The structure,specific heat,magnetic and electrical properties of MnTe1-xSbx(x=0,0.1,0.15,0.2 and 0.25) alloys have been investigated.The MnTe1-xSbx alloys crystallize in a hexagonal NiAs-type structure,and the impurity of MnSb phase appears when x≥0.15.The MnTe0.9Sb0.1 compound exhibits ferrimagnetic behavior with hysteresis loops even at 350 K,showing that the magnetic properties of MnTe compound are very sensitive to little compositional change.The ferromagnetism in the MnTe1-xSbx alloys with higher Sb contents may be attributed to the impurity of MnSb phase.Energy dispersive X-ray spectroscopy analysis on the MnTe0.9Sb0.1 compound indicates that Sb is very difficult to dope into the lattice of MnTe.So the anomaly of resistivity at 300 K of MnTe0.9Sb0.1 and the peak of specific heat around 304 K of all the alloys are thought to be related with the antiferromagnetic interactions of MnTe-based lattice.
The boron-oxide coated iron nanocapsules have been prepared by arc-discharge in a mixture of diborane and nitrogen,and then the boron-nitride coated iron nanocapsules by a subsequent annealing under a nitrogen atmosphere at 1100 ℃.After the arc-discharge,the boron-oxide coated iron nanocapsules form,which show an amorphous surface layer of B2O3 (and/or B) and a core of γ-Fe,α-Fe,FeB phases.After being annealed,part of the α-Fe phase transforms to the γ-Fe phase,and the FeB phase decomposes while the BN phase forms.The BN shell structure formed in the BN encapsulating iron nanocapsules is incomplete.Magnetic properties of the boron-oxide coated and the boron-nitride coated iron nanocapsules were compared and discussed in terms of the particles sizes,the phase components,and the surface structures.
Composited nanoparticles,consisting of Mn3O4,S-doped Mn3O4 and S,were synthesized by co-precipitation reaction and Mn3O4 nanoparticles were then obtained after removing the pure S from the composited nanoparticles.The Mn3O4-type phase with larger lattice constant a was formed by doping sulfur.At fixed temperatures below Curie temperature(TC),the magnetization of the S-doped Mn3O4/S composited nanoparticles was smaller than that of the Mn3O4 nanoparticles.The blocking temperature was 36.3 and 34.8 K for Sdoped Mn3O4/S composite and Mn3O4 nanoparticles,respectively.The anisotropy field of S-doped Mn3O4/S composite was determined to be about 55.3 kOe.
The microstructures and magnetic properties of nanoparticles, each composed of an antiferromagnetic(AFM)manganese-oxide shell and a ferromagnetic-like core of manganese–gallium(MnGa) compounds, are studied. The coreshell structure is confirmed by transmission electron microscope(TEM). The ferromagnetic-like core contains three kinds of MnGa binary compounds, i.e., ferrimagnetic(FI) D022-type Mn3 Ga, ferromagnetic(FM) Mn8Ga5, and AFM D019-type Mn3 Ga, of which the first two correspond respectively to a hard magnetic phase and to a soft one. Decoupling effect between these two phases is found at 1ow temperature, which weakens gradually with increasing temperature and disappears above 200 K. The exchange bias(EB) effect is observed simultaneously, which is caused by the exchange coupling between the AFM shell and FM-like core. A large coercivity of 6.96 kOe(1 Oe = 79.5775 A·m-1) and a maximum EB value of0.45 kOe are achieved at 300 K and 200 K respectively.
Anisotropic Pr–Fe–B films with soft-magnetic layer(Fe) and/or antiferromagnetic layer(Mn, Fe Mn or Mn O) were prepared by direct-current(DC) magnetron sputtering on Si(100) substrates heated at 650 °C. The influence of four types' different structures on the magnetic properties of Pr–Fe–B films was investigated.The phase and magnetic properties were characterized by means of X-ray diffraction(XRD) and superconducting quantum interference device(SQUID). Addition of antiferromagnetic layer enhances both the coercivity and the remanence ratios of Pr–Fe–B films with suitable structures. The interface number increases and the antiferromagnetic–ferromagnetic exchange interaction is likely to become stronger, which affect the improvement of magnetic properties. To further understand the influence of structures with soft-magnetic Fe layer and/or antiferromagnetic Fe Mn layer on the magnetic properties of Pr–Fe–B hard-magnetic films, the thickness of Pr–Fe–B layer was designed to decrease from 600 to 50 nm. The improvement of magnetic properties becomes obvious in Mo(50 nm)/Pr–Fe–B(25 nm)Mo(2 nm)Fe Mn(20 nm)Mo(2 nm)Pr–Fe–B(25 nm)/Mo(50 nm) film.
Recent advances in the study of exchange couplings in magnetic films are introduced.To provide a comprehensive understanding of exchange coupling,we have designed different bilayers,trilayers and multilayers,such as anisotropic hard/soft-magnetic multilayer films,ferromagnetic/antiferromagnetic/ferromagnetic trilayers,[Pt/Co]/NiFe/NiO heterostructures,Co/NiO and Co/NiO/Fe trilayers on an anodic aluminum oxide(AAO) template.The exchange-coupling interaction between soft-and hard-magnetic phases,interlayer and interfacial exchange couplings and magnetic and magnetotransport properties in these magnetic films have been investigated in detail by adjusting the magnetic anisotropy of ferromagnetic layers and by changing the thickness of the spacer layer,ferromagnetic layer,and antiferromagnetic layer.Some particular physical phenomena have been observed and explained.
