Magnetic behaviour of the cubic La(Fe,Al)13 compounds

The magnetic properties of the cubic NaZn₁₃ type pseudobinary compounds LaFe_XAl_13–x were studied in the temperature range T=4.2–300 K by means of⁵⁷Fe-Mössbauer spectroscopy, magnetization and zero-field susceptibility measurements. The compounds LaFe_xAl_13–x show a rather peculiar concentration dependence of the type of magnetic ordering as well as of the ordering temperature.     

Absence of morphotropic phase boundary effects in BiFeO<Subscript>3</Subscript>–PbTiO<Subscript>3</Subscript> thin films grown via a chemical multilayer deposition method

We report an unusual behavior observed in (BiFeO₃)_1−x –(PbTiO₃) _x (BF–xPT) thin films prepared using a multilayer chemical solution deposition method. Films of different compositions were grown by depositing several bilayers of BF and PT precursors of varying BF and PT layer thicknesses followed by heat treatment in air. X-ray diffraction showed that samples of all compositions show mixing of two compounds resulting in a single-phase mixture, also confirmed by transmission electron microscopy. In contrast to bulk compositions, samples show a monoclinic (M_A-type) structure suggesting disappearance of the morphotropic phase boundary (MPB) at x=0.30 as observed in the bulk. This is accompanied by the lack of any enhancement of the remanent polarization at the MPB, as shown by the ferroelectric measurements. Magnetic measurements showed an increase in the magnetization of the samples with increasing BF content. Significant magnetization in the samples indicates melting of spin spirals in the BF–xPT films, arising from a random distribution of iron atoms. Absence of Fe²⁺ ions was corroborated by X-ray photoelectron spectroscopy measurements. The results illustrate that thin film processing methodology significantly changes the structural evolution, in contrast to predictions from the equilibrium phase diagram, besides modifying the functional characteristics of the BP-xPT system dramatically.     

High magnetic field properties of mixed terbium-yttrium ferrite garnets

Magnetization measurements in d.c. magnetic fields up to 180 kOe have been performed on polycrystalline specimens and on single crystals of mixed terbium-yttrium iron garnets: Tb _x Y_3–x Fe₅O₁₂ in the 4.2–300 K temperature range. On polycrystals (x=2.5; 2; 1; 0.37) the concentration dependence of both compensation point and spontaneous magnetization has been determined. In the single crystals (x=2; 1; 0.37) a strong magnetic anisotropy has been observed with a change of the easy direction of magnetization from [111] to [100] whenx decreases; abrupt field-induced transitions have been observed at low temperatures when the external field is applied along the [100] direction.     

Synthesis and characterization of Ni-Zn ferrite nanoparticles

Nickel zinc ferrite nanoparticles Ni_xZn_1−xFe₂O₄ (x=0.1, 0.3, 0.5) have been synthesized by a chemical co-precipitation method. The samples were characterized by X-ray diffraction, Fourier transform infrared spectroscopy, electron paramagnetic resonance, dc magnetization and ac susceptibility measurements. The X-ray diffraction patterns confirm the synthesis of single crystalline Ni_xZn_1−xFe₂O₄ nanoparticles. The lattice parameter decreases with increase in Ni content resulting in a reduction in lattice strain. Similarly crystallite size increases with the concentration of Ni. The magnetic measurements show the superparamagnetic nature of the samples for x=0.1 and 0.3 whereas for x=0.5 the material is ferromagnetic. The saturation magnetization is 23.95 emu/g and increases with increase in Ni content. The superparamagnetic nature of the samples is supported by the EPR and ac susceptibility measurement studies. The blocking temperature increases with Ni concentration. The increase in blocking temperature is explained by the redistribution of the cations on tetrahedral (A) and octahedral (B) sites.     

The exponent λ (x, Q2) of the proton structure functionF2(x, Q2) at lowx

The exponent λ of the structure function F₂ ∼x ^−λ is calculated using the solution of the DGLAP equation for gluon at lowx reported recently by the present authors. The quantity λ is calculated both as a function ofx at fixedQ ² and as a function ofQ ² at fixedx and compared with the most recent data from H1     

Local canted spin behaviour in Co1.4−x Zn x Ge0.4Fe1.2O4 spinels: A macroscopic, mesoscopic and microscopic study

DC magnetization, neutron depolarization and neutron diffraction (with both polarized and unpolarized neutrons) measurements have been reported for the Co_1.1−x Zn _x Ge_0.1Fe_1.2O₁ spinels with x=0.5, 0.6 and 0.7. Neutron depolarization and neutron diffraction measurements confirm the presence of a long range ferrimagnetic ordering of the local canted spins in these ferrite samples. The observed features of low field magnetization have been explained under the framework of thermally activated domain wall movement of ferrimagnetic arrangement of local canted spins. An important role of magnetic anisotropy (due to the presence of Co²⁺ ions) in establishing the magnetic ordering and domain kinetics in these ferrites has been observed.     

Tb2AlFe16-xMnx化合物的结构、磁性及正电子湮没谱研究

通过X射线衍射、磁测量及正电子湮没谱等手段研究了Tb₂AlFe_16-xMn_x（x=1—8）化合物的结构和磁性.X射线衍射研究结果表明Tb₂AlFe_16-xMn_x化合物具有六角相的Th₂Ni₁₇型结构.室温下的正电子湮没实验研究表明,Mn对Fe的替代导致化合物中的铁磁相互作用减弱,并且化合物中存在着较强烈的磁弹耦合效应.磁测量研究结果表明,Mn的替代导致Tb₂AlFe_16-xMn_x化合物的居里温度及自发磁化强度急剧下降. 关键词： 2AlFe_16-xMn_x化合物')" href="#">Tb₂AlFe_16-xMn_x化合物 磁弹耦合效应 居里温度     

Theory of anisotropic diamagnetism, local moment magnetization and carrier spin-polarization in Pb1−x Eu x Te

We present theoretical analyses of anisotropic lattice diamagnetism, magnetization due to magnetic ions and carrier spin-polarization in the diluted magnetic semiconductor, Pb_1-x Eu _x Te. The lattice diamagnetism results from orbital susceptibility due to inter band effects and spin-orbit contributions. The spin-orbit contribution is found to be dominant. However, both the contributions show pronounced anisotropy. With increase in x, the diamagnetism decreases. We consider contributions from randomly distributed isolated magnetic ions and clusters of pairs and triads for the local moment magnetization. The isolated magnetic-ion contribution is the dominant one.We calculate the magnetization for two typical magnetic ion concentrations: x=0.03 and x=0.06. Temperature dependence of the magnetization is also considered. Apart from lattice and localized magnetic ions, the carrier contribution to the spin-density is also calculated for a carrier density of p=10¹⁸ cm⁻³. the relative spin-density of carriers increases with increase in the magnetic field strength and magnetic ion concentration. The agreement with experiment where available is reasonably good.     

Relaxation phenomena in amorphous Co75−x Mn x B25 induced by stress annealing

The change of the magnetization direction in amorphous ferromagnets by the application of a magnetic field and a tensile stress is investigated by magnetoresistivity measurements. Attention is focussed on permanently remaining influences on the domain structure induced by stress annealing treatments. To observe any dependence on the sign of the magnetostrictionλ _s, we investigated the amorphous Co_75?x Mn _x B₂₅ system where the sign ofλ _s changes from negative to positive values with increasing Mn content. Surprisingly the stress-annealed samples showed a similar behavior independent of the sign of the magnetostriction.     

Transferred hyperfine field in the pseudo-binary compound Y(Fe,Mn)2

The NMR of⁸⁹Y in Y(Fe_1−xMn_x)₂ has been observed. Two kinds of Mn moments were estimated by analyzing the⁸⁹Y hyperfine field: (1) the low spin state with about 0.6 μ_B in antiparallel to Fe moment and (2) the high spin state with about 2.8 μ_B in parallel to Fe moment. The magnetizations estimated from NMR results are in good agreement with those of magnetization measurements.     

Structure, transport and magnetic properties in La2xSr2−2xCo2xRu2−2xO6

The perovskite solid solutions of the type La_2xSr_2−2xCo_2xRu_2−2xO₆ with 0.25≤x≤0.75 have been investigated for their structural, magnetic and transport properties. All the compounds crystallize in double perovskite structure. The magnetization measurements indicate a complex magnetic ground state with strong competition between ferromagnetic and antiferromagnetic interactions. Resistivity of the compounds is in confirmation with hopping conduction behaviour though differences are noted especially for x=0.4 and 0.6. Most importantly, low field (50 Oe) magnetization measurements display negative magnetization during the zero field cooled cycle. X-ray photoelectron spectroscopy measurements indicate the presence of Co²⁺/Co³⁺ and Ru⁴⁺/Ru⁵⁺ redox couples in all compositions except x=0.5. Presence of magnetic ions like Ru⁴⁺ and Co³⁺ gives rise to additional ferromagnetic (Ru-rich) and antiferromagnetic sublattices and also explains the observed negative magnetization.     

Phase transitions in La1−x CaxMnO3−x/2 manganites

The crystal structure parameters and magnetic and electrical properties of La_1?x Ca_xMnO_3?x/2 reduced manganites with 0≤x≤0.5 are established. These investigations contribute to the understanding of magnetic interactions in manganites without Mn⁴⁺ ions. It is found that these manganites show a long-range antiferromagnetic order up to x=0.09 and transform into spin glasses at 0.09<x≤0.35. The compositions in the range 0.35<x≤0.5 show a strong increase in the spontaneous magnetization and critical point associated with the appearance of spontaneous magnetization and can therefore be viewed as inhomogenious ferromagnets. The magnetic and crystal structure peculiarities of La_0.5Ca_0.5MnO_2.75 are established by the neutron diffraction method. The strongly reduced samples show a large magnetoresistance below the point where the spontaneous magnetization develops. The magnetic phase diagram of La_1?x Ca_xMnO_3?x/2 is established by magnetization measurements. The magnetic behavior is interpreted assuming that the Mn³⁺-O-Mn³⁺ magnetic interaction is anisotropic (positive-negative) in the orbitally ordered phase and isotropic (positive) in the orbitally disordered phase. Introduction of the oxygen vacancies changes the magnetic interaction sign from positive to negative, thereby leading to a spin glass state in strongly reduced compounds. The results obtained reveal unusual features of strongly reduced manganites such as a large ferromagnetic component, a high magnetic ordering temperature, and a large magnetoresistance despite the absence of Mn³⁺-Mn⁴⁺ pairs. In order to explain these results, the oxygen vacancies are supposed to be ordered.     

Dc electrical conductivity of Ge2S3Agx glasses at high hydrostatic pressure

The paper deals with the influence of hydrostatic pressure on d.c. electrical conductivity in Ge₂S₃Ag _x glasses forx10%. The initial material exhibits high resistivity and the presence of Ag impurity yields strong increase in electrical conductivity. The experimental results suggest that there is a non-linear decrease of electrical resistivity at pressure ranging from 0·1 to 10³ MPa. The pressure coefficient of resistivity is a function ofx. All measurements were performed on bulk samples using graphite contacts. The experimental results are interpreted by means of ionic conductivity.     

Formation mechanism of ferromagnetism in Si1−xMnx diluted magnetic semiconductors

Si_1−xMn_x diluted magnetic semiconductor (DMS) bulks were formed by using an implantation and annealing method. Energy dispersive X-ray fluorescence, transmission electron microscopy (TEM), and double-crystal rocking X-ray diffraction (DCRXD) measurements showed that the grown materials were Si_1−xMn_x crystalline bulks. Hall effect measurements showed that annealed Si_1−xMn_x bulks were p-type semiconductors. The magnetization curve as a function of the magnetic field clearly showed that the ferromagnetism in the annealed Si_1−xMn_x bulks originated from the interaction between interstitial and substitutional Mn⁺ ions, which was confirmed by the DCRXD measurements. The magnetization curve as a function of the temperature showed that the ferromagnetic transition temperature was approximately 75 K. The present results can help to improve understanding of the formation mechanism of ferromagnetism in Si_1−xMn_x DMS bulks.     

Measurement of the proton structure function F 2 at low x and low Q 2 at HERA

We report on a measurement of the proton structure functionF ₂ in the range 3.5×10⁻⁵≤x≤4×10⁻³ and 1.5 GeV²≤Q ²≤15GeV² at theep collider HERA operating at a centre-of-mass energy of √s=300GeV. The rise ofF ₂ with decreasingx observed in the previous HERA measurements persists in this lowerx andQ ² range. TheQ ² evolution ofF ₂, even at the lowestQ ² andx measured, is consistent with perturbative QCD. supported by EU HCM contract ERB-CHRX-CT93-0376     

Tb$lt;sub$gt;0.3$lt;/sub$gt;Dy$lt;sub$gt;0.6$lt;/sub$gt;Pr$lt;sub$gt;0.1$lt;/sub$gt;(Fe$lt;sub$gt;1-$lt;i$gt;x$lt;/i$gt;$lt;/sub$gt;Al$lt;sub$gt;$lt;i$gt;x$lt;/i$gt;$lt;/sub$gt;)$lt;sub$gt;1.95$lt;/sub$gt;合金的磁性、磁致伸缩和穆斯堡尔谱研究

系统研究了室温下Tb_0.3Dy_0.6Pr_0.1（Fe_1-xAl_x）_1.95 （x=0.05,0.1,0.15,0.2,0.25,0.3）合金中元素Al替代Fe对结构、磁性、磁致伸缩性能和自旋重取向的影响.测量结果发现,x<0.2时Tb_0.3Dy_0.6Pr_0.1（Fe_1-xAl_x）_1.95合金基本上是纯的单相,x=0.2时出现其他杂相,杂相随Al替代量的增加不断增多.随Al替代量x的增加,点阵常数a接近于线性增大,Curie温度T_C逐渐下降,而矫顽力H_c急剧下降.振动样品磁强计（VSM）测量发现,磁化强度M随Al替代量x的变化较为复杂.VSM计和磁致伸缩效应测量共同表明,少量Al的替代有利于降低磁晶各向异性,而且随着Al替代量x的增多磁致伸缩系数快速减小,x>0.15时巨磁致伸缩效应消失.穆斯堡尔效应研究发现,随Al含量的增加Tb_0.3Dy_0.6Pr_0.1（Fe_1-xAl_x）_1.95合金中易磁化轴可能在{110}面逐渐偏离了立方晶体的主对称轴,发生自旋重取向,从而引起合金宏观磁性、磁致伸缩性能的变化. 关键词： 磁致伸缩 立方Laves相 自旋重取向 穆斯堡尔谱     

Magnetic properties of the pseudo-binary intermetallic compounds (CexY1−x) Fe2

Magnetic susceptibility and Mössbauer spectroscopy measurements on cubic Laves phase pseudo-binary compounds (Ce_xY_1?x)Fe₂ are reported. The thermal variation of the magnetization and the dependence of the hyperfine interactions, Curie temperature, saturation moments at 4K and lattice parameter on concentration are presented. The results show a difference in behaviour between the regions rich in Ce and in Y, which is attributed to a possible change of the valence of Ce.The direction of easy magnetization at 77K changes from 〈111〉 in YFe₂ to 〈101〉 in the pseudo-binary compounds rich in Ce.     

Charge-Ordered Antiferromagnetic to Ferromagnetic Phase Transition in Cr-Doped Nd0.5Ca0.5Mn1−x Cr x O3: EMR and Magnetization Study

The Cr-doped rare-earth manganites Nd_0.5Ca_0.5Mn_1−x Cr _x O₃ (x = 0.03, 0.05, 0.10) are studied by electron magnetic resonance (EMR) and magnetization measurements in the paramagnetic as well as in the ferromagnetic phase. The magnetization measurements show that the charge-ordered antiferromagnetic phase decreases at the expense of ferromagnetic metallic phase and for Cr doping of x = 0.1, the charge-ordered phase melts completely. The EMR shows multiple signals for all three compositions in the ferromagnetic phase indicative of an anisotropic ferromagnetic phase. The difference between the shift of the high-field and low-field signals decreases with Cr doping, indicating that the magnetic anisotropy decreases with the Cr doping. In the paramagnetic phase the EMR line width follows Causa's model as observed in other colossal magnetoresistant manganites. Authors' address: Ajay Sharma, Department of Physics, Indian Institute of Science, Bangalore, India     

Distinction of spin-glass freezing from superparamagnetic blocking

Experimental results on Eu_xSr_1?xS provide clear evidence for a cooperative phenomenon at the spin-glass transition, as distinguished from ordinary thermal blocking of superparamagnetic clusters. Only below the percolation threshold x_p = 0.13 can single-clusters aspects be separated clearly (superparamagnetic regime). In the spin-glass regime for x >x_p, susceptibility and remanent magnetization are studied near the freezing temperature in dependence on temperature, magnetic field and observation time. The anomalous slow relaxations of the remanent magnetization, which follow a power-law, exhibit a strong variation just near T_f0, the transition temperature deduced from static magnetization measurements. In addition, T_f values derived from ac-_χ measurements are distinctly frequency dependent; the frequency variation decreases towards low frequencies and seems to saturate near the T_f0 value. The strong sensitivity of _χ(T_f) to even small applied fields can be represented by a universal function independent of concentration. All these results emphasize the importance of the interactions among the spin clusters of spin glasses which are partially frustrated.     

Structural, electrical and magnetic characterizations of Ni-Cu-Zn ferrite synthesized by citrate precursor method

Fine powders of NiCuZn ferrite with composition Ni_(0.7−x)Cu_xZn_0.3Fe₂O₄ (where x=0, 0.2, 0.4 and 0.6) were prepared by the citrate precursor method. X-ray diffraction measurements confirm the formation of single-phase cubic spinel structure. The grain size was estimated by SEM micrograph which increases with Cu content. Dielectric constant (?) and loss tangent (tan δ) were measured as a function of frequency. The ? and tan δ show a decreasing trend with increase of frequency for all the samples. The DC resistivity was measured as a function of temperature. The temperature-dependent DC resistivity measurements show that the room-temperature DC resistivity of NiCuZn ferrite with x=0.2 is of the order of 10⁹ Ω cm. The AC conductivity (σ_AC) was studied as a function of frequency. The hysteresis data indicate that the maximum saturation magnetization of 38.66 emu/g is obtained for the composition with x=0.2.