Room-temperature Coercive Field Research Articles

Effects of Mn corrosion on the magnetic properties of Ni81Fe19/Ir20Mn80 exchange biased thin films

The effects of antiferromagnetic corrosion on the magnetic properties of exchange biased thin films were studied. A Ni81Fe19/Ir20Mn80 bilayer was grown using DC sputtering. The crystal structure, microstructure, and magnetic properties of the samples were examined using x-ray diffraction (XRD), scanning electron microscope along with energy dispersive spectrometer, and resonance-vibrating sample magnetometer, respectively. XRD patterns revealed that the crystalline structure was (111) for both IrMn and NiFe layers. After magnetic field cooling, the room-temperature exchange bias field and coercive field were determined from hysteresis loops and no training effect was observed during the remagnetization process. The magnetic properties of the exchange biased bilayer strongly depended on the level of Mn corrosion in deionized (DI) water. A step-like magnetization curve was observed in the bilayer after soaking in DI water for 10 min. A detailed analysis of the magnetic moment response indicated an increase in the depth and area of corroded Mn with increasing soaking time. Trace amounts of Mn2+ in DI water, detected by a spectrophotometric technique using 1-(2-pyridylazo)-2-naphthol as an indicator, confirmed increasing Mn corrosion with increasing soaking time.

The Influence of Mechanical Stresses on the Magnetic Properties of NiFe2O4 and CoFe2O4 Films

We have studied the influence of mechanical stresses on the magnetic properties of nickel ferrite (NiFev) and cobalt ferrite (CoFe2O4) films deposited on sapphire substrates with a- and c-oriented step terrace nanostructures. It is established that compressive stresses favor enhancement of the coercive field in thin ferrite films in the strain direction. Films of magnetically soft nickel ferrite with a room-temperature coercive field of 32.5 mT were obtained.

Влияние напряжений на магнитные свойства пленок NiFe-=SUB=-2-=/SUB=-O-=SUB=-4-=/SUB=- и CoFe-=SUB=-2-=/SUB=-O-=SUB=-4-=/SUB=- на сапфире

AbstractWe have studied the influence of mechanical stresses on the magnetic properties of nickel ferrite (NiFev) and cobalt ferrite (CoFe_2O_4) films deposited on sapphire substrates with a - and c -oriented step terrace nanostructures. It is established that compressive stresses favor enhancement of the coercive field in thin ferrite films in the strain direction. Films of magnetically soft nickel ferrite with a room-temperature coercive field of 32.5 mT were obtained.

Modification of magnetic anisotropy in Ni thin films by poling of (011) PMN-PT piezosubstrates

ABSTRACTThis study reports the magnetic and magnetotransport properties of 20 nm thick polycrystalline Ni films deposited by magnetron sputtering on unpoled piezoelectric (011) [PbMg1/3Nb2/3O3]0.68-[PbTiO3]0.32 (PMN-PT) substrates. The magnetoresistance (MR), as well as the magnetization reversal, is found to depend on the polarization state of the piezosubstrate. Upon poling the PMN-PT substrate, which results in a transfer of strain to the Ni film, the MR value decreases by a factor of 12 at room temperature and a factor of 21 at 50 K for the current direction along the PMN-PT [100] direction, and slightly increases for the [01] current direction. Simultaneously, a strong increase in the room temperature coercive field value is observed, while the ratio between the remnant and saturation magnetization shows a pronounced minimum for the [100] direction, indicating it as a hard axis, induced by poling the piezosubstrate.

Heterojunction metal-oxide-metal Au-Fe3O4-Au single nanowire device for spintronics

In this report, we present the synthesis of heterojunction magnetite nanowires in alumina template and describe magnetic and electrical properties from a single nanowire device for spintronics applications. Heterojunction Au-Fe-Au nanowire arrays were electrodeposited in porous aluminum oxide templates, and an extensive and controlled heat treatment process converted Fe segment to nanocrystalline cubic magnetite phase with well-defined Au-Fe3O4 interfaces as confirmed by the transmission electron microscopy. Magnetic measurements revealed Verwey transition shoulder around 120 K and a room temperature coercive field of 90 Oe. Current–voltage (I-V) characteristics of a single Au-Fe3O4-Au nanowire have exhibited Ohmic behavior. Anomalous positive magnetoresistance of about 0.5% is observed on a single nanowire, which is attributed to the high spin polarization in nanowire device with pure Fe3O4 phase and nanocontact barrier. This work demonstrates the ability to preserve the pristine Fe3O4 and well defined electrode contact metal (Au)–magnetite interface, which helps in attaining high spin polarized current.

Temperature dependent magnetic properties of CoFe 2 O 4 /CTAB nanocomposite synthesized by sol–gel auto-combustion technique

A CoFe 2 O 4 /cetyl trimethylammonium bromide (CTAB) nanocomposite has been fabricated by a sol–gel auto-combustion method. Characterization of the material revealed the composition of the crystalline phase as CoFe 2 O 4 while FT-IR confirmed the presence of CTAB on the nanoparticles. From X-ray line profile fitting, average crystallite size was estimated to be 22±6 nm. SEM analysis showed a porous sheet-like morphology with internal nanosize grains of about 30 nm. The room temperature coercive field ( H c ) of the CoFe 2 O 4 /CTAB nanocomposite was found to be 1045 Oe which is close to the previously reported room temperature values for bulk CoFe 2 O 4 . The H c was observed to decrease almost linearly with the square root of the temperature (√T) according to Kneller's law . From the linear fit of H c versus √T, the zero-temperature coercivity ( H c 0 ) and superparamagnetic blocking temperature ( T B ) of the CoFe 2 O 4 /CTAB nanocomposite were found to be ∼9.1 kOe and ∼425 K, respectively. The remanence magnetization ( M r ), the reduced remanent magnetization ( M r / M s ), and the effective magnetic anisotropy ( K eff ) decrease with increasing temperature. The M r / M s value of 0.6 at 10 K higher than the theoretical value of 0.5 for non-interacting single domain particles with the easy axis randomly oriented suggests the CoFe 2 O 4 /CTAB nanocomposite to have cubic magnetocrystalline anisotropy according to the Stoner–Wohlfarth model.

Spin reorientation transition and hard magnetic properties of MnBi intermetallic compound

The effects of mechanical grinding (MG) on the crystallite size, the spin reorientation transition temperature (TSR) and the hard magnetic properties in melt-spun low temperature phase (LTP) MnBi have been investigated in order to understand the origin of magnetic hardening induced by MG. The room-temperature coercive field (μ0Hcj) is enhanced dramatically from 0.08 T before MG to 1.5 T after MG for 43.2 ks while TSR is concurrently suppressed from 110 to 38 K. The coercive force exhibits positive temperature dependence approximately 50–60 K above TSR and the lowered TSR after MG could result in magnetic hardening at room temperature. The room-temperature coercive force of LTP-MnBi is highly dependent on the crystallite size (D) and is found to be described phenomenologically by the following relationship: μ0Hcj = μ0Ha(δ/D)n, where μ0Ha is ∼ 4 T, the Bloch wall width δ is 7 nm, and the exponent n is approximately 0.7. Our results suggest that the grain refinement is the primary origin of the hardening effect induced by MG with a possible minor hardening effect due to the suppression of the spin reorientation transition temperature.

Room-temperature ground magnetic state of ɛ-Fe2O3: In-field Mössbauer spectroscopy evidence for collinear ferrimagnet

ɛ-Fe2O3 is a remarkable iron(III) oxide polymorph exhibiting a large room-temperature (RT) coercive field, coupled magnetoelectric properties, and millimeter-wave ferromagnetic resonance. Despite great application potential, its room-temperature ground magnetic state is still under scrutiny. Employing in-field 57Fe Mössbauer spectroscopy, we unambiguously demonstrate that at room temperature, ɛ-Fe2O3 behaves as a collinear ferrimagnet, hence excluding any canting of sublattice magnetizations. When exposed to an external magnetic field, ɛ-Fe2O3 can be modeled as a two-sublattice ferrimagnetic nanomaterial with the highest coercivity among all currently known ferrimagnetic (nano)materials.

Preparation of ferroelectric BaTi2O5 thin films on Pt(1 1 1)/Ti/SiO2/Si substrates by pulsed laser deposition

Ferroelectric BaTi2O5 thin films were prepared on Pt(111)/Ti/SiO2/Si substrates by pulsed laser deposition under different substrate temperatures (Tsub=923–973K) and oxygen partial pressures (PO2=7.5–15 Pa). The effects of Tsub and PO2 on the phase, orientation and surface morphology of the as-deposited films were investigated. It was found that the crystallographic orientation of BaTi2O5 thin films strongly depended on Tsub and PO2. The BaTi2O5 film with the highest (020)-texture coefficient (TC(020)=0.78) was obtained at Tsub=943K and PO2=12.5 Pa, showing a higher degree of b-axis orientation as compared with those deposited under other parameters. The ferroelectric property of the BaTi2O5 thin films was then investigated and the polarization–electric field (P–E) loop was measured for the first time. The room temperature remanent polarization and coercive electric field of the BaTi2O5 thin film with a higher degree of b-axis orientation were 0.77×10−2Cm−2 and 1×106Vm−1, respectively.

Ferroelectric Domain Structures and Electrical Properties of Fine‐Grained Lead‐Free Sodium Potassium Niobate Ceramics

Piezoelectric ceramics of the composition Na0.5K0.5NbO3 (NKN) with grain sizes in the range of 0.2–1 μm were fabricated by spark plasma sintering. Ferroelectric domain size decreases with decreasing grain size and non‐180° ferroelectric domains walls were still visible in 200 nm sized grains. The Curie point of the ceramics was grain size independent. This suggests that the critical grain size for a single domain single grain structure for NKN is <200 nm. Optimized processing conditions enabled ceramics of high densities (>99.5% theoretical density) to be made at T≥850°C. For the dense ceramics (grain size ≥350 nm), the room temperature dielectric constant and coercive field increased with decreasing grain size. The remnant polarization was grain size independent. The material sintered at 850°C is a very good candidate for lead‐free piezoelectric applications because of its high piezoelectric constant (d33=160 ± 2 pC/N).

Chemical Vapor Deposition of Iron, Iron Carbides, and Iron Nitride Films from Amidinate Precursors

Iron bis(-diisopropylacetamidinate) and iron bis(-di-tert-butylacetamidinate) were used as precursors for the metallorganic chemical vapor deposition (MOCVD) of iron-containing compounds including pure iron, iron carbides, and , and iron nitrides . Their decomposition mechanism involves hydrogen migration followed by dissociation of the Fe–N bond and the release of free hydrogenated ligand (HL) and radicals. Surface intermediates are either released or decomposed on the surface providing Fe–N or Fe–C bonds. MOCVD experiments were run at 10 Torr, in the temperature ranges of with and with . Films prepared from contain Fe, , and . Those prepared from contain Fe, , and also or , depending on the temperature and hydrogen to precursor ratio (H/P) in the input gas. The room-temperature coercive field of films processed from is 3 times higher than that of the high temperature processed films.

Multiferroic Properties of Hexagonal YbMnO$_{3}$ Thin Films

The hexagonal (HX) YbMnO <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">3</sub> thin films were synthesized on the substrates of (111)Y <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sub> O <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">3</sub> :ZrO <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sub> and (111)Pt/(0001)Al <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sub> O <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">3</sub> by pulsed laser deposition (PLD), and their structural, magnetic, and electrical properties are measured. The temperature-dependent magnetization clearly displays an antiferromagnetic ordering near 80 K with field perpendicular to the film surface. In the curve of polarization-voltage, the HX-YbMnO <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">3</sub> thin films show distinct ferroelectricity with the room-temperature remanent polarization and coercive field being 1.1 muC/cm <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sup> and 58 kV/cm, respectively. These results indicate that the HX-YbMnO <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">3</sub> thin films are prominent candidates for the applications of multiferroic devices.

Structure, dielectric and ferroelectric properties of highly (1 0 0)-oriented BaTiO 3 grown under low-temperature conditions

The highly (1 0 0)-oriented BaTiO 3 thin films were fabricated on LaNiO 3(1 0 0)/Pt/Ti/SiO 2/Si substrates under low-temperature conditions. Substrate temperatures throughout the fabrication process remained at or below 400 °C, which allows this process to be compatible with many materials commonly used in integrated circuit manufacturing. X-ray diffraction data provided the evidence for single BaTiO 3 phase. Field-emission scanning electron microscopy was used to study the columnar structure of the films. The dielectric properties as a function of frequency in the range of 1 kHz to 1 MHz was obtained. The room temperature remanent polarization (2 P r) and coercive field were found to be ∼5 μC/cm 2 and 50 kV/cm, respectively. The BTO film maintains an excellent fatigue-free character even after 10 9 switching cycles.

Magnetic moment of Fe in oxide-free FePt nanoparticles

We present results of x-ray absorption spectroscopy and x-ray magnetic circular dichroism investigations at the ${L}_{3,2}$ edges of Fe in FePt nanoparticles. Plasma treated, oxide-free FePt nanoparticles with a high degree of $L{1}_{0}$ ordering and a mean diameter of about $6\phantom{\rule{0.3em}{0ex}}\mathrm{nm}$ were produced by gas phase condensation followed by in situ flight annealing. The presence of the $L{1}_{0}$ phase is observed by high resolution transmission electron microscopy. Compared to chemically disordered A1 FePt particles of similar size and composition, we find a fourfold enhanced orbital magnetic moment ${\ensuremath{\mu}}_{L}=0.19$ $(\ifmmode\pm\else\textpm\fi{}0.04){\ensuremath{\mu}}_{B}$, a nearly unchanged effective spin magnetic moment ${\ensuremath{\mu}}_{S}^{\mathrm{eff}}=2.21$ $(\ifmmode\pm\else\textpm\fi{}0.24){\ensuremath{\mu}}_{B}$ and a 2% increase in the white-line ratio of the ${L}_{3}$ and ${L}_{2}$ Fe edges. Nevertheless, the room temperature coercive field amounts to ${\ensuremath{\mu}}_{0}{H}_{C}=38(\ifmmode\pm\else\textpm\fi{}7)\phantom{\rule{0.3em}{0ex}}\mathrm{mT}$ only. These results are discussed in relation to possible effects of chemical order and surface anisotropy.

Preparation of Ferroelectric BaTiO3 Films by Electrophoretic Deposition Technique

Barium titanate ferroelectric films on Pt substrates were fabricated by electrophoretic deposition (EPD) technique. The barium titanate films sintered at different temperature (600°C, 900°C, 1050°C, 1150°C, 1200°C) for 2h, which were prepared via repeated EPD-sintering route 2~3 times were sufficiently dense and had uniform microstructure. The XRD pattern and SEM microphotography have been measured in order to investigate the effects of the final annealing temperature on the phase compositions and microstructure of the film. The experiment results showed that barium titanate films were crystallized into the tetragonal phase at 1050°C and above. The room temperature dielectric constant (ε) and loss tangent (tanδ) at 1kHz were respectively determined for different samples sintered at 600°C, 900°C, 1050°C, 1150°C and 1200°C. Both ε and tanδ showed anomaly peaks at 125°C. The results showed that typical BaTiO3 films sintered at 1050°C having higher dielectric constant (ε=2300) and lower dielectric loss (tanδ=0.02). The room temperature remanant polarization (Pr) and coercive field (EC) were found to be 1.9μC/cm2 and 35kV/cm, respectively.

Lead zirconate titanate thin films prepared on metal substrates by the sol–gel methods

Pb(Zr0.53Ti0.47)O3 (PZT) thin films with thickness near 0.8 μm were prepared on LaNiO3 buffered Ti, NiCr and stainless steel (SS) substrates by the sol–gel methods. PZT thin films crystallized into the perovskite structure at temperatures of ≥550 °C. The room-temperature dielectric constant, tanδ, remnant polarization and coercive field achieved of 433, 0.03, 20 μC/cm2 and 50 kV/cm, respectively, for PZT thin films prepared on the NiCr substrate. The Curie temperature of PZT thin films on Ti, NiCr and SS was determined to be 330, 360 and 410 °C, respectively.

Electric Field Effect in Diluted Magnetic Insulator AnataseCo: TiO2

An external electric field induced reversible modulation of a room temperature magnetic moment and coercive field is achieved in an epitaxial and insulating thin film of dilutely cobalt-doped anatase TiO2. This first demonstration of an electric field effect in any oxide-based diluted ferromagnet is realized in a high quality epitaxial heterostructure of PbZr(0.2)Ti(0.8)O(3)/Co: TiO(2)/SrRuO(3) grown on (001) LaAlO3. The observed effect, which is about 15% in strength in a given heterostructure, can be modulated over several cycles. Possible mechanisms for electric field induced modulation of insulating ferromagnetism are discussed.

Surfaces and local anisotropy effect in the magnetic order of Fe–Co–B nanoparticles

3 nm (Fe x Co 1− x ) y B 1− y ( 0 ⩽ x ⩽ 1 , y ≈ 0.6 ) nanoparticles were synthesized by chemical route. XDR and TEM measurement show the amorphous nature of the samples. Size distribution was characterized by light-scattering measurement. Magnetization vs. magnetic field measurements at room temperature show hysteresis loop for all compositions, typical of blocked single domains. In powder samples, room temperature coercive field and remanent are larger for Fe- or Co-rich composition, and saturation magnetization exhibit a minimum at x = 0.15 . This behaviour is related to the composition of the different local anisotropy associated to Fe and Co ions.

Structure and magnetic properties of nanocrystalline (Fe1−xCox)90Zr7B2Cu1 (0⩽x⩽0.6)

Nanocrystalline (Fe1−xCox)90Zr7B2Cu1 (0⩽x⩽0.6) alloys were investigated by x-ray diffraction, Fe57 Mössbauer spectroscopy, and magnetic measurements. The grain size did not change significantly with composition. Co was preferentially partitioned to the residual amorphous phase, and the bcc grains were accordingly enriched by Fe. The room-temperature coercive field increased with the Co addition, which is attributed to the increasing magnetostriction constant.

Surface and Internal Spin Canting in γ-Fe2O3 Nanoparticles

Structural and magnetic properties of γ-Fe2O3 have been studied in isometric nanoparticles ranging from 3 to 14 nm with a narrow particle size distribution. Cation vacancy order is observed for particles larger than 5 nm in diameter giving rise to a cubic superstructure, while for the smallest particles these vacancies are disordered. All magnetic properties measured showed a strong dependence on the average crystallite size. For the ordered samples, saturation magnetization was found to decrease linearly with decreasing crystallite size due to a surface spin canting effect. However, a stronger decrease was observed in the disordered samples, suggesting that also an internal spin canting (cation vacancy order−disorder) has to be taken into account to explain the magnetic properties of nanoparticles. The room-temperature coercive field decreases with decreasing crystallite size; however at low temperatures, the coercivity increases as the size decreases, reaching values larger than 3000 Oe. A model to expl...