Magnetic and related properties of GdCu5.1In6.9

Magnetic measurements performed between 1.7 and 300K show that GdCu_5.1In_6.9 is an antiferromagnet below T _N = 13.4(1) K. At temperatures 17–300K the Curie-Weiss law is followed with p _eff = 7.57 μ _B and θ = -33.8K. Electrical resistivity measurements do not show any pronounced anomaly, but the resistivity is rather low with RRR ≈ 59. The EPR experiment shows that the resonance exists between 10 and 300 K. A temperature independent g-shift (Δg = -0.036(10)) and a Korringa.type linewidth broadening of 2.6 G/K was observed at temperatures higher than 55 K. The linewith increase found at high temperature well above T _N can suggest a significant amount of short. range order. ¹⁵⁵Gd Mössbauer effect examinations show that H _hf is perpendicular to the c-axis and therefore magnetic moments of Gd are located within the ab-plane.     

Magnetic and magnetoelastic properties of GdZn single crystals

The magnetic and magnetoelastic properties of GdZn have been investigated by various ways: magnetization, magnetic susceptibility, magnetocaloric effect, pressure dependence of the Curie temperature, spontaneous magnetostriction, parastriction and sound velocity measurements. The γ-mode strain is large for an S-state ion, and two orders of magnitude larger than the ?-one. Both the first-order B^γ,2 and the three isotropic second-order magnetoelastic coefficients exhibit a m²(1 ? 0.5m²) thermal variation (where m(T, H) is the reduced magnetization), which differs from the classical behaviour. All the results suggest a noticeable contribution of the conduction band to the magnetism of GdZn.     

Mechanically driven domain wall movement in magnetoelastic nanomagnets

Magnetic domain walls are fundamental objects arising in ferromagnetic materials, largely investigated both through micromagnetic simulations and experiments. While current- and field-based techniques for inducing domain wall propagation have been widely studied for fundamental understanding and application-oriented purposes, the possibility to manipulate domain walls using mechanical stress in magnetoelastic materials has only recently drawn interest. Here, a complete analytical model describing stress-induced transverse domain wall movement in ferromagnetic nanostripe with variable cross-section is presented. This approach yields a nonlinear integro-differential equation describing the magnetization field. Its numerical implementation, based on the nonlinear relaxation method, demonstrates the possibility to precisely control the position of a domain wall through mechanical action.     

Mechanical properties of polycrystalline RuSr2GdCu2O8 superconductor

The main objective of this paper is to report the room temperature hardness and elastic modulus of the RuSr₂GdCu₂O₈ superconductor phase by instrumented indentation. Polycrystalline samples were produced by a solid state reaction technique. The samples were also characterized by scanning electron microscopy, X-ray diffraction and electrical resistivity measurements. The influence of porosity on the mechanical properties was avoided by considering only those indentations inside the grains. The hardness and elastic modulus were 8.6 GPa and 145 GPa, respectively. These values are comparable with those of Y-123. The indentation fracture toughness evaluated after conventional Vickers indentation was 1.9 MPa m^1/2.     

The magnetoelastic interaction of exchange nature

An expression for the energy of the magnetoelastic interaction of the exchange nature in magnetic structures and an analysis of the conditions when it is nonzero is presented. The effect of a magnetic field on these conditions is considered on the example of specific materials of hexagonal structures, and an important role of phase transitions on the magnetic field with the restructuring of the magnetic structure is noted.     

NMR Study on Coexistence of Magnetic Order and Superconductivity in RuSr2GdCu2O8

Electronic and magnetic properties of RuSr₂GdCu₂O₈ have been investigated by resistivity, magnetization and NMR measurements. Magnetic order (T _C=133 K) and superconducting transition (T _S(onset) 52 K) have been confirmed in RuSr₂GdCu₂O₈. We observed two kinds of Ru-NMR signals (the hyperfine fields of ¹⁰¹Ru are 590 kOe and 290 kOe), suggesting a possible charge segregation of Ru⁴⁺(S=1) and Ru⁵⁺(S=3/2) in the RuO₂ layers. Holes can be inherently doped in the CuO₂ layers from the (Ru⁴⁺, Ru⁵⁺)O₂ layers, and the superconductivity can occur under weak magnetic interactions between Ru and Cu spins in RuSr₂GdCu₂O₈.     

Crystalline fields in systems with exchange and magnetoelastic interaction

The influence of the Kondo effect on the state of the crystalline field in the localized-moment regime is studied. It is shown that the exchange interaction leads to an anomalous temperature dependence of the intensity of the inelastic magnetic scattering of neutrons. An unconventional theory is constructed for the magnetoelastic interaction induced by Kondo scattering. The proposed model is in quantitative agreement with the results of neutron and thermodynamic investigations of the compound CeAl₃. Pis’ma Zh. éksp. Teor. Fiz. 66, No. 7, 460–465 (10 October 1997)     

The magnetotransport properties of the intermetallic compound GdCu6

We have studied the temperature and magnetic field dependence of the electrical resistivity of GdCu(6) and have co-related the results with the temperature dependence of heat capacity and magnetization. The magnetoresistance of GdCu(6) is found to be positive both in the paramagnetic and antiferromagnetic regimes. Within the antiferromagnetic regime, the magnetoresistance is very high and increases to still higher values both with increasing field and decreasing temperature. In the paramagnetic regime the magnetoresistance continues to exhibit a finite positive value up to temperatures much higher than that corresponding to the antiferromagnetic to paramagnetic phase transition. We have shown through quantitative analysis that both the temperature dependences of resistivity and heat capacity indicate the presence of spin fluctuations within the paramagnetic regime of GdCu(6). The field dependence of electrical resistivity indicates that the positive magnetoresistance in the paramagnetic phase is not related to the orbital motion of the conduction electrons in a magnetic field (the Kohler rule). In contrast, our analysis indicates that these spin fluctuations are responsible for the positive magnetoresistance observed within this paramagnetic regime. The nature of the field dependence of electrical resistivity is found to be qualitatively similar both in the antiferromagnetic and paramagnetic regimes, which probably indicates that spin fluctuations in the paramagnetic regime are of the antiferromagnetic type.     

Nd-Ce-Fe-B纳米复合薄膜的磁性及交换耦合作用

采用磁控溅射技术制备了具有永磁特征的Nd-Ce-Fe-B多层纳米复合薄膜,并对其进行了退火处理.通过改变退火温度,研究其对薄膜磁性能和晶体结构的影响.结果表明,随着退火温度的提高薄膜磁性能逐渐增大,但当温度达到695℃以上时,薄膜的磁性能急剧下降.当退火温度为675℃时,薄膜的矫顽力Hci=10.1 kOe(1Oe=79.5775 A/m),垂直于薄膜表面方向的剩余磁化强度4πM_(r⊥)=5.91 kG(1 G=10~3/(4π)A/m).薄膜的X射线衍射结果表明,磁性薄膜具有较好的c轴取向.通过对薄膜磁化反转过程的研究,发现随着外加磁场的增大,M_(rev)的极小值向M_(irr)减小的方向移动,这与畴壁弯曲模型类似,表明在薄膜中存在较强烈的局部钉扎作用,而剩余磁化强度曲线表明这种钉扎作用在薄膜矫顽力机制中并不占支配作用.此外,薄膜的Henkel曲线结果表明在薄膜中存在较强的交换耦合作用,在经过685℃退火的薄膜中磁相互作用更加显著.     

Magnetic properties of ErIG and approximation of isotropic exchange

A one-ion model calculation which considers the Er³⁺ ion subject to the crystal field, the isotropic exchange field and the applied magnetic field is compared with the following experimental data: the easy axis direction, the transition temperature, the temperature and field dependence of the magnetization, the compensation temperature, the magnetocrystalline anisotropy and the umbrella structure of Er³⁺ magnetic moments in ErIG. The crystal field parameters in Y(Er)GG and ErGG are discussed and determined first. The same parameters are used for ErIG, only those of second order are allowed to vary. In spite of the isotropic exchange approximation, the experiments (except the controversial umbrella structure and anisotropy data) are well reproduced within the framework of this model. Further improvements are expected by inclusion of the anisotropy of the exchange interaction.Dedicated to Dr. Svatopluk Krupika on the occasion of his 65th birthday.     

Intrinsic Josephson effects in the magnetic superconductor RuSr2GdCu2O8

We have measured interlayer current transport in small-sized RuSr2GdCu2O8 single crystals. We find a clear intrinsic Josephson effect showing that the material acts as a natural superconductor-insulator-ferromagnet-insulator-superconductor superlattice. Thus far, we detected no unconventional behavior due to the magnetism of the RuO2 layers.     

Thermoelectric power factor of RuSr2GdCu2O8

The influence of thermal treatment between 1273 and 1333?K in an oxygen atmosphere on the perovskite system RuSr₂GdCu₂O₈ was studied by X-ray diffraction (XRD), scanning electron microscopy, electrical resistivity and Seebeck coefficient measurements. The XRD patterns revealed that the phase purity depends on the sintering process. The samples were found to exhibit very small crystallite sizes in the nanometer range. The electrical resistivity was found to be strongly correlated with the heat treatment. The temperature dependence of electrical resistivity for one sample revealed semiconducting behavior, whereas the others exhibit metallic behavior. All the investigated samples exhibit a positive thermoelectric power, indicating the predominance of positive charge carriers. It was found that the power factor reaches a maximum value of 0.4?×?10^?4?W?m^?1?K^?2 at 300?K.     

Magnetic and structure phase transitions investigated by standing magnetoelastic waves

The theory of the experimental apparatus used for producing and revealing magnetomechanical waves, was elaborated. It was demonstrated that, in the investigated case, the measured amplitude of the elastomagnetic waves is a function of the reversible permeability as well as the elastic and piezomagnetic coefficients. All the last parameters are sensitive to both structure changes and magnetic interaction variations. Therefore during the heat treatment the magnetoelastic wave amplitude is a physical sensor with which we can investigate phase transitions. On this basis the effects of the structural relaxation, the ferro-paramagnetic state transition and the amorphous-crystalline structure development, were investigated in samples of metallic glass.     

高纯度超导氧化物RuSr2GdCu2O8的合成与超导电性

RuSr2GdCu2O8据报道是转变温度为30－40K的超导体，其合成的主要问题是，在合成过程中有相当多的铁磁性的SrRuO3杂相伴随着主相一起生成，本文报道了合成RuSr2GdCu2O8（Ru-1212相）纯相的新方法，即在O2和水蒸气气氛中首先合成纯相的Sr2GdRuO6(Ru-211相）先驱物，然后Sr2GcRuO6与CuO高温烧结，生成RuSr2GdCu2O8。合成的RuSr2GdCu2O8电阻为半导体温度行为，该体系的超导转变与生成的杂相有关。     

Magnetic properties of the spin S = 1/2 Heisenberg chain with hexamer modulation of exchange

We consider the spin-1/2 Heisenberg chain with alternating spin exchange in the presence of additional modulation of exchange on odd bonds with period 3. We study the ground state magnetic phase diagram of this hexamer spin chain in the limit of very strong antiferromagnetic (AF) exchange on odd bonds using the numerical Lanczos method and bosonization approach. In the limit of strong magnetic field commensurate with the dominating AF exchange, the model is mapped onto an effective XXZ Heisenberg chain in the presence of uniform and spatially modulated fields, which is studied using the standard continuum-limit bosonization approach. In the absence of additional hexamer modulation, the model undergoes a quantum phase transition from a gapped phase into the only one gapless Lüttinger liquid (LL) phase by increasing the magnetic field. In the presence of hexamer modulation, two new gapped phases are identified in the ground state at magnetization equal to [Formula: see text] and [Formula: see text] of the saturation value. These phases reveal themselves also in the magnetization curve as plateaus at corresponding values of magnetization. As a result, the magnetic phase diagram of the hexamer chain shows seven different quantum phases, four gapped and three gapless, and the system is characterized by six critical fields which mark quantum phase transitions between the ordered gapped and the LL gapless phases.     

Magnetic structure and exchange interaction in DyCu2

Using the 12-sublattice model with Ising spin , we analyze the magnetization process of DyCu₂ theoretically. The necessary conditions for the exchange constants and the possible magnetic structures of DyCu₂ are suggested.     

Magnetic properties of doped GdI2

Motivated by the recent experimental studies on layered ferromagnetic metallic system GdI₂  and its doped variant GdI₂H_x we develop a model to understand their ground state magnetic phase diagram. Based on first principle electronic structure calculations we write down a phenomenological model and solve it under certain approximations to obtain the ground state energy. In the process we work out the phase diagram of the correlated double exchange model on a triangular lattice for the specific band structure at hand.