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We have fabricated Cr-doped bulk Ge single crystal using the vertical gradient solidification method. The material shows ferromagnetic ordering at 126 K, as determined from temperature-dependent magnetization and resistance measurements. A sample with x=0.01 was p type with nh=3×1017 cm−3 at 350 K. The measured magnetic moment per Cr was 0.83μB at 5 K.

We report on ferromagnetic characteristics of Zn1−xMnxO (x=0.1 and 0.3) thin films grown on Al2O3(00⋅1) substrates using laser molecular-beam epitaxy. By increasing the Mn content, the films exhibited increases in both the c-axis lattice constant and fundamental band gap energy. The Curie temperature obtained from temperature-dependent magnetization curves was 45 K for the film with x=0.3, depending on the Mn composition in the films. The remanent magnetization and coercive field of Zn0.9Mn0.1O at 5 K were 0.9 emu/g and 300 Oe, respectively. For Zn0.7Mn0.3O, the remanent magnetization at 5 K increased to 3.4 emu/g.

We report on the discovery of a room-temperature ferromagnetism in Cr-doped GaN single crystals with a Tc=280 K. The addition of Cr into GaN single crystals grown by the flux method induces the lattice constant increase due to the larger Cr atomic radius. In x-ray photoelectron spectroscopy measurement, Cr 2p3/2 core-level exhibited spectra near 575.7 eV. This binding energy is similar to the reported value of CrN. The coercive field by magnetization–magnetic field (M–H) hysteresis curve at 250 K was 54 Oe. We verified the presence of ferromagnetic transition in the temperature dependence of the electrical resistance measurements. We discuss the ferromagnetic ordering in Cr-doped GaN bulk single crystals excluding the contribution of the substrate crystal structure.

We have successfully grown Mn-doped chalcopyrite ZnSnAs 2 single crystals from the melt using the vertical-temperature-gradient Bridgman method. We have observed that Mn-doped ZnSnAs 2 is ferromagnetic with a Curie temperature of 329 K. The coercive field is 18 Oe at 300 K. The calculated magnetic moment from the saturation magnetization was 3.63 μ B per Mn atom at 5 K.

We have observed a large increase in the magnetoresistance (MR) of polycrystalline and epitaxial thin Bi films, which were subjected to a post-annealing procedure at 3°C below the Bi melting point. We have achieved an increase in the MR by a factor of 2560 at 5 K as compared with 343 for an as-grown epitaxial film due to enhanced carrier mobilities.

We report on the experimental observation of ferromagnetic ordering in the tetragonally distorted $\ensuremath{\alpha}$ phase of Cr, based on the anomalous Hall effect hysteresis and corroborated by magnetization hysteresis. The ferromagnetic ordering is reasonably ascribed to an increase in the out-of-plane lattice parameter of the $\ensuremath{\alpha}\text{-Cr}$ phase due to the low-dimensional connection to the $\ensuremath{\delta}\text{-Cr}$ crystal-lattice matrix, which suffers a large compressive lattice-mismatch strain from the substrate under two-dimensional growth. The low proportion of the $\ensuremath{\alpha}$ phase in the Cr film results in a weak macroscopic-scale ferromagnetic moment.

We fabricated bismuth (Bi) nanowires with low energy electron beam lithography using silver (Ag) nanocrystal shadowmasks and a subsequent chlorine reactive ion etching. Submicron-size metal contacts on the single Bi nanowire were successfully prepared by in situ focused ion beam metal deposition for transport measurements. The temperature dependent resistance measurements on the 50 nm wide Bi nanowires showed that the resistance increased with decreasing temperature, which is characteristic of semiconductors and insulators.

Using a recently developed broadband microwave measurement technique, we have studied the hysteretic appearance and disappearance with in-plane magnetic field of the uniform ferromagnetic resonance (FMR) mode of a patterned permalloy disk array. The observed features are consistent with our micromagnetic simulations (performed on an infinite array of such disks), which predict that on decreasing the magnetic field from a positively magnetized state at positive fields the array will: (i) pass continuously into a double-vortex state; (ii) followed by a discontinuous transition to a single-vortex state; and finally (iii) discontinuously into a negatively magnetized state at some negative field. The hysteretic counterpart occurs on reversing the field sweep and returning to positive fields. The FMR data are consistent with the hysteretic dc magnetization measurements performed earlier on samples patterned in an identical manner.

We report that the thermal strain due to the thermal-expansion difference between a Mn film and a semiconductor substrate is strong enough to overcome the thermal energy for a paramagnetic (PM) state and also to break antiferromagnetic (AF) magnetic symmetry, inducing ferromagnetic (FM) ordering at high temperatures. A Mn film on GaAs (100) showed FM ordering up to $9000\text{ }\text{\AA{}}$ with a Curie temperature $({T}_{C})$ of over 750 K and a net magnetic moment of $0.33{\ensuremath{\mu}}_{B}/\text{Mn}$, instead of AF (N\'eel temperature, ${T}_{N}=95\text{ }\text{K}$) and PM orderings in bulk.

We report a simple method for preparing polycrystalline ZnO thin films with good luminescent properties: the oxidization of metallic Zn films. In photoluminescence (PL) studies at room temperature for wavelengths between 370 and 675 nm, we have observed a single exciton peak around 390 nm without any deep-level emission and a small PL full width at half maximum (23 meV), indicating that the concentrations of the defects responsible for the deep-level emissions are negligible. We have also observed optically pumped lasing action in these films. The threshold intensity for lasing was ∼9 MW/cm2.

We have successfully grown Bi2Te3 thin films on CdTe(111)B using molecular-beam epitaxy. Structural and transport properties have been investigated using in situ reflection high-energy electron diffraction, θ–2θ x-ray diffraction analysis, thermopower, and Hall measurements. Both the crystallinity and the transport are found to be strongly affected by nonstoichiometry. The most stoichiometric sample had a high crystallinity, high thermopower, and high electron mobility. However, Bi2Te3 films with excess Te had a reduced lattice constant, poorer crystallinity, reduced magnitude of the thermopower, and reduced mobility. All of these observations can be explained in terms of antisite defects in which excess Te occupies Bi lattice sites and behaves as a n-type dopant.

Coherent phonons in mixed crystals of Bi and Sb, and Bi/Sb superlattices are observed by a reflection type pump-probe method. Combining this time domain measurement with Raman measurements, the behavior of the coherent phonons is examined.

We report magneto-transport and thermoelectric properties of FeSb2 thin film epitaxially grown on the MgO substrate using molecular beam epitaxy. The film exhibits compressive strain of 1.74% owing to large lattice mismatch, whose physical consequences are nontrivial. Magnetic phase has been changed from diamagnetic in bulk, as evidenced by anomalous Hall effect (AHE) and negative magneto-resistance (MR). The FeSb2 film is semiconducting without any metallic transition unlike the bulk counterpart. In particular, hysteresis in MR with distinct feature of AHE is evident with coercive field of 500 and 110 Oe for T = 20 and 50 K, respectively. Furthermore, from the Seebeck coefficients and temperature dependence of the resistivity, it is evident that the film is semiconducting with small band gap: 3.76 meV for T 40 K, respectively, where maximum thermoelectric power factor of 12 μV/cm·K at T = 50 K.

We have investigated the chemical distributions and the local electronic structure of potential diluted magnetic semiconductor Ge0.94Mn0.06 single crystals using scanning photoelectron microscopy (SPEM), x-ray absorption spectroscopy (XAS), and photoemission spectroscopy (PES). The SPEM image shows the stripe-shaped microstructures, which arise from the chemical phase separation between the Mn-rich and Mn-depleted phases. The Mn 2p XAS shows that the Mn ions in the Mn-rich region are in the divalent high-spin Mn2+ states but that they do not form metallic Mn clusters. The Mn 3d PES spectrum exhibits a peak centered at approximately 4 eV below E(F) and the negligible spectral weight near E(F). This study suggests that the observed ferromagnetism in Ge1-xMnx arises from the phase-separated Mn-rich phase.

We have prepared YBa2Cu3O7−δ (YBCO) superconducting wires by electrophoretic deposition. Ag wire was used as a substrate. Adding a small amount of BaF2 tends to remove cracks in the YBCO layer which develop during the heating process. The suppression of cracks produced a dramatic improvement in the critical current density (Jc). At 77 K, Jc increased from 18 A/cm2 for BaF2‐free YBCO wire to 646 A/cm2 for a critical concentration of 2.7 wt% BaF2 after which it decreased monotonically with increasing BaF2 content.

Gray tin films enriched by over 95% ${}^{119}\mathrm{Sn}$ and grown by molecular beam epitaxy on CdTe(001) wafers are characterized by inelastic nuclear resonance spectroscopy and investigated theoretically by embedded-cluster density-functional theory methods. Experimental tin phonon densities of states are obtained via analysis of resonant scattering of the 23.88-keV nuclear transition, making use of a high-resolution spectrometer at the Advanced Photon Source. Conventional M\"ossbauer spectroscopy is used in the scattering mode to determine hyperfine parameters of the \ensuremath{\alpha}-Sn phase and, after thermal treatment, the \ensuremath{\beta} phase. Electronic structure in the vicinity of Sn-Cd and Sn-Te interfaces is calculated in order to determine local charge transfer and changes in hyperfine parameters for ${}^{119}\mathrm{Sn}$ atoms in the interface region. Although, due to sample thickness, both experiments reveal properties essentially of the bulk, the calculations allow investigation of surface and interface regions at an atomic level, thus providing complementary information. Effects of interlayer relaxation are explored.

We report that the layered structure of Bi/sub 2/Te/sub 3/-based materials can be prepared with layer-by-layer growth using MBE; i.e., we sequentially deposit Te and Bi monolayers according to the sequence of Bi/sub 2/Te/sub 3/. The sequence of the layered structure is Te-Bi-Te-Bi-Te and three such sequences make a unit cell with a total of 6 Bi layers and 9 Te layers. In bulk and thin film (BiSb)/sub 2/Te/sub 3/ prepared by co-deposition, Bi and Sb occupy lattice sites randomly. In order to engineer the electronic band structure to achieve better thermoelectric properties and/or reduce the lattice thermal conductivity by increasing phonon scattering at interfaces, we have prepared artificially ordered (BiSb)/sub 2/Te/sub 3/. We will discuss the growth and thermoelectric properties of artificially layered (BiSb)/sub 2/Te/sub 3/ thin films and compare their properties with conventional structures.

We have grown Bi and BiSb alloy thin films at an oblique angle on (211) CdTe substrates, which were tilted by 19/spl deg/ to the trigonal axis. We have studied the anisotropic Seebeck and magneto-Seebeck coefficients in magnetic fields of 0-0.7T and have observed a strong dependence on the crystal-axis and the magnetic field direction in Seebeck coefficients.

We have grown Sb/sub 2/Te/sub 3/ thin films on CdTe[111]B and GaAs[111]B substrates by the conventional co-deposition method using molecular beam epitaxy. In order to investigate and reduce the antisite defects, we varied the relative ratio of the flow-rates of Sb and Te. X-ray diffraction patterns (/spl theta/-2/spl theta/ scans) of the films show that they are well aligned with their (00.1) axis normal to the substrates, regardless of the relative flow-rate ratio. The measurement of the rocking curves of the films shows that they are of high quality, despite a rather large lattice mismatch between the substrate and the film deposited at 200/spl deg/C, with a rocking curve FWHM less than 0.17/spl deg/. The change in the relative flow-rate ratios of Te to Sb causes a remarkable shift in the temperature-dependent thermopower, resistivity, and Hall coefficient of the films. These results demonstrate that by controlling the antisite defects, Sb/sub 2/Se/sub 3/ can be a promising thermoelectric material.

We propose a new approach for potentially achieving high-ZT materials: artificially ordered alloy structures. We have prepared artificially ordered Bi/Sb alloys with different (Bi/Sb) periods from 7.7 /spl Aring/ to 55 /spl Aring/ by MBE. Atomic-scale ordering effects on the structural and transport properties have been studied. The formation of an ordered alloy was confirmed by the presence of XRD superlattice satellites. Using electrical resistivity, thermopower, and magneto-transport measurements, we have observed a semimetal-semiconductor transition in an ordered BiSb superlattice. The intentional ordering of the layered Bi-Sb structure has produced a new phase and the measured differences in the electronic spectrum relative to the random alloy are a consequence of its atomic structure.

We have investigated the structural and thermoelectric properties of (Sb/sub 1-x/Bi/sub x/)/sub 2/Te/sub 3/ MBE grown thin films on CdTe(111). Analysis of X-ray diffraction patterns (/spl theta/-2/spl theta/ scans and rocking curves) of the films shows that they are of high quality and that they are well aligned with their (00.l) axis normal to the substrates. Measurements of the temperature-dependent thermoelectric power of the films were performed with respect to the binary composition of Sb and Bi, x. For the samples in the range 0.2

We have successfully grown BiSb alloy thin films on CdTe(111)B over a wide range of Sb compositions using molecular beam epitaxy. It is well known that small bandgap (/spl sim/18 meV) bulk BiSb alloys are good n-type thermoelements at liquid nitrogen temperature. We have observed that the power factor (S/sup 2//spl sigma/) for MBE-grown 1 /spl mu/m thick BiSb thin films grown on CdTe(111) peak at a significantly higher temperature (250 K) than previous results for the bulk alloy (80 K), possibly due to an enhanced bandgap. For doping experiments we used the group IV(VI) element Sn(Te) as an acceptor(donor). Thermoelectric Power (TEP) and electrical resistivity were studied in the range of temperatures 2-300 K. Doping Sn into the BiSb system causes the TEP to change sign (from negative to positive), and the maximum value of the TEP can be controlled with the Sn dopant concentration.

We have successfully fabricated highly (up to 6%) Mn-doped bulk Ge single crystals. The lattice constant increases linearly with Mn concentration due to the larger Mn atomic radius compared with Ge, strongly indicating that Mn ions are being incorporated into the host Ge lattice. Alloys with lower Mn concentrations showed paramagnetism due to localized magnetic ions. ${\mathrm{Ge}}_{0.94}{\mathrm{Mn}}_{0.06}$ showed ferromagnetic ordering at \ensuremath{\sim}285 K, as determined from temperature-dependent magnetization and resistance measurements. The coersive field was 1260 Oe at 250 K.

We report on the discovery of a room-temperature ferromagnetic semiconductor in chalcopyrite $({\mathrm{Zn}}_{1\ensuremath{-}x}{\mathrm{Mn}}_{x}){\mathrm{GeP}}_{2}$ with ${T}_{c}\phantom{\rule{0ex}{0ex}}=\phantom{\rule{0ex}{0ex}}312\mathrm{K}$. We have also observed that, at temperatures below 47 K, samples for $x\phantom{\rule{0ex}{0ex}}=\phantom{\rule{0ex}{0ex}}0.056$ and 0.2 show a transition to the antiferromagnetic (AFM) state, so that ferromagnetism is well defined to be present between 47 and 312 K. The observation that the AFM phase is most stable at low temperatures is consistent with the predictions of full-potential linearized augmented plane wave total energy calculations and has consequences for other chalcopyrite materials.

The epitaxial Mn0.92Ca0.08As thin film was grown on Al2O3(0001) substrate by molecular beam epitaxy. The Curie temperature (TC) around 340 K was enhanced with the addition of Ca, compared to that of bulk MnAs (TC ∼ 318 K). The maxima magnetoresistance, ∼2.08% at 0.7 T, was observed near the critical magnetic transition temperature. Moreover, the giant magnetocaloric effect was found with the maximum magnetic entropy change, ∼200 J/kgK, around 330 K at 5 T.

The Fe1−xGax thin films (x = 0.4, 0.5) have been grown on GaSb(100) substrate using molecular beam epitaxy. An epitaxial film with bcc α-Fe crystal structure (A2) is observed in Fe0.6Ga0.4 film, while an impure Fe3Ga phase with DO3 structure is appeared in Fe0.5Ga0.5 film. The saturated magnetizations at room temperature are observed to be 570 emu/cm3 and 180 emu/cm3 and the coercivities to be 170 and 364 Oe for Fe0.6Ga0.4 and Fe0.5Ga0.5, respectively. A hysteresis trend in Hall resistance vs. magnetic field is observed for Fe0.5Ga0.5 film. However, there is a weak hysteresis noticed in Fe0.4Ga0.6 thin film.

We have fabricated Bi/Sb superlattice alloys that are artificially ordered on the atomic scale using molecular-beam epitaxy. We observe that by changing the superlattice period thickness, the electronic structure can be ``tuned'' from a semimetal, through zero gap, to a narrow-gap semiconductor. These unique properties, which are distinct from those in random alloys, are believed to be a consequence of ordered atomic configurations.

We report on the discovery of a room-temperature ferromagnetic semiconductor in chalcopyrite (Zn1-xMnx)GeP2 with Tc = 312 K. We have also observed that, at temperatures below 47 K, samples for x = 0.056 and 0.2 show a transition to the antiferromagnetic (AFM) state, so that ferromagnetism is well defined to be present between 47 and 312 K. The observation that the AFM phase is most stable at low temperatures is consistent with the predictions of full-potential linearized augmented plane wave total energy calculations and has consequences for other chalcopyrite materials.

We have observed an epilayer-thickness-dependent polarity inversion for the growth of CdTe on Sb(Bi)/CdTe(111)B. For films with Sb(Bi) thicknesses of less than 40 A (15 A), the CdTe layer shows a B (Te-terminated) face, but it switches to an A (Cd-terminated) face for thicker layers. On the other hand, a CdTe layer grown on Bi(Sb)/CdTe(111)A always shows the A face regardless of Sb or Bi layer thicknesses. In order to address the observations we have performed ab initio calculations, which suggest that the polarity of a polar material on a nonpolar one results from the binding energy difference between the two possible surface configurations.

We have studied the compositional dependence of the layered structure of ${\mathrm{Bi}}_{1+x}{\mathrm{Te}}_{1\ensuremath{-}x}$ thin films and its relation with the transport properties. We have observed that the ${\mathrm{Bi}}_{1+x}{\mathrm{Te}}_{1\ensuremath{-}x}$ films have a stable structure near the ${\mathrm{Bi}}_{1}{\mathrm{Te}}_{1}$ composition and that their crystallinity depends strongly upon the compositional deviation from stoichiometric ${\mathrm{Bi}}_{1}{\mathrm{Te}}_{1}.$ We have determined possible layered structures, configured with two sequences of Bi--Bi and Te--Bi--Te--Bi--Te, corresponding to Bi and Te binary compositions using x-ray diffraction analysis. Their c-axis lattice constants were in the range of 36 \AA{} and 136 \AA{}. Temperature-dependent thermopowers of the films reveal that as the composition changes from Te rich to Bi rich, the polarity varies from n type to p type.

We report artificially atomic-scale ordered superlattice alloy systems, new scheme to pursue high-ZT materials. We have fabricated Bi/Sb superlattice alloys that are artificially ordered on the atomic scale using MBE, confirmed by the presence of XRD superlattice satellites. We have observed that the electronic structure can be modified from semimetal, through zero-gap, to semiconductor by changing the superlattice period and sublayer thicknesses using electrical resistivity, thermopower, and magneto-transport measurements. InSb/Bi superlattice alloys have also been prepared and studied using XRD and thermopower measurements, which shows that their thermoelectric transport properties can be modified in accordance with structural modification. This superlattice alloy scheme gives us one more tool to control and tune the electronic structure and consequently the thermoelectric properties.

The temperature-dependent cross-plane thermal conductivity of a 1-μm thick 50Å Bi / 50Å Sb superlattice on a (111) CdTe substrate was measured, using a differential 3-ω method. This method uses the temperature difference between the superlattice sample and a reference sample to calculate its cross-plane thermal conductivity. However, the substrate thermal conductivity is comparable to or smaller than the superlattice thermal conductivity near room temperature. This results in a very small or negative temperature difference, making the existing data reduction method inapplicable. Based on an improved model, the temperature-dependent thermal conductivity of the Bi/Sb superlattice is obtained and is about half of the literature value of Bi0.5Sb0.5 bulk alloy.

We have grown Bi1-xSbx alloy thin films on CdTe(111)B over a wide range of Sb concentrations (0≤x≤0.183) using MBE. We have observed several differences with the bulk system. The 3.5 and 5.1% Sb alloys show semiconducting behavior, and the Sb concentration with the maximum bandgap is shifted to a lower Sb concentration, from 15% in bulk to 9%. The power factor S2/ρ (where S is thermoelectric power(TEP) and ρ electrical resistivity) peaks at a significantly higher temperature (250K) than previously reported for the bulk alloy (80K). The magnetotransport properties of Bi1-x,Sbx thin films (x = 0, 0.09, and 0.16) and Bi/CdTe superlattices have been determined by applying the Quantitative Mobility Spectrum Analysis (QMSA) and multicarrier fitting to the magneticfield- dependent resistivities and Hall coefficients, using algorithms which account for the strong anisotropy of the mobilities. The calculated S values are in good agreement with experimental results. The structural stability of bulk Bi is studied using the local density linear muffin-tin orbital method. It is shown that the internal displacement changes the Bi electronic structure from a metal to a semimetal, in qualitative agreement with a Jones-Peierls-type transition. The total energy is calculated to have a double well dependence on the internal displacement, and to provide a stabilization of the trigonal phase. We show that an increase of the trigonal shear angle leads to a semimetal-semiconductor transition in Bi.

We have grown high quality Bi2Te3 thin films on CdTe(111)B substrates using MBE. Structural properties have been investigated using in-situ reflection high-energy electron diffraction (RHEED) and θ-2θ X-ray diffraction analysis. They show that Bi2Te3films on CdTe(111) grow along the (00.l) in the hexagonal cell with a layer-by-layer growth mode, resulting in a smooth surface, and an X-ray Bragg peak FWHM of 0.2°. The thermopower and electrical conductivity of the stoichiometric Bi2Te3 films were ∼200 μV/K and 103(Ωcm)−1, respectively, comparable to the single crystal bulk values. We have observed the antisite defect effect in Te-rich Bi2Te3films: excess Te occupies Bi lattice sites and behaves as an n-type dopant. Crystallinity and transport properties are strongly affected by non-stoichiometry.

Thin films of the hexagonal phase of Bi1-xTe1+x have been grown on CdTe(111) substrates using molecular beam epitaxy (MBE). Analysis of X-ray diffraction patterns (θ-2θ scans and rocking curves) of the films shows that their crystallinity depends upon the compositional deviation from stoichiometric BiTe. Measurements of the temperature-dependent thermoelectric power (TEP) of the films reveals that compositional changes cause the TEP to vary from electron dominant (n-type) to hole dominant (p-type), implying their possible application as a thermoelectric cooler or power generator. Measurements of the temperature-dependent resistivity of the films were conducted, and the analysis shows semimetallic behavior. These results demonstrate that Bi1-xTe1+xis an appropriate model system to study the dependencies of thermoelectric and structural properties on binary composition.

We have measured the thermoelectric power (TEP) of MBE-grown epitaxial Bi and Bi1−xSbx alloy thin films and superlattices as a function of temperature in the range 20–300 K. We have observed that the TEP of a Bi thin film of 1 μm thickness is in good agreement with the bulk single crystal value and that the TEPs for superlattices with 400 Å and 800 Å Bi well thicknesses are enhanced over the bulk values. For x=0.072 and 0.088 in Bi1−xSbx thin films showing semiconducting behavior, TEP enhancement was observed by a factor of two. However as Bi or Bi1−xSbx well thickness decreases in superlattice geometry, the TEP decreases, which may be due to unintentional p-type doping.

Epitaxial ferromagnetic Mn5Ge3 thin films were stabilized on GaSb(001) and GaAs(001) substrates using molecular beam epitaxy. Compared to bulk Mn5Ge3 materials, an enhancement of the Curie temperature above 350 K and about 320 K was observed for Mn5Ge3/GaAs(001) and Mn5Ge3/GaSb(001) heterostructures, respectively. The magnetization was found to decrease from 323 to 245 emu/cm3 for films grown on GaSb(001) and GaAs(001). Anomalous Hall effect measurements provide evidence of the strain-induced large spin polarization from density-functional study. Furthermore, our calculated results in bulk Mn5Ge3 under strain indicate that the strain is the origin of different physical properties of Mn5Ge3 grown on different substrates.

We report on the epitaxial growth and magnetic properties of Mn2O3 thin films grown on MgO(001) substrate by molecular beam epitaxy. We observed the reduction in binding energy of Mn valence states, the increase in satellite separation up to 12.7 eV, and the smaller band gap of 3.32 eV. In addition, the antiferromagnetic ordering below 90 K in bulk changed to ferrimagnetic up to 175 K. The results were possibly to be explained by a lattice mismatch strain on Mn2O3 film on MgO(001) substrate.

In this work, the growth and ferromagnetic properties of e-FeSi thin film on Si(100) substrate prepared by molecular beam epitaxy are reported. The inter-diffusion of Fe layer on Si(100) substrate at 600 °C results in polycrystalline e-FeSi layer. The determined activation energy was 0.044 eV. The modified magnetism from paramagnetic in bulk to ferromagnetic states in e-FeSi thin films was observed. The saturated magnetization and coercive field of e-FeSi film are 4.6 emu/cm3 and 29 Oe at 300 K, respectively.

Ferromagnetic Mn3Ge2 thin films were successfully grown on GaAs(001) and GaSb(001) substrates using molecular beam epitaxy. The results of our work revealed that the substrate facilitates to modify magnetic and electrical properties of Mn3Ge2 films due to tensile/compressive strain effect between films and substrates. The characteristic spin-flopping transition at around 150 K for the bulk Mn3Ge2 disappeared completely for both samples. The antiferromagnetism below 150 K changed to ferromagnetism and retained above room temperature. The saturation magnetization was found to be 0.23 and 1.32 μB/Mn atom at 10 K for the samples grown on GaSb(001) and GaAs(001), respectively.

We calculated the electronic structure and magnetism of 3d or 4d transition metal-doped ZnO (TM0.25Zn0.75O: TM=Ti, Cr, Mn, Fe, Co, Ni, Ru, Pd, and Ag), using the full potential linearized augmented plane method based on general gradient approximation for exchange–correlation potential. The magnetic moments of Ti, Cr, Mn, Fe, Co, Ni, Ru, Pd, and Ag in the systems were calculated to be 1.24, 3.78, 4.93, 4.24, 3.00, 2.00, 0.74, 1.00, and 0.00 μB, respectively. The calculated magnetic moment of Ti is not negligible in marked contrast to the previously calculated zero magnetic moment with Korringa–Kohn–Rostoker. The magnetic moment of a type of oxygen is sizable (up to 0.18 μB).

The epitaxial Mn0.92Ba0.08As thin film was grown on Al2O3(0001) substrate by molecular beam epitaxy. The Curie temperature (TC) around 350 K was enhanced with the addition of Ba, compared to that of bulk MnAs (TC ∼ 318 K). We have observed the linear resistivity versus the square of temperature and high negative magnetoresistance near Curie temperature. Moreover, the giant magnetocaloric effect was found with maximum magnetic entropy change, 65 J/kgK, around room temperature at 5 T.

Epitaxial Fe–Ga thin films in disordered bcc α-Fe crystal structure (A2) have been grown on GaAs(001) by molecular beam epitaxy. The saturated magnetization (MS) decreased from 1371 to 1105 kA/m with increasing Ga concentration from 10.5 to 24.3 % at room temperature. The lattice parameter increased with the increase in Ga content because of the larger atomic radius of Ga atom than that of Fe. The increase in carrier density with Ga content caused in lower resistivity.

We propose a new electrical-phase-change magnetic material, namely Fe-doped In-Sb-Te (FIST), for possible non-volatile multi-bit memory applications. FIST was formed by typical co-sputter method with Fe 10 at.% doping in In3Sb1Te2. FIST offers the electrical-phase-change and magnetic properties by way of the change of In 4d chemical bonding density and embedded Fe nanoclusters with the size of 4∼5 nm, respectively. It maintained the amorphous phase on the electrical-phase-change. Chemical state of In was only changed to increase the density of In-In chemical bonding during the electrical-phase-change without Fe nanoclusters contribution. Also, the magnetic property by Fe nanoclusters was not changed by the electrical-phase-change. On this basis, we propose the FIST material with the individual electrical-phase-change and magnetic properties for the multi-bit nonvolatile memory materials.

Epitaxial BaMn2As2 thin films were grown on GaAs(001) using molecular beam epitaxy. The samples exhibited temperature-dependent resistivity, a behavior typical of semiconductors. Activation energies for samples grown at 350, 450, and 550 °C were 24.1, 24.3, and 51.9 meV, respectively. Holes are the dominant carrier for the samples grown at 450 and 550 °C, while electrons are the dominant carrier for the sample grown at 350 °C. Negative magnetoresistance was obtained at low temperature and became positive at high temperature, which was attributed to MnAs nanoclusters.

We have newly synthesized the α-Mn structured Mn3Ge thin films on GaAs(001) substrate. The single phase Mn3Ge film was grown at a growth temperature of 150 °C, while the secondary phase was observed above a growth temperature of 250 °C. The Mn3Ge films exhibited ferrimagnetism with a Curie temperature of 334 K. The saturation magnetizations were 255.9 and 313.8 emu/cm3 and the corresponding coercive fields were 453 and 1166 Oe at 10 K for the samples grown at 150 and 300 °C, respectively. The ferrimagnetism was confirmed by the anomalous Hall effect data.

We report on the carrier type changes of the p-type for as-grown Mn:Ge films to n-type for post-annealed samples in a hydrogen ambient. The hydrogen-annealed samples exhibit the increased Curie temperature, from 165 to 198 K, and the enhanced magnetic moment, from 0.78 to 1.10 μB/Mn. The first principles calculation using the all-electron full-potential linearized augmented plane wave method indicates that the addition of an electron carrier strengthens the ferromagnetic coupling between the Mn atoms, while the hole carrier caused it to weaken.

Ferrimagnetic Mn2As thin films with perpendicular magnetic anisotropy were successfully grown on Si(100) by molecular-beam epitaxy. From the reflection high-energy electron diffraction and X-ray diffraction patterns, the orientation of the Mn2As film on Si was along the c-axis in the tetragonal crystal structure. Mn2As film exhibited ferrimagnetic ordering at temperatures greater than 300 K, which differs from antiferromagnetic or paramagnetic behaviors in the bulk form. The magnetic moment of Mn2As determined by saturated magnetization was 0.51 µB per unit cell.