroelectric thin films during electric field-induced polarization switching is important for a full microscopic understanding of the coupled motion of charges, atoms and domain walls. We combine standard ferroelectric test-cycles with time-resolved x-ray diffraction to investigate the response of a nanoscale ferroelectric oxide capacitor upon charging, discharging and switching. Piezoelectric strain develops during the electronic RC time constant and additionally during structural domain-wall creep. The complex atomic motion during ferroelectric polarization reversal starts with a negative piezoelectric response to the charge flow triggered by voltage pulses. Incomplete screening limits the compressive strain. The piezoelectric modulation of the unit cell tweaks the energy barrier between the two polarization states. Domain wall motion is evidenced by a broadening of the in-plane components of Bragg reflections. Such simultaneous measurements on a working device elucidate and visualize the complex interplay of charge flow and structural motion and challenges theoretical modelling.The applications of ferroelectric (FE) materials in technology have many facets based on the fundamental aspects of charge transport, structural changes of the crystal lattice and the motion of domain walls. Sensors and actuators mostly rely on the large piezoelectric coefficient d 33 , which can be particularly high e.g. in relaxor ferroelectrics [1] or at morphotropic phase boundaries [2]. In electronic circuits the large dielectric constant yields a high capacitance C = 0 A/d in capacitors with area A and thickness d. Recently, the concept of negative capacitance has re-attracted attention [3,4]. Considerable research efforts were devoted to finding the minimum thickness for sustaining ferroelectricity [5], not only because d is in the denominator of the capacitance, but mainly because of the quest for FE-RAMs with high storage density and low power consumption [6][7][8]. The switchable FE polarization P S allows storing an information bit as

The electric field-dependence of structural dynamics in a tetragonal ferroelectric lead zirconate titanate thin film is investigated under sub-coercive and above-coercive fields using time-resolved X-ray diffraction. During the application of an external field to the pre-poled thin film capacitor, structural signatures of domain nucleation and growth include broadening of the in-plane peak width of a Bragg reflection concomitant with a decrease of the peak intensity. This disordered domain state is remanent and can be erased with an appropriate voltage pulse sequence.Ferroelectrics (FE) are not only technologically interesting because of their electromechanical properties that enable their application in transducer devices. The reversible spontaneous polarization of FE has been used in memory devices with a reported data retention of about 10 years [1]. FE memory devices make use of the remnant polarization state obtained after poling or reversing the FE polarization by an electric field to store the boolean algebraic logic states "0" and "1". Operating FEs above their coercive field leads to fatigue, which limits device lifetime [2][3][4][5][6]. Also, the quest for low power consumption requires operating such devices under the lowest possible bias. Hence there is growing interest in sub-coercive field applications and associated remnant states [7][8][9][10][11]. It is well known that FE thin films do not reverse their polarity as a whole when an external field is applied. After domain nucleation, the regions with opposite polarization are separated by domain walls (DW) [12,13]. One of the domain polarization directions prevails as the external field approaches the saturation field, however, the time required to fully suppress domains with the opposite polarization is determined by the domain wall velocity. The DWs are mobile, add structural disorder within the sample volume, and reduce the observed maximum polarization. DWs contribute to the observed piezoelectric strain in FE devices already at very low fields [14,15]. This has lead to new devices in magnetic and FE materials for DW logic and DW diode applications [16][17][18]. It has recently been demonstrated that multiple memory states can be created due to the coupling between remnant strain and domain states [7,19]. Some actuator applications require fast actuation with reproducible length changes that are not affected by drifts on longer time-scale. To study the time-dependent response of FE ceramics, time-resolved X-ray diffraction (TR-XRD) has been used to probe the dynamics under electrical loading, offering the possibility to distinguish between the intrinsic piezoelectric response of individ-ual domains and extrinsic contributions originating from changes of the volume fraction of the domains. [14,15]. In the last years, in-situ synchrotron XRD has been used to quantify the electromechanical response and fatigue behavior of FE thin films and powders under loading, with the advantage of yielding appropriate temporal and spatial resolution as compared...