Erratum: ''Magnetization of 2.6 T in gadolinium thin films'' [Appl. Phys. Lett. 101, 142407 (2012)]
No abstract prepared.
75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
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Reentrant Insulating State in Ultrathin Manganite Films
The transport and magnetic properties of La{sub 0.7}Sr{sub 0.3}MnO{sub 3} thin-films grown by pulsed laser deposition on (LaAlO{sub 3}){sub 0.3}(SrAl{sub 0.5}Ta{sub 0.5}O{sub 3}){sub 0.7} single crystal substrates have been investigated. A systematic series with various thicknesses of La{sub 0.7}Sr{sub 0.3}MnO{sub 3} was used to establish a phase diagram - which showed a clear difference compared to films grown on SrTiO{sub 3} substrates, highlighting the importance of film thickness and substrate strain. At 8 unit cells, the boundary between the metallic and insulating ground states, a second abrupt metal-insulator transition was observed at low temperatures, which could be tuned with by magnetic field, and is interpreted as a signature of electronic phase separation.
71 CLASSICAL AND QUANTUM MECHANICS, GENERAL PHYSIC↗
Magnetoelectric coupling of multiferroic chromium doped barium titanate thin film probed by magneto-impedance spectroscopy
Thin film of BaTiO{sub 3} doped with 0.1 at. % Cr (Cr:BTO) has been prepared by pulsed laser deposition technique. Film was deposited on Pt/SrTiO{sub 3} substrate at 500 °C in 50 mTorr Oxygen gas pressure using KrF (298 nm) laser. Polycrystalline growth of single phase Cr:BTO thin film has been confirmed by grazing angle X-ray diffraction. Cr:BTO film exhibited remnant polarization 6.4 μC/cm{sup 2} and 0.79 MV/cm coercivity. Magnetization measurement of Cr:BTO film showed magnetic moment 12 emu/cc. Formation of weakly magnetic domains has been captured by magnetic force microscopy. Theoretical impedance equation fitted to experimental data in Cole-Cole plot for thin film in presence of transverse magnetic field resolved the increase in grain capacitance from 4.58 × 10{sup −12} to 5.4 × 10{sup −11} F. Film exhibited high value 137 mV/cm-Oe magneto-electric (ME) coupling coefficient at room temperature. The high value of ME coupling obtained can reduce the typical processing steps involved in multilayer deposition to obtain multiferrocity in thin film. Barium titanate being best ferroelectric material has been tailored to be multiferroic by non ferromagnetic element, Cr, doping in thin film form opens an avenue for more stable and reliable spintronic material for low power magnetoelectric random excess memory applications.
36 MATERIALS SCIENCE↗
Local structure and magnetic properties of B2- and B20-like ultrathin Mn films grown on Si(001)
The structural and magnetic properties of ultrathin Mn layers deposited onto Si(001) by molecular beam epitaxy at low temperature are reported. X-ray absorption fine structure studies reveal that the structure of the silicide layer that forms depends on the growth temperature of the capping layer. A capping layer grown at 200 C on 0.35-monolayer (ML) Mn results in a metastable MnSi phase with a B2-like (CsCl) structure, whereas a cap grown at room temperature on 0.5 ML followed by annealing at 200 C produces a lower coordinated MnSi phase with a B20-like structure. Increasing the Mn thickness from 0.5 to 4 monolayers does not trigger a structural transformation but drives the structure closer to MnSi-B20. The sample with B2-like structure has the largest Mn magnetic moment of 0.33 {mu}{sub B}/Mn at T = 2 K, and a Curie temperature T{sub c} above 250 K. MnSi-B20 layers showed lower moments and much lower T{sub c}'s, in line with those reported for MnSi-B20 thin films.
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Spin and orbital magnetic moments of molecular beam epitaxy {gamma}{sup '}-Fe{sub 4}N films on LaAlO{sub 3}(001) and MgO(001) substrates by x-ray magnetic circular dichroism
10-nm-thick {gamma}{sup '}-Fe{sub 4}N films were grown epitaxially on LaAlO{sub 3}(001) and MgO(001) substrates by molecular beam epitaxy using solid Fe and a radio-frequency NH{sub 3} plasma. The lattice mismatch of these substrates to {gamma}{sup '}-Fe{sub 4}N is 0% and 11%, respectively. Spin and orbital magnetic moments of these {gamma}{sup '}-Fe{sub 4}N epitaxial films were deduced by x-ray magnetic circular dichroism measurements at 300 K. The total magnetic moments are almost the same for the two substrates, that is, 2.44{+-}0.06 {mu}{sub B} and 2.47{+-}0.06 {mu}{sub B}, respectively. These values are very close to those predicted theoretically, and distinctively larger than that for {alpha}-Fe.
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Highly (001) oriented L1{sub 0}-CoPt/TiN multilayer films on glass substrates with perpendicular magnetic anisotropy
To obtain strong perpendicular magnetic anisotropy (PMA) based on L1{sub 0} structure for magnetic storage devices, costly single crystalline substrates are generally required to achieve (001) texture. Recently, various studies also have focused on depositing different kinds of seed layers on glass or other amorphous substrates to promote (001) preferred orientation of L1{sub 0} CoPt and FePt. TiN is a very promising seed layer material because of its cubic crystalline structure (similar to MgO) and excellent diffusion barring property even at high temperatures. In the present work, highly (001) oriented L1{sub 0}-CoPt/TiN multilayer films have been successfully deposited on glass substrates. After annealing at 700 °C, the film exhibits PMA, and a strong (001) peak is detected from the x-ray diffraction profiles, indicating the ordering transformation of CoPt layers from fcc (A1) to L1{sub 0} structure. It also is found that alternate deposition of cubic TiN and CoPt effectively improves the crystallinity and (001) preferred orientation of CoPt layers. This effect is verified by the substantial enhancement of (001) reflection and PMA with increasing the period number of the multilayer films.
36 MATERIALS SCIENCE↗
Random Magnetic Anisotropy Studies in SmCo{sub 5} Thin Films
SmCo{sub 5} thin films with different thicknesses were prepared by electron beam evaporation on Kapton substrates. The out-of-plane hysteresis loops for different thicknesses reveal a maximum coercive field when the thickness is 15 nm. Using random magnetic anisotropy model, the thickness dependence of magnetic properties was studied in SmCo{sub 5} nanocrystalline films and several fundamental magnetic parameters were extracted. We have determined the local magnetic anisotropy constant K{sub 1} which is found to increase with increasing film thickness except for t = 7 nm which is thought to arise from the structural imperfection of the SmCo{sub 5} films.
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Critical currents, magnetic relaxation, and pinning in NdBa2Cu3O7-delta films with BaZrO3-generated columnar defects
The critical current density Jc and the magnetic relaxation ( creep ) properties have been studied for a set of NdBa2Cu3O7- (NdBCO) films doped with BaZrO3 (BZO) nanoparticles to form columnar defects. The dependence of Jc on the magnitude and orientation of the applied magnetic field Happ (0 6.5 T); and temperature T (5 K Tc) was investigated. The normalized flux-creep rate S = d ln(J ) / d ln(t) was determined as a function of T. The current dependence of the effective activation energy Ueff(J) was derived using the formalism developed by Maley. The results are well described by an inverse power-law type barrier of the form 0 0 ( ) ~ ( / ) eff U J U J J with fitted values for the pinning energy scale U0 and the glassy exponent . When comparing values for these parameters in the BZO-doped samples with those for their undoped control counterparts, the most striking difference is the larger scale of current density J0 in the doped samples (a factor of 2.4 higher), while the other pinning parameters do not differ strongly. In the BZO-doped materials, the pinning energy scale U0 increases with vortex density and J0 decreases, with both following simple power law dependencies on field.
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Effect of Substrate Temperature on Structural, Morphological, Magnetic, and Electrical Properties of Fe{sub 2}CoSi Heusler Alloy Thin Films for Spin-Based Device Applications
Fe{sub 2}CoSi based Heusler alloy thin films are deposited on single crystal Si (111) substrate at different substrate temperatures varying from room temperature to 600 °C using ultrahigh vacuum DC magnetron sputtering. Structural analysis of the prepared thin films is carried out using GI-XRD measurement and it conform ordered L2{sub 1} crystal structure of the films deposited at 450 °C and above. The atomic force microscopic (AFM) images of Fe{sub 2}CoSi thin films exhibiting 3D-like growth on Si (111) substrate at varying temperatures. The magnetic property of the thin films is studied using vibrating sample magnetometer (VSM). At 450 °C of substrate temperature, the prepared thin film exhibits high saturation magnetization (M{sub s} = 948 emu/cc) and low coercivity (H{sub c} = 8 Oe). The self-energy magnetization of the film and its own field is very high, when the temperature of the substrate was maintained at 450 °C and switching field ratio for this film was obtained as ~ 0.9 due to its high crystallinity and atomic ordering. The electrical property of Fe{sub 2}CoSi thin film is investigated using four-probe technique and a positive magnetoresistive behavior was observed for thin film deposited at a substrate temperature of 450 °C which indicates the possible half-metallic nature at room temperature. The enhanced magnetic and electrical properties obtained for the thin film prepared at 450 °C substrate temperature is highly suitable for spin based device applications.
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Multiferroic properties of Pb{sub 0.90}Sr{sub 0.10}TiO{sub 3}-CoFe{sub 2}O{sub 4} nanostructured bilayered thin film
Pb{sub 0.90}Sr{sub 0.10}TiO{sub 3}-CoFe{sub 2}O{sub 4}(PST10-CFO) nanostructured bilayered thin film were grown on Si (100) substrate by using metallo-organic decomposition chemical route and spin coating technique. Results show that PST (pervoskite structure) and CFO (spinel) phase coexist in the bilayered thin films, annealed at 650°C for 2hr and no obvious impurity phase can be detected. The structural, surface morphology and micro structural properties were confirmed by X-Ray diffraction (XRD), atomic force microscope (AFM) respectively. Excellent ferroelectric behavior at different voltage was observed, with two platinum electrodes only at surface of the bilayer thin film. A room temperature ferromagnetic behavior was observed in the bilayered Pb{sub 0.90}Sr{sub 0.10}TiO{sub 3}-CoFe{sub 2}O{sub 4} nanostructured thin film. The saturation magnetization and variation in coercivity value of the bilayer thin film is lower than that of the pure CFO film in the presence of non ferromagnetic PST layer which is the attributed that the significant coupling between the two phases.
71 CLASSICAL AND QUANTUM MECHANICS, GENERAL PHYSIC↗
Systematic control of strain-induced perpendicular magnetic anisotropy in epitaxial europium and terbium iron garnet thin films
We show tunable strain-induced perpendicular magnetic anisotropy (PMA) over a wide range of thicknesses in epitaxial ferrimagnetic insulator Eu 3 Fe 5 O 12 (EuIG) and Tb 3 Fe 5 O 12 (TbIG) thin films grown by pulsed-laser deposition on Gd 3 Ga 5 O 12 with (001) and (111) orientations, respectively. The PMA field is determined by measuring the induced anomalous Hall loops in Pt deposited on the garnet films. Due to positive magnetostriction constants, compressive in-plane strain induces a PMA field as large as 32.9 kOe for 4 nm thick EuIG and 66.7 kOe for 5 nm thick TbIG at 300 K and relaxes extremely slowly as the garnet film thickness increases. In bilayers consisting of Pt and EuIG or Pt and TbIG, robust PMA is revealed by squared anomalous Hall hysteresis loops in Pt, the magnitude of which appears to be only related to the net magnetic moment of iron sublattices. Furthermore, the magnetostriction constant is found to be 2.7 × 10 -5 for EuIG and 1.35 × 10 -5 for TbIG, comparable with the values for bulk crystals. Our results demonstrate a general approach of tailoring magnetic anisotropy of rare earth iron garnets by utilizing modulated strain via epitaxial growth.
36 MATERIALS SCIENCE↗
Insight into magnetic, ferroelectric and elastic properties of strained BiFeO{sub 3} thin films through Mössbauer spectroscopy
We have studied the magnetic order of highly strained (001)-oriented BiFeO{sub 3} (BFO) thin films using {sup 57}Fe Conversion Electron Mössbauer Spectrometry. From 90 K to 620 K the films exhibit a collinear antiferromagnetic structure, in contrast with the cycloidal structure observed in bulk BFO. Moreover, we find that both the planar magnetic anisotropy for compressive strain and out-of-plane anisotropy for tensile strain persist from 90 K up to the Néel temperature (T{sub N}), which itself shows only a weak strain dependence. An analysis of the line asymmetry of the paramagnetic doublet for temperatures above T{sub N} is used to reveal the strain-dependent rotation of the polarization direction, consistent with previous observations. Our results show that the lattice dynamics in BFO films are strongly strain-dependent, offering avenues toward acoustic phonon devices. Finally, we use the versatility of Mössbauer spectroscopy technique to reveal various multi-property features including magnetic states, polarization direction and elastic strain.
71 CLASSICAL AND QUANTUM MECHANICS, GENERAL PHYSIC↗
Growth and magnetic property of antiperovskite manganese nitride films doped with Cu by molecular beam epitaxy
Manganese nitrides thin films on MgO (100) substrates with and without Cu-doping have been fabricated by plasma assisted molecular beam epitaxy. Antiperovskite compounds Mn{sub 3.6}Cu{sub 0.4}N have been grown in the case of Cu-doping, and the pure Mn{sub 3}N{sub 2} single crystal has been obtained without Cu-doping. The Mn{sub 3.6}Cu{sub 0.4}N exhibits ferrimagnetism, and the magnetization of Mn{sub 3.6}Cu{sub 0.4}N increases upon the temperature decreasing from 300 K to 5 K, similar to Mn{sub 4}N. The exchange bias (EB) effects emerge in the Mn{sub 3.6}Cu{sub 0.4}N films. The EB behavior is originated from the interfaces between ferrimagnetic Mn{sub 3.6}Cu{sub 0.4}N and antiferromagnetic metal Mn, which is verified to be formed by the data of x-ray photoelectron spectroscopy. The present results not only provide a strategy for producing functional antiperovskite manganese nitrides, but also shed promising light on fabricating the exchange bias part of spintronic devices.
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Impact of the Field of a Magnetic Force Microscope Probe on the Skyrmion State in a Modified Co/Pt Film with Perpendicular Anisotropy
We present the results of experiments on the local magnetization reversal of artificial magnetic skyrmions in a Co/Pt multilayer film with a perpendicular magnetization by a magnetic force microscope (MFM) probe. The sample was a Co/Pt film containing an array of cylindrical regions with reduced anisotropy, modified by a focused He{sup +} ion beam. The magnetic state of the sample was monitored by magnetic force microscopy. The magnetization reversal was performed by the MFM probe field during passes over the sample at low altitudes. The effects of the interaction of the field of the MFM probe with the skyrmion state of magnetization in these structures are investigated by micromagnetic simulation.
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Unraveling the magnetic properties of BiFe{sub 0.5}Cr{sub 0.5}O{sub 3} thin films
We investigate the structural, chemical, and magnetic properties on BiFe{sub 0.5}Cr{sub 0.5}O{sub 3} (BFCO) thin films grown on (001) (110) and (111) oriented SrTiO{sub 3} (STO) substrates by x-ray magnetic circular dichroism and x-ray diffraction. We show how highly pure BFCO films, differently from the theoretically expected ferrimagnetic behavior, present a very weak dichroic signal at Cr and Fe edges, with both moments aligned with the external field. Chemically sensitive hysteresis loops show no hysteretic behavior and no saturation up to 6.8 T. The linear responses are induced by the tilting of the Cr and Fe moments along the applied magnetic field.
36 MATERIALS SCIENCE↗
Swift heavy ion irradiation induced magnetism in magnetically frustrated BiMn{sub 2}O{sub 5} thin films
The swift heavy ion (SHI) irradiation induces weak ferrimagnetism (FM) in magnetically frustrated polycrystalline BiMn{sub 2}O{sub 5} thin films. This is manifested from irradiation induced higher energetic configuration that accounts for evolution of the Mn{sup 2+} state in the Mn{sup 3+}/Mn{sup 4+} network. Basically, this is the root of large magnetic moment in the irradiated samples. X-ray diffraction and Raman-scattering data of the samples indicate considerable modifications in the crystal structure after the SHI irradiation. FM in the irradiated samples and magnetically frustrated behavior of the pristine sample is apparent from dc magnetization measurements. Element specific characterizations such as near-edge x-ray absorption fine structure spectroscopy at O K and Mn L{sub 3,2} edges along with x-ray magnetic circular dichroism at Mn L{sub 3,2} edge show the evolution of the Mn{sup 2+} at disbursement of the Mn{sup 4+}. The microscopic origin behind the induced weak FM is found to be the increased orbital moment in the irradiated thin films.
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Electrodeposition of Magnonic V(tetracyanoethylene) 2 Thin Films
Molecule-based magnetic materials have been identified as promising candidates for application in magnonic technologies, owing not only to their solution processability but also because they can exhibit narrow ferromagnetic resonance (FMR) linewidths and low Gilbert damping coefficients—crucial prerequisites for the transmission of coherent magnons over macroscopic distances. In particular, V(TCNE) 2 , a compound with a threedimensional network structure composed of vanadium(II) centers linked by tetracyanoethylene (TCNE •− ) radical anions, displays magnonic properties comparable to yttrium iron garnet, the quintessential magnonic material in the field. However, existing solution and chemical vapor deposition methods for synthesizing V(TCNE) 2 require the use of highly reactive zero-valent molecular vanadium precursors, stymying research on this important material. Herein, we report a facile electrochemical method for the deposition of thin films of V(TCNE) 2 using readily obtainable and stable divalent vanadium precursors and TCNE •− anions generated by electrochemical reduction. Magnetization measurements reveal that the films exhibit ferrimagnetic ordering above room temperature, consistent with V(TCNE) 2 films synthesized via other methods. Moreover, the electrodeposited films exhibit narrow FMR linewidths as low as 17.5 G and a low Gilbert damping coefficient of 1.1 × 10 −3 , values that are on par with some currently integrated metallic magnonic materials. More generally, these results demonstrate that electrodeposition can provide a straightforward means of generating highperformance magnonic materials using readily available molecular precursors.
37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
Magnetic properties of low-moment ferrimagnetic Heusler Cr 2 CoGa thin films grown by molecular beam epitaxy
Recently, theorists have predicted many materials with a low magnetic moment and large spin-polarization for spintronic applications. These compounds are predicted to form in the inverse Heusler structure; however, many of these compounds have been found to phase segregate. In this study, ordered Cr 2 CoGa thin films were synthesized without phase segregation using molecular beam epitaxy. The present as-grown films exhibit a low magnetic moment from antiferromagnetically coupled Cr and Co atoms as measured with superconducting quantum interface device magnetometry and soft X-ray magnetic circular dichroism. Electrical measurements demonstrated a thermally-activated semiconductor-like resistivity component with an activation energy of 87 meV. Finally, these results confirm spin gapless semiconducting behavior, which makes these thin films well positioned for future devices.
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