S. A. Shaheen

Preparation of Y‐Ba‐Cu oxide superconductor thin films using pulsed laser evaporation from high Tc bulk material

We report the first successful preparation of thin films of Y‐Ba‐Cu‐O superconductors using pulsed excimer laser evaporation of a single bulk material target in vacuum. Rutherford backscattering spectrometry showed the composition of these films to be close to that of the bulk material. Growth rates were typically 0.1 nm per laser shot. After an annealing treatment in oxygen the films exhibited superconductivity with an onset at 95 K and zero resistance at 85 and 75 K on SrTiO3 and Al2O3 substrates, respectively. This new deposition method is relatively simple, very versatile, and does not require the use of ultrahigh vacuum techniques.

Systematics of thin films formed by excimer laser ablation: Results on SmBa2Cu3O7

Excimer laser ablation was used to prepare thin films from a bulk target of SmBa2Cu3O7. The systematic variation in film thickness, stoichiometry, and microstructure, as a function of laser fluence and angle from the target surface normal, was determined. We show that films which are stoichiometric over wide solid angles can be rapidly prepared from this material by use of high laser fluence. Films prepared from various Bi‐Sr‐Ca‐Cu‐O targets at high laser fluence also reproduce bulk stoichiometry. In contrast, films prepared by this technique from a YBa2Cu3O7 target are deficient in Ba and Cu for laser fluences required to produce compositional homogeneity over wide areas.

Sputtered Sm–Co films: Microstructure and magnetic properties

Films of Sm–Co have been sputtered on heated polycrystalline Al2O3 substrates. The effect of variations of the Sm content on microstructure and hard magnetic properties was studied for otherwise constant process parameters. As generally observed, the samples possess a magnetic texture where the easy magnetization directions of the grains lay preferably in the film plane. For a lower Sm content the TbCu7-type structure is stabilized and for a higher Sm content the CaCu5-type structure is stabilized. The crossover occurs for a Sm content of around 17 at. %. Consistent with the changes in the intrinsic properties, coercivity increases and remanence decreases with increasing the Sm content. The grain size increases with increasing the Sm content and is attributed to a higher surface mobility during crystallization and grain growth. This behavior is also assumed to cause the improvement in the in-plane texture with increasing the Sm content, that had been quantified by magnetic and crystallographic investigations.

SMCO BASED SPUTTERED FILMS WITH CACU5 AND TBCU7 STRUCTURES

SmCo based films containing 20 at. % Fe and with Sm varying from 15.5 to 17 at. % have been synthesized to show the transition from ordered CaCu5 to disordered TbCu7 phase. For either phase, the demagnetization energy present during deposition can result in films with the crystallite c axes randomly splayed onto the film plane. It has been possible to synthesize the high anisotropy CaCu5 phase with either a (200) or (110) texture by adjusting the sputtering parameters to correspond to either a relatively high or relatively low surface mobility during the film deposition. It has been possible to synthesize ordered CaCu5 type films with very low values of BR(⊥)/BR(∥)=0.042. Previously, SmCo based single phase TbCu7 structure films have been synthesized with close to the usual high energy product 2–17 compositions of nominally 7 at. % Cu and 2 at. % Zr. The films have been characterized by vibrating-sample magnetometer and superconducting quantum interference device magnetometry, x-ray diffraction, and scann...

Static magnetic and microwave properties of Li-ferrite films prepared by pulsed laser deposition

Highly textured Li-ferrite films have been synthesized by pulsed laser deposition from bulk targets onto c-plane sapphire substrates. For substrate temperatures approaching 1000 °C the growth mode was predominantly (333). A similar growth mode was recently reported for Ni-ferrite films grown onto c-plane sapphire substrates. The films were 4–8 μm thick and were grown at deposition rates of 3–5 A/s at oxygen partial pressures of 200–400 mTorr. Magnetic measurements were made by SQUID and 9.5 GHz ferromagnetic resonance (FMR) on the as deposited films. Textured Li-ferrite films with x-ray diffractometer intensity ratios of I(333)/I(311)=10.3 for films made in 200 mTorr oxygen and 14.5 for films made in 400 mTorr oxygen exhibited room temperature in-plane intrinsic coercivities of <100 Oe for SQUID magnetometer measurements. Highly (333) textured Li-ferrite films made in 400 mTorr oxygen exhibited clean symmetric FMR absorption lines with a derivative peak-to-peak linewidth of 335 Oe for the in-plane static ...

Variable texture NiOFe2O3 ferrite films prepared by pulsed laser deposition

Pulsed laser deposition using bulk NiOFe2O3 targets onto heated substrates has been used to synthesize single phase Ni spinel ferrite films onto various substrates. Flowing oxygen has been used during the deposition to maintain the oxygen stoichiometry. Ni ferrite films have been deposited onto C‐, R‐, and A‐plane sapphire, polycrystalline Al2O3, and fused silica. Single‐crystal (111) oriented NiOFe2O3 films have been made onto C‐plane sapphire for substrate temperatures of greater than 900 °C. Polycrystalline highly (400) textured Ni ferrite films have been made onto R‐plane sapphire with I(400)/I(311)=6.15. Films made onto A‐plane sapphire, polycrystalline alumina, and fused silica showed only moderate texturing. The coercive force of the (111) oriented NiOFe2O3 was 120 Oe perpendicular to the film plane and 95 Oe in plane.

Structures and magnetocrystalline anisotropies of RCo10Mo2 compounds

Abstract A new series of alloys with composition RCo 10 Mo 2 (R = Y, Ce, Pr, Nd, Gd, Sm, Dy and Er) has been synthesized and investigated by X-ray and magnetometry techniques. All of the compounds in this series crystallize in the tetragonal ThMn 12 -type structure. Magnetic studies indicate that the 3d sublattice favors a uniaxial anisotropy in this system. The easy direction of magnetization is along the c -axis for R = Y, Ce, Pr, Nd, Gd and Dy at room temperature. The DyCo 10 Mo 2 compound has the largest anisotropy field (48 kOe) at 300 K. SmCo 10 Mo 2 has an easy plane and ErCo 10 Mo 2 exhibits a conical anisotropy at room temperature. A spin re-orientation from planar to conical was observed for SmCo 10 Mo 2 at about 450 K with increasing temperature. With increasing temperature the ErCo 10 Mo 2 compound undergoes two spin re-orientations, from planar to conical at 143 K and from conical to axial at 350 K.

CeSi: A non‐Kondo trivalent Ce compound

The magnetic properties of CeSi, which crystallizes in the FeB‐type orthorhombic structure, have been investigated. CeSi orders antiferromagnetically at 5.6 K. Its ground‐state magnetic moment attains a value of 1.47 μB in a field of 57 kOe at 3.0 K, which is far above the highest value ever observed for any Ce compound. The magnetic properties of this compound are like conventional stable moment rare‐earth compounds and differ from other nearly trivalent Ce compounds. More specifically, unlike nearly trivalent Ce intermetallic compounds, no evidence for Kondo effect is apparent in this compound.

The anomalous magnetism of CeRh3B2 under pressure

Abstract Whereas CeRh3B2 possesses the highest magnetic ordering temperature (Tc ≈ 115 K) of any Ce-compound with nonmagnetic constituents, LaRh3B2 becomes superconducting below 2.5 K. Recent magnetization measurements under pressure as well as lattice parameter and specific heat studies shed light on the nature of the anomalous magnetic state in CeRh3B2.

Optimization of (Gd)5Si4 based materials: A step toward self-controlled hyperthermia applications

Structural and magnetic properties have been studied across the Gd5(Si1−xGex)4 and (Gd1−xRx)5Si4 series, with R=Ce Nd, Er, and Ho, in the context of their use as ferromagnetic materials in the self-controlled hyperthermia treatment of cancer. The study shows that these materials have high magnetization values and their magnetic ordering temperatures (TC) can be varied linearly over a broad range by adjusting the composition of the constituent elements. The magnetization values of these materials are close to the bulk value of α-Fe and are substantially higher than other transition metal and Fe based magnetic materials, e.g., oxide and ferrites. The high magnetization and optimality of TC values for self-controlled hyperthermia applications observed in these materials distinguish them as magnetic material of choice for such applications.