Magnetic properties of the CoxNi1−xMnGe system

Magnetic properties of the Co_xNi_1?xMnGe system have been studied by magnetometric measurements. It was shown that the solid solutions exist for 0 ? χ ? 1, with the crystal structure of NiTiSi type. The samples with the low Co concentrations (0 ? χ ? 0.2) have antiferromagnetic properties. At higher concentrations (0.3 ? χ ? 0.5) the samples exhibit a more complex behaviour, at low temperatures having antiferromagnetic properties. At growing temperatures the change of the magnetic ordering is observed. The samples with large Co concentration (0.6 ? χ ? 1.0) are ferromagnets.     

Effects of the substitution of gadolinium for neodymium on the crystal and magnetic properties of the Nd1−xGdxCo4B compounds

The crystal and magnetic properties of the Nd_1−xGd_xCo₄B compounds for 0?x?1 have been studied by X-ray powder diffraction, magnetization and differential scanning calorimetry (DSC) measurements. These compounds crystallize in a hexagonal CeCo₄B-type structure with the P6/mmm space group. The substitution of Gd for Nd leads to a decrease of the unit-cell parameter a and the unit-cell volume V, while the unit-cell parameter c remains almost constant. Magnetic measurements indicate that all samples are ordered magnetically below room temperature. The Curie temperatures determined by the DSC technique increase linearly as Nd is substituted by Gd. The saturation magnetization at 5 K decreases upon the Gd substitution up to x=0.6, and then increases again.     

Thermomagnetic history effects in LaCo5xNi5−5x and ThCo5xNi5−5x compounds

The magnetization versus temperature curves of several compounds of the series LaCo_5xNi_5?5x were found to give rise to an abrupt increase at temperatures being higher in accordance as the applied field strengths are smaller. The magnetic properties strongly depend on the magnetic as well as on the thermal history. The observed magnetic behaviour is discussed in terms of mictomagnetism and narrow Block wall propagation.     

Picosecond time-resolved photoluminescence studies of exciton-magnetic polaron complexes in Cd1−xMnxSe

The evolution of magnetic polarons in Cd_1?xMn_xSe was examined using time-resolved photoluminescence spectra of excitons at cryogenic temperatures. Sample with manganese concentration x = 0.05, 0.10 and 0.20 were studied using a streak camera, with a system resolution of 80 psec. The formation of magnetic polarons was observed to have a large effect on the exciton lifetime, and to be strongly dependent on temperature and manganese concentration.     

Characterization of magnetic phases in the FexMn0.65−xAl0.35 disordered alloys

Melted alloys of the Fe_xMn_0.65−xAl_0.35 disordered system, 0.25?x?0.65, were experimentally studied by Mössbauer spectrometry, vibrating sample magnetometry and AC magnetic susceptibility. All the alloys exhibit the BCC structure with a nearly constant lattice parameter (2.92 Å). Mössbauer studies at room temperature (RT) show that in the 0.25 ?x?0.45 range the alloys are paramagnetic (P) while in the 0.50?x?0.65 range, they are ferromagnetic. At 77 K, Mössbauer studies show that the alloy with x=0.25$x=0.25$ presents weak magnetic character that is consistent with an antiferromagnetic (AF) behavior due to the high Mn content, while those with 0.30?x?0.40 are paramagnetic, and those in the 0.45?x  ?0.65 range are ferromagnetic (F) with a mean field increasing with the Fe content. Hysteresis cycles at RT prove the paramagnetic character of the alloys between x=0.25$x=0.25$ and 0.40 and the ferromagnetic character for x?0.45$x?0.45$. Complementary measurements using AC magnetic susceptibility permit a magnetic phase diagram to be proposed, with the P phase for high temperature and all the compositions, the AF phase for low Fe content and at low temperature, the F phase for high Fe content above RT and the spin glass phase for all the compositions and at temperatures lower than 46 K. In addition, the mean field renormalization group (MFRG) method, applied to a random competitive and site dilute Ising model with nearest-neighbor, gives rise to magnetic phase diagram, which fairly agrees with previous experimental one.     

Magnetic properties of TbMn6Sn6-xGax (x=0.0－1.2) compounds

Effects of Ga substitution for Sn on the structure and magnetic properties of TbMn₆Sn_6-xGa_x (x=0.0－1.2) compounds have been investigated by means of x-ray diffraction, magnetization measurement and ¹¹⁹Sn M?ssbauer spectroscopy. The substitution of Ga for Sn results in a decrease in lattice constants and unit-cell volumes. The magnetic ordering temperature decreases monotonically with increasing Ga content from 423 K for x=0.0 to 390 K for x=1.2. At room temperature, the easy magnetization direction changes from the c-axis to the ab-plane. This variation implies that the substitution of Ga for Sn leads to a decrease in the c-axis anisotropy of the Tb sublattice. An increase in the non-magnetic Ga concentration results in a monotonic decrease of the spontaneous magnetization M_s at room temperature. Since there are three non-equivalent Sn sites, 2c (0.33, 0.67,0), 2d (0.33, 0.67,0.5) and 2e (0,0,0.34) in the TbMn₆Sn_6-xGa_x compounds, the ¹¹⁹Sn M?ssbauer spectra of the TbMn₆Sn₆ and TbMn₆Sn_5.4Ga_0.6 compounds can be fitted by three sextets. The hyperfine fields (HFs) decrease in the order of HF(2d)>HF(2e)>HF(2c), which is in agreement with the magnetic structure.     

Structural and magnetic properties of Dy2Co17—xMnx compounds

Using x-ray diffraction and magnetic measurements, we have studied the structural and magnetic properties of Dy₂Co_17-xMn_x (x=0∽5) compounds with a rhombohedral Th₂Zn₁₇-type structure. With an increasing Mn concentration x, the unit-cell volume V was found to increase linearly. The Curie temperature T_c decreases linearly, and the saturation magnetization M_s at 5K first increases slightly for x<1, then decreases rapidly for x>1 with a further increase of Mn concentration x. In compounds for x=1～3, a spin reorientation was found. A magnetic diagram of the compounds is given.     

Magnetic properties of CuCr2Se4 single crystals

The magnetic properties of CuCr₂Se₄ single crystals, which were grown by chemical transport reactions using iodine as a carrier, have been investigated. The magnetic moment at 0 K is found to be 5.07 μ_B per mole. The susceptibility at high temperatures follows a Curie-Weiss law with an asymptotic Curie temperature 430 K and a Curie constant 2.55 emu · $\text{deg}\text{mol}$. The magnetocrystalline anisotropy constants K₁ and K₂ are ? 6.9x 10⁵ and ? 0.9x 10⁵$\text{erg}\text{cm}{}^3$, respectively, at 5.1 K.In order to examine the effects of annealing on the magnetocrystalline anisotropy, the ferromagnetic resonance at room temperature was measured after annealing in vacuum and subsequently in an atmosphere of Se. It is found that the absolute values of K₁ and K₂ decrease after annealing in vacuum and increase to the initial values after annealing in an atmosphere of Se.     

Absorption spectra near the absorption edge of the system HgxZn1−xCr2Se4

Optical absorption spectra near the absorption edge of the system Hg_xZn_1?xCr₂Se₄ have been measured for various compositions in the temperature range between room and liquid helium temperatures. A correlation between the optical properties and magnetic structures becomes obvious from the measurements of the energy at the absorption edge and the change in the magnetic property with composition variation, and by measuring the optical absorption spectra under the applied magnetic field.     

Magnetic properties of the Lu2Fe17−xMnx single crystals

Magnetic properties of the single-crystalline Lu₂Fe_17−xMn_x compounds, in which x=0, 0.5, and 2, with the Th₂Ni₁₇-type crystal structure are reported. The Lu₂Fe_17−xMn_x compounds with x=0 and 0.5 are ferromagnets at low temperatures and antiferromagnets at high temperatures. The compound with x=2 is always a ferromagnet. The easy-plane magnetic anisotropy in the Lu₂Fe_17−xMn_x ferromagnets drastically weakens with increase in Mn content up to x=2. The temperature dependence of the first magnetic anisotropy constant was obtained and compared with the single-ion model prediction.     

(La1-xPrx)2/3Sr1/3MnO3系列的磁致伸缩效应研究

用溶胶-凝胶方法制备了一系列的(La_1-xPr_x)_2/3Sr_{1/3MnO3多晶样品,研究了其电磁性能及磁致伸缩效应,发现样品低温下的磁致伸缩主要以线伸缩为主,且在低场下达到饱和,在Pr含量为0.3时达到最大值,约为-90×10^-6.随Pr掺杂含量的逐渐减小,磁致伸缩的饱和场也逐渐减小. 关键词：}     

Magnetoabsorption and magnetization of Zn1−xMnxTe mixed crystals

Excitonic magnetoabsorption (on samples of thickness less than 1 μm) of Zn_1?xMn_xTe (x < 0.1) was measured for magnetic fields up to B = 5T at T = 2.2 K. A strong (about 80 meV) exchange splitting of the exciton was observed. In the absence of magnetic field the variation of energy gap with composition of the crystals, as well as the coefficients dEg/dT were studied at 2.2 < T < 275 K. The magnetization measurements were performed at temperatures of T = 2.2 K and 4.2 K for B < 15T on the same samples that were optically tested. As a result, the s-d exchange constants were evaluated: N_oα = 0.19 eV, N_oβ = ?1.1 eV.     

Magnetic properties of the Pr1−xGdxCo4B compounds

In this work, we have investigated the effect of the substitution of Gd for Pr on the crystal structure and magnetic properties of the Pr_1−xGd_xCo₄B compounds for 0?x?1 using X-ray powder diffraction, magnetic measurements, and differential scanning calorimetry (DSC). These compounds have hexagonal CeCo₄B-type structure with the space group P6/mmm. The substitution of Gd for Pr leads to a decrease of the unit-cell parameters a and the unit-cell volume V, while the unit-cell parameter c increases slightly. Magnetic measurements indicate that all samples are ordered magnetically below room temperature. The Curie temperatures determined by DSC technique increase as Pr is substituted by Gd. The saturation magnetization at 5 K decreases upon Gd substitution up to x=0.6, and then increases again.     

Elaboration,caracterisation et proprietes magnetiques de cristaux d'oxyde Sm2O3

Single crystals of samarium oxide Sm₂O₃ with monoclinic B structure were prepared by the Verneuil process adapted to a plasma torch. Some properties of these crystals have been studied (cleavage, hardness …) especially the magnetic properties. Paramagnetic susceptibilities measurements have been performed for various orientations of the crystal with respect to the magnetic field at constant temperatures (5, 77, 300 K) as well as at increasing temperatures (5–1000 K) and indicate an anisotropy. An interpretation of this phenomena is proposed.     

Neutron scattering investigation of the tricritical point in DyPO4

Neutron scattering experiments on DyPO₄ were performed without and with external field at temperatures between 1.65 and 3.5 K in order to determine the phase diagram and critical properties. In contrast to previous results the M(H)-curve shows typical first order behaviour fot T ? 2 K and H ? 4.2. kG. The H_c(T)-curve agrees quite well with the previous results. Critical scattering was observed at 1.65 K around the (110) magnetic Gragg-peak. A structure refinement at room temperature was also done mainly in order to check for the importance of extinction.     

La1-xCaxMnO3的巨磁电阻效应

通过测量La_2/3Ca_1/3MnO₃，La_0.6Ca_0.4MnO₃单相多晶样品的磁电阻、电阻与温度的依赖关系，发现在La_1-xCa_xMnO₃体系中随x的变化，其磁电阻峰和电阻峰都发生了位移．作者认为体系中Mn⁴⁺含量是受Ca含量调制的，正是Mn⁴⁺含量的变化，导致磁性 关键词：     

On the mixed valence of the chromium ions in the noncollinear ferrimagnetic spinels Mn1−xCuxCr2S4 (Where x = 0.85, 0.90, 0.95)

For the polycrystalline samples of Mn_1?xCu_xCr₂S₄ (x = 0.85, 0.90, 0.95) the magnetization was measured in the temperature range between 77 K and the Curie temperature, T_C, using a magnetic balance (Faraday's method) and pulsed magnetic fields up to 2.0 T. The magnetic susceptibility was measured between T_C and about 600 K. The Curie temperatures were obtained using the kink point method.In the temperature range between 4.2 and 77 K the magnetization was measured in stationary magnetic fields up to 14 T. The data indicate a noncollinear ferrimagnetic structure. The compounds under investigation can be treated as CuCr₂S₄ slightly doped with Mn, with a valence distribution Mn²⁺_1?xCu¹⁺_xCr³⁺_2?xCr⁴⁺_xS^2?₄.     

Helimagnetism in MnP-type compounds: MnP,FeP, CrAs and CrAs1−xSbx mixed crystals

The solid solution CrAs_1?xSb_x has been investigated by neutron diffraction at various temperatures. The phase boundary between mixed crystals with MnP-structure and those with NiAs-structure moves from 59 mol% CrAs at room temperature to 48 mol% CrAs at liquid helium temperature. The mixed crystals with NiAs-type structure at 4.2K have the collinear magnetic structure of CrSb. Samples having the MnP-type structure exhibit a “double spiral” spin structure like CrAs. The variation of the magnetic moment and the spiral structure have been studied. Using neutron diffraction data for the magnetic propagation vector and the phase difference of the two helices, the signs and the ratios of the exchange integrals are discussed in a Heisenberg model. The stability regions in parameter space are determined by a matrix method for the ferromagnetic mode observed in MnP above 50 K and for the helical modes observed in MnP below 50 K, and in FeP, CrAs and CrAs_1?xSb_x. We have also considered the possibility of antisymmetric and symmetric exchange between nearest neighbours only, using a group theoretical approach.The high ratios of antisymmetric to symmetric exchange would be necessary to explain the observed helical structures preclude however antisymmetric exchange as a dominant factor.     

Equilibrium spin orientations in Rb2MnxCr1−xCl4 mixed crystals from an average model

For the mixed crystal system Rb₂Mn_xCr_1?xCl₄, we have calculated the magnetic phase diagram at low temperatures by means of an average model. The calculations have been performed as a function of concentration x and as a function of external field parallel and perpendicular to the crystallographic c-axis. The results are in agreement with the available experimental data. The essential details of the results are the prediction of an oblique antiferromagnetic phase for 0.925≤×≤0.945 and of ferrimagnetic order for 0.13≤×≤0.85 if there is a long range order for these concentrations.     

Magnetic phase diagram of amorphous (FexNil-x)75P16B6Al3 alloys

We have studied the temperature dependence of the magnetic response of amorphous (Fe_xNi_l-x)₇₅P₁₆B₆A$\text{l}$₃ ribbons to a small low frequency applied field. For x ? 0.16 we identify a paramagnet-spin glass transition. With 0.17 ? x ? 0.4 a paramagnet-ferromagnet transition is observed which is followed at lower T by a spin freezing phenomenon. A magnetic phase diagram is proposed and discussed in terms of recent theories.