Investigation of the magnetic properties and magnetic structure parameters of nanocrystalline Fe<Subscript>79</Subscript>Zr<Subscript>10</Subscript>N<Subscript>11</Subscript> films

The magnetic properties (magnetization curve, ferromagnetic resonance spectrum) of nanocrystalline Fe₇₉Zr₁₀N₁₁ films obtained by RF magnetron sputtering with subsequent annealing were studied experimentally, along with the fundamental magnetic constants of these films (saturation magnetization M _S, local magnetic anisotropy energy K, and the exchange coupling constant A). The magnetic properties are discussed within the random magnetic model, which determines the correlation of the magnetic properties with the fundamental magnetic constants and nanostructure parameters (grain size, magnetic anisotropy, and correlation radius R _C). The exchange correlation length 2R _L for the film magnetic microstructure was determined by correlation magnetometry.     

Magnetic Resonance in [(CoP)<Subscript>soft</Subscript>/NiP/(CoP)<Subscript>hard</Subscript>/NiP]<Subscript><Emphasis Type="Italic">n</Emphasis></Subscript> Multilayer Magnetic Springs

The magnetic resonance properties of [(CoP)_soft/NiP/(CoP)_hard/NiP]_n multilayer films with the properties of magnetic springs have been experimentally studied. It has been found that the deposition of a NiP nonmagnetic amorphous layer on a (CoP)_soft magnetic layer induces the appearance of perpendicular interface anisotropy. The increase in the number of blocks n in the multilayer structure leads to the appearance of the third absorption peak, which is explained by the formation of a noncollinear three-sublattice magnetic structure.     

Coercive field enhancement in microstructured (La<Subscript>0.4</Subscript>Pr<Subscript>0.6</Subscript>)<Subscript>0.67</Subscript>Ca<Subscript>0.33</Subscript>MnO<Subscript>3</Subscript> thin films

The perovskite material (La_0.4Pr_0.6)_0.67Ca_0.33MnO₃ (LPCMO) has complex electronic and magnetic behavior based on phase competition between ferromagnetic metallic (FMM) and insulating phases with similar free energies. Experimental evidence has indicated that in-plane stress anisotropy influences these phases and can affect electronic and magnetic properties. Here we investigate the roles that both stress and shape anisotropies may play in controlling the coercive field of the material. LPCMO thin films of various thicknesses (20, 25, and 30 nm) were deposited on (110) NdGaO₃ (NGO) substrates using pulsed laser deposition and the coercive fields were measured. Photolithography was then used to fabricate microstructured arrays of LPCMO on the NGO substrates for each of the films. The coercive fields of these arrays of LPCMO were compared to the behavior of the corresponding unpatterned LPCMO thin films across a range of temperatures. Microstructure arrays for the thicker (25 and 30 nm) films showed a substantial increase in the coercive field after forming the arrays, whereas a thinner film (20 nm) showed almost no change in the coercive field. Stress anisotropy continues to play a dominant role in the behavior of LPCMO thin films and dimensionality of the magnetic domains also influences the results. The films show 2D behavior when film thickness approaches the size of the critical radius for single-to-multidomain transitions. Making thicker films allows for 3D behavior and a role for shape anisotropy to influence the coercive fields.     

Magnetostructural transformations in Ni<Subscript>51</Subscript>Mn<Subscript>36</Subscript>Sn<Subscript>13</Subscript> Heusler alloy thin films

In this paper we report structural, magnetic and transport properties of strongly textured Ni₅₁Mn₃₆Sn₁₃ thin films. The off-stoichiometric Heusler alloy films with 200 nm thickness were sputter-deposited on a MgO(100) substrate at 500 K and after annealed at 1000 K in UHV conditions. The textured growth was confirmed by x-ray diffraction in Bragg-Brentano geometry. The temperature dependence of the magnetic properties was measured by VSM and FMR methods. The electron transport measurements were carried out in function of temperature in 0 Oe and 50 kOe fields. All measurements corroborate the existence of the martensitic transformation in the film. Furthermore, transport measurements reveal an influence of the magnetic field on the transition temperature.     

Modification of the “Transcritical” state in Ni<Subscript>75</Subscript>Fe<Subscript>16</Subscript>Cu<Subscript>5</Subscript>Mo<Subscript>4</Subscript> films produced by RF sputtering

The saturation magnetization, the perpendicular and rotational anisotropy constants, and the coercitivity of Ni₇₅Fe₁₆Cu₅Mo₄ thin magnetic films produced by rf sputtering are measured in the initial state and after annealing. A relation between the presence of perpendicular anisotropy and the “transcritical” state in the films is established. It is shown that, after additional thermal treatment, the magnetic softness of the films can be improved.     

Magnetotransport characteristics of strained La<Subscript>0.7</Subscript>Sr<Subscript>0.3</Subscript>MnO<Subscript>3</Subscript> epitaxial manganite films

The electrical and magnetic characteristics of La_0.7Sr_0.3MnO₃ (LSMO) epitaxial manganite films are investigated by different methods under conditions when the crystal structure is strongly strained as a result of mismatch between the lattice parameters of the LSMO crystal and the substrate. Substrates with lattice parameters larger and smaller than the nominal lattice parameter of the LSMO crystal are used in experiments. It is shown that the behavior of the temperature dependence of the electrical resistance for the films in the low-temperature range does not depend on the strain of the film and agrees well with the results obtained from the calculations with allowance made for the interaction of electrons with magnetic excitations in the framework of the double-exchange model for systems with strongly correlated electronic states. Investigations of the magneto- optical Kerr effect have revealed that an insignificant (0.3%) orthorhombic distortion of the cubic lattice in the plane of the NdGaO₃(110) substrate leads to uniaxial anisotropy of the magnetization of the film, with the easy-magnetization axis lying in the substrate plane. However, LSMO films on substrates (((LaAlO₃)_0.3+(Sr₂AlTaO₆)_0.7)(001)) ensuring minimum strain of the films exhibit a biaxial anisotropy typical of cubic crystals. The study of the ferromagnetic resonance lines at a frequency of 9.76 GHz confirms the results of magnetooptical investigations and indicates that the ferromagnetic phase in the LSMO films is weakly inhomogeneous.     

FMR Studies of Ultra-Thin Epitaxial Pd<Subscript>0.92</Subscript>Fe<Subscript>0.08</Subscript> Film

Magnetic anisotropies of 20 nm epitaxial film of palladium–iron alloy Pd_0.92Fe_0.08 grown on the (001) MgO substrate were studied. Ferromagnetic resonance (FMR) spectroscopy and vibrating sample magnetometry (VSM) were exploited to determine magnetic parameters of the film. It was found that the synthesized film reveals cubic anisotropy with tetragonal distortion. The simulated magnetic hysteresis loops, obtained utilizing the magnetic anisotropy constants taken from the FMR spectra analysis, agree well with those measured by VSM.     

La<Subscript>0.7</Subscript>Sr<Subscript>0.3</Subscript>MnO<Subscript>3</Subscript> thin films on SrTiO<Subscript>3</Subscript> and CaTiO<Subscript>3</Subscript> buffered Si substrates: structural,static, and dynamic magnetic properties

Nearly 50-nm thick La_0.7Sr_0.3MnO₃ (LSMO) films were grown on Si substrates using molecular beam epitaxy on (001) Si substrates over-layered by a 20 nm thick SrTiO₃ (STO) or by a 20 nm thick CaTiO₃ (CTO) film. In addition, a reference LSMO film was directly deposited on a (001) STO substrate by pulsed laser deposition. For all the samples, X-ray diffraction revealed an excellent epitaxy of the LSMO film and small mosaicity around (001), with in-plane [100] and [010] cubic axes. The LSMO/CTO films are in-plane compressed while the LSMO/STO ones are in-plane extended. The temperature dependence of their static magnetic properties was studied using a SQUID, showing a Curie temperature overpassing 315 K for all the samples. Hysteresis loops performed at room temperature (294 K) with the help of a vibrating sample magnetometer (VSM) are also discussed. At 294 K Micro-strip ferromagnetic resonance (MS-FMR) was used to investigate the dynamic magnetic properties. It allows concluding to a strong anisotropy perpendicular to the films and to a weak fourfold in-plane anisotropy with easy axes along the [110] and [1[`1]0 1\bar{1}0 ] directions. Their values strongly depend on the studied sample and are presumably related to the strains suffered by the films.     

Crystal structure and magnetic anisotropy of ludwigite Co<Subscript>2</Subscript>FeO<Subscript>2</Subscript>BO<Subscript>3</Subscript>

Co₃O₂BO₃ and Co₂FeO₂BO₃ single crystals with a ludwigite structure are fabricated, and their crystal structure and magnetic properties are studied in detail. Substituted ludwigite Co₂FeO₂BO₃ undergoes two-stage magnetic ordering at the temperatures characteristic of Fe₃O₂BO₃ (T _N1 ≈ 110 K, T _N2 ≈ 70 K) rather than Co₃O₂BO₃ (T _N = 42 K). This effect is explained in terms of preferred occupation of nonequivalent crystallographic positions by iron, which was detected by X-ray diffraction. Both materials exhibit a pronounced uniaxial magnetic anisotropy. Crystallographic direction b is an easy magnetization axis. Upon iron substitution, the cobalt ludwigite acquires a very high magnetic hardness.     

Magnetic properties of the CuCoAlBO<Subscript>5</Subscript> single crystal

High-quality CuCoAlBO₅ single crystals have been grown, and their crystal structure, magnetic susceptibility, and magnetization have been studied. It has been established that the CuCoAlBO₅ compound is an uncompensated antiferromagnet or ferrimagnet with a small magnetic moment and the magnetic ordering temperature T _N = 28 K. A model has been proposed for the magnetic structure. A strong anisotropy of the magnetic properties has been revealed.     

Observation of the magnetic domain structure in Cu<Subscript>0.47</Subscript>Ni<Subscript>0.53</Subscript> thin films at low temperatures

We report on the first experimental visualization of domain structure in films of weakly ferromagnetic Cu_0.47Ni_0.53 alloy with different thickness at liquid helium temperatures. Improved high-resolution Bitter decoration technique was used to map the magnetic contrast on the surface of the films well below the Curie temperature T_Curie (∼60 K). In contrast to magnetic force microscopy, this technique allowed visualization of the domain structure without its disturbance while the larger areas of the sample were probed. Maze-like domain patterns, typical for perpendicular magnetic anisotropy, were observed. The average domain width was found to be about 100 nm. The article is published in the original.     

Multiple magnetic transitions in single crystals of Ce<Subscript>12</Subscript>Fe<Subscript>57.5</Subscript>As<Subscript>41</Subscript> and La<Subscript>12</Subscript>Fe<Subscript>57.5</Subscript>As<Subscript>41</Subscript>

Measurements of magnetic and transport properties were performed on needle-shaped single crystals of Ce₁₂Fe_57.5As₄₁ and La₁₂Fe_57.5As₄₁. The availability of a complete set of data enabled a side-by-side comparison between these two rare earth compounds. Both compounds exhibited multiple magnetic orders within 2–300 K and metamagnetic transitions at various fields. Ferromagnetic transitions with Curie temperatures of 100 and 125 K were found for Ce₁₂Fe_57.5As₄₁ and La₁₂Fe_57.5As₄₁, respectively, followed by antiferromagnetic type spin reorientations near Curie temperatures. The magnetic properties underwent complex evolution in the magnetic field for both compounds. An antiferromagnetic phase transition at about 60 K and 0.2 T was observed merely for Ce₁₂Fe_57.5As₄₁. The field-induced magnetic phase transition occurred from antiferromagnetic to ferromagnetic structure. A strong magnetocrystalline anisotropy was evident from magnetization measurements of Ce₁₂Fe_57.5As₄₁. A temperature-field phase diagram was present for these two rare earth systems. In addition, a logarithmic temperature dependence of electrical resistivity was observed in the two compounds within a large temperature range of 150–300 K, which is rarely found in 3D-based compounds. It may be related to Kondo scattering described by independent localized Fe 3d moments interacting with conduction electrons.     

Properties of ferromagnetic resonance in Fe<Subscript>73.5</Subscript>CuNb<Subscript>3</Subscript>Si<Subscript>13.5</Subscript>B<Subscript>9</Subscript> nanocrystalline alloys

The structural properties and parameters of ferromagnetic resonance have been studied for Fe_73.5CuNb₃Si_13.5B₉ nanocrystalline alloys produced from the initial amorphous state via annealing under different conditions. The dependence of the linewidth of the ferromagnetic resonance on the grain size ΔH ∼ D ⁶ has been found. The result is discussed within the framework of the random magnetic anisotropy model.     

Methods for spin injection managing in inGaAs/GaAs/Al<Subscript>2</Subscript>O<Subscript>3</Subscript>/CoPt spin light-emitting diodes

Spin injection in CoPt/Al₂O₃/(Al)GaAs spin light-emitting diodes (SLEDs) was studied. The oscillations of the degree of circular polarization upon variation of a distance between the active region of the SLED and a CoPt ferromagnetic injector were observed. The oscillations depend neither on a SLED material (GaAs or AlGaAs), nor on the type of injected spin-polarized carriers (electrons and holes) and are related to the action of a perpendicular magnetic field on the injected spin-polarized carriers that causes their precession. During the transfer to the active region through a distance of 50–100 nm from the injector, a z–component of a spin changes a phase that is detected experimentally as the change in sign of the degree of circular polarization of luminescence. Conceivably, a source of the internal magnetic field leading to spin precession is the magnetic field of the nonuniformly magnetized CoPt contact.     

Phase separation effects in charge-ordered Pr<Subscript>0.5</Subscript>Ca<Subscript>0.5</Subscript>MnO<Subscript>3</Subscript> thin film

Compressed Pr_0.5Ca_0.5MnO₃ films (250 nm) deposited on LaAlO₃ have been studied by Electron Spin Resonance technique under high frequency and high magnetic field. We show evidences for the presence of a ferromagnetic phase (FM) embedded in the charge-order phase (CO), in form of thin layers which size depends on the strength and orientation of the magnetic field (parallel or perpendicular to the substrate plane). This FM phase presents an easy plane magnetic anisotropy with an anisotropy constant 100 times bigger than typical bulk values. When the magnetic field is applied perpendicular to the substrate plane, the FM phase is strongly coupled to the CO phase whereas for the parallel orientation it keeps an independent ferromagnetic resonance even when the CO phase becomes antiferromagnetic.     

Magnetic phases in UNi<Subscript>2</Subscript>Si<Subscript>2</Subscript>

The tetragonal compound UNi₂Si₂ exhibits in zero magnetic field three different antiferromagnetic phases belowT _N =124 K. They are formed by ferromagnetic basal planes, which are antiferromagnetically coupled along thec-axis with the propagation vectorq=(0, 0, q _z ). Two additional order-order magnetic phase transitions are observed below T _N , namely atT ₁=108 K and T ₂=40 K in zero magnetic field. All three phases exhibit strong uniaxial anisotropy confining the U moments to a direction parallel to the c-axis. UNi₂Si₂ single crystals were studied in detail by measuring bulk thermodynamic properties, such as thermal expansion, resistivity, susceptibility, and specific heat. A microscopic study using neutron diffraction was performed in magnetic fields up to 14.5 T parallel to the c-axis, and a complex magnetic phase diagram has been determined. Here, we present the analysis of specific-heat data measured in magnetic fields up to 14 T compared with the results of the neutron-diffraction study and with other thermodynamic properties of UNi₂Si₂.     

Electro-optic properties of epitaxial Sr<Subscript>0.6</Subscript>Ba<Subscript>0.4</Subscript>Nb<Subscript>2</Subscript>O<Subscript>6</Subscript> films grown on MgO substrates using Li<Subscript>x</Subscript>Ni<Subscript>2-x</Subscript>O buffer layer

Textured Li_xNi_2-xO (LNO) thin films have been fabricated on (001)MgO substrates by pulsed laser deposition technique. The as-deposited LNO films shows a conductivity of 2.5×10^-3 Ω m and possess a transmittance of about 35% in the visible region. Subsequent deposition of Sr_0.6Ba_0.4Nb₂O₆ (SBN60) thin film on these LNO-coated MgO substrates resulted in a textured SBN layer with a 〈001〉 orientation perpendicular to the substrate plane. Phi scans on the (221) plane of the SBN layer indicated that the films have two in-plane orientations with respect to the substrate. The SBN unit cells were rotated in the plane of the film by ± 8.2° as well as ± 45° with respect to the LNO/MgO substrate. Besides the highly (00l)-orientation, the SBN films also exhibited a dense microstructure as shown by scanning electron microscopy. The electro-optic coefficient (r₃₃) of the SBN film was measured to be 186 pm/V. On the basis of our results, we have demonstrated that the LNO film can be used as a buffer layer as well as a transparent bottom electrode for waveguide applications. The SBN/LNO heterostructure is also a suitable candidate for integrated electro-optics devices. PACS  42.79.Gn; 42.82.Et; 78.20.Ci     

Modulation of ultrafast laser-induced magnetization precession in BiFeO<Subscript>3</Subscript>-coated La<Subscript>0.67</Subscript>Sr<Subscript>0.33</Subscript>MnO<Subscript>3</Subscript> thin films

The ultrafast laser-excited magnetization dynamics of ferromagnetic (FM) La_0.67Sr_0.33MnO₃ (LSMO) thin films with BiFeO₃ (BFO) coating layers grown by laser molecular beam epitaxy are investigated using the optical pump-probe technique. Uniform magnetization precessions are observed in the films under an applied external magnetic field by measuring the time-resolved magneto-optical Kerr effect. The magnetization precession frequencies of the LSMO thin films with the BFO coating layers are lower than those of uncoated LSMO films, which is attributed to the suppression of the anisotropy field induced by the exchange interaction at the interface between the antiferromagnetic order of BFO and the FM order of LSMO.     

Lattice structure and magnetization of LaCoO<Subscript>3</Subscript> thin films

We investigate the structure and magnetic properties of thin films of the LaCoO₃ compound. Thin films are deposited by pulsed laser deposition on various substrates in order to tune the strain from compressive to tensile. Single-phase (001) oriented LaCoO₃ layers were grown on all substrates despite large misfits. The tetragonal distortion of the films covers a wide range from -2% to 2.8%. Our LaCoO₃ films are ferromagnetic with Curie temperature around 85 K, contrary to the bulk. The total magnetic moment is below 1μ _B /Co³⁺, a value relatively small for an exited spin-state of the Co³⁺ ions, but comparable to values reported in literature. A correlation of strain states and magnetic moment of Co³⁺ ions in LaCoO₃ thin films is observed.     

Low-temperature structural anomalies in Pr<Subscript>0.5</Subscript>Sr<Subscript>0.5</Subscript>CoO<Subscript>3</Subscript>

The magnetic and crystal structures of the Pr_0.5Sr_0.5CoO₃ metallic ferromagnet have been studied by the neutron diffraction technique. It is demonstrated that below 150 K, the compound is mesoscopically separated into two crystalline phases with different spatial symmetries and with different directions of the magnetic anisotropy. The phase separation exists down to 1.5 K, and at temperatures below 90 K, the low-symmetry phase occupies about 80% of the sample volume. The main structural difference between the phases is the configuration of oxygen atoms around praseodymium and, to a certain extent, around cobalt. The ferromagnetic structure with the magnetic moment lying in the basal plane of the structure (μ_Co ≈ 1.7 μ _B at 1.5 K) arises at 234 K, whereas the component directed along the long axis of the unit cell appears at 130 K. The formation of the new structural phase and change in the orientation of the magnetic moment give rise to the anomalies of the physical and magnetic characteristics of this compound observed earlier at temperatures about 120 K.