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We investigate the variations from as-deposited Zn1−xCoxO magnetic semiconductors to the post-annealed Co–ZnCoO granular composite. The as-deposited Zn1−xCoxO magnetic semiconductor deposited under thermal non-equilibrium conditions is composed of Zn1−xCoxO nanograins of high Co concentration. The room-temperature ferromagnetism with high magnetization and large negative magnetoresistance are found in the as-deposited samples. By annealing, the samples become of granular composite consisting of the Co metal grains and the remanent Zn1−xCoxO matrix. Although the magnetization is enhanced after annealing, the spin-dependent negative magnetoresistance disappears at room temperature. The magnetoresistance observed in the annealed samples in the high field region has no relation with the ferromagnetism, which in turn indicates that the room-temperature ferromagnetism and large negative magnetoresistance observed in the as-deposited are the intrinsic properties of the Zn1−xCoxO magnetic semiconductor.

Magnetic multilayers [Co-Nb(1.5 or 3.6 nm)/Pd(x nm)]40 were fabricated by radio frequency sputtering synthesis. The structures and magnetic properties of the Co-Nb/Pd multilayers were studied by x-ray diffraction, vibrating sample magnetometer, torque magnetometer and ferromagnetic resonance measurements. The oscillatory dependence of the phase structure, the strain, the ferromagnetic interlayer coupling and the spacer polarization of multilayers on the increase of Pd spacer thickness was observed. The relationship among phase structure, strain, interlayer coupling and the polarization of Pd spacers was discussed. The magnetic polarization of Pd spacers will enhance the ferromagnetic coupling between magnetic layers and will restrain antiferromagnetic coupling to occur. The spin-dependent electron transport along the normal direction of multilayers and its exchange interaction play key roles in causing these oscillatory behaviors.

Magnetic multilayers [Co(1.5 nm)/Pd(x nm)]40 grown by rf sputtering were studied by x-ray diffraction, vibrating sample magnetometer, torque magnetometer and magnetoresistance measurements. The dependences of the interfacial roughness and the structure perfectness of Co/Pd multilayers on the spacer Pd layer thickness have been revealed from x-ray diffraction data. An oscillatory variation of saturation magnetization versus the thickness of the Pd spacer was observed. A similar oscillatory behavior in the dependence of its magnetic anisotropy on the thickness of the Pd spacer was observed. It is suggested from these two phenomena that the magnetic polarization of Pd spacers oscillates between ferromagnetic and antiferromagnetic polarization with the increase of Pd spacer thickness under a RKKY-like interaction. Evidence is found for the antiferromagnetic polarization of the inner-part of the Pd spacer. The antiferromagnetic coupling between two Co layers and giant magnetoresistance effect in Co/Pd multilayer system were not observed. The relationship among structure, interlayer coupling and magnetic polarization effect of the Pd spacer was discussed.

An oscillatory behavior in specific saturation magnetization of Fe/Pd multilayers is observed. The conversion electron Mossbauer spectroscopy and other experiments indicate that this behavior is caused by the magnetic polarization of Pd spacers, which alternates between positive and negative polarization with respect to the magnetic moments of Fe layers. The interlayer coupling between two Fe layers always keeps ferromagnetic. Then, the interlayer couplings in ferromagnetic metal/nearly ferromagnetic metal multilayers were calculated by using the model of Barnas. The results of calculation prove that the above phenomenon might appear under some condition. The influence of magnetic polarization potential of spacers and interface chemical potential on the interlayer couplings is also discussed.

Nanogranular Fe0.35/(In2O3)0.65 films with complex magnetic structure were prepared by the rf sputtering method. An extra-large magnetoresistance up to 506% was obtained at 2.2 K, which is two orders of magnitude larger than that obtained at room temperature. This is related to the interaction with the impurities influencing the local magnetization, which is quite different from the spin-dependent tunnelling effect at room temperature. The interspacing Fe atoms dispersed in the In2O3 matrix play an important role in the transportation properties of carriers at low temperature.

Calculations of the magnetic domain structure (domain wall energy density, domain wall thickness, domain width and critical diameter of single domain particles) in Nd 2 Fe 14 B have been made by using its intrinsic parameters (lattice constants, magnetic moments of the atoms, Curie temperature, spontaneous magnetization and magneto-crystalline anisotropy constant). The four stages of magnetization reversal processes in oriented sintered Nd-Fe-B magnet after saturation magnetization along its easy direction are studied in detail in this paper. The results show that the nucleation of the reverse-magnetization nuclei in the surface layer of the grains of hard magnetic phase Nd 2 Fe 14 B, as well as the irreversible domain wall motion from the surface to the inside of the grains are dominant factors controlling the intrinsic coercivity of the Nd-Fe-B alloy.

Fe-doped In2O3 films are grown epitaxially on YSZ (100) substrates by pulsed laser deposition. The in-situ reflection high-energy electron diffraction, the atomic force microscopy, and the x-ray diffraction patterns show that the films have a well defined cubic structure epitaxially oriented in the (100) direction. Room temperature ferromagnetism is observed by an alternating gradient magnetometer. Strong perpendicular magnetic anisotropy with a remnant magnetization ratio of 0.83 and a coercivity of 2.5kOe is revealed. Both the structural and the magnetic measurements suggest that this ferromagnetism is an intrinsic property deriving from the spin-orbit coupling between the diluted Fe atoms.

La0.67Ca0.33MnO3 films with thickness between 25 and 400nm were fabricated on (001) SrTiO3 and (001) LaAlO3 substrates, using pulsed laser deposition. The magnetization and resistivity p of the films were studied as functions of thickness. The reduction of t causes the decrease of the Curie temperature T-C in addition to the increase of p of the films. Compared with the compressive strain in the La0.67Ca0.33MnO3/LaAlO3 films I the tensile strain in the La0.67Ca0.33MnO3/SrTiO3 films causes a faster reduction of T-C with t, and a larger value of rho(0). The low-temperature rho is found to follow well rho = rho(0) + Bomega(s)/sinh(2) (homega(s)/2k(B)T) + CTn, with rho(0) being the residual resistivity. The second term arises from the scattering by a soft optical phonon mode, and the third term denotes the other possible transport mechanisms. B, omega(s) ( the frequency of a soft optical mode) and C are fitting parameters. At temperatures higher than T-C, rho of all the films show activated conduction with rho = DTexp(E-a/k(B) T). Here, E-a is the activation energy. Based on the investigation of rho(0), omega(s) and E-a,E- the thickness and strain effects in the films are discussed, separately. Further study shows that the variation of T-C is mainly associated with E-a and omega(a), confirming the crucial role of the electron-phonon coupling in the strain effects on T-C.

Magnetic properties and giant magneto-impedance (GMI) effects of Fe73.5Cu1Nb3Si13.5B9 single layered films and sandwiched fimls using Cu or Ag as the central layer prepared by radio frequency sputtering are investigated. The as-deposited single layered films are in amorphous state. The domain structures of single layered films annealed as 380℃ show that the films are in nanocrystalline state with homogeneous magnetization. The samples possess excellent soft magnetic properties and have the maxiumum values of GMI effects, the maxiumum GMI ratios are 18% and 14% in longitudinal and transverse fields, respectively, at 13MHz. Sandwiched films in the as-deposited state possess large GMI effects, the maximum GMI ratios of sandwiched films with a Cu central layer are 32% and 11% for longitudinal and transverse cases, respectively, and those of sandwiched films with a Ag central layer are 47% and 57% for longitudinal and transverse cases, respectively. Sandwiched films using Cu as the inner layer annealed at 250℃ exhibit large magneto-inductance effect at low frequencies. The maximum magneto-inductance ratio is 1733% at 100kHz.