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We conducted lateral force microscopy measurements on seven [LaMnO$_{3}$]$_{m}$/[SrMnO$_{3}$]$_{n}$ superlattices with varied layer thicknesses. We observe that the friction forces and the friction coefficients initially increase with increasing LaMnO3 top layer thickness, followed by saturation when the top layer thickness exceeds a few nanometers. These observations clearly demonstrate that sliding friction is affected by sub-surface material properties to a depth of several nanometers and is not just determined by dynamics in the contact interface. We argue that the sub-surface dissipated energy is governed by damping in the elastically strained volume below the AFM tip, an effect which we estimate via thermoelasticity. The absence of a correlation between friction and the thermal resistivity of our superlattices shows furthermore that high-frequency phonons and heat conduction do not play a role in determining friction. Our observations thus demonstrate that friction can be tailored by sub-surface material properties., Comment: The document contains both the manuscript and the supporting information (starting on page 22)

In this Letter, we present investigations of thermal transport in (LaMnO$_3$)$_n$/(SrMnO$_3$)$_n$ superlattices (SLs) with SL periods $\Lambda=2n$ between $2$ and $12$ unit cells. The analysis of the experimental data clearly reveals a minimum in the thermal conductivity $\kappa$ at $\Lambda=6$ u.c. Furthermore, we theoretically estimate the phonon mean free path to be about $3\Lambda$ in our SLs. These findings clearly show that, in a wide temperature range of $\pm 100\,$K around room temperature, thermal transport in our manganite SLs is coherent. In addition, we demonstrate that antiferromagnetic magnetic ordering can control the degree of coherency. This opens the challenging perspective for active control of coherent transport in correlated matter.

Two series of B-site ordered, double-perovskite A2CoMnO6 and A2NiMnO6 (A = La, Pr, Nd, Sm, Gd) epitaxial films with thickness d ~ 100 nm were grown on SrTiO3(111) substrates via metalorganic aerosol deposition. Polarization and temperature-dependent Raman spectroscopy were carried out in order to determine the spin-phonon coupling constant, λ, and the impact of the A-site cation radius on the phonon properties. The reduction of the A-site cation radius from La3+ down to Gd3+ systematically shifts the Raman modes to lower wavenumbers, and decreases the magnetization-induced softening of the Ag breathing mode, described by the spin-phonon coupling constant, λ, which changes from λ = 1.42 cm−1 (La2CoMnO6) and λ = 1.53 cm−1 (La2NiMnO6) down to λ = 0.58 cm−1 (Gd2CoMnO6) and λ = 0.44 cm−1 (Gd2NiMnO6). A similar effect of the A-cation radius was established for the c-lattice parameter and Curie temperature, TC, in this series of double-perovskite films. Our observations directly demonstrate a strong impact of the lattice structure on the ferromagnetic superexchange interaction in double perovskites. Moreover, the A2CoMnO6 and A2NiMnO6 series exhibit very similar behavior of spin-phonon coupling due to the only moderate difference of Co2+ and Ni2+ cation size.

Perovskite SrRuO$_3$ is a prototypical itinerant ferromagnet which allows interface engineering of its electronic and magnetic properties. We report synthesis and investigation of atomically flat artificial multilayers of SrRuO$_3$ with the spin-orbit semimetal SrIrO$_3$ in combination with band-structure calculations with a Hubbard $U$ term and topological analysis. They reveal an electronic reconstruction and emergence of flat Ru-4d$_{xz}$ bands near the interface, ferromagnetic interlayer coupling and negative Berry-curvature contribution to the anomalous Hall effect. We analyze the Hall effect and magnetoresistance measurements as a function of the field angle from out of plane towards in-plane orientation (either parallel or perpendicular to the current direction) by a two-channel model. The magnetic easy direction is tilted by about $20^\circ$ from the sample normal for low magnetic fields, rotating towards the out-of-plane direction by increasing fields. Fully strained epitaxial growth enables a strong anisotropy of magnetoresistance. An additional Hall effect contribution, not accounted for by the two-channel model is compatible with stable skyrmions only up to a critical angle of roughly $45^\circ$ from the sample normal. Within about $20^\circ$ from the thin film plane an additional peak-like contribution to the Hall effect suggests the formation of a non-trivial spin structure., Comment: to be published in Phys. Rev. B

Heterostructures of strongly correlated oxides demonstrate various intriguing and potentially useful interfacial phenomena. LaMnO3/SrMnO3 superlattices are presented showcasing a new high‐temperature ferromagnetic phase with Curie temperature, T C ≈360 K, caused by electron transfer from the surface of the LaMnO3 donor layer into the neighboring SrMnO3 acceptor layer. As a result, the SrMnO3 (top)/LaMnO3 (bottom) interface shows an enhancement of the magnetization as depth‐profiled by polarized neutron reflectometry. The length scale of charge transfer, λTF ≈2 unit cells, is obtained from in situ growth monitoring by optical ellipsometry, supported by optical simulations, and further confirmed by high resolution electron microscopy and spectroscopy. A model of the inhomogeneous distribution of electron density in LaMnO3/SrMnO3 layers along the growth direction is concluded to account for a complex interplay between ferromagnetic and antiferromagnetic layers in superlattices.

Transition metal functional oxides, e.g., perovskite manganites, with strong electron, spin and lattice correlations, are well-known for different phase transitions and field-induced colossal effects at the phase transition. Recently, the interfaces between dissimilar perovskites were shown to be a promising concept for the search of emerging phases with novel functionalities. We demonstrate that the properties of manganite films are effectively controlled by low dimensional emerging phases at intrinsic and extrinsic interfaces and appeared as a result of symmetry breaking. The examples include correlated Jahn−Teller polarons in the phase-separated (La1−yPry)0.7Ca0.3MnO3, electron-rich Jahn−Teller-distorted surface or “dead” layer in La0.7Sr0.3MnO3, electric-field-induced healing of “dead” layer as an origin of resistance switching effect, and high-TC ferromagnetic emerging phase at the SrMnO3/LaMnO3 interface in superlattices. These 2D polaronic phases with short-range electron, spin, and lattice reconstructions could be extremely sensitive to external fields, thus, providing a rational explanation of colossal effects in perovskite manganites.

Spatially resolved analysis of magnetic properties on the nanoscale remains challenging, yet strain and defects on this length-scale can profoundly affect a material's bulk performance. We present a detailed investigation of the magnetic properties of La0.67Sr0.33MnO3 thin films in both free-standing and nanowire form and assess the role of strain and local defects in modifying the films' magnetic properties. Lorentz transmission electron microscopy is used to measure the magnetocrystalline anisotropy and to map the Curie temperature and saturation magnetization with nanometric spatial resolution. Atomic-scale defects are identified as pinning sites for magnetic domain wall propagation. Measurement of domain wall widths and crystalline strain are used to identify a strong magnetoelastic contribution to the magnetic anisotropy. Together, these results provide unique insight into the relationship between the nanostructure and magnetic functionality of a ferromagnetic complex oxide film. peerReviewed

A number of techniques to reduce cache leakage have so far been proposed. However, it is not clear that 1) what kind of algorithm can be considered and 2) how much they have impact on energy and performance. To answer the questions, this paper classifies cache-leakage reduction techniques and evaluates their energy-performance efficiency. As a result, we have found that an approach employed by the Drowsy cache [1] achieves the best energy-performance efficiency with low complexity. Moreover, we investigate the potential of the approach on multi-thread program executions.

This paper presents an architectural enhancement for reducing memory requirements of MPEG video coding based on incremental memory sharing between the reconstructed picture frames. The method exploits the temporal locality of block-based hybrid coding by dynamically replacing the processed macroblocks of the previously reconstructed picture frame with macroblocks of a newly reconstructed picture frame. Simulation results show that using this method we can reduce the total memory size by a 13%-32% for bidirectional prediction and almost half for unidirectional prediction schemes without any impact on image quality and throughput.

This paper proposes a low-energy instruction-cache architecture, called history-based tag-comparison (HBTC) cache. The HBTC cache attempts to re-use tag-comparison results for avoiding unnecessary way activation in setassociative caches. The cache records tag-comparison results in an extended BTB, and re-uses them for directly selecting only the hit-way which includes the target instruction. In our simulation, it is observed that the HBTC cache can achieve 62% of energy reduction, with less than 1% performance degradation, compared with a conventional cache.

This paper proposes a history-based tag-comparison scheme for reducing energy consumption of direct-mapped instruction caches. The proposed cache efficiently exploits programexecution footprints recorded in the Branch Target Buffer (BTB), and attempts to detect and eliminate unnecessary tag checks at run time. Simulation results show that our approach can eliminate up to 95% of tag checks, saving the cache energy by 17%, while affecting the processor performance by only 0.2%.

これまでに我々は，ダイレクト・マップ命令キャッシュの低消費エネルギー化を目的として，ヒストリ・ ベース・タグ比較(HBTC: History Based Tag-Comparison) 方式を提案した．従来型キャッシュでは，ヒット/ミス判 定のために，タグ比較が毎アクセス実行される．これに対し，HBTC キャッシュでは，プログラムの実行履歴に基づ き必要に応じてタグ比較を行う．そして，無駄なタグ比較処理を動的に検出・削除し，命令キャッシュの低消費エネル ギー化を実現する．本稿では，これまでに提案したHBTC キャッシュを改良し，オーバヘッドの小さい新しい実現方 式を示す．また，信号処理アプリケーションを中心としたベンチマーク・プログラムを用いて，性能ならびに消費エ ネルギーに関するより詳細な評価を行う．, We have proposed a history-based tag-comparison cache (HBL cache) architecture for low-energy consumption. In conventional direct-mapped caches, tag checks are performed to examine whether the current reference hits the cache. On the other hand, the HBTC cache attempts to reduce the frequency of tag checks by exploiting execution footprints. In this paper, we improve the proposed HBTC cache, and evaluate performance/energy efficiency by using media applications. Simulation results show that such an approach can eliminate up to 95% of tag checks, saving the cache energy by 17%, while affecting the processor performance by 0.2%.

One of uncompromising requirements from portable computing is energy efficiency, because that affects directly the battery life. On the other hand, portable computing will target more demanding applications, for example moving pictures, so that higher performance is still required. Cache memories have been employed as one of the most important components of computer systems. In this paper, we briefly survey architectural techniques for high performance, low power cache memories

This paper presents an optimized MPEG2 video codec implementation, which drastically reduces the number of computations and memory accesses required for video compression. Unlike traditional scheme, we reuse data stored in frame memory to omit unnecessary coding operations and memory read/writes for unchanged macroblocks. Due to dynamic memory sharing among reference frames, data-driven macroblock characterization and selective macroblock processing, we perform less than 15% of the total operations required by a conventional coder while maintaining high picture quality., {"references":["","M. Takahashi, et al, A 60-MHz240mW MPEG-4 Videophone LSI with 16Mb Embedded DRAM, IEEE JSSC, 35 (11), pp.1713-1721, Nov.2000.","T. Hashimoto, et al, A 90mW MPEG4 Video Codec LSI with the Capability for Core Profile, IEEE ISSCC 2001, pp.140-141.","J. Tuan, et al, On the data reuse and memory bandwidth analysis for full-search block-matching VLSI architecture, IEEE Trans. CASVT, 12 (1) pp.61-72, 2002","J. Davidson, et al, Memory access coalescing: A technique for eliminating redundant memory accesses, PLDI, 29 (6) 1994.","D.Kolson, et al, Integrating program transformations in the memory based synthesis of image and video applications, IEEE ICCAD'94, 27-30.","S. Wuytack, et al, ''Formalized methodology for data reuse exploration for low-power hierarchical memory mappings'', IEEE TVLSI Systems, 6 (4) pp.529-537, Dec. 1998..","T. Onoye, et al., A VLSI architecture for MPEG2 real time motion estimator, IEEE ISCAS 1996","V. G. Moshnyaga, Reduction of memory accesses in motion estimation by block-data data reuse, Proc. IEEE ICASSP'02","V.G. Moshnyaga, A new computationally adaptive formulation of block-matching motion estimation, IEEE Trans. CASVT, 11(1), Jan. 2001."]}

Emerging portable devices relay on DRAM/flash memory system to satisfy requirements on fast and large data storage and low-energy consumption. This paper presents a novel approach to reduce energy of memory system, which unlike others, lowers energy of refresh operation in DRAM. The approach is based on two key ideas: (1) DRAM-based flash cache that keeps dirty pages to reduce the number of accesses to flash memory; and (2) OS-controlled page allocation/aging to stop the refresh operations in banks, whose pages are clean and not accessed for a long time. Simulations show that by using this technique we can decrease the overall energy consumption of DRAM/flash memory on video applications by 8-26% while reducing the DRAM refresh energy by 59-74%.

This thesis is devoted to investigation of new materials with ferroic and multiferroic properties by the means of Raman spectroscopy.The first discussed compound is chloromenite Cu9O2(SeO3)4Cl6. The crystal structure of the compound contains copper in five different coordination, which leads to a complicated magnetic structure. The chloromenite exhibits long range magnetic ordering at TN = 37 K and a polar ordering at TE = 270 K. The Raman study reveals signs of both magnetic and electric phase transitions: spin-phonon coupling below TN, and a symmetry lowering for T < TE. Rearrangement of magnetic subsystem below 20 K and an additional lattice instability in the temperature range 90 – 120 K is first discovered using Raman spectroscopy. In the mixed halide compound Fe(Te1.5Se0.5)O5Cl iron ions in the high-spin state form weakly coupled dimers showing the regime of short-range correlations at TM= 70 K and long-range magnetic order at TN = 22 K. Magnetic excitations revealed by the Raman study allow to determine the energy of magnetic interaction. A serious contradiction between the screening effect of metallic electrons and dielectric polarization has been recently overcome in LiOsO3. In the presented work we studied the isostructural compound LiReO3. The phonon anomalies point to the phase transition at T=175 K with a crossover regime down to temperatures as low as 140 K. The hysteresis in the temperature evolution of ReO6 related modes i contrast to an abrupt softening and damping of Li vibrations in the ferroelectric phase speak in favour of a decoupling of polar degrees of freedom and itinerant electrons. Creation of low dimensional magnetic structures is not the only possible effect of lone electron pair cations of p-elements. Features of the electronic structure cause a structural transition to a non-centrosymmetric state, which contributes to the manifestation of such actual physical properties as ferroelectricity, piezoelectricity, and optical activity like second-harmonic generation. Two new second-harmonic generation active iodates K3Sc(IO3)6 and KSc(IO3)3Cl, are discussed in this thesis. The large anharmonicity in the optical response of both compounds is confirmed by an anomalous temperature dependence of optical phonon energies as well as their enhanced Raman scattering intensities. The latter corresponds to a very large electronic polarizability., Die vorliegende Dissertation widmet sich der Untersuchung neuer Materialien mit ferroischen und multiferroischen Eigenschaften mittels Raman-Spektroskopie. Die erste diskutierte Verbindung ist Chloromenit Cu9O2(SeO3)4Cl6. Die Kristallstruktur der Verbindung enthält Kupfer in fünf verschiedenen Koordinationen, was zu einer komplizierten magnetischen Struktur führt. Chloromenit weist eine magneti-sche Fernordnung bei TN = 37 K und eine polare Ordnung bei TE = 270 K auf. Die Untersuchung mit der Raman-Methode ermöglicht die Untersuchung für magnetische und elektrische Phasenübergänge: Unterhalb von TN eine Spin-Phonon-Kopplung und für T < TE eine Symmetrieerniedrigung. Mit Hilfe der Raman-Spektroskopie wurden erstmals eine Neuordnung des magnetischen Subsystems bei Temperaturen unter 20 K und darüber hinaus eine Gitterinstabilität im Temperaturbereich von 90 – 120 K entdeckt. In der gemischten Halogenidverbindung Fe(Te1.5Se0.5)O5Cl bilden Eisenionen im High-Spin- Zustand schwach gekoppelte Dimere mit dem Überwiegen von Korrelationen kurzer Reichweite bei TM = 70 K und einer magnetischen Fernordnung bei TN = 22 K. Magnetische Anregungen, entdeckt durch die Raman Methode, ermöglicht die Bestimmung von Energie der magnetischen Wechselwirkung. Kürzlich wurde ein gravierender Widerspruch zwischen der Abschirmwirkung metallischer Elektronen und der dielektrischen Polarisation bei LiOsO3 überwunden. In vorliegender Arbeit wurde die isostrukturelle Verbindung LiReO3 untersucht. Die Phononenanomalien deuten auf einen Phasenübergang bei T = 175 K hin, wobei die Anomalien bis zu einer Tiefsttemperatur von T = 140 K auftreten. Die Hysterese der Temperaturentwicklung von auf ReO6 bezogene Moden – im Gegensatz zu einer abrupten Abschwächung und Dämpfung von Li-Schwingungen in der ferroelektrischen Phase – spricht für eine Entkopplung polarer Freiheitsgrade und itineranter Elektronen. Merkmale der elektronischen Struktur bewirken einen strukturellen Übergang in einen nicht zentrosymmetrischen Zustand, der zu einer Manifestation physikalischer Eigenschaften wie Ferroelektrizität und optischer Aktivität. Zwei neue, frequenzverdoppelnde Jodate werden diskutiert: K3Sc(IO3)6 und KSc(IO3)3Cl. Die große Anharmonizität in der optischen Reaktion der beiden Verbindungen wird durch eine anomale Temperaturabhängigkeit von optischen Phononenenergien sowie ihre vergrößerten Intensitäten bei der Raman-Streuung bestätigt.