Using a "pump and probe" technique, the time scale of spin relaxation effects in ferromagnetic thin films is investigated. Samples are excited by a 3 eV "pump" laser pulse ͑t ഠ 170 fs͒, and electrons are photoemitted by a 6 eV "probe" pulse, after delays ranging up to 1 ns. The spin polarization of the photoelectrons is measured using a Mott detector. The time dependence of the spin polarization of thin Ni films on Ag is explained in a local magnetic moment picture with two excitation processes. Stoner excitations are responsible for the reduction of the observed spin polarization on a time scale of 1 ps and phonon-magnon scattering leads to the loss of long range magnetic order on a time scale of 500 ps. [S0031-9007(97)04890-4] The interactions between quasiparticles like electronelectron, electron-phonon, and electron-magnon scattering determine the macroscopic properties of matter at finite temperatures, and the dynamical response to external excitations; also properties like superconductivity and giant magnetoresistance are governed by them. Experimentally these interactions are reflected by the lifetime broadening of spectroscopic features. If these interactions are specifically included in the interpretation of experimental results, then they are usually treated as instantaneous, meaning that the system under consideration is always in thermodynamical equilibrium, whereby the true dynamics of these processes is neglected.The magnetism of transition metals at finite temperatures is one of the most challenging topics in modern physics and much work has been done to calculate thermodynamic properties like the magnetization M, the susceptibility x, and the Curie temperature T C from first principles. An itinerant ferromagnet shows two types of magnetic excitations. Magnons which follow an approximately quadratic dispersion law are responsible for the low and medium temperature properties, whereas single particle excitations, the Stoner excitations, cost much more energy. Early models either neglected spin fluctuations (Stoner model) and thus predicted much too high Curie temperatures, or neglected the itinerant character leading to a Heisenberg-like description. Modern theories combine both pictures. A Stoner-type intinerant part leads to the formation of local moments and a Heisenberg-like part describes their interaction [1,2]. We will show in this Letter that both kinds of magnetic excitations are important to understand the dynamics of transition metal ferromagnets.An experimental approach to investigate these interactions within a real-time experiment is very difficult, because a time resolution on the time scale of the electronelectron scattering (ϳfs) has to be achieved [3][4][5][6][7]. In the last few years these time scales became accessible by the development of commercial laser systems generating ultrashort pulses. These laser systems are most prominently applied in investigating electron scattering dynamics in semiconductors due to the industrial interest in high frequency devices [8][9][10][11]....

We report on the novel effect of magnetic x-ray dichroism in core-level photoemission from ferromagnets with circularly polarized radiation. Depending on the relative orientation of photon spin and sample magnetization (parallel or antiparallel), a single emission line may be resolved into two lines, due to exchange splitting of the core level. The mechanism is explained in terms of spin-selective dipole transitions in the presence of spin-orbit coupling. Possible applications of magnetic x-ray dichroism in photoemission from magnetic samples are pointed out.PACS numbers: 79.60. Cn, 75.50.Bb, 78.20.Ls The transmission or reflection of circularly polarized light interacting with magnetic matter may depend on its helicity, i.e., the sense of rotation of the electric vector of the electromagnetic wave. A familiar example for this "magnetic dichroism" is the magneto-optic Kerr effect. The coupling between the aligned electron spins (s = y ) and the photon spin (s = 1) is in this case, as well as in all others to be discussed below, provided by the spinorbit interaction of the electronic states-either in the initial or in the final state, or in both. A counterpart to the optical polar Kerr effect was recently reported in the x-ray region. 1,2 It was found that the absorption cross section for x-ray photons at core levels of ferromagnets depends on the relative orientation of the photon spin and the sample magnetization. This was successfully interpreted in terms of the spin-split density of states at and above the Fermi level. 3 As shown earlier by van der Laan et at., 4 magnetic x-ray dichroism may in special cases even be observed with linearly polarized radiation. A general theoretical treatment of linear and circular dichroism in absorption was very recently given by Carra and Altarelli. 5 The new phenomenon we report on here is distinct from all the above in that it occurs in emission of electrons from core levels into free-electron states, rather than absorption of photons at core-level edges. The basic observation is that a single core-level emission peak from a ferromagnet may be resolved into two energetically separated lines, if excited by circularly polarized x rays with the photon spin aligned with the sample polarization. The relative intensity of these lines reverses when the magnetization of the sample or the helicity of the photons is reversed. Since the final energy of the electrons is far above the Fermi level, we basically probe the spin-split electronic structure of the core levels, rather than the spin-split empty density of states in the valence band. "Magnetic x-ray dichroism in photoemission" may find wide application in the study of the elementspecific local magnetic structure on the atomic scale in ferromagnets, ferrimagnets, and antiferromagnets in the near-surface region. Our observations also shed new light on a long-standing issue of the interpretation of exchange splittings in the x-ray photoelectron spectrum of iron.A number of proposals for the production of circularly polarized lig...

Note: This paper is part of the Special Topic on Materials and Devices Utilizing Ferroelectricity in Halfnium Oxide.

The energy distribution curves for 2p-core-level photoemission of Fe have been calculated based on a completely relativistic treatment of the core as well as the final states. In accordance with recent experiments, a pronounced dependence on the helicity of the exciting radiation has been found. All features of the experimental spectra could be explained in terms of ground-state properties calculated within the framework of local-spin-density-functional theory. From the results it is concluded that exchange interaction will in general contribute to an appreciable extent to the linewidth of core lines of magnetic systems.

The interface formation between ferroelectric HfO2 layers and TiN bottom electrodes was studied by hard X-ray photoelectron spectroscopy and directly correlated to the electric polarization characteristics of the TiN/HfO2/TiN capacitors. We consistently deduced the interface chemistry from HfO2- and TiN-related core levels, dependent on the oxygen flow ṁ supplied before and during physical vapor deposition (PVD) growth of HfO2. The results underline the critical, twofold impact of oxygen supply on HfO2 and interface properties. When supplied before growth, the supplied oxygen stabilizes the TiN/HfO2 interface by oxidation and formation of a self-limiting (noninsulating) TiO2 intralayer. When supplied during growth, on the other hand, oxygen flows above a critical threshold reduce the oxygen vacancy concentration within the HfO2 film. We reveal a direct relation between the maximum ferroelectric remanent polarization and a critical threshold PVD oxygen exposure flow rate. The results allow for advancement of the PVD growth process in terms of a more flexible design of the ferroelectric HfO2 films with chemically stable TiN interfaces.