Li Qing-An

Magnetic properties of Sm2Fe17Ny with Al substituted for Fe

By means of X-ray diffraction analysis, it is shown for x < 0.4 that all the interstitial Sm-2(Fe1-xAlx)(17)N-y nitrides and the parent compounds crystallize with Th2Zn(17)-type structure. The lattice constants of the parent compounds increase linearly with Al concentration. The introduction of nitrogen atoms leads to a further increase in the lattice constants, but the increase becomes smaller with increasing Al concentration; this can be related to the fact that the nitrogen content introduced into the parent compounds decreases nearly linearly with increasing Al concentration. The dependence on composition of T-c of the parent compounds exhibits a maximum, whereas T-c of the nitrides decreases monotonically with Al content from 750 K for x=0 to 313 K for x=0.4. The introduction of nitrogen leads to enhancement of the average magnetic moment of Fe in Sm2Fe17, whereas the substitution of Al for Fe leads to a decrease in the average magnetic moment of Fe in both the nitrides and the parent compounds. The anisotropy field B-a of nitrides is almost independent of the Al concentration for x less than or equal to 0.3, then decreases very fast and becomes zero at about x = 0.4.

STRUCTURE AND MAGNETIC-PROPERTIES OF SM-FE-SI NITRIDES WITH SMFE5 PHASE

Abstract A study on the structure and magnetic properties of Sm10Fe79Si11Nx has been performed. The Curie temperature was found to reach 641 K. There are also substantial increases in magnetization and magnetocrystalline anisotropy, showing suitable intrinsic magnetic properties for permanent magnet applications.

Fe-doping induced Griffiths-like phase in La0.7Ba0.3CoO3

The effect of Fe-doping on the magnetic properties of the ABO3-type perovskite cobaltites La0.7Ba0.3Co1–yFeyO3 (0 ≤ y ≤ 0.80) is reported. With no apparent structural change in any doped sample, the Curie temperature (TC) and the magnetization (M) are greatly suppressed for y ≤ 0.30 samples, while a distinct increase in TC for the y = 0.40 sample is observed. With the further increase of Fe concentration, TC increases monotonically. Griffiths-like phases in 0.40 ≤ y ≤ 0.60 samples are confirmed. The formation of the Griffiths-like phase is ascribed to B-site disordering induced isolation of ferromagnetic (FM) clusters above TC.

Growth of Mn5Ge3 ultrathin film on Ge(111)

The growth of Mn5Ge3 ultrathin films with different thicknesses, prepared by solid phase epitaxy, is studied. The results of scanning tunnelling microscopy and low energy electron diffraction studies show that the film can be formed and it is terminated with a (?3 ? ?3) R30? surface reconstruction when the thickness of Mn exceeds 3 monolayers. The magnetic properties show that the Curie temperature is about 300 K and the T2-dependent behaviour is observed to remain up to 220 K.

Spontaneous magnetization and resistivity jumps in bilayered manganite (La0.8Eu0.2)4/3Sr5/3Mn2O7 single crystals

Owing to the inhomogeneous state resulting from the doping of a small number of Eu ions into La4/3Sr5/3Mn2O7, from the resulting single crystal (La0.8Eu0.2)4/3Sr5/3Mn2O7 we have observed the magnetization jump, the resistivity jump, as well as the relaxation phenomena. For (La0.8Eu0.2)4/3Sr5/3Mn2O7, it has a very delicate ground state due to the interplays among spin, charge, orbital, lattice degrees of freedom. Consequently, the magnetization state is sensitive to temperature, magnetic field, as well as time. Meanwhile, the evolution of the magnetization with time shows a spontaneous jump when both the temperature and the magnetic field are constant. Similar step-like behaviours are also observed in resistivity. All these results suggest that Eu doping can greatly modulate the physical properties of La4/3Sr5/3Mn2O7 and cause such interesting behaviours.

Evidence of phase separation in Nd1-xSrxMnO3 (x=0.50, 0.51, 0.52, 0.53, 0.54, 0.55)

The temperature dependence of Mn ion magnetization and the conductivity difference versus temperature provide phase separation evidence in Nd1-xSrxMnO3 (x=0.50, 0.51, 0.52, 0.53, 0.54, 0.55). This is different from other reports and may suggest that a fully charge-ordered state exists in quite a narrow range; the sample preparation procedure affects the charge ordering. The polaron effect also plays an important role in explaining the conductivity.

Magnetic properties of Nd0.5Pb0.5-xSrxMnO3 materials

The structure and magnetic properties of Nd0.5Pb0.5-xSrxMnO3 (0 less than or equal to x less than or equal to 0.4) manganites were systematically investigated. Significant changes in Curie temperature and metal-insulator (MI) transition temperature of the samples were observed. All samples exhibited a transition from paramagnetic semiconducting to ferromagnetic metallic state. Curie temperature T-C and the MI transition temperature T-p increased with increasing Sr content. We attributed these behaviours to the enhancing of both the double exchange mechanism and the Jahn-Teller electron-phonon coupling.

Magnetoresistance probe of ultrathin Mn(5)Ge(3) films with Anderson weak localization

We present the magnetoresistance measurements of ultrathin Mn(5) Ge(3) films with different thicknesses at low temperatures. Owing to the lattice mismatch between Mn(5)Ge(3) and Cc (111), the thickness of Mn(5) Ge(3) films has a significant effect on the magnetoresistance. When the thickness of Mn is more than 72 monolayers (MLs), the magnetoresistance of the Mn(5)Ge(3) films appears a peak at about 6kOe, which shows that the magnetoresistance results from the Anderson weak localization effect and the variable range hopping in the presence of a magnetic field. The magnetic and semiconducting properties indicate that the Mn(5)Ge(3) film is a potential material for spin injection.

Local structural distortion and magnetotransport properties of Nd0.5Pb0.5−xSrx (Mn, Fe)O3

Structural and magnetotransport properties of Fe-doped Nd0.5Pb0.5−xSrxMnO3 are investigated by means of x-ray diffraction (XRD), Mossbauer spectroscopy and transport measurements. Both XRD patterns and Mossbauer spectra indicate that structural distortion decreases with Sr doping. Furthermore, it is found that Sr doping results in decrease of the resistivity at room temperature and increase of magnetoresistance. In samples, the same ratio of Mn3+ to Mn4+ is kept. So we would rather attribute these changes to the local structural distortion than the double exchange (DE) interaction. The local structural distortion of the Mn(Fe)O6 octahedron which results from the Jahn–Teller effect, can localize the conduction electrons. In this regard, we provide another evidence to prove that this Jahn–Teller distortion is an important factor that affects the transport property above Tc besides the DE coupling.

Floating zone growth and magnetic and specific heat properties of La0.67Ca0.33Mn1−xFexO3 (x=0.00, 0.04) single crystals

Single crystals of La0.67Ca0.33MnO3 and La0.67Ca0.33Mn0.96Fe0.04O3 were obtained by floating zone method. Laue diffraction pattern and rocking curve of the single crystals show that their quality is good. The magnetic behaviours of these compounds have been studied. Fe doping significantly depresses the magnetic contribution to the total specific heat C-P, but slightly influences the lattice contribution at temperatures above 50K. The peak of C-P, shifts towards high temperatures with increasing magnetic field. Both single crystals exhibit the first-order magnetic transition around the Curie temperature.