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1 Jun 1998

Volume 83, Issue 11, pp. 5609-7398

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Band offsets at the InAlGaAs/InAlAs (001) heterostructures lattice matched to an InP substrate

X. H. Zhang, S. J. Chua, S. J. Xu, and W. J. Fan

J. Appl. Phys. 83, 5852 (1998); http://dx.doi.org/10.1063/1.367443 (3 pages) | Cited 2 times

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The first-principles pseudopotential method combined with virtual crystal approximation is used to calculate band offsets at the In0.53(AlzGa1−z)0.47As/In0.52Al0.48As (001) heterostructures lattice matched to an InP substrate. It is found that the valence-band offset (VBO) varies with respect to the aluminum composition as VBO = 0.18–0.16z–0.02z2 eV, while the conduction-band offset (CBO) varies as CBO = 0.51–0.33z–0.18z2 eV. Our results are in good agreement with the experimental data. © 1998 American Institute of Physics.
Show PACS
73.20.At Surface states, band structure, electron density of states
73.61.Ey III-V semiconductors
73.40.Kp III-V semiconductor-to-semiconductor contacts, p-n junctions, and heterojunctions
71.15.Dx Computational methodology (Brillouin zone sampling, iterative diagonalization, pseudopotential construction)

Thermoelectric power in porous silicon

R. G. Mathur, R. M. Mehra, and P. C. Mathur

J. Appl. Phys. 83, 5855 (1998); http://dx.doi.org/10.1063/1.367444 (3 pages) | Cited 8 times

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Thermoelectric power measurements have been made on macroporous (pore width >500 Å°) porous silicon samples prepared by an anodic dissolution technique. The sign of thermopower is found to be negative indicating that conduction takes place due to electrons in the conduction band. The conduction mechanism is found to be due to variable range hopping near the Fermi level for temperatures below 150 K. At higher temperatures the conduction is due to the tunneling of carriers in the localized states in the band edges. It was concluded that these localized states are formed because the nanocrystallites in porous silicon are randomly distributed in size and orientation leading to fluctuations in band gap. This results in the constitution of a disordered system on a macroscopic scale. © 1998 American Institute of Physics.
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72.80.Cw Elemental semiconductors
72.20.Pa Thermoelectric and thermomagnetic effects
72.20.Fr Low-field transport and mobility; piezoresistance
71.55.Jv Disordered structures; amorphous and glassy solids

Electrical properties of Ga and ZnS doped ZnO prepared by mechanical alloying

B. A. Cook, J. L. Harringa, and C. B. Vining

J. Appl. Phys. 83, 5858 (1998); http://dx.doi.org/10.1063/1.367445 (4 pages) | Cited 8 times

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A series of n-type ZnO alloys doped with Ga and ZnS were prepared by mechanical alloying. Densities of 95% to 98% of theoretical density were achieved by hot pressing the milled powders at 1000 and 1200 °C, respectively. The electrical resistivity and Seebeck coefficient of alloys containing 0.25–3.0 at. % Ga were characterized between 22 and 1000 °C. The magnitude of the resistivity and Seebeck coefficient at 22 °C ranged from 0.2 mΩ cm and −25 μV/°C for the most heavily doped specimen to 1.1 mΩ cm and −70 μV/°C for the lightly doped material. The alloys exhibit a positive temperature coefficient of resistivity and Seebeck coefficient with a nearly constant slope over the temperature range studied. Thermal diffusivity measurements on a specimen containing 1.0 at. % Ga were performed over the same temperature range. The thermal conductivity appears to follow a T−1 dependence, decreasing from 180 mW/cm °C at 22 °C to 82 mW/cm °C at 1000 °C. An estimate of the maximum dimensionless thermoelectric figure of merit, ZT, in this system at 1000 °C gives a value of 0.26, a factor of three to four less than current state-of-the-art materials such as Si–Ge. A significant reduction in thermal conductivity would be required to make these alloys competitive with existing thermoelectric power generation materials. © 1998 American Institute of Physics.
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72.80.Ey III-V and II-VI semiconductors
81.05.Dz II-VI semiconductors
72.20.Fr Low-field transport and mobility; piezoresistance
72.20.Pa Thermoelectric and thermomagnetic effects
81.20.Ev Powder processing: powder metallurgy, compaction, sintering, mechanical alloying, and granulation
66.70.-f Nonelectronic thermal conduction and heat-pulse propagation in solids; thermal waves

Electron mobility in In0.5Ga0.5P

B. R. Nag and Madhumita Das

J. Appl. Phys. 83, 5862 (1998); http://dx.doi.org/10.1063/1.367446 (3 pages) | Cited 4 times

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The Hall mobility of electrons is calculated for In0.5Ga0.5P by using the experimental values of the effective mass and the band gap, and the estimated values of other constants. The experimental results are explained by taking the alloy scattering potential and the acoustic phonon deformation potential to be 0.435 and 12 eV, respectively. It is concluded that the experimental samples had impurity concentrations lying mostly between 5 and 15 times the electron concentration. © 1998 American Institute of Physics.
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72.80.Ey III-V and II-VI semiconductors
72.20.My Galvanomagnetic and other magnetotransport effects
72.20.Jv Charge carriers: generation, recombination, lifetime, and trapping
71.20.Nr Semiconductor compounds

Electrical properties of buried B/Si surface phases

A. V. Zotov, V. G. Lifshits, T. Rupp, and I. Eisele

J. Appl. Phys. 83, 5865 (1998); http://dx.doi.org/10.1063/1.367447 (5 pages) | Cited 1 time

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Conductivity and Hall-effect measurements have been carried out at 24 K for a set of various layered structures with buried B/Si surface phases used as delta-doped layers. Evidence is found for hole mobility enhancement as a consequence of boron dopant ordering. The electrical measurements reveal a basic difference in room temperature adsorption for boron on Si(100) and Si(111) surfaces. The characterization of the samples containing buried B/Si(111) interfaces and extra-thin Ge layers suggests promise for improving the structure and electrical properties of the buried surface phases. The hole mobility in epi-Si/Ge/B/Si(111) structures is found to be about 2.5 times higher than in epi-Si/B/Si(111) samples. © 1998 American Institute of Physics.
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73.40.Lq Other semiconductor-to-semiconductor contacts, p-n junctions, and heterojunctions
73.61.Cw Elemental semiconductors
72.20.My Galvanomagnetic and other magnetotransport effects
73.50.Jt Galvanomagnetic and other magnetotransport effects (including thermomagnetic effects)
68.03.Fg Evaporation and condensation of liquids
68.43.Mn Adsorption kinetics
73.50.Dn Low-field transport and mobility; piezoresistance
72.20.Fr Low-field transport and mobility; piezoresistance

Charge injection and conduction on the surface of insulators

M. P. Pépin and H. J. Wintle

J. Appl. Phys. 83, 5870 (1998); http://dx.doi.org/10.1063/1.367448 (10 pages) | Cited 4 times

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We have calculated numerically the flow of charge onto an insulator surface by injection from an electrode touching the surface, using conformal mapping in conjunction with the boundary element method. We have assumed that the driving fields are due to the electrodes and to the surface charge itself, while the natural conductivity of the surface is negligible. We have considered three geometries used experimentally. In general, we find that for strong injection, the surface charge is confined to the region close to the injecting electrode, that the absorption current behaves as I∝t−γ,γ ∼ 1/3, and that the absorption and resorption currents do not exhibit mirror symmetry. Furthermore, if the active electrode can inject charges of either sign, then on shorting the electrodes a counter charge is injected, which leads to a more rapid discharge at early times but does not give rise to a current reversal (anomalous current). Materials of higher dielectric constant store more surface charge. We compare our results with previous calculations and with existing experimental work. © 1998 American Institute of Physics.
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73.25.+i Surface conductivity and carrier phenomena
77.22.Jp Dielectric breakdown and space-charge effects

The origin of Ga2O3 passivation for reconstructed GaAs(001) surfaces

Jiang Guo-Ping and Harry E. Ruda

J. Appl. Phys. 83, 5880 (1998); http://dx.doi.org/10.1063/1.367449 (5 pages) | Cited 10 times

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Ab initio molecular-orbital calculations are used to study the origin of the Ga2O3 passivation mechanism for GaAs(100) reconstructed surfaces. Two cluster models are used to simulate the main features of reconstructed and oxygen chemisorbed GaAs(100) surfaces. The simulation results show that the reduction in the density of surface states located within the bulk energy gap derives from the initial near-bridge-bonded O atoms. The calculated electronic energy spectra reveal that the surface-state energy gap lies completely outside of the bulk energy gap in distinct contrast to the case for S passivation. At the optimized geometry, each surface Ga atom (situated beneath the adsorbed O) is distorted by 0.40 Å from its ideal position, resulting in a strained surface. O atoms are almost buried in the GaAs(100) surface; each is located 0.30 and 0.25 Å above the reconstructed GaAs(100) surface, respectively. The O–Ga bond length is 1.63 Å and the Ga–O–Ga bond angle is 157.4°. Each O atom deviates from the bridge position by 0.11 and 0.19 Å from the vertical position, respectively. This causes further deposition to result in the formation of an amorphous oxide film, which provides an effective protection layer against further oxidation of the near-bridge-site oxidized GaAs surface. The calculated electronic structure and local density of states also reflect a large charge accumulation near the adsorbed O atoms.
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81.05.Ea III-V semiconductors
73.20.Hb Impurity and defect levels; energy states of adsorbed species
81.65.Rv Passivation
73.20.At Surface states, band structure, electron density of states
72.80.Ey III-V and II-VI semiconductors
68.03.Fg Evaporation and condensation of liquids
68.43.Mn Adsorption kinetics
68.35.B- Structure of clean surfaces (and surface reconstruction)
68.35.Rh Phase transitions and critical phenomena

Investigation of the properties of plasma-enhanced chemical vapor deposited silicon nitride and its effect on silicon surface passivation

L. Cai, A. Rohatgi, S. Han, G. May, and M. Zou

J. Appl. Phys. 83, 5885 (1998); http://dx.doi.org/10.1063/1.367450 (5 pages) | Cited 13 times

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Silicon nitride films grown by plasma-enhanced chemical vapor deposition (PECVD) are used for a variety of applications in integrated circuit and solar cell industries, such as surface passivation and insulation. The objective of this article is to investigate and understand the impact of the PECVD deposition parameters on the silicon surface passivation and establish the correlation between the properties of the silicon nitride and the ensuing silicon surface recombination velocity. All the films were annealed at 350 °C for 20 min in a rapid thermal annealer after the deposition. It is shown that bonded hydrogen and positive charge in the annealed PECVD silicon nitride films have the opposite effect on the surface passivation. The surface recombination velocity decreases with the increase in the positive charge density and the decrease in the bonded hydrogen content. It is found that the deposition temperature has the most influence on achieving low surface recombination velocity. Higher deposition temperature in the range of 200–300 °C produces lower surface recombination velocity. Optimal silicon nitride deposition conditions resulted in a surface recombination velocity of 119 cm/s on 2 Ω cm p-type silicon. © 1998 American Institute of Physics.  
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72.80.Cw Elemental semiconductors
81.15.Gh Chemical vapor deposition (including plasma-enhanced CVD, MOCVD, ALD, etc.)
81.65.Rv Passivation
81.05.Cy Elemental semiconductors
68.55.-a Thin film structure and morphology
52.77.Bn Etching and cleaning
52.77.Dq Plasma-based ion implantation and deposition

Current–voltage characteristics of the partially Ga-terminated Si (111) surface studied by scanning tunneling microscopy

Yukihiro Kusumi, Ken Fujita, and Masakazu Ichikawa

J. Appl. Phys. 83, 5890 (1998); http://dx.doi.org/10.1063/1.367451 (6 pages) | Cited 1 time

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We investigated the current–voltage (I–V) characteristics of the Si (111) surface partially terminated by Ga atoms by using scanning tunneling microscopy. On the surface, Si (111) 7×7 and Si (111) √3×√3 Ga terraces alternated. The I–V curves of the 7×7 terraces exhibited semiconductive features, not metallic. The √3×√3 Ga terraces on the surface had narrower surface band gaps than usual √3×√3 Ga surfaces. These features could be explained by taking into account the adatom replacement between Ga and Si adatom sites. An amorphous Si layer was deposited on the surface after Sb was selectively adsorbed on the 7×7 terraces. The alternate structure was preserved after recrystallization of the Si layer. © 1998 American Institute of Physics.
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68.35.B- Structure of clean surfaces (and surface reconstruction)
68.35.Rh Phase transitions and critical phenomena
72.80.Cw Elemental semiconductors
73.25.+i Surface conductivity and carrier phenomena
73.20.At Surface states, band structure, electron density of states
68.03.Fg Evaporation and condensation of liquids
68.43.Mn Adsorption kinetics

Transport simulation of bulk AlxGa1−xN and the two-dimensional electron gas at the AlxGa1−xN/GaN interface

Mahesh S. Krishnan, Neil Goldsman, and Aris Christou

J. Appl. Phys. 83, 5896 (1998); http://dx.doi.org/10.1063/1.367452 (8 pages) | Cited 5 times

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In this work, a hybrid Monte Carlo simulation with the inclusion of degenerate statistics has been performed to analyze electron transport in bulk AlxGa1−xN, and the two-dimensional electron gas at the AlxGa1−xN/GaN interface. The results of the steady-state drift velocity, average electron energy, and distribution functions for bulk AlxGa1−xN are presented. A study of the change in transport properties with compositional variations has been made and presented here. Degeneracy has been found to affect electron transport in both the low- and the high-field regions. The inclusion of degeneracy caused a pronounced negative differential mobility. Simulation of the two-dimensional electron gas takes into account three subbands at the AlxGa1−xN/GaN interface. A self-consistent solution of the Schrödinger and Poisson equations at the heterointerface is obtained through a Rayleigh–Ritz method that should result in more accurate electron wave functions, and hence, more accurate scattering rates for the two-dimensional electron gas. The inclusion of degenerate statistics caused an increase in the interband occupancy in addition to an increase in the electron kinetic energy in the subbands. © 1998 American Institute of Physics.
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72.80.Ey III-V and II-VI semiconductors
73.21.-b Electron states and collective excitations in multilayers, quantum wells, mesoscopic, and nanoscale systems

Electrical deactivation of interstitial Zn in heteroepitaxial InP by hydrogen and its effect on electronic properties

S. A. Ringel and B. Chatterjee

J. Appl. Phys. 83, 5904 (1998); http://dx.doi.org/10.1063/1.367453 (9 pages) | Cited 3 times

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Hydrogen passivation of InP layers grown on lattice-mismatched substrates can achieve thermally stable deactivation of dislocation-related deep levels, making this a promising process for improving the performance of heteroepitaxial InP space solar cells. However, in addition to dislocation-related defects, interstitial Zn (Zni) defects that are characteristic of Zn-doped InP and which form deep donor states within the InP band gap, are important considerations for optimizing the electronic quality of these layers. Here, we show that hydrogen forms complexes with and deactivates Zni donor states within Zn-doped InP grown by metalorganic chemical vapor deposition. A combination of photoluminescence (PL), electrochemical capacitance–voltage dopant profiling, secondary ion mass spectroscopy and current–voltage (I–V) measurements are applied to a set of samples receiving systematic hydrogenation and annealing treatments. We find that the deactivation of Zni deep donors, as detected by monitoring the evolution of the donor–acceptor transition using PL measurements, causes an increase of ∼50% in the net acceptor concentration of heavily Zn-doped heteroepitaxial InP by elimination of the acceptor compensation effect due to active Zni donors. Analysis of I–V characteristics indicates that Zni passivation sharply reduces depletion region recombination and shunt currents within heteroepitaxial diodes, causing an increase in the diode turn-on voltage from 680 to 960 mV. Subsequent annealing above 500 °C reactivates the Zni defects, resulting in a systematic increase in doping compensation as well as a decrease in VTO toward the original, as-grown value. A study of the reactivation kinetics for the H–Zni complex reveals a greater thermal stability than that of H–Zn acceptor complexes but less than that of H-dislocation complexes in InP, with an estimated dissociation energy for the H–Zni complex of 2.3 eV. While these effects are observed for both homoepitaxial and heteroepitaxial Zn-doped layers, the effect is far more pronounced for the heteroepitaxial layers due to the relatively high Zni concentration in the latter. © 1998 American Institute of Physics.
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81.65.Rv Passivation
61.72.J- Point defects and defect clusters
61.72.Yx Interaction between different crystal defects; gettering effect
79.20.Rf Atomic, molecular, and ion beam impact and interactions with surfaces
81.05.Ea III-V semiconductors
82.80.Ms Mass spectrometry (including SIMS, multiphoton ionization and resonance ionization mass spectrometry, MALDI)
82.80.Fk Electrochemical methods
84.60.Jt Photoelectric conversion
78.55.Cr III-V semiconductors
73.61.Ey III-V semiconductors
71.55.Eq III-V semiconductors
61.72.Cc Kinetics of defect formation and annealing
68.60.Dv Thermal stability; thermal effects

Growth and small polaron properties of epitaxial La1−xCaxMnO3 thin films

D. C. Worledge, L. Miéville, and T. H. Geballe

J. Appl. Phys. 83, 5913 (1998); http://dx.doi.org/10.1063/1.367454 (4 pages) | Cited 12 times

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We report on the epitaxial growth and properties of La1−xCaxMnO3 thin films deposited by pulsed laser ablation. We grew and characterized 11 thin films covering the entire doping range, from x = 0 to x = 1. A presence of oxygen during postdeposition annealing is shown to be required in order to reduce the resistivity of the samples and to obtain reproducible samples. The lattice constant and phonon frequency that appear in the Emin–Holstein, [D. Emin and T. Holstein, Ann. Phys. 53, 439 (1969).] adiabatic small polaron conductivity formula are reported. Resistivity data from 20 to 300 K are also reported. © 1998 American Institute of Physics.
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81.15.Fg Pulsed laser ablation deposition
73.50.Jt Galvanomagnetic and other magnetotransport effects (including thermomagnetic effects)
71.38.-k Polarons and electron-phonon interactions
73.61.Ng Insulators

Experimental study of the effective secondary emission coefficient for rare gases and copper electrodes

G. Auday, Ph. Guillot, J. Galy, and H. Brunet

J. Appl. Phys. 83, 5917 (1998); http://dx.doi.org/10.1063/1.367455 (5 pages) | Cited 36 times

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Measurements are made for variations of the effective secondary emission coefficient γ with reduced field E/p. Plane-parallel copper electrodes (5 cm diameter) are sustained with a dc voltage (0<V<1 kV) and can be separated by a variable distance (2 mm<d<1 cm). Current–voltage characteristics, Paschen curves, and γ(E/p) variations are shown for various rare gases (neon, argon, krypton, and xenon). γ(E/p) values are deduced from Paschen curves and published α/p(E/p) variations by using the self-sustain condition. Comparisons are made with various experimental or calculated results taken from the literature. © 1998 American Institute of Physics.
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79.20.Hx Electron impact: secondary emission

Theory of magnetoelastic dissipation due to domain wall width oscillation

Y. Liu and P. Grütter

J. Appl. Phys. 83, 5922 (1998); http://dx.doi.org/10.1063/1.367456 (5 pages) | Cited 8 times

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This article presents a general treatment of magnetic dissipation due to domain wall width oscillation via magnetostriction in magnetic samples. The domain wall width is modeled as a harmonic oscillator. The parameters governing this oscillator (effective mass, stiffness, damping coefficient and driving force) are derived and expressed in terms of intrinsic magnetic parameters of magnetic materials. The magnetostriction induced damping of wall width oscillations is frictional in nature. An external ac magnetic field serves as a driving force of the oscillator. It is found that the response to the driving force depends very much on the micromagnetic structures of the magnetic domain wall. Different micromagnetic structures lead to different magnetic dissipation for a given external field. Besides giving a quantitative microscopic explanation to magnetic dissipation data measured by magnetic dissipation force microscopy, this theory predicts two new phenomena: one is that there is a minimum driving force for the wall width to oscillate and the other is a new resonance phenomenon, domain wall width resonance. © 1998 American Institute of Physics.
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75.80.+q Magnetomechanical effects, magnetostriction
75.60.Ch Domain walls and domain structure

Magnetoresistance, Hall effect, and thermoelectric power in spin valves

H. Sato, S. Miya, Y. Kobayashi, Y. Aoki, H. Yamamoto, and M. Nakada

J. Appl. Phys. 83, 5927 (1998); http://dx.doi.org/10.1063/1.367457 (6 pages) | Cited 5 times

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Comparison of the magnetoresistance (MR) on two groups of spin-valve multilayers, NiO/NiFe/Cu/NiFe/Cu/NiO and NiO/NiFe/Cu/NiFe/Cu, has been made in order to investigate the possibility of the enhanced specular scattering at NiO/metal interface. No clear difference in MR between the two systems has been found, suggesting that the enhancement of specular scattering at interfaces is not the origin of the large MR. For the field direction almost perpendicular to the plane, we found a sensitive angular dependence of MR along with a large unidirectional anisotropy. To sort out any specific characteristics of the spin-valve system compared to the multilayers, thermoelectric power and Hall effect have been investigated for the first time. © 1998 American Institute of Physics.
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73.50.Jt Galvanomagnetic and other magnetotransport effects (including thermomagnetic effects)
72.15.Jf Thermoelectric and thermomagnetic effects
75.47.De Giant magnetoresistance
73.61.At Metal and metallic alloys
75.70.Cn Magnetic properties of interfaces (multilayers, superlattices, heterostructures)
72.15.Gd Galvanomagnetic and other magnetotransport effects
75.30.Gw Magnetic anisotropy
75.50.Bb Fe and its alloys

Generalized inclusion model for the coercivity of soft magnetic materials

L. Lopez Diaz and E. Della Torre

J. Appl. Phys. 83, 5933 (1998); http://dx.doi.org/10.1063/1.367458 (9 pages) | Cited 9 times

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The principal causes of coercivity in soft magnetic materials are the imperfections in the structure of the crystal, such as inclusion and grain boundaries, that pin domain walls. The models that have been proposed so far in order to explain this effect are only valid for a specific range of material parameters. In this paper, we present a two-dimensional micromagnetic model for Barkhausen coercivity due to inclusions that is valid for all physically realizable material parameters. The details of the interaction between Bloch walls and nonmagnetic inclusions are presented for some interesting special cases. One of the results the model predicts is that walls are stable when they are centered on the inclusion. Furthermore, much higher values of the coercivity are obtained than those predicted by previous models. © 1998 American Institute of Physics.
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75.60.Ej Magnetization curves, hysteresis, Barkhausen and related effects
61.72.Qq Microscopic defects (voids, inclusions, etc.)
75.60.Ch Domain walls and domain structure

Magnetic relaxation in Sm2Fe14Ga3 and Sm2Fe14Ga3C

N. Mommer, M. Gerlach, J. van Lier, and H. Kronmüller

J. Appl. Phys. 83, 5942 (1998); http://dx.doi.org/10.1063/1.367459 (3 pages) | Cited 1 time

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Magnetic after-effect measurements of Sm2Fe14Ga3 and the carbide Sm2Fe14Ga3C were performed in the temperature range of 140 to 450 K. In the case of Sm2Fe14Ga3C, the relaxation spectrum is composed of two characteristic maxima at 220 and 320 K. The latter maximum is not present in Sm2Fe14Ga3 and therefore assigned to local jumps of interstitially dissolved carbon atoms while the former is attributed to hydrogen. Numerical evaluation yielded an activation enthalpy of (0.96 ± 0.02) eV and a pre-exponential factor τ0 = 3×10−14±0.5 s for the short-range diffusion of C atoms. The corresponding values for the short-range diffusion of hydrogen are (0.64±0.04) eV and τ0 = 3×10−14±1 s. © 1998 American Institute of Physics.
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75.50.Bb Fe and its alloys
75.30.Gw Magnetic anisotropy
75.60.Lr Magnetic aftereffects
76.50.+g Ferromagnetic, antiferromagnetic, and ferrimagnetic resonances; spin-wave resonance
75.50.Ww Permanent magnets

Effects of Ga substitution on structure and magnetocrystalline anisotropy of Tm2Fe17

Bao-gen Shen, Zhao-hua Cheng, Fang-wei Wang, Qi-wei Yan, Hong Tang, Bing Liang, Shao-ying Zhang, F. R. de Boer, K. H. J. Buschow, and S. Ridwan

J. Appl. Phys. 83, 5945 (1998); http://dx.doi.org/10.1063/1.367990 (10 pages) | Cited 11 times

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A detailed investigation of the structure and magnetic properties of Tm2Fe17−xGax (x = 0, 1, 2, 3, 4, 5, 6, 7, and 8) compounds has been performed by means of x-ray-diffraction, neutron-diffraction, magnetization, and ac-susceptibility measurements. Crystal-structure studies have shown that the prepared samples are single phase with the hexagonal Th2Ni17 for x ⩽ 3 and the rhombohedral Th2Zn17 structure for x ≥ 5. In Tm2Fe13Ga4 the Th2Zn17 structure coexists with the Th2Ni17 structure. Substitution of Ga for Fe in Tm2Fe17 leads to an increase of the unit-cell volume, which is linear with the Ga concentration. In Tm2Fe17−xGax, the saturation magnetization at 1.5 K decreases linearly with increasing Ga content with a rate of 2.3 μB per substituted Ga atom. The Curie temperature is found first to increase with increasing Ga content, going through a maximum value of 485 K at about x = 3, then to decrease. Between x = 6 and 7, a minimum value of TC is reached and for higher x values TC increases again. X-ray-diffraction measurements on magnetically aligned Tm2Fe17−xGax powders show that the compounds with x ⩽ 6 have an easy-plane type of magnetic anisotropy, whereas the compounds with x ≥ 7 exhibit easy c-axis anisotropy at room temperature. All Tm2Fe17−xGax compounds exhibit a spin-reorientation transition at low temperature, except for the sample with x = 6, which shows an easy-magnetization direction perpendicular to the c axis in the temperature range from 5 to 300 K. For x ⩽ 5, the spin-reorientation temperature is found first to increase with x and then to decrease, having a maximum value of 211 K at about x = 3. In the samples with x ≥ 7, an easy-plane anisotropy was observed at low temperature, but an easy-axis preference of the magnetization at room temperature was observed. The results obtained for Tm2Fe17−xGax indicate that the mutually competing Tm- and Fe-sublattice anisotropies both change their sign with increasing Ga concentration. © 1998 American Institute of Physics.
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75.30.Gw Magnetic anisotropy
75.60.Ej Magnetization curves, hysteresis, Barkhausen and related effects
75.50.Tt Fine-particle systems; nanocrystalline materials
75.25.-j Spin arrangements in magnetically ordered materials (including neutron and spin-polarized electron studies, synchrotron-source x-ray scattering, etc.)
61.66.Dk Alloys
75.30.Cr Saturation moments and magnetic susceptibilities
75.40.Gb Dynamic properties (dynamic susceptibility, spin waves, spin diffusion, dynamic scaling, etc.)
75.30.Kz Magnetic phase boundaries (including classical and quantum magnetic transitions, metamagnetism, etc.)

Magnetic and structural properties of epitaxially grown FeTaN thin films

L. Varga, H. Jiang, T. J. Klemmer, W. D. Doyle, and E. A. Payzant

J. Appl. Phys. 83, 5955 (1998); http://dx.doi.org/10.1063/1.367460 (12 pages) | Cited 11 times

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Epitaxial FeTaN films (∼1500 Å) were grown as a function of nitrogen flow rate on epitaxial Cu(001) buffer layers (∼2000 Å) on Si(001) single crystal substrates to investigate the effect of Ta and nitrogen on the magnetocrystalline anisotropy and magnetostriction. Detailed structural investigation by transmission electron microscopy and x-ray diffraction showed that the FeTaN films were epitaxial with the Pitsch orientation relationship of FeTaN(110)∥Cu(001) and FeTaN〈111〉∥Cu〈110〉, which allows four different in-plane variants to coexist in the film. It was found that the saturation magnetization did not change with nitrogen addition (∼1600 emu/cc) up to 2% lattice dilation. The values of K1 and λ100 of Fe decreased slightly (20% and 10%, respectively), while λ111 increased with increasing nitrogen content and eventually changed sign at ∼2% normalized lattice dilation. These results qualitatively agree with our earlier findings on (001) oriented FeTaN epitaxial films on MgO single crystal substrates. Also, our calculated saturation magnetostriction for nanocrystalline samples agrees very well with published data on the same FeTaN composition. Based on Hoffmann’s ripple theory the ripple constant is calculated for nanocrystalline films using the Doyle–Finnegan model for the local average anisotropy and our measured single crystal constants. It was found that the effect of nitrogen on reducing the average anisotropy through the fundamental constants is not significant, and therefore the major factor in achieving a low ripple constant (i.e., soft magnetic properties) is the grain size, the number of grains across the thickness and the thin film stress. © 1998 American Institute of Physics.  
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68.55.-a Thin film structure and morphology
75.70.Ak Magnetic properties of monolayers and thin films
75.30.Gw Magnetic anisotropy
75.80.+q Magnetomechanical effects, magnetostriction
61.50.Lt Crystal binding; cohesive energy
75.60.Ej Magnetization curves, hysteresis, Barkhausen and related effects
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