In-plane Loops Research Articles

Electrical and magnetic properties of Aurivillius phase Bi5Fe1-xNixTi3O15 thin films prepared by chemical solution deposition

The Aurivillius Bi5Fe1-xNixTi3O15 (BFNT-x) (0≤x≤0.5) thin films were deposited by chemical solution deposition route. The microstructures, electrical and magnetic properties were systematically investigated in BFNT films. It has been found that the c-orientation of the films increases with the increase of Ni content. The coexistence of weak ferromagnetism and ferroelectricity at room temperature were observed in BFNT films except the x = 0.5 sample. The BFNT-0.1 sample exhibits a maximum remnant polarization 2Pr ∼49.3 μC/cm2, which is enhanced by 12.6% compared with that of the Ni-free thin film. The leakage current is decreased evidently with Ni content less than 0.3. The BFNT-0.1 film also shows the highest remnant magnetization 2Mr ∼2.14 emu/cm3. The origins of weak ferromagnetism in the BFNT films are attributed to the spin canting of the antiferromagnetic (AFM) coupling caused by Dzyaloshinskii-Moriya (DM) interaction based the Fe-O and Ni-O octahedral and affected by other causes as discussed. The saturation magnetization values of in-plane loops are smaller than that of the out-of-plane loops, indicating obvious anisotropic magnetism. These results demonstrate that partial substitution of Ni for Fe is an effective way for improving the multiferroic properties of Aurivillius compounds.

Microstructure and magnetic properties of FePt film with combined MoC/(Mg–X)O (X=Cu, Ni, Co) intermediate layers

The magnetic properties and microstructure of FePt films grown on MoC layer and MoC/(Mg–X)O (X=Cu, Ni, Co) combined intermediate layers were studied. The (Mg–X)O (X=Cu, Ni, Co) layer with thickness of 5nm was deposited on CrRu seed layer at 395°C. The CrRu (200) texture was enhanced which may due to well grains growth in specific orientation and small lattice mismatch with (Mg–X)O (X=Cu, Ni, Co). Finally, the FePt/MoC layers were deposited on (Mg–X)O layer at 425°C. Using MoC/MgCuO combined intermediate layers, the rocking width of FePt (001) and CrRu (200) diffraction peak were changed from 7.1° to 6.1°, and 5.7° to 3.8°, respectively. For MoC/MgCoO dual intermediate layers, the rocking width of FePt (001) and CrRu (200) diffraction peak were 6.7° and 4.1°. The FePt/MoC/MgCoO film illustrates perpendicular magnetic anisotropy with out-of plane coercivity of 9.3kOe which is higher than FePt film deposited on MoC layer (8.5kOe) and the in-plane loops is linear. From microstructure, the FePt grains were more separated on MoC/(Mg–X)O (X=Cu, Ni, Co) combined intermediate layers.

Naturally Produced Co/CoO Nanocrystalline Magnetic Multilayers: Structure and Inverted Hysteresis.

Cobalt-based multilayers with excellent sequencing are grown via radiofrequency magnetron sputtering with the use of one Co target and natural oxidation. The Co layers are continuous, fully textured {111} and have the face centered cubic structure. At the end of deposition of each Co layer air is let to flow into the vacuum chamber via a fine (leak) valve. The top of Co is oxidized. The oxidized layers consist of cubic CoO crystallites. Near the film surface hexagonal Co(OH)2 is also detected. Magneto-optical Kerr effect hysteresis loops show in-plane magnetized films. The magnetic saturation field in the out-of-plane measurements is large exceeding 12 kOe. This observation supports indirectly the fact that Co is face centered cubic; if it was c-axis textured hexagonal the magnetocrystalline anisotropy would be large resulting in smaller values of the saturation field. As the Co-layer thickness decreases the in-plane loops show reduced remanence, slow approach to magnetic saturation and the out-of-plane loops show inverted hysteresis and/or crossing loop features with sizeable remanence. The effects are discussed with respect to the enhanced orbital magnetic moment of Co and the antiferromagnetic coupling between Co spins at the Co/CoO interface.

MoC intermediate layer for FePt magnetic recording media

A (001) textured FePt film was deposited on MoC/CrRu/glass at a substrate temperature of 380 °C by using magnetron sputtering. The MoC conductive intermediate layer was used to resist the Cr diffusion up to high deposition temperatures and promotes the epitaxial growth of the (001) textured FePt film. The FePt film showed high perpendicular magnetization and the out-of-plane coercivity increased with MoC thickness. The FePt/MoC (5 nm)/CrRu film showed a square out-of-plane magnetic hysteresis loop with a coercivity of 6.0 kOe and a linear-like in-plane loop. A multi-functional MoC intermediate layer exhibited heteroepitaxial relation with FePt and CrRu and was capable of resisting the interlayer diffusion at high deposition temperatures.

Structure and property changes and femtosecond laser-induced magnetization dynamics of two-year-old high coercive TbFeCo films

An uncoated TbFeCo film on glass substrate exposed to dry air for 2 years is studied using magneto-optical polar Kerr spectroscopy and vibrating sample magnetometry (VSM). The out-of-plane hysteresis loop by VSM is found to become slanted and meanwhile, an in-plane loop is also observable. The Kerr loop measured from the exposed surface is also slanted compared to that measured from the substrate-contacted surface, which indicates that the exposed surface is oxidized. So a bilayer structure of the film is proposed. When a pump laser is switched on, the Kerr loops measured from both surfaces at the delay time of −5ps become anomalous, showing the occurrence of magnetization reversal across magnetization compensation temperature. Unlike that measured from the substrate-contacted surface, femtosecond laser-induced magnetization dynamics measured from the exposed surface does not show magnetization reversal crossing zero magnetization. This can be explained by the bilayer structure as the compensation effect of demagnetization recovery of the oxidized layer on magnetization reversal of perpendicularly anisotropic TbFeCo layer across magnetization compensation temperature. Above experimental results show that the uncoated TbFeCo film cannot resist oxidation in dry air at room temperature for 2 years while the SiO2-coated surface can do so for over 2 years.

Electric-Field Effect on Magnetic Properties of FePt/PZN-PT Heterostructures

FePt films on PZN-PT single-crystal substrate, the ferromagnetic/piezoelectric (FM/PE) heterostructures, were fabricated by magnetron sputtering. The effects of the electric field on the coercivity and magnetization of the FePt at room temperature in FM/PE heterostructures were investigated. The as-grown FePt film showed an in-plane magnetic anisotropy. Upon applying an electric field, the out-of-plane magnetic loops of the heterostructure changed obviously, but the in-plane loops remained unchanged. When the applied E field increased from 0 to 5 kV/cm, the coercivity of out-of-plane increased from 4614 to 4907 Oe. The change of out-of-plane coercivity with different E field is consistent with the strain-electric-field loop of piezoelectric materials. Therefore, the increase of the coercivity can be attributed to that the electric-field-induced strain resulted in increased anisotropy normal to the film plane. The magnetization reversal process of easy direction was mainly due to domain wall motion, which may explain the invariability of the in-plane loops. Based on these results, it was believed that the electric-field-induced piezoelectric strain from the bottom PZN-PT substrate was effectively transferred to the top FePt layer.

Fabrication of a ${\rm Bi}_{2}{\rm Sr}_{2}{\rm CaCu}_{2}{\rm O}_{8+x}$ Intrinsic DC-SQUID With a Shunt Resistor

We fabricated Bi <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sub> Sr <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sub> CaCu <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sub> O <i xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">x</i> (Bi-2212) SQUIDs with two stacks of intrinsic Josephson junctions by an acid-treatment process. The stacks were fabricated from a single crystal of Bi-2212. The in-plane loop of a dc-SQUID was surrounded by an acid-treated product, which was produced by immersing the Bi-2212 single crystal in dilute hydrochloric acid (pH=1.65). The critical aspect of this process is that the surrounding acid-treated product (BiOCl) is transparent. The SQUID exhibited a large hysteresis with a ratio of the critical current to the return current of 0.4 at 77 K. Applying a magnetic field modulated the critical current of a dc-SQUID for fields of up to about 10 G. In addition, we fabricated dc-SQUIDs attached to a shunt resistor, which exhibited nonhysteretic current-voltage characteristics. Appling a magnetic field modulated the voltage; the maximum voltage modulation was about 30 μV at 77 K.

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 ( K 1). 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 K 1, are quite low over the K 1 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 K 1 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 K 1 is estimated to be − 1.2 × 10 6 erg/cm 3, which is significantly higher than that of − 6×10 5 erg/cm 3 for bulk Co, but is in good agreement with the values of − 1.3 to − 1.6 × 10 6 erg/cm 3 reported for Co thin films.

Impact of Anisotropic Exchange on M-H Loops: Application to ECC Media

Micromagnetic simulation results on Co-based recording media are presented which examine the impact of a modified near-neighbor exchange interaction between grains of the form <i xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">J</i> <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">z</sup> (M <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">i</sub> <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">z</sup> M <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">j</sub> <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">z</sup> ), reflecting the hexagonal crystal symmetry. Both out-of-plane and in-plane M-H loops are calculated, with an emphasis on a model fit to data reported by Wang . [ <i xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">IEEE Trans. Magn</i> , vol. 43, p. 682 (2007)] on exchange coupled composite perpendicular media. The principle effect of <i xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">J</i> <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">z</sup> is to increase the coercivity and slope of both hard and soft layers. Improved agreement with experimental data for the in-plane loops is achieved by assuming a substantial value for <i xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">J</i> <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">z</sup> . Possibilities for measurement of J <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">z</sup> through spin-wave excitations are discussed. Thermal fluctuation effects are also examined through simulations of the magnetization vs temperature.

Multijunction SQUID Based on Intrinsic Josephson Junctions

We have numerically and experimentally investigated multijunction superconducting quantum interference device (SQUID) based on intrinsic Josephson junctions (IJJs) of in order to improve the flux to voltage transfer coefficient. Numerical simulations suggest that the modulation depth of critical current decreases with an increase in the number of junctions in the stack and the SQUID consisting of few junctions will yield the best performance. The SQUIDs with in-plane loop geometry incorporating two stacks of IJJs were successfully fabricated from (BSCCO). The advantages of this layout are that the multijunction SQUID can be achieved without an increase in device size and the stack of IJJs is less affected by an applying magnetic field. At 4.2 K, the SQUIDs showed hysteretic current-voltage characteristics with typical multiple resistive branches. As the temperature was increased, the hysteresis disappeared and the SQUID showed clear periodic voltage-flux characteristics due to the quantum interference between the weakest junctions in the stacks.

Superconducting quantum interference phenomenon inBi2Sr2CaCu2O8+δsingle crystals

The operational direct-current superconducting quantum interference device (dc-SQUID) based on intrinsic Josephson junctions in ${\mathrm{Bi}}_{2}{\mathrm{Sr}}_{2}{\mathrm{CaCu}}_{2}{\mathrm{O}}_{8+\ensuremath{\delta}}$ high-${T}_{c}$ superconductor is fabricated and studied. The in-plane loop layout and the developed in situ end-point detection method allowed an accurate control of the number of junctions in the SQUID. A clear periodic modulation of the superconducting current as a function of magnetic flux through the SQUID loop is observed. This is an unambiguous evidence for the quantum interference phenomenon in ${\mathrm{Bi}}_{2}{\mathrm{Sr}}_{2}{\mathrm{CaCu}}_{2}{\mathrm{O}}_{8+\ensuremath{\delta}}$ single crystals.

Exchange bias and vertical loop shifts in a Co(32Å)∕NiO(10Å)∕[Co(4Å)∕Pt(6Å)]4 multilayer

Investigation has been performed on exchange bias in a Co(32Å)∕NiO(10Å)∕[Co(4Å)∕Pt(6Å)]4 multilayer after cooling at remanence. The easy axes of the Co∕Pt multilayer and the 32Å Co layer are different. Both exchange bias and vertical loop shifts have been observed in the out-of-plane loop, and they disappear at the same temperature of 170K. No obvious vertical shift is observed in the in-plane loops, but the exchange bias transitions from negative at T&amp;lt;50K to positive at T&amp;gt;50K. These phenomena have been ascribed to the interfacial induced net moment in the NiO spacer.

Magnetic properties of densely packed arrays of Ni nanowires as a function of their diameter and lattice parameter

High-quality densely packed hexagonal arrays of Ni nanowires have been prepared by filling self-ordered nanopores in alumina membranes. Nanowires with different diameter d (18–83 nm) and lattice parameter D (65 and 105 nm) have been studied by atomic force, high resolution scanning electron microscopies, Rutherford backscattering, and vibrating sample magnetometer techniques. Axial loops coercivity and remanence decrease with increasing ratio diameter to lattice parameter, r, until nanowires start to interconnect locally. Additionally, hysteresis of in-plane loops increases with packing factor. In order to interpret the experimental results, multipolar magnetostatic interactions among nanowires with increasing ratio r are considered.

Out-of-plane exchange coupling between epitaxial Ni (50 Å) and NiO (600 Å) bilayers

We have investigated the exchange coupling between an epitaxial Ni (50 Å) film with an out-of-plane magnetic easy axis and a NiO (600 Å) film by polar magneto-optic Kerr-effect measurements. The temperature dependences of exchange field HE for both as-deposited and field-cooled states exhibit the same blocking temperature TB∼130 °C. The exchange field HE for the field-cooled state is lower than that for the as-deposited state. The hard-axis in-plane loop shows a much smaller value of HE. No coercivity enhancement is observed. The data are suggestive of linear coupling across the ferromagnet/antiferromagnet interface.

Thin soft sendust laminated CoPt hard films

The C-axis of the Co-based permanent magnet films tends to grow gradually toward perpendicular direction as the film thickness increases. Reported here is a novel way to solve this problem. That is to laminate the Co-based hard magnet films with thin soft magnetic films. The effects of soft film underlayer and lamination, on the magnetic properties of CoPt films has been studied and reported here. Three types of soft magnetic material NiFe, NiFeRe and FeAlSi were chosen to conduct the experiments. Amorphous thin soft sendust film was found to meet the goal. It is found that there was a dramatic improvement of the in-plane loop squareness by inserting a 100 /spl Aring/ amorphous FeAlSi film into the 1200 /spl Aring/ CoPt film. The squareness (S) and the remnant magnetization thickness product (MrT) of the CoPt film (1200 /spl Aring/) without soft FeAlSi film lamination are 0.27 and 3.0 memu/cm/sup 2/, respectively, while the S and the MrT of the CoPt film (1200 /spl Aring/) with soft FeAlSi lamination are 0.60 and 6.32 memu/cm/sup 2/, respectively. Multi-lamination is possible if thick CoPt film is required in applications.

Effects of a transition layer on CoCr films

The effects of a transition layer separating the substrate and the columnar structure of rf sputtered CoCr films on their magnetic and structural properties have been investigated. The films were removed from glass substrates and the transition layer was etched directly by rf sputtering. It is shown that the abrupt change or anomalous jump observed in the in-plane magnetization hysteresis loop of some CoCr films is caused by a fine-grained transition layer which is about 1000 Å thick and has a coercivity of 200 Oe. The measured in-plane coercivity increased to 1000 Oe when the transition layer was completely removed while no change was observed in the perpendicular coercivity or saturation magnetization. Only films having a transition layer showed a large decrease in the effective anisotropy field as determined from the in-plane loop when sputter etched to a depth of 2000 Å from the top surface. The dispersion of the hcp (002) axes was found to be 3° for films without and 16° for films with a transition layer. These dispersions were found to be independent of the sputter-etched depth indicating that the intrinsic dispersion of the orientation of CoCr films is established by the transition layer.