Magnetic properties of NiFe2O4 thin films grown on La0.7Sr0.3MnO3-buffered Si substrate

Nickel ferrite NiFe₂O₄ (NFO) thin films have been prepared on a Si substrate (NFO/Si) and La_0.7Sr_0.3MnO₃ (LSMO)-coated Si (100) substrate (NFO/LSMO/Si) by RF magnetron sputtering. The microstructures and magnetic properties of the two films were systematically investigated. X-ray diffraction (XRD) and atomic force microscopy (AFM) revealed that highly (331)-oriented NFO films with a smooth surface were grown on the LSMO/Si substrate. The magnetization of the films was measured at room temperature. It showed a clear hysteresis loop in both samples, with the magnetic field applied in the plane. However, no hysteresis loop is seen with the magnetic field applied perpendicular to the film plane. This indicates the presence of an anisotropy favoring the orientation of the magnetization in the direction parallel to the film plane. A study of magnetization hysteresis loop measurements indicates that the LSMO buffer layer may improve the magnetic properties of NFO thin films, and that the saturation magnetization increases from 4.15 × 10⁴ to 3.5 × 10⁵ A/m.     

Structural order and magnetic properties of Fe3Si/Si(100) heterostructures grown by pulsed-laser deposition

The single-phase Fe₃Si thin films with preferred (220) growth orientation were prepared on Si(100) substrates by pulsed-laser deposition. Different states of order were developed by changing the substrate temperature from room temperature to 500 °C. X-ray diffraction, Mössbauer spectroscopy and macroscopic magnetic measurements were used to analyze changes of structural order and magnetic properties with the substrate temperature. The results show that over the whole range of substrate temperatures considered all films are of Fe₃Si single phase, highly oriented along the (220) plane. With increasing the substrate temperature, the structural order type changes from A2 through B2 to DO₃ and the order degree gradually increases. Meanwhile, the saturation magnetization remarkably decreases with the increase of the substrate temperature, induced by Si segregation from the substrate and embedment into the film probably as the amorphous phase. The room temperature grown film has a high saturation magnetization of 917 kA m^− 1, which nearly equals that of bulk DO₃-Fe₃Si.     

Epitaxial growth of MgFe2O4 (111) thin films on sapphire (0001) substrate

Pulsed laser deposition technique is used to fabricate thin films of MgFe₂O₄ on sapphire substrate. X-ray diffraction patterns show that films are epitaxial along (???) direction on c-axis oriented sapphire. The observation of six fold symmetry in phi scan for the film suggests the presence of twinned in-plane alignments. The presence of magnetic hysteresis loop at room temperature indicates the ferromagnetic behavior of the film. The coercive field of 742 Oe and remnant magnetization of 151 emu/cm² is observed at room temperature. The coercive field and remnant magnetization decrease with increase in temperature.     

Positive exchange bias in epitaxial permalloy/MgO integrated with Si (1 0 0)

In magnetic random access memory (MRAM) devices, soft magnetic thin film elements such as permalloy (Py) are used as unit cells of information. The epitaxial integration of these elements with the technologically important substrate Si (1 0 0) and a thorough understanding of their magnetic properties are critical for CMOS-based magnetic devices. We report on the epitaxial growth of Ni_82.5Fe_17.5 (permalloy, Py) on Si (1 0 0) using a TiN/MgO buffer layer. Initial stages of growth are characterized by the formation of discrete islands that gradually merge into a continuous film as deposition times are extended. Interestingly, we find that the magnetic features of Py films in early stages of island coalescence are distinctly different from the films formed initially (discrete islands) and after extended deposition times (narrow distribution of equiaxed granular films). Isothermal in-plane and out-of-plane magnetic measurements performed on these transitional films show highly anisotropic magnetic behavior with an easy magnetization axis lying in the plane of the film. Importantly, when this sample is zero-field cooled, a positive exchange bias and vertical loop shift are observed, unusual for a soft ferromagnet like Py. Repeated field cycling and hysteresis loops up to the fields of 7T produced reproducible hysteresis loops indicating the existence of strongly pinned spin configurations. Classical interface related exchange bias models cannot explain the observed magnetic features of the transitional Py films. We believe that the anomalous magnetic behavior of such Py films may be explained by considering the highly irregular morphology that develops at intermediate growth times that are possibly also undergoing a transition from Bloch to Neel domain wall structures as a function of Py island size. This study broadens the current understanding of magnetic properties of Py thin layers for technological applications in magneto-electronic devices, integrated with Si (1 0 0).     

Influence of Interfacial LSMO Nanoparticles/Layer on the Vortex Pinning Properties of YBCO Thin Film

YBa₂Cu₃O_7?δ (YBCO) thin films have been deposited on bare and La_0.67Sr_0.33MnO₃ (LSMO) modified single crystal SrTiO₃ (STO) substrates. The effect of randomly distributed ferromagnetic LSMO nanoparticles and a complete LSMO layer, present at STO/YBCO interface, on the superconducting properties of YBCO thin films has been investigated by temperature dependent magnetization studies. The YBCO thin film on LSMO nanoparticles decorated STO substrate shows significant improvement in the critical current density and pinning force density as compared to the YBCO thin film deposited on bare STO substrate and this improvement is more significant at higher applied magnetic field. However, the LSMO/YBCO bilayer showed the improved flux pinning properties only up to a magnetic field of 1.5 T above which it deteriorates. In the case of LSMO/YBCO bilayer, the underlying LSMO layer gives rise to magnetic inhomogeneities due to domain structure, which leads to improved flux pinning properties limited to lower field. However, in the case of LSMO nanoparticles decorated substrate, the presence of LSMO nanoparticles at YBCO/STO interface seems to introduce magnetic inhomogeneities as well as structural defects, which might be acting as correlated pinning sites leading to improved flux pinning properties of the YBCO thin film over a wide range of applied magnetic field.     

Growth and characterization of La5/8Sr3/8MnO3 thin films prepared by pulsed laser deposition on different substrates

Colossal magnetoresistance La_5/8Sr_3/8MnO₃ (LSMO) thin films were directly grown on MgO(100), Si(100) wafer and glass substrates by pulsed laser deposition technique. The films were characterized using X-ray diffraction (XRD), field emission-scanning electron microscope and atomic force microscopy (AFM). The electrical and magnetic properties of the films are studied. From the XRD patterns, the films are found to be polycrystalline single-phases. The surface appears porous and cauliflower-like morphology for all LSMO films. From AFM images, the LSMO films deposited on glass substrate were presented smooth morphologies of the top surfaces as comparing with the films were deposited on Si(100) and MgO(100). The highest magnetoresistance (MR) value obtained was ?17.21 % for LSMO/MgO film followed by ?15.65 % for LSMO/Si and ?14.60 % for LSMO/Cg films at 80 K in a 1T magnetic field. Phase transition temperature (T_P) is 224 K for LSMO/MgO, 200 K for LSMO/Si and above room temperature for films deposited on glass substrates. The films exhibit ferromagnetic transition at a temperature (T_C) around 363 K for LSMO/MgO, 307 K for LSMO/Si and 352 K for LSMO/Cg thin film. T_C such as 363 and 352 K are the high T_C that has ever been reported for LSMO films deposited on MgO substrate with high lattice mismatch parameter and glass substrates with amorphous nature.     

Energetic ion irradiation induced crystallization of Ni–Mn–Sn ferromagnetic shape memory alloy thin film

The ion irradiation induced crystallization of Ni–Mn–Sn ferromagnetic shape memory alloy (FSMA) thin film is investigated. Thin films of Ni–Mn–Sn FSMA synthesized by DC magnetron sputtering on Si substrate at 200 °C are irradiated by a beam of 120 MeV Ag ions at different fluence varying from 1 × 10¹² to 6 × 10¹² ions/cm². X-ray diffraction pattern reveals that the pristine film grows in L2₁ cubic austenite phase with poor crystallinity and crystallinity of the film improves with increasing ion fluence, which is attributed to the strain relaxation by the energy deposited by incoming ions and promotes the grain growth. Grain growth is further confirmed by Atomic force microscopy. The temperature dependent magnetization measurements show improvement in the magnetic and shape memory properties of the films with increasing fluence, which is ascribed to the ordering of austenite phase. Nanoindentation measurements show that with increasing fluence of 120 MeV Ag ions, films exhibit a greater stiffness and smaller tendency towards plastic deformation.     

Growth and characterization of (Pb,La)TiO3 films with and without a special buffer layer prepared by RF magnetron sputtering

The (Pb, La)TiO₃ (PLT) ferroelectric thin films with and without a special buffer layer of PbO_x have been deposited on Pt/Ti/SiO₂/Si(100) substrates by RF magnetron sputtering technique at room temperature. The microstructure and the surface morphology of the films annealed at 600 °C for 1 h have been investigated by X-ray diffraction (XRD) and atomic force microscope (AFM). The surface roughness of the PLT thin film with a special buffer layer was 4.45 nm (5 μm × 5 μm) in comparison to that of 31.6 nm (5 μm × 5 μm) of the PLT thin film without a special buffer layer. Ferroelectric properties such as polarization hysteresis loop (P–V loop) and capacitance–voltage curve (C–V curve) of the films were investigated. The remanent polarization (P_r) and the coercive field (E_c) are 21 μC/cm² and 130 kV/cm respectively, and the pyroelectric coefficient is 2.75 × 10^− 8 C/cm² K for the PLT film with a special buffer layer. The results indicate that the (Pb, La)TiO₃ ferroelectric thin films with excellent ferroelectric properties can be deposited by RF magnetron sputtering with a special buffer layer.     

Ferroelectric, electrical, and magnetic properties of BiFe0.95Mn0.05O3 thin films epitaxially grown on conductive Nb:SrTiO3 and La0.7Sr0.3MnO3-buffered Nb:SrTiO3 substrates

BiFe_0.95Mn_0.05O₃ (BFMO) thin films with different thicknesses have been epitaxially grown on <001>-oriented Nb-doped SrTiO₃ (NbSTO) and La_0.7Sr_0.3MnO₃(LSMO)-buffered NbSTO substrates by pulsed laser deposition. At high bias field the space-charge-limited current (SCLC) is the dominant conduction mechanism for all BFMO films while at low bias field the Ohmic conduction is the predominant mechanism. An analysis of leakage current characteristics reveals that the ferroelectric properties are critically dependent on the density of defects in BFMO films. For the BFMO/LSMO/NbSTO structure, the coercive field of the BFMO film is much smaller than that of the BFMO film directly grown on the NbSTO substrate, which is attributed to the suppression of the substrate-induced clamping effect. For both BFMO/NbSTO and BFMO/LSMO/NbSTO structures, the ferroelectric hysteresis loops show no change under a magnetic field up to 9 T, which is explained in terms of weak ferromagnetic-ferroelectric coupling in the BFMO film and the very low magnetic-field-induced electric voltage drop across the LSMO layer.     

Multiferroic properties of BiFeO3/Bi4Ti3O12 double-layered thin films fabricated by chemical solution deposition

Multiferroic BiFeO₃/Bi₄Ti₃O₁₂ (BFO/BTO) double-layered film was fabricated on a Pt(111)/Ti/SiO₂/Si(100) substrate by a chemical solution deposition method. The effect of an interfacial BTO layer on electrical and magnetic properties of BFO was investigated by comparing those of pure BFO and BTO films prepared by the same condition. The X-ray diffraction result showed that no additional phase was formed in the double-layered film, except BFO and BTO phases. The remnant polarization (2P_r) of the double-layered film capacitor was 100 μC/cm² at 250 kV/cm, which is much larger than that of the pure BFO film capacitor. The magnetization-magnetic field hysteresis loop revealed weak ferromagnetic response with remnant magnetization (2M_r) of 0.4 kA/m. The values of dielectric constant and dielectric loss of the double-layered film capacitor were 240 and 0.03 at 100 kHz, respectively. Leakage current density measured from the double-layered film capacitor was 6.1 × 10^− 7 A/cm² at 50 kV/cm, which is lower than the pure BFO and BTO film capacitors.     

Pulsed laser deposition of epitaxial ferroelectric Pb(Zr,Ti)O3 films on silicon substrates

We report on the epitaxial growth and electrical properties of Pb_0.52Zr_0.48TiO₃ (PZT) thin films deposited by Pulsed Laser Deposition (PLD) on SrTiO₃ (STO)-buffered Si(001). Previously to PZT growth, 40 nm-thick (La,Sr)MnO₃ (LSMO) layer was deposited to serve as electrical bottom electrode. The 200 nm-thick PZT film epitaxy was optimized by PLD on STO-buffered Si(001).The high contrast of stable artificially poled ferroelectric surfaces evidences the good ferroelectric properties of the PZT thin film. The structural as well as the physical properties of the PZT/LSMO/STO/Si(001) structure prove that very good quality layers have been obtained for films grown on silicon substrate.     

Epitaxial La2 / 3Sr1 / 3MnO3 thin films with unconventional magnetic and electric properties near the Curie temperature

We used Pulsed Laser Deposition (PLD) in oxidizing environment to epitaxially grow optimally doped manganite La_2 / 3Sr_1 / 3MnO₃ (LSMO) thin films over a (001) oriented SrTiO₃ substrate. Synthesized samples show good room temperature magnetic properties accompanied by a peculiar extension of the metallic conduction regime to temperatures higher than the Curie point.In this paper we present a study of the dependence of transport and magnetic properties of LSMO thin films on the oxygen pressure during PLD growth. We show how interaction of the growing films with O₂ molecules is fundamental for a correct synthesis and in which way it is possible to adjust PLD experimental parameters in order to tune LSMO thin film properties.The persistence of the metallic conduction regime above the Curie temperature indicates some minor changes of the electronic structure near the Fermi level, which is responsible for the half-metallic behavior of LSMO at low temperature. This feature is rather intriguing from the technological point of view, as it could pave the way to the increase of operating temperature of devices based on LSMO.     

The structure and ferromagnetic properties of (Fe0.12CuxZn0.88−x)O thin films deposited on Si substrates by R.F. sputtering

Fe–Cu co-doped ZnO thin films deposited on silicon substrates were prepared by R.F. magnetron sputtering. The effects of various amounts of copper on the microstructure, surface morphology, composition, and magnetic properties of ZnO thin films were examined. The results of the experiments show that the structures of the ZnO thin films grown on the silicon substrate have a preferred orientation of (002). By increasing the copper concentration, the Fe ions exist as Fe²⁺ in the Fe_0.12Cu_xZn_0.88−xO system, but Cu²⁺ and Cu¹⁺ ions coexist when the Cu replaces the Zn. In addition, the ZnO thin films show ferromagnetic behaviour at room temperature and the largest saturation magnetization (Ms) is 5.64 × 10⁴ A/m for the as-grown Fe_0.12Cu_0.02Zn_0.86O thin film.     

Calculation of hysteresis loops in face-centered cubic thin films

A total energy equation for a single-crystalline face-centered cubic thin film with its close-packed (111) plane parallel to the film plane is used to calculate in-plane and out-of-plane hysteresis loops at various values of the cubic magnetocrystalline anisotropy constant (K₁). In-plane loops show that the easy and hard axes are the <112> and <110> directions, respectively, and that the coercivities, which are nearly independent of the sign of K₁, are quite low over the K₁ values due to the small variation of the magnetocrystalline anisotropy energy during the field sweep. The out-of-plane loops are similarly shaped to those of typical thin films, except for the appearance of a small hysteresis loop near the origin, which is attributed to an irreversible magnetization jump from one easy axis to another in the (111) plane. The magnetic parameters such as K₁ are estimated by comparing the theoretical results for in-plane and out-of-plane hysteresis loops with the experimental results measured for an epitaxial Co thin film. The value of K₁ is estimated to be − 1.2 × 10⁶ erg/cm³, which is significantly higher than that of − 6×10⁵ erg/cm³ for bulk Co, but is in good agreement with the values of − 1.3 to − 1.6 × 10⁶ erg/cm³ reported for Co thin films.     

Enhanced dielectric properties of Mn doped Ba0.6Sr0.4TiO3 thin films fabricated by pulsed laser deposition

Pure and 2 mol% Mn doped Ba_0.6Sr_0.4TiO₃ (BST) thin films have been deposited on La_0.67Sr_0.33MnO₃ (LSMO) coated single-crystal (001) oriented LaAlO₃ substrates using pulsed-laser deposition technique. The bilayer films of BST and LSMO were epitaxially grown in pure single-oriented perovskite phases for both samples, and an enhanced crystallization effect in the BST film was obtained by the addition of Mn, which were confirmed by X-ray diffraction (XRD) and in situ reflective high energy electron diffraction (RHEED) analyses. The dielectric properties of the BST thin films were measured at 100 kHz and 300 K with a parallel-plate capacitor configuration. The results have revealed that an appropriate concentration acceptor doping is very effective to increase dielectric tunability, and to reduce loss tangent and leakage current of BST thin films. The figure-of-merit (FOM) factor value increases from 11 (undoped) to 40 (Mn doped) under an applied electric field of 200 kV/cm. The leakage current density of the BST thin films at a negative bias field of 200 kV/cm decreases from 2.5 × 10^− 4 A/cm² to 1.1 × 10^− 6 A/cm² by Mn doping. Furthermore, a scanning-tip microwave near-field microscope has been employed to study the local microwave dielectric properties of the BST thin films at 2.48 GHz. The Mn doped BST film is more homogeneous, demonstrating its more potential applications in tunable microwave devices.     

Structure and Magnetic Properties of La0.66Sr0.33MnO3 Thin Films Derived Using Sol-Gel Technique

In this paper the results of a study of the structural and magnetic properties of La_0.66Sr_0.33MnO₃ (LSMO) polycrystalline films grown on glass substrate using Sol-Gel technique are presented. The samples were structurally characterized using X-ray diffraction (XRD) and scanning electron microscope (SEM) techniques. The average grain size range of 30 nm has been obtained from XRD investigations of granular LSMO samples. Zero Field Cooling (ZFC) and Field Cooling (FC) magnetization measurements have been performed and magnetic hysteresis loops of LSMO were recorded at various temperatures. The temperature dependences of the magnetization of LSMO films recorded in ZFC and FC regimes exhibited considerable difference between the curves. The blocking and the ferromagnetic phase transition temperatures of about 262?K and 300?K, respectively, were observed from magnetization measurements.     

Integration of BiFeO3 thin films on Si wafer via a simple sol-gel method

Integration of BiFeO₃ (BFO) films on Si substrate is desirable from an application point of view. The growth of (110)-textured BFO thin films with high quality on Si(100) substrate was realized by a seeding technique via a simple sol-gel method. Obviously switchable ferroelectric domains were observed, and in the meantime, the BFO films also exhibited a weak magnetization which somewhat showed dependence on the film thickness. Such an integration of the BFO films on Si constructed a metal/ferroelectric/insulator/semiconductor structure, which presented a memory feature as evidenced by capacitance-voltage hysteresis.     

Structure,conduction mechanisms and multiferroic properties of (Sm,Cr) co-doped Bi0.89Sm0.11Fe0.97Cr0.03O3–NiFe2O4 composition thin films

(Sm, Cr) co-doped Bi_0.89Sm_0.11Fe_0.97 Cr_0.03O₃ (BSFC)–NiFe₂O₄ (NFO) composition thin films were successfully prepared on FTO/glass (SnO₂:F) substrates via a sol–gel method. The structure, surface morphology, leakage current, ferroelectricity and ferromagnetism of BSFC–NFO composition thin film have been investigated. X-ray diffraction analysis indicates that the thin film is polycrystalline and consisted of a rhombohedral perovskite (R3m space group) BiFeO₃ phase and a cubic (Fd-3m space group) inverse spinel NiFe₂O₄ phase. The BSFC–NFO composition thin film is promising in practical application because of its well saturated ferromagnetic (Ms = 19.45 emu/cm³) and ferroelectric (Pr = 39 µC/cm²) hysteresis loops with low order of leakage current density (J = 6.73 × 10^?6 A/cm², at an applied electric field of 100 kV/cm). Which suggest the ferroelectric and ferromagnetic properties can be improved by this composition thin film structure. Moreover, the various conduction mechanisms of BSFC–NFO composition thin film have also been studied.     

Electrical transport and magnetoresistance in La2/3Sr1/3MnO3 polycrystalline composite thin films

The manganite La_2/3Sr_1/3MnO₃ (LSMO)/CuO and LSMO/Al₂O₃ polycrystalline composite thin films are deposited on Si (111) substrates in a magnetron sputtering system, using the tandem deposition method. The electrical transport and magnetoresistance properties of the films have been systematically investigated. By considering two parallel conduction channels at the grain boundary, we obtain a general expression for the temperature dependency of the resistance that agrees with the experimental data measured in LSMO polycrystalline composite thin films at whole temperature region of 300 K-10 K under the condition of zero magnetic field. Also, the resistance vs. temperature curve under an external magnetic field can be obtained by only varying one parameter in the model. It provides an effective way to obtain the high-temperature grain boundary magnetoresistance in the polycrystalline manganite.     

Underlayer dependence of microtexture, microstructure and magnetic properties of c-axis oriented strontium ferrite thin films

Strontium ferrite (SrM) thin films were prepared by dc magnetron sputtering system on thermally oxidized silicon wafer (SiO₂/Si), single-crystal sapphire with (00l) orientation and single-crystal MgO with (111) orientation and the effect of Au and Pt underlayers on morphology and magnetic properties was studied. Experimental results revealed that with the application of underlayers, the crystallization temperature of SrM was reduced. Strontium ferrite thin films with uniaxial anisotropy were formed on all substrate specimens. Comparison of the results obtained on all thin films indicated that the maximum saturation magnetization and coercivity in the perpendicular direction were 0.377 T and 0.382 MAm^− 1, respectively, for thin films with Au underlayer and SiO₂/Si substrate.