The properties of La0.5-xNdxBa0.5CoO3 (0 <= x <= 0.425) has been investigated. All samples show a cubic structure at room temperature. The Curie temperature T-C and the estimated molecular magnetic moment of the samples at 5K decrease monotonically with increasing Nd-doping level. The results are discussed in terms of the double exchange (DE) interaction associated with the variation of Co-O bond length and Co-O bond angle due to the substitution of smaller Nd3+ ions for larger La3+ ions. At low temperature, the ferromagnetic (FM) interaction is greatly suppressed by the Nd-doping, illustrating a special noncollinear spin structure. The spin state of Co ions derived from the Curie constant is not affected by the Nd doping and remains an intermediate spin state. The electric resistance measurements show that the conduction of the materials belongs to the thermal activation process below T-C, while it belongs to the variable range hopping conduction of polarons over T-C except for parent La0.5Ba0.5CoO3.

The magnetic and electrical properties of the La0.67Ca0.25Sr0.08MnO3/xAg composite system are systematically investigated as a function of Ag-added content. With increasing the Ag dopant amount, the magnetization decreases a little while Curie temperature (TC) is almost independent of Ag content around 312 K. The resistivity reduces rapidly with Ag addition ( x < 0.25 ) due to the decomposed metal Ag, and then it increases slightly which is probably induced by the less Ag content related to the volatilization of Ag during calcinations. At low temperature, the ρ – T curves fit well by the expression of ρ =ρ0 +ρ2T2 +ρ4.5T4.5 while all data for the above TC can be fitted by using the adiabatic small-polaron-hopping model ρ=ρ0T exp (E/kBT ). The enhancement of MR effect ( 41% ) at room temperature is mainly related to the coexistence of intrinsic MR properties and the spin dependent scattering of conduction electrons at the interfaces. These results indicate that combining the doping effect with the composite method is an effective selection in enhancement of MR at room temperature, which is very meaningful for the application research.

The magnetic and electrical properties of La0.67Sr0.33MnO3 ( LSMO ) are influenced very much by the Nb dopant. However, this doping effect is restricted by the limited Nb solution into LSMO due to the low calcined temperature. As a result, a second phase LaNbO4 appears in our samples. Enhancements of the low-field magnetoresistance (LFMR) were observed both at 77 K and room temperature in the manganite system prepared by doping Nb2O5 into LSMO powders. The doping amount x of Nb ions ranges from 0-10 % molar ratio. The MR ratios at 77 K with H = 1 T and H = 0.1 T are 33.8 % and 24 % for the x = 0.07 doped sample, respectively. A MR effect up to 9 % was also found for the sample with x = 0.05 at room temperature, which is 2.2 times as large as that for LSMO (4.1%). The spin dependent tunneling and scattering at the interfaces of the grain boundaries are responsible for the LFMR while the high field magnetoresistance (HFMR) originates from the spin dependent transport related to noncollinear spin structure at the interfaces.

The soft magnetic properties and giant magnetoimpedance (GMI) effect of the multilayered structure (F/SiO2)3/Ag/(SiO2/F)3 (F≡Fe71.5Cu1Cr2.5V4Si12B9) films, which were prepared by radio frequency sputtering without and with a longitudinal magnetic field of about 72 kA/m, are studied. The results show that the GMI effect almost cannot be detected in the samples deposited without field, whereas, a longitudinal magnetic field applied during deposition process obviously optimizes the soft magnetic properties of the films, and noticeable GMI effect is obtained. The maximum values of the longitudinal and transverse GMI ratios are 45% and 44% at the frequency of 6.81 MHz, respectively. In addition, the dependence of magnetoimpedance ratio, magnetoresistance ratio, magnetoreactance ratio and effective permeability ratio on the frequency has been investigated. We found that the GMI spectrum curves in the longitudinal and transverse cases almost overlap for the field-deposited sample. The GMI effect is mainly a giant magnetoinductive effect at low frequencies. When f >9 MHz, magnetoreactance ratio changes to a negative, i.e., the property of reactance changes from inductive to capacitive.

The magnetic and magnetoimpedance behavior of FeCuCrVSiB and (F/SiO2)(3)/Ag/(SiO2/F)(3) (F = FeCuCrVSiB) soft magnetic amorphous films deposited in a magnetic field have been investigated systematically. The samples were deposited by the RF sputtering with or without a static magnetic field of 900 Oe applied in the film plane. It is found that the magnetic field applied during the deposition process improves the soft magnetic properties of the sample significantly. The coercive force of the sample is about 0.8 Oe, which is much smaller than that deposited without a field. Moreover, remarkable GMI effects were obtained at relatively low frequencies, which contrasts with the samples deposited without field. In the magnetic field-deposited state the maximum GMI ratios of 21.5% and 19.5% were achieved for the single-layer films in longitudinal and transverse fields at a frequency of 13 MHz, while for the multilayered films, the maximum values of longitudinal and transverse GMI ratios are 45% and 44% at a frequency of 6.81 MHz, respectively. These superior GMI behaviors of the as-deposited films are related to the magnetic field used in the preparation process and the inserted SiO2 layers.

Magnetism and its dependence on annealing temperature for r.f. sputtered Co/Cu multilayers have been investigated. It was found that the easy magnetization axes of the films are parallel to the substrate and the magnetic properties of both as-sputtered and annealed multilayers are isotropic in the film plane. The coercive field H-c is 4.8 kA/m and the ratio of remanence-to-saturation magnetization M-Gamma/M-s is about 0.73 for as-sputtered samples. Both H-c and M-Gamma/M-s increase with increasing annealing temperatures, especially when annealing temperatures are higher than 400 degrees C. These experimental results can be interpreted using the ferromagnetic exchange coupling and the pinning theory of the coercivity.

FeCuCrVSiB soft magnetic films have been prepared using radio frequency sputtering without or with a constant magnetic field of about 72 kA/m along the longitudinal direction of film plane,and then their soft magnetic properties and giant magnetoimpedance(GMI) effects were measured.The results obtained show that the magnetic field applied during the deposition process improves significantly the soft magnetic properties of the sample.For example,its coercive force decreases from 1.080 kA/m of the non-field-deposited state to around 0.064 kA/m and its effective permeability ratio increases from 10%to 106%.The GMI effect is closely connected with this permeability ratio. The GMI effect can not almost be detected in non-field-deposited samples,while it becomes evident for field-deposited samples.The maximum values of longitudinal and transverse GMI ratios are 22% and 20%at the frequency of 13 MHz,respectively.The GMI effect in the field-deposited sample is much better than in annealed FeCuNbSiB film with the same thickness.

[FeNi(3 nm)/Zn1-xCoxO(3 nm)](2)/ZnO(d nm)/[Zn1-xCoxO(3 nm)/Co(3 nm)](2) (d=3 and 10) semiconductor junctions were prepared by magnetron sputtering system and photolithography. The spin valve effect was observed in these junctions because the utility of the ferromagnetic composite layers acted as soft and hard magnetic layers. The electrical detection was performed by measuring the magnetoresistance of these junctions to investigate the current spin polarization alpha(sc) in the ZnO layer and the spin injection efficiency eta of spin-polarized electrons. alpha(sc) was reduced from 11.7% (and 10.5%) at 90 K to 7.31% (and 5.93%) at room temperature for d=3 (and d=10). And eta was reduced from 39.5% (and 35.5%) at 90 K to 24.7% (and 20.0%) at room temperature for d=3 (and d=10).

2 x (FeNi/CoZnO)/ZnO/(CoZnO/Co) x 2 spin-injection devices were prepared by sputtering and photo-lithography. In the devices, two composite magnetic layers 2 x (FeNi/CoZnO) and (CoZnO/Co) x 2 with different coercivities were used to fabricate the ZnO-based semiconductor spin valve. Since the CoZnO ferromagnetic semiconductor layers touched the ZnO space layer directly, the significant spin injection from CoZnO into ZnO was observed by measuring the magnetoresistance of the spin-injection devices. The magnetoresistance reduced linearly with increasing temperature, from 1.12% at 90 K to 0.35% at room temperature.

Fe/In2O3 granular films have been prepared by RF sputtering method.The susceptibility measurements manifest that the blocking temperature is 50 K.At a certain freezing temperature Tf about 10 K,the film transits from ferromagnetic state to particle-spin-cluster state.A maximum GMR ratio up to 506% is obtained at the metal-semiconductor transition temperature about 2.2 K.The mechanism of this GMR is related to the interaction with the impurities influencing the local magnetization,which is quite different to spin-dependent tunneling effect at room temperature.The magnetic field aligns the particle-spin-clusters and increases the mobility of the electron's hopping between these clusters which causes the magnetoresistance effect to increase significantly.

(Fe0.88Zr0.07 B0.05)97Cu3 films were grown by RF sputtering on Si substrates. The as-deposited films were found to be amorphous with X-ray diffraction (XRD). Its magnetic behavior was studied in the frequency range of 5 kHz to 13 MHz. The results show that the films have excellent soft magnetic properties and giant magnetoimpedence (GMI). For example, its coercive force is only about 58 A/m;its saturation magnetization is around 1.15 × 106 A/m and its maximum GMI ratio is 17% at a frequency of 13 MHz. We found that the permeability ratio and GMI ratio depend on external magnetic field, peaking at a transverse anisotropic field of Hk=0.4 kA/m. We propose that the GMI effect of the films is closely connected with the changes in the effective permeability induced by dc magnetic field.

Structural, magnetic, electrical, and magnetotransport properties have been carried out on the Ag-added La0.67Ba0.33MnO3/(TiO2)0.035 (LBT) (abbreviated by LBT/Agx,) composites. Ag addition has little influence on the magnetization or Curie temperature (TC), but decreases the resistivity (ρ) and sharps the ρ peak evidently. The ρ in the ferromagnetic (FM) metallic regime is proportional to T2, reflecting that the conductive mechanism mainly arises from the electron–electron scattering. In the paramagnetic (PM) insulating region, the ρ data fit well to the self-trapped small polaron hopping model. The ρ–T curves for x=0.27 and 0.30 samples fit well with the phenomenological percolation approach, which is based on the phases segregation of ferromagnetic metallic clusters and paramagnetic insulating regions. These excellent agreements highlight the dominant intrinsic behavior of LBT. In addition, from the magnetotransport measurements, a large magnetoresistance (MR) ratio up to 41% was obtained at 280K, and 10kOe for x=0.27 sample. The good fits between the field dependence of MR and Brillouin function indicate that the MR behavior in the Ag-added LBT is induced by the spin-dependent hopping of the electrons among the spin clusters, and which is related to the increase and growth of the FM spin clusters.

We have prepared a series of polycrystalline manganites with the nominal compositions, La0.67Ba0.33Mn0.88Cr0.12O3/Agx (LBMCO/Agx) (x is the mole fraction) with x=0, 0.05, 0.1, 0.15, 0.2, 0.23, 0.27, 0.3, 0.35. The X-ray diffraction patterns show that the samples with x>0.05 are two-phase composites. The Ag addition in LBMCO improves the properties of grain surfaces/boundaries and reduces the resistivity of the composites. For x=0.30 sample, a minimum resistivity is obtained and a maximum room temperature magnetoresistance up to −54.5% was observed at 288K, 1T field. The room temperature TC and the reduced resistivity are responsible for the enhancement of room temperature MR.

With a small quantity of additive as the ameliorant,LaFe_(0.25)Ni_(0.75)O_3 ceramic was prepared by means of traditional solid-phase reaction.The study shows ameliorant leads to obvious improvement of the wettability and the accession mode play the important role.The wettability greatly affects the distribution of ceramic in the silver base and at the same time affects the service performance of the electrical contact materials.

The samples were prepared by doping Nb_2O_5 into the La_(0.67)Sr_(0.33)MnO_3 powder,which is synthesized by the sol-gel method.The XRD result indicates that all samples can be indexed based on the rhombohedral structure with single phase.The resistivities of the samples are influenced remarkably by Nb~(5+) addition.There is a maximum resistivity ρ for the sample with x=0.06(x is the molar ratio of the Nb ions to LSMO), which is higher than that for LSMO by five orders of magnitude.It is due to the enhancement of spin dependent and independent scattering and tunneling effects on the interfaces of grain boundaries and inside the grains.Enhancements of the low-field magnetoresistance(LFMR) and high-field magnetoresistance(HFMR) were observed.The maximum MR ratios at 77K with H=1T and H=0.1T are 42% and 25% for the 0.07molar ratio doped sample,which are 2 times and 1.7 times as large as that for LSMO,respectively.A MR effect up to 7% was also found for the sample with x=0.03 at room temperature.The spin dependent tunneling and scattering at the interfaces of grain boundaries are responsible for the LFMR while the HFMR originates from a noncollinear spin structure in the surface layer.

Two-phase composites LCBMO/Pdx were synthesized using the sol–gel technique followed by the solid-state reaction. Pd addition induces a remarkable decrease in resistivity, which is mainly related to the improvement of grain boundaries/surfaces caused by the segregation of Pd. The resistivity data for all samples follow the adiabatic small-polaron-hopping model at high temperature above the Curie temperature TC, while in the low temperature region, they are proportional to T2, reflecting that the electron–electron scattering mechanism is dominant in the ferromagnetic metallic state. In addition, Pd addition induces a large enhancement of room temperature magnetoresistance (MR). Especially for the x = 0.27 sample, an extra large magnetoresistance over 170% is obtained at 10 kOe and 289 K. This is the largest MR obtained at room temperature in all kinds of colossal magnetoresistance (CMR) materials. The good conductivity and polarizing effect of Pd are responsible for the enhancement of MR. The former leads to the decrease in resistivity and the latter induces a large number of spin clusters.

Fe–ZnO inhomogeneous magnetic semiconductor films were synthesized by alternately sputtering very thin Fe layers and ZnO layers under thermal non-equilibrium conditions. The obtained films are in the amorphous state and show large saturation magnetization at room temperature. The angular dependence of the ferromagnetic resonance field for the samples with different compositions was studied. As the Fe content increases, the saturation magnetization increases, and the resonance field in normal resonance mode increases. The linewidth of the ferromagnetic resonance reduces as the Fe content increases, indicating that the inhomogeneity in chemical composition reduces with increasing Fe content. Suitably increasing Fe content is favorable to obtain magnetic semiconductor films with high saturation magnetization at room temperature.

A series of La0.67(Ca0.65Ba0.35)0.33MnO3∕Pdx composites were synthesized using a sol-gel method followed by a conventional solid-state reaction route. The results show that the resistivity of the composites decreases dramatically with Pd addition, while the room-temperature magnetoresistance (MR) increases remarkably. A large MR of about 170% is obtained at room temperature and 1T applied magnetic field for x=0.27 sample. The large enhancement of the MR can be attributed to the decrease in resistivity caused by the good conductive metal Pd, which improves the disordered atomic structure and magnetic property on the grain surfaces/boundaries. In addition, the polarization of Pd atoms near the Mn ions on the grain surfaces/boundaries also plays a very important role on the enhancement of the MR, which induces a large number of spin clusters.

The polar Kerr rotation and ellipticity spectra of the as-deposited and annealed Zn1−xCoxO inhomogeneous magnetic semiconductors were measured. The Kerr rotation spectra versus the photon energy can be greatly modulated by adjusting the Co concentration or annealing the samples. Moreover, the observed maximal Kerr rotation, 0.72°, in an annealed sample is higher than that of pure Co films, Pt∕Co multilayers, and PtxCo1−x alloys. The enhanced Kerr rotation in the annealed samples can be explained by the fact that the annealed samples became a nanocomposite system consisting of Co clusters and Zn1−xCoxO magnetic semiconductor.

Giant magneto-impedance (GMI) effect of a multilayered film with the structure o f (FM/SiO2)3/Ag/(SiO2/FM)3 (FM≡FeCu CrVSiB) was studied. The multilayere d film was deposited by radio frequency sputtering onto a single crystal Si subs trate. A constant magnetic field of about 72kA/m was applied along the longitudi nal direction of the film plane during deposition process, and then the samples were annealed at different temperatures. Results obtained show that the multila yered film has good soft magnetic properties and GMI effect even though in the a s-deposited state. The maximum magnetoimpedance ratios are about 45% and 44% in longitudinal and transverse cases, respectively. After the samples were annealed at 230℃ for 90min, the best GMI effect could be obtained. The maximum longitud inal and transverse magnetoimpedance ratio up to 251% and 277% were obtained at the frequency of 8.5MHz, respectively. The GMI effect in this multilayered struc ture is much stronger than the one in FeCuCrVSiB/Ag/FeCuCrVSiB sandwiched film w ith the same thickness of total magnetic layers.