X-ray diffraction, transmission electron microscopy, and magnetization measurements are employed to study the structural and magnetic properties of Mn-rich (Mn,Ga)As nanocrystals embedded in GaAs. These nanocomposites are obtained by moderate (400C) and high temperature (560 and 630C) annealing of (Ga,Mn)As layers with Mn concentrations between 0.1 and 2%, grown by molecular beam epitaxy at 270oC. Decomposition of (Ga,Mn)As is already observed at the lowest annealing temperature of 400C for layers with initial Mn content of 1% and 2%. Both cubic and hexagonal (Mn,Ga)As nanocrystals, with similar diameters of 7 - 10 nm are observed to coexist in layers with an initial Mn content of 0.5% after higher temperature annealing. Measurements of magnetization relaxation in the time span 0.1 - 10 000 s provide evidence for superparamagnetic properties of the (Mn,Ga)As nanocrystals, as well as for the absence of spin-glass dynamics. These findings point to weak coupling between nanocrystals even in layers with the highest nanocrystal density.
Nearly 30% increase of the ferromagnetic phase transition temperature has been achieved in strained MnAs nanocrystals embedded in a wurtzite GaAs matrix. Wurtzite GaAs exerts tensile stress on hexagonal MnAs nanocrystals, preventing a hexagonal to orthorhombic structural phase transition, which in the bulk MnAs is combined with the magnetic one. This effect results in a remarkable shift of the magneto-structural phase transition temperature from 313 K in the bulk MnAs to above 400 K in the tensely strained MnAs nanocrystals. This finding is corroborated by the state of the art transmission ele…
Structural, magnetic, and optical properties of zinc- and copper- substituted nickel ferrite nanocrystals
铁氧体纳米晶由于其丰富的物理性质而成为人们感兴趣的材料。在这里，我们将掺杂剂Zn和Cu添加到镍铁氧体纳米晶体Ni 1-xMxFe 2 O 4（0<=x<=1，M{ \in }{Cu，Zn}）中，并表征样品的相关性质如何相应地改变。基本上，这些掺杂导致Fe+3离子重排到两个预先存在的八面体和四面体位置。事实上，这，我们表明，诱导相关的磁性掺杂样品。在Cu掺杂的情况下，Jahn-Teller效应也出现了，我们通过样品的FTIR光谱来识别。此外，我们发现掺杂样品的晶格参数增加，以及掺杂样品的超顺磁性行为，而Jahn-Teller效应排除了CuFe 2 O 4纳米晶体中类似的行为。采用室温光致发光法研究了Zn和Cu掺杂对镍铁氧体纳米晶光学性质的影响。
The high-spectral-resolution spectroscopic studies of the energy gap evolution, supplemented with electronic, magnetic and structural characterization, show that the modification of the GaAs valence band caused by Mn incorporation occurs already for a very low Mn content, much lower than that required to support ferromagnetic spin - spin coupling in (Ga,Mn)As. Only for n-type (Ga,Mn)As with the Mn content below about 0.3% the Mn-related extended states are visible as a feature detached from the valence-band edge and partly occupied with electrons. The combined magnetic and low-temperature phot…
In this paper we report on detailed temperature and magnetic field dependence of m agnetization of IV-VI semiconductor PbTe doped with mixed valence transition metal Cr$^{2+/3+}$. The material is studied solely by an integral superconducting quantum interference device magnetometer in order to quantitatively determine the contribution of single substitutional Cr$^{3+}$ as well as of various Cr-Te magnetic nanocrystals, including their identification. The applied experimental procedure reveals the presence of about $10^{19}$~cm$^{-3}$ paramagnetic Cr$^{3+}$ ions formed via self-ionization of Cr…
Enhanced grain surface effect on magnetic properties of nanometric La0.7Ca0.3MnO3 manganite : Evidence of surface spin freezing of manganite nanoparticles
Enhancing the magnetism and giant anomalous Hall effect in thin Fe-Al films via B2 nanophase growth
Lobachevsky State University of Nizhny Novgorod（下诺夫哥罗德洛巴切夫斯基国立大学）；Institute for Physics of Microstructures, Russian Academy of Sciences（俄罗斯科学院微观结构物理研究所）
Here we report on detailed studies of the magnetic properties of the wurtzite (Ga,Mn)As cylindrical shells. Ga$_{0.94}$Mn$_{0.06}$As shells have been grown by molecular beam epitaxy at low temperature as a part of multishell cylinders overgrown on wurtzite (Ga,In)As nanowires cores, synthesized on GaAs (111)B substrates. Our studies clearly indicate the presence of a low temperature ferromagnetic coupling, which despite a reasonably high Mn contents of 6\% is limited only to below 30~K. A set of dedicated measurements shows that despite a high structural quality of the material the magnetic or…
