Showing papers on "Magnetoresistance published in 2005"

Revival of the Magnetoelectric Effect

Abstract: Recent research activities on the linear magnetoelectric (ME) effect?induction of magnetization by an electric field or of polarization by a magnetic field?are reviewed. Beginning with a brief summary of the history of the ME effect since its prediction in 1894, the paper focuses on the present revival of the effect. Two major sources for 'large' ME effects are identified. (i) In composite materials the ME effect is generated as a product property of a magnetostrictive and a piezoelectric compound. A linear ME polarization is induced by a weak ac magnetic field oscillating in the presence of a strong dc bias field. The ME effect is large if the ME coefficient coupling the magnetic and electric fields is large. Experiments on sintered granular composites and on laminated layers of the constituents as well as theories on the interaction between the constituents are described. In the vicinity of electromechanical resonances a ME voltage coefficient of up to 90?V?cm?1?Oe?1 is achieved, which exceeds the ME response of single-phase compounds by 3?5 orders of magnitude. Microwave devices, sensors, transducers and heterogeneous read/write devices are among the suggested technical implementations of the composite ME effect. (ii) In multiferroics the internal magnetic and/or electric fields are enhanced by the presence of multiple long-range ordering. The ME effect is strong enough to trigger magnetic or electrical phase transitions. ME effects in multiferroics are thus 'large' if the corresponding contribution to the free energy is large. Clamped ME switching of electrical and magnetic domains, ferroelectric reorientation induced by applied magnetic fields and induction of ferromagnetic ordering in applied electric fields were observed. Mechanisms favouring multiferroicity are summarized, and multiferroics in reduced dimensions are discussed. In addition to composites and multiferroics, novel and exotic manifestations of ME behaviour are investigated. This includes (i) optical second harmonic generation as a tool to study magnetic, electrical and ME properties in one setup and with access to domain structures; (ii) ME effects in colossal magnetoresistive manganites, superconductors and phosphates of the LiMPO4 type; (iii) the concept of the toroidal moment as manifestation of a ME dipole moment; (iv) pronounced ME effects in photonic crystals with a possibility of electromagnetic unidirectionality. The review concludes with a summary and an outlook to the future development of magnetoelectrics research.

Towards molecular spintronics.

Abstract: The ability to manipulate electron spin in organic molecular materials offers a new and extremely tantalizing route towards spin electronics, both from fundamental and technological points of view. This is mainly due to the unquestionable advantage of weak spin–orbit and hyperfine interactions in organic molecules, which leads to the possibility of preserving spin-coherence over times and distances much longer than in conventional metals or semiconductors. Here we demonstrate theoretically that organic spin valves, obtained by sandwiching an organic molecule between magnetic contacts, can show a large bias-dependent magnetoresistance and that this can be engineered by an appropriate choice of molecules and anchoring groups. Our results, obtained through a combination of state-of-the-art non-equilibrium transport methods and density functional theory, show that although the magnitude of the effect varies with the details of the molecule, large magnetoresistance can be found both in the tunnelling and the metallic limit.

230% room temperature magnetoresistance in CoFeB/MgO/CoFeB magnetic tunnel junctions

Abstract: The magnetoresistance ratio of 230% at room temperature is reported. This was achieved in spin-valve type magnetic tunnel junctions using MgO barrier layer and amorphous CoFeB ferromagnetic electrodes fabricated on thermally oxidized Si substrates. The amorphous CoFeB electrodes are of great advantage to the polycrystalline FeCo electrodes in achieving a high homogeneity in small 100 nm-sized MTJs.

Magnetodielectric effect without multiferroic coupling

Abstract: The existence of a magnetodielectric (magnetocapacitance) effect is often used as a test for multiferroic behavior in new material systems. However, strong magnetodielectric effects can also be achieved through a combination of magnetoresistance and the Maxwell-Wagner effect, unrelated to multiferroic coupling. The fact that this resistive magnetocapacitance does not require multiferroic materials may be advantageous for some practical applications. Conversely, it also implies that magnetocapacitance per se is not sufficient to establish multiferroic coupling.

The single-phase multiferroic oxides: from bulk to thin film

Abstract: Complex perovskite oxides exhibit a rich spectrum of properties, including magnetism, ferroelectricity, strongly correlated electron behaviour, superconductivity and magnetoresistance, which have been research areas of great interest among the scientific and technological community for decades. There exist very few materials which exhibit multiple functional properties; one such class of materials is called the multiferroics. Multiferroics are interesting because they exhibit simultaneously ferromagnetic and ferroelectric polarizations and a coupling between them. Due to the nontrivial lattice coupling between the magnetic and electronic domains (the magnetoelectric effect), the magnetic polarization can be switched by applying an electric field; likewise the ferroelectric polarization can be switched by applying a magnetic field. As a consequence, multiferroics offer rich physics and novel devices concepts, which have recently become of great interest to researchers. In this review article the recent experimental status, for both the bulk single phase and the thin film form, has been presented. Current studies on the ceramic compounds in the bulk form including Bi(Fe,Mn)O3, REMnO3 andthe series of REMn2O5 single crystals (RE = rare earth) are discussed in the first section and a detailed overview on multiferroic thin films grown artificially (multilayers and nanocomposites) is presented in the second section.

Electric field modulation of galvanomagnetic properties of mesoscopic graphite.

Abstract: Electric field effect devices based on mesoscopic graphite are fabricated for galvanomagnetic measurements. Strong modulation of magnetoresistance and Hall resistance as a function of the gate voltage is observed as the sample thickness approaches the screening length. Electric field dependent Landau level formation is detected from Shubnikov--de Haas oscillations. The effective mass of electron and hole carriers has been measured from the temperature dependent behavior of these oscillations.

Large magnetoresistance in nonmagnetic π -conjugated semiconductor thin film devices

Abstract: Following the recent observation of large magnetoresistance at room temperature in polyfluorene sandwich devices, we have performed a comprehensive magnetoresistance study on a set of organic semiconductor sandwich devices made from different $\ensuremath{\pi}$-conjugated polymers and small molecules The study includes a range of materials that show greatly different chemical structure, mobility, and spin-orbit coupling strength We study both hole and electron transporters at temperatures ranging from 10 K to 300 K We observe large negative or positive magnetoresistance (up to 10% at 300 K and 10 mT) depending on material and device operating conditions We discuss our results in the framework of known magnetoresistance mechanisms and find that none of the existing models can explain our results

Electric Field Modulation of Galvanomagnetic Properties of Mesoscopic Graphite

Abstract: 0031-9007= Electric field effect devices based on mesoscopic graphite are fabricated for galvanomagnetic measurements. Strong modulation of magnetoresistance and Hall resistance as a function of the gate voltage is observed as the sample thickness approaches the screening length. Electric field dependent Landau level formation is detected from Shubnikov–de Haas oscillations. The effective mass of electron and hole carriers has been measured from the temperature dependent behavior of these oscillations.

Revival of the Magnetoelectric Effect

Abstract: Recent research activities on the linear magnetoelectric (ME) effect?induction of magnetization by an electric field or of polarization by a magnetic field?are reviewed. Beginning with a brief summary of the history of the ME effect since its prediction in 1894, the paper focuses on the present revival of the effect. Two major sources for 'large' ME effects are identified. (i) In composite materials the ME effect is generated as a product property of a magnetostrictive and a piezoelectric compound. A linear ME polarization is induced by a weak ac magnetic field oscillating in the presence of a strong dc bias field. The ME effect is large if the ME coefficient coupling the magnetic and electric fields is large. Experiments on sintered granular composites and on laminated layers of the constituents as well as theories on the interaction between the constituents are described. In the vicinity of electromechanical resonances a ME voltage coefficient of up to 90?V?cm?1?Oe?1 is achieved, which exceeds the ME response of single-phase compounds by 3?5 orders of magnitude. Microwave devices, sensors, transducers and heterogeneous read/write devices are among the suggested technical implementations of the composite ME effect. (ii) In multiferroics the internal magnetic and/or electric fields are enhanced by the presence of multiple long-range ordering. The ME effect is strong enough to trigger magnetic or electrical phase transitions. ME effects in multiferroics are thus 'large' if the corresponding contribution to the free energy is large. Clamped ME switching of electrical and magnetic domains, ferroelectric reorientation induced by applied magnetic fields and induction of ferromagnetic ordering in applied electric fields were observed. Mechanisms favouring multiferroicity are summarized, and multiferroics in reduced dimensions are discussed. In addition to composites and multiferroics, novel and exotic manifestations of ME behaviour are investigated. This includes (i) optical second harmonic generation as a tool to study magnetic, electrical and ME properties in one setup and with access to domain structures; (ii) ME effects in colossal magnetoresistive manganites, superconductors and phosphates of the LiMPO4 type; (iii) the concept of the toroidal moment as manifestation of a ME dipole moment; (iv) pronounced ME effects in photonic crystals with a possibility of electromagnetic unidirectionality. The review concludes with a summary and an outlook to the future development of magnetoelectrics research.

Electric field control of spin transport

Abstract: Spintronics aims to develop electronic devices whose resistance is controlled by the spin of the charge carriers that flow through them1,2,3. This approach is illustrated by the operation of the most basic spintronic device, the spin valve4,5,6, which can be formed if two ferromagnetic electrodes are separated by a thin tunnelling barrier. In most cases, its resistance is greater when the two electrodes are magnetized in opposite directions than when they are magnetized in the same direction7,8. The relative difference in resistance, the so-called magnetoresistance, is then positive. However, if the transport of carriers inside the device is spin- or energy-dependent3, the opposite can occur and the magnetoresistance is negative9. The next step is to construct an analogous device to a field-effect transistor by using this effect to control spin transport and magnetoresistance with a voltage applied to a gate10,11. In practice though, implementing such a device has proved difficult. Here, we report on a pronounced gate-field-controlled magnetoresistance response in carbon nanotubes connected by ferromagnetic leads. Both the magnitude and the sign of the magnetoresistance in the resulting devices can be tuned in a predictable manner. This opens an important route to the realization of multifunctional spintronic devices.

Transformation of spin information into large electrical signals via carbon nanotubes

Abstract: Spin electronics (spintronics) exploits the magnetic nature of the electron, and is commercially exploited in the spin valves of disc-drive read heads. There is currently widespread interest in using industrially relevant semiconductors in new types of spintronic devices based on the manipulation of spins injected into a semiconducting channel between a spin-polarized source and drain. However, the transformation of spin information into large electrical signals is limited by spin relaxation such that the magnetoresistive signals are below 1%. We overcome this long standing problem in spintronics by demonstrating large magnetoresistance effects of 61% at 5 K in devices where the non-magnetic channel is a multiwall carbon nanotube that spans a 1.5 micron gap between epitaxial electrodes of the highly spin polarized manganite La0.7Sr0.3MnO3. This improvement arises because the spin lifetime in nanotubes is long due the small spin-orbit coupling of carbon, because the high nanotube Fermi velocity permits the carrier dwell time to not significantly exceed this spin lifetime, because the manganite remains highly spin polarized up to the manganite-nanotube interface, and because the interfacial barrier is of an appropriate height. We support these latter statements regarding the interface using density functional theory calculations. The success of our experiments with such chemically and geometrically different materials should inspire adventure in materials selection for some future spintronics

Transport and magnetic properties of Gd Ba Co 2 O 5 + x single crystals: A cobalt oxide with square-lattice Co O 2 planes over a wide range of electron and hole doping

Abstract: Single crystals of the layered perovskite GdBaCo_{2}O_{5+x} (GBCO) have been grown by the floating-zone method, and their transport, magnetic, and structural properties have been studied in detail over a wide range of oxygen contents. The obtained data are used to establish a rich phase diagram centered at the "parent'' compound GdBaCo_{2}O_{5.5} -- an insulator with Co ions in the 3+ state. An attractive feature of GBCO is that it allows a precise and continuous doping of CoO_{2} planes with either electrons or holes, spanning a wide range from the charge-ordered insulator at 50% electron doping (x=0) to the undoped band insulator (x=0.5), and further towards the heavily hole-doped metallic state. This continuous doping is clearly manifested in the behavior of thermoelectric power which exhibits a spectacular divergence with approaching x=0.5, where it reaches large absolute values and abruptly changes its sign. At low temperatures, the homogeneous distribution of doped carriers in GBCO becomes unstable, and both the magnetic and transport properties point to an intriguing nanoscopic phase separation. We also find that throughout the composition range the magnetic behavior in GBCO is governed by a delicate balance between ferromagnetic (FM) and antiferromagnetic (AF) interactions, which can be easily affected by temperature, doping, or magnetic field, bringing about FM-AF transitions and a giant magnetoresistance (MR) phenomenon. An exceptionally strong uniaxial anisotropy of the Co spins, which dramatically simplifies the possible spin arrangements, together with the possibility of continuous ambipolar doping turn GBCO into a model system for studying the competing magnetic interactions, nanoscopic phase separation and accompanying magnetoresistance phenomena.

Single Crystalline Magnetite Nanotubes

Abstract: We descried a method to synthesize single crystalline Fe3O4 nanotubes by wet-etching the MgO inner cores of MgO/Fe3O4 core−shell nanowires. Homogeneous Fe3O4 nanotubes with controllable length, diameter, and wall thickness have been obtained. Resistivity of the Fe3O4 nanotubes was estimated to be ∼4 × 10-2 Ω cm at room temperature. Magnetoresistance of ∼1% was observed at T = 77 K when a magnetic field of B = 0.7 T was applied. The synthetic strategy presented here may be extended to a variety of materials such as YBCO, PZT, and LCMO which should provide ideal candidates for fundamental studies of superconductivity, piezoelectricity, and ferromagnetism in nanoscale structures.

Magnetoelectronics with magnetoelectrics

Abstract: Magnetoelectric films are proposed as key components for spintronic applications. The net magnetic moment created by an electric field in a magnetoelectric thin film influences the magnetization state of a neighbouring ferromagnetic layer through exchange coupling. Pure electrical control of magnetic configurations of giant magnetoresistance spin valves and tunnelling magnetoresistance elements is therefore achievable. Estimates based on documented magnetoelectric tensor values show that exchange fields reaching 100 mT can be obtained. We propose a mechanism alternative to current-induced magnetization switching, providing access to a wide range of device impedance values and opening the possibility of simple logic functions.

Giant tunneling magnetoresistance effect in low-resistance CoFeB∕MgO(001)∕CoFeB magnetic tunnel junctions for read-head applications

Abstract: The giant tunneling magnetoresistance effect has been achieved in low-resistance CoFeB∕MgO(001)∕CoFeB magnetic tunnel junctions (MTJs) at room temperature. A magnetoresistance (MR) ratio as high as 138%, seven times that of state-of-the-art MTJs for magnetic sensor application, was obtained at room temperature in MTJs with a resistance-area product (RA) as low as 2.4Ωμm2. Such a high MR ratio at such a low resistance was made possible by introducing an ultrathin Mg metal layer with a thickness of 4 A between the CoFeB bottom electrode layer and the MgO(001) tunnel barrier layer. The Mg layer was slightly but not fully oxidized, which resulted in a reduction in MR for a thicker MgO barrier (high RA) region and in an increase in MR for a thinner barrier (low RA) region. The Mg layer improves the crystalline orientation of the MgO(001) layer when the MgO(001) layer is thin. These MTJs will accelerate the realization of highly sensitive read heads for ultrahigh-density hard-disk drives.

Macrospin models of spin transfer dynamics

Abstract: The current-induced magnetization dynamics of a spin valve are studied using a macrospin (single-domain) approximation and numerical solutions of a generalized Landau-Lifshitz-Gilbert equation. For the purpose of quantitative comparison to experiment [S. I. Kiselev, J. C. Sankey, I. N. Krivortov, N. C. Emley, R. J. Schoelkopf, R. A. Buhrman, and D. C. Ralph, Nature 425, 380 (2003)], we calculate the resistance and microwave power as a function of current and external field, including the effects of anisotropies, damping, spin-transfer torque, thermal fluctuations, spin-pumping, and incomplete absorption of transverse spin current. Although many features of experiment appear in the simulations, there are two significant discrepancies: the current dependence of the precession frequency and the presence and/or absence of a microwave quiet magnetic phase with a distinct magnetoresistance signature. Comparison is made to micromagnetic simulations designed to model the same experiment.

Huge Spin-Polarization of L21-Ordered Co2MnSi Epitaxial Heusler Alloy Film

Abstract: Magnetic tunnel junctions (MTJs) with a stacking structure of epitaxial Co2MnSi/Al–O barrier/poly-crystalline Co75Fe25 were fabricated using an ultrahigh vacuum sputtering system. The epitaxial Co2MnSi bottom electrode exhibited highly ordered L21 structure and very smooth surface morphology. Observed magnetoresistance (MR) ratios of 70% at room temperature (RT) and 159% at 2 K are the highest values to date for MTJs using a Heusler alloy electrode. A high spin-polarization of 0.89 at 2 K for Co2MnSi obtained from Julliere's model coincided with the half-metallic band structure that was predicted by theoretical calculations.

Classical magnetotransport of inhomogeneous conductors

Abstract: We present a model of magnetotransport of inhomogeneous conductors based on an array of coupled four-terminal elements We show that this model generically yields nonsaturating magnetoresistance at large fields We also discuss how this approach simplifies finite-element analysis of bulk inhomogeneous semiconductors in complex geometries We argue that this is an explanation of the observed nonsaturating magnetoresistance in silver chalcogenides and potentially in other disordered conductors Our method may be used to design the magnetoresistive response of a microfabricated array

Low-frequency noise measurements on commercial magnetoresistive magnetic field sensors

Abstract: Low-frequency noise was measured in the frequency range from 0.1Hzto10kHz on a variety of commercially available magnetic sensors. The types of sensors investigated include anisotropic magnetoresistance (AMR), giant magnetoresistance (GMR), and tunnel magnetoresistance (TMR) effect devices. The 1∕f noise components of electronic and magnetic origin are identified by measuring sensor noise and sensitivity at various applied magnetic fields. Commercial magnetometers typically consist of four elements in a Wheatstone bridge configuration and are biased with either a constant voltage or current. Voltage fluctuations at the sensor output are amplified by a pair of battery powered low-noise preamplifiers and input to a spectrum analyzer. A two-channel cross-correlation technique is used when the performance of a single preamplifier is not sufficient. For the AMR and GMR sensors investigated, both electronic and magnetic components contribute to the overall sensor noise. Maximum noise occurs at the bias field wh...

Magnetic tunnel junction having diffusion stop layer

Abstract: Magnetic or magnetoresistive tunnel junctions (MTJs) having diffusion stop layers to eliminate or reduce diffusion of oxygen, nitrogen or other particles from the barrier layer to the ferromagnetic layers during the film deposition process including the barrier oxidation or nitridation process and the post annealing process. Such MTJs may be used in various applications including magnetic memory (MRAM) devices and magnetic recording heads.

Metal-insulator-like behavior in semimetallic bismuth and graphite.

Abstract: When high quality bismuth or graphite crystals are placed in a magnetic field directed along the c axis (trigonal axis for bismuth) and the temperature is lowered, the resistance increases as it does in an insulator but then saturates. We show that the combination of unusual features specific to semimetals, i.e., low carrier density, small effective mass, high purity, and an equal number of electrons and holes (compensation), gives rise to a unique ordering and spacing of three characteristic energy scales, which not only is specific to semimetals but which concomitantly provides a wide window for the observation of apparent field-induced metal-insulator behavior. Using magnetotransport and Hall measurements, the details of this unusual behavior are captured with a conventional multiband model, thus confirming the occupation by semimetals of a unique niche between conventional metals and semiconductors.

Magnetic microscopy of nanostructures

Abstract: Imaging Magnetic Microspectroscopy.- Study of Ferromagnet-Antiferromagnet Interfaces Using X-Ray PEEM.- Time Domain Optical Imaging of Ferromagnetodynamics.- Lorentz Microscopy.- Electron Holography of Magnetic Nanostructures.- SPLEEM.- SEMPA Studies of Thin Films, Structures, and Exchange Coupled Layers.- Spin-SEM of Storage Media.- High Resolution Magnetic Imaging by Local Tunneling Magnetoresistance.- Spin-Polarized Scanning Tunneling Spectroscopy.- Magnetic Force Microscopy: Images of Nanostructures and Contrast Modeling.- Magnetic Force Microscopy - Towards Higher Resolution.- Scanning Probe Methods for Magnetic Imaging.

Spin Transfer Switching and Spin Polarization in Magnetic Tunnel Junctions with Mgo and Alox Barriers

Abstract: We present spin transfer switching results for MgO based magnetic tunneling junctions (MTJs)with large tunneling magnetoresistance (TMR) ratio of up to 150% and low intrinsic switching current density of 2-3 x 10 MA/cm2. The switching data are compared to those obtained on similar MTJ nanostructures with AlOx barrier. It is observed that the switching current density for MgO based MTJs is 3-4 times smaller than that for AlOx based MTJs, and that can be attributed to higher tunneling spin polarization (TSP) in MgO based MTJs. In addition, we report a qualitative study of TSP for a set of samples, ranging from 0.22 for AlOx to 0.46 for MgO based MTJs, and that shows the TSP (at finite bias) responsible for the current-driven magnetization switching is suppressed as compared to zero-bias tunneling spin polarization determined from TMR.

Room temperature ferromagnetic n-type semiconductor in (In1−xFex)2O3−σ

Abstract: The thin film synthesis and characterization of room temperature ferromagnetic semiconductor (In1−xFex)2O3−σ are reported. The high thermodynamic solubility, up to 20%, of Fe ions in the In2O3 is demonstrated by a combinatorial phase mapping study where the lattice constant decreases almost linearly as Fe doping concentration increases. Extensive structural, magnetic and magneto-transport including anomalous Hall effect studies on thin film samples consistently point to a source of magnetism within the host lattice rather than from an impurity phase.

Giant magnetoresistance in ferromagnet/superconductor superlattices.

Abstract: We show magnetoresistance in excess of 1000% in trilayers containing highly spin-polarized La_(0.7)Ca_(0.3)MnO_(3) and high-T_(c) superconducting YBa_(2)Cu_(3)O_(7). This large magnetoresistance is reminiscent of the giant magnetoresistance (GMR) in metallic superlattices but with much larger values, and originates at spin imbalance due to the injection of spin-polarized carriers. Furthermore, in contrast to ordinary GMR, the magnetoresistance is intimately related to the superconductivity in the YBa_(2)Cu_(3)O_(7) layer and vanishes in the normal state. This result, aside from its fundamental importance, may be of interest for the design of novel spintronic devices based on ferromagnet/superconductor structures.

Spin barrier enhanced magnetoresistance effect element and magnetic memory using the same

Abstract: A method and system for providing a magnetic element that is used in a magnetic memory device. The magnetic element includes pinned (122), spacer (13), free (140), and spin barrier layers (150). The spacer layer (130) is nonmagnetic and resides between the pinned (122) and free layers (140). The free layer (140) can be switched using spin transfer when a write current is passed through the magnetic element. The free layer (140) resides between the spacer layer (130) and the spin barrier (150) layer. The spin barrier layer (150) is configured to reduce an outer surface contribution to a damping constant of the free layer (140).

Positive colossal magnetoresistance from interface effect in p-n junction of La0.9Sr0.1MnO3 and SrNb0.01Ti0.99O3

Abstract: Different from the negative colossal magnetoresistance (CMR) of the LaMnO3 compound family, a positive CMR has been discovered at low applied magnetic field and high temperature in the epitaxial p-n heterostructure we fabricated with Sr-doped LaMnO3 and Nb-doped SrTiO3 by laser molecular-beam epitaxy. The mechanism causing the unusual positive CMR is proposed as a interface effect, i.e., the creation of a space charge region at the interface with different electron filling in bands comparing to that in the homogeneous region in Sr-doped LaMnO3. Other puzzling CMR features with bias voltage, temperature, and even composition are well explained by the present scenario.

Electrical and magnetic properties of polyaniline/Fe3O4 nanostructures

Abstract: We report on electrical and magnetic properties of polyaniline (PANI) nanotubes (∼150 nm in diameter) and PANI/Fe 3 O 4 nanowires (∼140 nm in diameter) containing Fe 3 O 4 nanoparticles with a typical size of 12 nm. These systems were prepared by a template-free method. The conductivity of the nanostructures is 10 −1 –10 −2 S/cm; and the temperature dependent resistivity follows a ln ρ∼T −1/2 law. The composites (6 and 20 wt% of Fe 3 O 4 ) show a large negative magnetoresistance compared with that of pure PANI nanotubes and a considerably lower saturated magnetization ( M s =3.45 emu/g at 300 K and 4.21 emu/g at 4 K) compared with the values measured from bulk magnetite ( M s =84 emu/g) and pure Fe 3 O 4 nanoparticles ( M s =65 emu/g). AC magnetic susceptibility was also measured. It is found that the peak position of the AC susceptibility of the nanocomposites shifts to a higher temperature (>245 K) compared with that of pure Fe 3 O 4 nanoparticles (190–200 K). These results suggest that interactions between the polymer matrix and nanoparticles take place in these nanocomposites.