Ferromagnetic Hysteresis Loops Research Articles

Microwave synthesis and phase transitions in nanoscale BiFeO3

Nanosized multiferroic BiFeO3 powders were synthesized by a microwave combustion method. The average crystallite sizes of the samples stay at a same level with the ratio of fuel glycine 0.5 ≤ G/N ≤ 1.5 and it increases significantly with G/N = 2.0. An inhomogeneity of amorphous and microcrystallites is observed directly by HRTEM. A ferromagnetic hysteresis loop with a saturation magnetization (M S) of ~0.09 μ B /Fe has been observed at room temperature in the sample with a crystallite size of 53 nm, whereas other powders with much smaller crystallite size (~20 nm) will not saturate even at 20 kOe. These magnetic behaviors were ascribed to a combination of the magnetic enhancement effect of a decreased crystallite size and superparamagnetic mechanism.

Effect of BaTiO3 buffer layer on multiferroic properties of BiFeO3 thin films

BiFeO 3 (BFO) films were processed on BaTiO3 (BTO) buffered (111) Pt/Ti/SiO2/Si substrate by pulsed laser deposition. Improved ferroelectric properties, as well as induced ferromagnetism, were observed by the insertion of a BTO layer for rather thick BFO films (450 nm) deposited at an oxygen pressure of 40 mTorr. Reduced leakage current, coercive field, and increased ferroelectric saturation of BFO/BTO bilayer films were obtained and compared with those of BFO films. In order to better understand the buffer layer effect on the magnetic properties, two thinner (140 and 220 nm) BFO films were also deposited and investigated. Both films showed ferromagnetic hysteresis loops and larger in-plane magnetization than out-of-plane magnetization. By introducing the BTO barrier layer, the remnant and saturated magnetizations were also increased. These results demonstrated not only the interface constraint effect but also a coupling between ferroelectric BTO and magnetic BFO, which deserve further investigation.

Ferromagnetism of manganese-doped indium tin oxide films deposited on polyethylene naphthalate substrates

Mn-doped indium tin oxide (ITO) films were deposited on polyethylene naphthalate (PEN) substrates using radio-frequency magnetron sputtering. The magnetic, electrical, and optical properties of the films deposited on PEN substrates were investigated by comparing with the properties of films grown on glass substrates at the same growth conditions. Thin films on PEN substrates exhibited low electrical resistivity of the order of 10−4 Ω cm and high optical transmittance between 75% and 90% in the visible region. Ferromagnetic hysteresis loops were observed at room temperature for the samples grown on PEN substrates. Mn-doped ITO films can be one of the most promising candidates of transparent ferromagnetic materials for flexible spintronic devices.

Magnetoelectricity in multiferroically composed multilayers and multiglasses

Single-crystalline magnetoelectric (ME) antiferromagnetic Cr 2O 3 exchange coupled to a ferromagnetic multilayer (Pt/Co/Pt) n , n⩾1, represents a multiphase multiferroic material with sophisticated multifunctional properties. They comprise the possibility of switching the exchange bias (EB) of the ferromagnetic hysteresis loop via the linear ME effect of Cr 2O 3, and to design MERAM and logic cells operating at room temperature. Quadratic and cubic ME effects – promoted by soft-mode quantum fluctuations – are observed at lowest order in ceramic Sr 0.98Mn 0.02TiO 3 at low temperatures. Dipolar and spin glass orders occur simultaneously on the Mn 2+ subsystem and form a multiglass by analogy with conventional multiferroics.

Magnetic properties of SrTiO3-buffered Ba(Fe0.2Zr0.8)O3−δ films on Si(001) substrates

Ba ( Fe 0.2 Zr 0.8 ) O 3 − δ (BFZO) films were synthesized on Si(001) substrates using SrTiO3 (STO) buffer layers by pulsed laser-beam deposition method. The results of the x-ray diffraction revealed that the STO buffer layers and the BFZO films had polycrystalline nature. The STO-buffered BFZO films showed ferromagnetic hysteresis loops at room temperature, and their saturation magnetization was 3.3 times as large as that of the BFZO films directly deposited on Si(001) substrates. The STO-buffered BFZO films partially grew epitaxially on the STO buffer layers with orientation relationships. The results of the x-ray photoelectron spectroscopy analysis using soft x-ray radiation indicated that the relative amount of the Fe4+ ions fairly increased for the STO-buffered BFZO films rather than for the BFZO films directly deposited on Si substrates.

Fine-grained multiferroic BaTiO 3/(Ni 0.5Zn 0.5)Fe 2O 4 composite ceramics synthesized by novel powder-in-sol precursor hybrid processing route

Dense, homogeneous, and fine-grained multiferroic BaTiO 3/(Ni 0.5Zn 0.5)Fe 2O 4 composite ceramics are synthesized by a novel powder-in-sol precursor hybrid processing route. This route includes the dispersion of nanosized BaTiO 3 ferroelectric powders prepared via conventional sold-state ceramic process into (Ni 0.5Zn 0.5)Fe 2O 4 ferromagnetic sol–gel precursor prepared via sol–gel wet chemistry process. Uniformly distributed slurry is obtained after ball milling and used in the fabrication of the ceramics with low sintering temperatures. The ceramics show coexistence of ferromagnetic and ferroelectric phases with obvious ferromagnetic and ferroelectric hysteresis loops at room temperature, besides exhibiting excellent magnetic and dielectric properties in a wide range of frequency. The combination of high permeability and permittivity with low losses in the ceramics enables significant miniaturization of electronic devices based on the ceramics.

Ferroelectricity and ferromagnetism in fine-grained multiferroic BaTiO 3/(Ni 0.5Zn 0.5)Fe 2O 4 composites prepared by a novel hybrid process

Dense, homogeneous, and fine-grained multiferroic BaTiO 3/(Ni 0.5Zn 0.5)Fe 2O 4 composite ceramics are synthesized by a novel powder-in-sol precursor hybrid processing route. This route includes the dispersion of nanosized BaTiO 3 ferroelectric powders prepared via conventional sold-state ceramic process into (Ni 0.5Zn 0.5)Fe 2O 4 ferromagnetic sol-gel precursor prepared via a sol-gel wet chemistry process. The composite ceramics show coexistence of obvious ferroelectric and ferromagnetic hysteresis loops at room temperature. Very low dielectric loss of about 0.02–0.0067 in the range of 10 kHz–10 MHz can be achieved, which is about an order of magnitude lower than the results of many reports using conventional processes at room temperature. The combination of high permeability and permittivity with low losses in the ceramics enables significant miniaturization of electronic devices based on the ceramics.

Electric and Magnetic Properties of Multiferroic BiFeO$_{3}$ and YMnO$_{3}$ Thin Films

<para xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> We grew rhombohedrally distorted BiFeO<formula formulatype="inline"> <tex Notation="TeX">$_{3}$</tex></formula> and hexagonal YMnO<formula formulatype="inline"> <tex Notation="TeX">$_{3}$</tex></formula> thin films on Pt/TiO<formula formulatype="inline"> <tex Notation="TeX">$_{2}$</tex></formula>/SiO<formula formulatype="inline"> <tex Notation="TeX">$_{2}$</tex></formula>/Si substrates via RF magnetron sputtering technique in a pure oxygen atmosphere. BiFeO<formula formulatype="inline"> <tex Notation="TeX">$_{3}$</tex></formula> and YMnO<formula formulatype="inline"> <tex Notation="TeX">$_{3}$</tex></formula> targets were self-made by the usual solid-state reaction method. We investigated the effects of deposition temperature upon crystalline structure, surface morphology, magnetization, and electrical polarization of BiFeO<formula formulatype="inline"><tex Notation="TeX">$_{3}$</tex> </formula> and YMnO<formula formulatype="inline"><tex Notation="TeX">$_{3}$</tex> </formula> thin films. The crystalline structure was studied by X-ray diffraction, and the topography of film surface was analyzed by atomic force microscopy. We also conducted measurements of ferroelectric and ferromagnetic hysteresis loops to study the electrical and magnetic behavior of the samples. Polarization, as a function of electric field in capacitor structures based on our BiFeO<formula formulatype="inline"><tex Notation="TeX">$_{3}$</tex></formula> films, shows hysteretic behavior with a coercive field of 54 kV/cm and a remanent polarization of 21 <formula formulatype="inline"><tex Notation="TeX">$\mu$</tex></formula>C/cm<formula formulatype="inline"><tex Notation="TeX">$^{2}$</tex></formula>; whereas, YMnO<formula formulatype="inline"><tex Notation="TeX">$_{3}$</tex></formula> films show hysteretic behavior with coercive field of 2.4 kV/cm, remanent polarization of 1.2 <formula formulatype="inline"><tex Notation="TeX">$\mu$</tex></formula>C/cm<formula formulatype="inline"><tex Notation="TeX">$^{2}$</tex></formula>, and saturation polarization of 3.5 <formula formulatype="inline"><tex Notation="TeX">$\mu$</tex> </formula>C/cm<formula formulatype="inline"><tex Notation="TeX">$^{2}$</tex> </formula>. Magnetization measurements of the BiFeO<formula formulatype="inline"> <tex Notation="TeX">$_{3}$</tex></formula> films evidence weak ferromagnetism, that can be related to the presence of a small quantity of ferromagnetic impurities. </para>

Room temperature ferromagnetism of Fe-implanted ZnO film

The ZnO-based diluted magnetic semiconductors (DMSs) with room temperature ferromagnetism were achieved by ion implantation. Fe+ ions at 80keV with doses ranging from 1×1016to8×1016cm−2 were implanted into n-type ZnO films at room temperature. Subsequently, the samples were annealed at 700°C for 1h in air ambient. The Fe-implanted content was determined by proton induced x-ray emission. The magnetic property was measured by the Quantum Design MPMS superconducting quantum interference device magnetometer. No trace of secondary phases or clusters was observed within the sensitivity of x-ray diffraction. Raman spectrum showed that the Fe ions replaced Zn atoms and incorporated into the crystal lattice positions of ZnO. Apparent ferromagnetic hysteresis loops measured at 300K were observed, and the temperature-dependent magnetization showed that their Curie temperature exceeded room temperature.

Ferromagnetic modification of ZnO film by Fe + ions implantation

The ZnO-based diluted magnetic semiconductors (DMSs) were achieved by ion implantation. Eighty kilo-electron-volt Fe + ions were implanted into n-type ZnO films at room temperature with doses ranging from 1 × 10 16 cm −2 to 8 × 10 16 cm −2 and subsequently annealed at 700 °C for 1 h in air ambient. PIXE was employed to determine the Fe-implanted content. The magnetic property was measured by the Quantum Design MPMS SQUID magnetometer. No secondary phases or clusters were detected within the sensitivity of XRD. Raman spectrum measurement showed that the Fe ions incorporated into the crystal lattice positions of ZnO through substitution of Zn atoms. Apparent ferromagnetic hysteresis loops measured at 10 K were presented. The relationships between the Fe-implanted content and the ferromagnetic property are discussed.

Room-temperature ferromagnetic properties and Mössbauer investigation of the 0.7FeTiO 3–0.3Fe 2O 3 solid solution

The 0.7FeTiO 3–0.3Fe 2O 3 solid solution were prepared by slow cooling and quenching heat treatments and studied by X-ray diffraction, Mössbauer spectroscopy, and vibrating sample magnetometer (VSM). The crystal structure of samples were found to be rhombohedral structure with the lattice constants of the slow-cooled sample a=5.082 Å and c=13.945 Å, and those of the quenched sample a=5.085 Å and c=13.964 Å. Mössbauer spectra of two samples were taken at various temperatures ranging from 4.2 to 400 K and anomalous absorption curves are observed. Mössbauer spectra was fitted to three magnetic components correspond to Fe 3+ and Fe 2+ in A and B sublattices. At 4.2 K, the magnetic hyperfine fields were H hf=512, 481, and 309 kA/m for the slow-cooled sample and 512, 479, and 305 kA/m for the quenched sample, respectively. The Mössbauer spectra below the Néel temperature, T N, reveal line broadening accompanying relaxation effects and intensity ratio different from usual powder pattern, indicating preferred spin orientation. The Néel temperature, T N, was determined to be 380 K for the slow-cooled sample and 400 K for the quenched sample. The temperature dependence of the magnetization taken in zero-field-cooling (ZFC) and field-cooling (FC) condition of the slow-cooled and quenched samples exhibits the great irreversibility between ZFC and FC magnetization. Magnetization measurements have shown ferromagnetic hysteresis loops at room temperature.

Anomalous Hall effect in anatase Ti1−xCoxO2−δ above room temperature

Presence of spin polarized electrons was confirmed by observing anomalous Hall effect in a ferromagnetic semiconductor anatase Ti1−xCoxO2−δ up to 600K. The anomalous Hall resistivity exhibited apparent ferromagnetic hysteresis loop from 300to600K with insignificant change in the magnitude, indicating that the Curie temperature is higher than 600K. The measurements above 500K induced an annealing effect represented by the decrease in resistivity, whereas kept the anomalous Hall resistivity nearly constant.

The appearance of clear ferromagnetism for p-type InMnP:Zn implanted with Mn of 1 at.%

The p-type InP:Zn was prepared by the liquid encapsulated Czochralski method and subsequently implanted with Mn + of 5 × 10 15 cm −2. The results of energy dispersive X-ray displayed that the concentration of incorporated Mn into InP:Zn is 1 at.%. The cross-sectional transmission electron microscopy showed that the thickness of Mn-incorporated layer was ∼300 nm. For photoluminescence measurements, the Mn-related optical transitions caused by incorporation of Mn were broadly observed at the energy region of 1.034, 0.985, and 0.958 eV. The samples clearly showed ferromagnetic hysteresis loops at 10 K, and the ferromagnetic behavior was observed to persist up to 360 K. Thus, the Curie temperature of Mn +-implanted InMnP:Zn (Mn ∼ 1 at.%) is expected to be above 300 K. It is found that a room-temperature-ferromagnetism of InMnP:Zn can be formed by ion implantation of a relatively low concentration of Mn (1 at.%).

Optical, structural, and magnetic properties of p-type InMnP:Zn implanted with the Mn (1 and 10 at.%)

The p-type InP:Zn was prepared by the liquid encapsulated Czochralski method and subsequently implanted with Mn + of 5×10 15 cm −2 (1 at.%) and 5×10 16 cm −2 (10 at.%). The results of energy dispersive X-ray showed that the concentrations of Mn incorporated into InP:Zn is about 1 and 10 at.%. For photoluminescence measurements, the Mn-related optical transitions of the InMnP:Zn samples annealed at 350 ∘C for 60 s and at 450 ∘C for 30 s with Mn (1 at.%) were broadly observed at the energy region around 1.0 eV. The InMnP:Zn samples implanted with Mn (1 at.%) clearly showed ferromagnetic hysteresis loops at 10 K, and the ferromagnetic behavior was observed to persist up to 291 K. Curie temperature ( T C ) at 291 K has originated from MnP. The InMnP:Zn samples implanted with Mn (10 at.%) were annealed at 350 ∘C for 60 s and at 450 ∘C for 30 s. Using transmittance electron microscopy, both single crystalline and polycrystalline structures containing MnP and InMn 3 sized ∼20 nm were observed depending on the annealing condition. These samples exhibited two different Curie temperatures: T C 1 at 291 K and another ( T C 2 ) well above 291 K. The high-temperature ferromagnetic behavior up to T C 1 and above T C 2 is believed to have originated from two magnetic MnP and InMn 3 phases, respectively.

Ferromagnetism in nanoscale BiFeO3

A remarkably high saturation magnetization of ∼0.4μB∕Fe along with room temperature ferromagnetic hysteresis loop has been observed in nanoscale (4–40nm) multiferroic BiFeO3 which in bulk form exhibits weak magnetization (∼0.02μB∕Fe) and an antiferromagnetic order. The magnetic hysteresis loops exhibit exchange bias and vertical asymmetry which could be because of spin pinning at the boundaries between ferromagnetic and antiferromagnetic domains. Interestingly, both the calorimetric and dielectric permittivity data in nanoscale BiFeO3 exhibit characteristic features at the magnetic transition point. These features establish the formation of a true ferromagnetic-ferroelectric system with a coupling between the respective order parameters in nanoscale BiFeO3.

Relevant, systematic variation of morphology and magnetism according to annealing in InMnP:Zn

InMnP:Zn epilayers doped with Mn (0.290 at.%) were annealed at 723–873 K for 60 s and 473–573 K for 30 min. Using Auger electron spectroscopy, the changes in concentration profiles of the epilayers correlated to the ferromagnetic origin as a function of the annealing conditions. The epilayers annealed at 723–873 K for 60 s exhibited InMn 3 persisting up to 583 K. For InMnP:Zn epilayers annealed at 523–573 K for 30 min, the concentration depth profiles remained flat so that the stoichiometry was well maintained without precipitates such as InMn 3 and MnP comparable to the as-grown InP:Zn before doping Mn. These samples showed clear ferromagnetic hysteresis loops. Curie temperature was about 150 K. A ferromagnetic hysteresis loop was obtained even at very lower annealing temperature of 473 K.

Scanning probe imaging of coexistent ferromagnetism and ferroelectricity at room temperature

Room temperature coexistence of ferromagnetism and ferroelectricity in a thin film of nominal composition PbTi0.5Fe0.5O3−δ is probed by standard ferroelectric and ferromagnetic hysteresis loop measurements and by scanning probe microscopy. Both magnetic domains and ferroelectric domains are observed in the same spatial region of the material, implying phase coexistence in this system. Sample morphology strongly affects the roughness of the domain walls for both order parameters.

A ferromagnetic ferroelectric cofired ceramic for hyperfrequency

A series of composite materials were prepared by cofired ceramics technology with 0.8Pb(Ni1∕3Nb2∕3)O3–0.2PbTiO3 (PNNT) and Ba2Zn1.2Cu0.8Fe12O22 as two components. The weight fraction of PNNT, signed as x, varied from 0.1 to 0.9. The coexistence of two phases in the composites was observed directly via scanning electron microscopy, and proved by x-ray diffraction spectra. The composites show excellent cofiring behavior. According to ferromagnetic and ferroelectric hysteresis loops, the composites exhibit both ferromagnetic and ferroelectric properties over a wide composition range (x=0.1–0.9). The composites have excellent magnetic and dielectric properties in hyperfrequency. With the rise of x, permeability decreases and permittivity increases. The permittivity resonant peak shifts to higher frequency with the decrease of x. Maxwell-Garnett equations are used to fit the permeability and permittivity of the composites. It can give valuable predication for composite material design. These composites are promising for applying in truly integrated passive filter in hyperfrequency.

High pressure high temperature (HPHT) synthesis and magnetism of Cr-12s2 copper oxides with fluorite-structured layers between CuO2 planes

The three first members of the Cr-12s2 (s=1,2,3) homologous series, i.e. CrSr2YCu2O8 (Cr-1212), CrSr2(Y1.5Ce0.5)Cu2O10 (Cr-1222) and CrSr2(Y1Ce2)Cu2O12(Cr-1232) are synthesized by high pressure high temperature (HPHT) 6GPa and 1550°C process. Though the Cr-1212 and Cr-1232 could not be formed in single phase with full Cr, the Cr-1222 is achieved in pure phase with space group I4/mmm. These compounds belong to the multi-layered copper oxides series that differ from each other only in terms of the (Ce,Y)-[O2-(Ce,Y)]s−1 layer blocks between two identical CuO2 planes with s=1, 2 and 3. At 5K, the magnetization M(H) experiments showed some ferromagnetic like hysteresis loops though the characteristic Mr and Hc were not seen clearly. None of the studied compounds exhibited superconductivity down to 5K.

Room temperature deposition of magnetite thin films on organic substrate

We report on the growth of magnetite films directly on thin layers of organic semiconductors by means of an electron beam ablation method. The deposition was performed at room temperature in a reactive plasma atmosphere. Thin films show ferromagnetic (FM) hysteresis loops and coercive fields of hundreds of Oersted. Micro Raman analysis indicates no presence of spurious phases. The morphology of the magnetite film is strongly influenced by the morphology of the underlayer of the organic semiconductor. These results open the way for the application of magnetite thin films in the field of organic spintronics.