Ferromagnetism and spin reorientation in Sm12Fe14Al5

The single crystal of the new ternary compound Sm₁₂Fe₁₄Al₅ was grown and its crystallographic and magnetic properties were investigated. Sm₁₂Fe₁₄Al₅ has a hexagonal structure of the space group p-3m1 and shows ferromagnetism with a Curie temperature of 245 K. The easy direction of magnetization is parallel to the c-axis at temperatures between 245 and 85 K; however, it changes to the c-plane below 85 K through a first-order-like phase transition. No saturation is observed in the magnetization curve even under the applied field of 55 kOe at 5 K. Sm₁₂Fe₁₄Al₅ seems to have a large coercive field at very low temperatures. The anisotropy field was estimated at 5 and 120 K and the saturation magnetization of low temperature phase is explained assuming a ferromagnetic coupling between Fe and Sm sublattices.     

Magnetic structures of R3Cu4Si4 (R=Dy, Ho and Er)

Polycrystalline samples of R₃Cu₄Si₄ (R=Dy, Ho, Er) intermetallics were studied with neutron diffraction methods. All of them crystallize in the orthorhombic structure of Gd₃Cu₄Ge₄-type and order antiferromagnetically at low temperatures. Magnetic moments localized at the rare earth atoms, that occupy two non-equivalent 2d and 4e sublattices, order simultaneously in Dy₃Cu₄Si₄. The order is described by the propagation vector accompanied by , δ=0.025(2). In Ho₃Cu₄Si₄ two propagation vectors are needed to model the magnetic order. These are: for the 4e sublattice, which disorders as the first when the temperature increases, and for the 2d sublattice. A similar situation is observed for Er₃Cu₄Si₄ where the propagation vectors are: k=(0,1−δ,0), δ=0.097(2) for the 4e sublattice, which disorders as the first with increasing temperature, and , δ=0.0015(6) for the 2d sublattice.     

相分离Nd0.5Ca0.5MnO3体系的再入型自旋玻璃行为和电荷有序

研究了Nd_0.5Ca_0.5MnO₃体系的结构和输运特性. 结构 分析表明，在300K下，体系表现为O′型正交结构并存在典型的Jahn-Teller畸变.在8 T磁场 下，体系出现顺磁绝缘-铁磁金属的转变，庞磁电阻效应发生. 磁测量发现，样品的奈尔温 度T_N和电荷有序转变温度T_CO分别在150和240K左右，在41K左右出 现典型再入型自旋玻璃行为，同时观察到了负的磁化率异常. 结果表明，Nd关键词： 庞磁电阻 自旋玻璃态 负磁化强度 电荷有序     

Magnetic order of Mn5Si3-type Tb5Sb3 and Tb5Si1.5Sb1.5

Neutron diffraction study has been performed on the Tb₅Sb₃ and Tb₅Si_1.5Sb_1.5 compounds (hexagonal Mn₅Si₃-type, hP16, P6₃/mcm) to understand their magnetic structures. The temperature dependence of neutron diffraction results proves that these intermetallics show a complex magnetic ordering. The Tb₅Sb₃ presents five subsequent changes in magnetic structure at ∼150, 119, 85, 70 and 54 K on cooling: paramagnet→antiferromagnetic flat spiral→ferromagnetic cone→antiferromagnetically canted ferromagnetic cone→canted AF→sine modulated AF. The Tb₅Si_1.5Sb_1.5 shows two subsequent changes in magnetic structure at 123 and 66 K: paramagnet→sine modulated antiferromagnet I→sine modulated antiferromagnet II. The Tb₅Si₃, Tb₅Sb₃ and Tb₅Si_1.5Sb_1.5 have the different magnetic structure in the full temperature range.     

Crystal structure and magnetic properties of Mn substituted ludwigite Co3O2BO3

The needle shape single crystals Co_3−x Mn_xO₂BO₃ with ludwigite structure have been prepared. According to the X-ray diffraction data the preferable character of distinct crystallographic positions occupation by Mn ions is established. Magnetization field and temperature dependencies are measured. Paramagnetic Curie temperature value Θ=−100 K points out the predominance of antiferromagnetic interactions. Spin-glass magnetic ordering takes the onset at T_N=41 K. The crystallographic and magnetic properties of Co₃O₂BO₃:Mn are compared with the same for the isostructural analogs Co₃O₂BO₃ and CoO₂BO₃:Fe.     

正交LiMnO2中的重入自旋玻璃行为

用水热技术合成了单相正交LiMnO₂(o-LiMnO₂)粉末，X射线衍射表明其空间群为Pmnm.X射线衍射精修结果指出该材料存在少量的阳离子无序，但这种无序对材料的磁性没有表现出明显的影响.静态和动态的磁性研究结果表明o-LiMnO₂中存在重入自旋玻璃行为，即在T≤T_C≈118K，反铁磁态转向铁磁态，在T≤T_f≈50K，铁磁态又转向自旋倾斜玻璃态.     

Magnetic structure of the La3NiGe2-type Tb3NiGe2 and Mn5Si3-type Tb5NixGe3−x (x=0 and 0.3)

We present a neutron powder diffraction investigation of the magnetic structure of La₃NiGe₂-type Tb₃NiGe₂ and Mn₅Si₃-type Tb₅Ni_xGe_3−x (x=0, 0.3) compounds. It is found that below∼135 K Tb₃NiGe₂ exhibits a commensurate b-collinear ferrimagnetic ordering with C_2h′={1, m_z, 1′×2_z, 1′×1?} magnetic point group. The Mn₅Si₃-type Tb₅Ge₃ and Tb₅Ni_0.3Ge_2.7 compounds are found to present a flat spiral type antiferromagnetic ordering at 85 and ≥89 K, respectively. The Ni for Ge substitution is found to decrease the flat spiral ordered magnetic unit cell from a×a×40c of Tb₅Ge₃ (below 40 K) down to a×a×5c for Tb₅Ni_0.3Ge_2.7 (below ∼10 K).     

Magnetic properties of a cermet on the base of Al2O3

The zero-field-cooled and field-cooled magnetizations, magnetization versus field, and remanent magnetization were measured for a cermet on the base of Al₂O₃ using a SQUID magnetometer in the temperature range of 2–360 K. It was shown that magnetic properties of the cermet are determined by independent ferromagnetic, paramagnetic and spin-glass contributions. The spin-glass behavior was studied.     

Magnetic structure of the Sm5Ge4-type Tb2Ti3Ge4

The orthorhombic Sm₅Ge₄-type Tb₂Ti₃Ge₄ shows square modulated non-collinear magnetic ordering with wave vector K=[±1/3, 1/2, 1/2] at 2 K. The terbium magnetic moments lie in the bc plane and magnetic moment value of 7.5(2) μ_B/Tb is obtained at 2 K.     

Reentrant spin glass behaviour in Nd0.84K0.12MnO3

Polycrystalline Nd_0.84K_0.12MnO₃ was prepared in single phase form with Pbnm space group. The magnetic properties are studied from magnetization, linear and non-linear susceptibility, and thermoremanent magnetization measurements. The sample exhibits paramagnetic to ferromagnetic transition followed by low temperature spin glass like transition. From frequency variation of ac susceptibility measurements, the spin glass transition temperature is found to be 97.6±0.1 K with critical exponents zυ=1.13±0.06. The critical exponent γ corresponding to spin glass transition has been determined from the third harmonic susceptibility analysis and it is found to be 3.09±0.05. The effective number of spins blocked under frustration and their correlation length are determined from the analysis of thermoremanent magnetization.     

Charge order and spin order in Nd0.5Sr0.5Mn1? x (Ga x , Ti x )O3 system

Magnetic properties of Nd0.5Sr0.5Mn1-x(Gax,Tix)O3 system (0.04≤x≤0.4) were investigated through magnetization and electron spin resonance (ESR) measurements. It was observed that a small amount of Ti substitution for Mn will destroy the charge-ordering (CO) phase completely and induce the cluster-spin-glass phase in the system, which displays a procedure of collapse of CO and of an enhancement of spin ordering (SO) phase. In contrast, the Ga substitution for Mn induces a melting of CO phase in the system. It was observed that with substitution the CO phase is suppressed gradually and the remanent CO phase is retained all the while, and withal, there is a co-existence of AFM CO phase and FM SO at low temperature. In addition, an abrupt rise of magnetization was observed in M-Tcurves. We attributed this abnormal phenomenon to a transition from canted AFM SO to FM SO in CO region.     

Superspin glass state in MnFe2O4 nanoparticles

Nanosized MnFe₂O₄ ferrites were synthesized by a simple method, which is based on the solid state ball-milling and calcinations of nitrate precursors and citric acid. The samples were characterized by using different methods. The results indicate that the products mainly consist of MnFe₂O₄ nanoparticles. The effect of different annealing temperatures on particle sizes and crystallinity of the samples was also studied. By increasing the particle size, the coercivity and magnetization of the samples increase. The increase of magnetization by increasing the crystallite size could be attributed to the lower surface spin canting and surface spin disorder of the larger magnetic nanoparticles. Our analysis of ac susceptibility measurements shows that the interparticle magnetic interaction leads to the superspin glass-like behavior in these nanoparticle samples.     

La0.3Ca0.7Mn1－xVxO3体系的有序相和再入型自旋玻璃行为研究

通过对La_0.3Ca_0.7Mn_1－xV_xO₃(x=0.05,0.10,0.134,0.20)体系的M-T曲线、ρ-T曲线、ESR谱的测量,研究了Mn位掺V对La_0.3Ca_0.7MnO₃体系电荷序和自旋序的影响.结果表明,当0.05≤x≤0.134时, 体系存在电荷有序(CO)相,其自旋序随温度降低发生顺磁(PM)-电荷有序(CO)-反铁磁(AFM)变化.当x＝0.20时,CO相逐步融化,在40 K发生自旋玻璃转变,表现出再入型的自旋玻璃行为,低温下的基态存在着多种复杂的磁相互作用之间的竞争机理. 关键词： 电荷有序 自旋序 相分离 再入型自旋玻璃行为     

Magnetic structure of the Mn5Si3-type Er5Ge3 compound

The Er₅Ge₃ compound (Mn₅Si₃-type, hP16, P6₃/mcm) at 4 K shows magnetic ordering of the antiferromagnetic type. Its magnetic structure consists of sine modulated collinear magnetic moments of Er that are parallel to the c axis (with a propagation vector k=[0 0 ±0.3]). This corresponds to the magnetic unit cell (a a 10c), the values of the magnetic moment of the Er atoms being, as a general formula, M_z≈M₀ cos [2π(Z–1/4)(1–kZ)], with M₀=9.2(2) μ_B at 4 K.     

Spectroscopic analysis and magnetic susceptibility of CuO-TeO2-V2O5 glasses

This article reports on the structure of the glassy system xCuO-65TeO₂-(35−x)V₂O₅, 5≤x≤10 mol% which was studied using infrared (IR) and Raman spectroscopy methods as well as magnetic susceptibility measurements. IR and Raman spectroscopy analysis reveals the presence of four main absorption bands attributed to [TeO₃], [TeO₄], [VO₄], and [VO₅] structure units. It suggests that Cu²⁺ ions occupy the available open spaces of the Te-O network without straining the bonds too much. Increasing the concentration of Cu²⁺ ions beyond 5 mol% results in the modification of the glass by straining and locally distorting the surrounding of the Te-O network. The magnetic susceptibility of these materials was investigated in the temperature range of 5-200 K revealing the paramagnetic behavior described by the Curie-Weiss law and indicating the presence of weak antiferromagnetic exchange interactions between Cu ions. The magnetic entropy change of the glasses was determined based on the temperature and magnetic field dependence of magnetization.     

Reentrant spin glass behavior in antiferromagnetic single crystalline Ba6Mn24O48 nanoribbons

Single crystalline Ba₆Mn₂₄O₄₈ nanoribbons with diameters ranging from one hundred nanometers to a few hundred nanometers and length up to tens of microns are synthesized via a facile molten salt method. These nanoribbons are characterized by a range of methods including X-ray diffraction (XRD), scanning electron microscopy (SEM), transmission electron microscopy (TEM), energy dispersive X-ray spectroscopy (EDS), selected area electron diffraction (SAED) and high-resolution transmission electron microscopy (HRTEM). The magnetic properties of Ba₆Mn₂₄O₄₈ nanoribbons are investigated by the zero-field-cooled (ZFC), field-cooled (FC) magnetization, and ac susceptibility. Upon cooling, we find the reentrant spin glass (RSG) behavior in these nanoribbons, i.e., paramagnetic (PM), antiferromagnetic (AFM), and spin glass (SG). The RSG behavior might be due to the surface spin disorder, geometrical frustration and Mn³⁺/Mn⁴⁺ mixture in Ba₆Mn₂₄O₄₈ nanoribbons.     

Synthesis, structural and magnetic properties of spin ladder compound Ca1−xCoxCu2O3

MCu₂O₃ (M=Ca and Co) system has two-leg spin ladder structure similar to that of the prototype SrCu₂O₃ system except that the rungs are buckled with an angle of 123° and 105° for CaCu₂O₃ and CoCu₂O₃ compounds, respectively. We have synthesized powder samples of (Ca_1−xCo_x)Cu₂O₃ (x=0.00-1.00) by the solid state reaction method and their structural and magnetic properties have been investigated. All the synthesized compounds crystallize in orthorhombic structure with space group Pmmn. Lattice parameters of (Ca_1−xCo_x)Cu₂O₃ decrease with the increase in Co content. DC magnetic susceptibility χ(T) results of the end products CaCu₂O₃ and CoCu₂O₃ show antiferromagnetic transition (T_N) at 27 and 215 K, respectively. Co doping into (Ca_1−xCo_x)Cu₂O₃ enhances its T_N systematically with increasing Co concentration. The χ(T) of CoCu₂O₃ shows a broad transition with the peak temperature around 215 K and it was found to be field independent up to 90 kOe. The ambiguity concerning the transition was ruled out by recording the temperature dependent X-ray diffraction pattern on CoCu₂O₃ system, which indicated that there is no structural transition in the investigated temperature range of 115-300 K. Further, specific heat measurement on CoCu₂O₃ confirms the magnetic phase transition by the appearance of a sharp peak at 215 K.     

Crystal field analysis of Er in Sc2O3 transparent ceramics

A crystal field investigation of Er³⁺-doped Sc₂O₃ transparent ceramics is presented.The established energy level diagram is analyzed with crystal-field Hamiltonian of C₂ symmetry including J-mixing effect. Very satisfactory correlations were obtained between 53 calculated and experimental Stark energy levels, with an rms of 7.7 cm⁻¹. These results are compared with those reported for other rare earth ions in the same host and with Er³⁺ ions in other sesquioxides. The concordance between the crystal-field strength parameters indicates the consistence of our analysis. Furthermore, based on the extended electrostatic point charge model, a theoretical trend is proposed for rare earth ions in Sc₂O₃ in comparison with Y₂O₃. Based on this trend, very satisfactory results are obtained for Yb³⁺ ion in Sc₂O₃.     

Magnetic properties of the intermetallic compound Ce5Ge4

Magnetic and magnetocaloric properties of the compound Ce₅Ge₄ have been studied. This compound has orthorhombic Sm₅Ge₄-type structure (space group Pnma, no. 62) and orders ferromagnetically at ~12 K (T_C). The paramagnetic Curie temperature is ~−20 K suggesting the presence of competing ferromagnetic and antiferromagnetic interactions in this compound. The magnetization does not seem to saturate even in fields of 90 kOe at 3 K consistent with the presence of competing interactions. Saturation magnetization value (extrapolated to 1/H→0) of only 0.8μ_B/Ce³⁺ is obtained compared to the free ion value of 2.14μ_B/Ce³⁺. This moment reduction in the ordered state of Ce₅Ge₄ could be due to partial antiferromagnetic/paramagnetic ordering of the Ce moments and may also be due to crystalline electric field effects. Magnetic entropy change near T_C, calculated from the magnetization vs. field data, is found to be moderate with a maximum value of ~9 J/kg/K at ~11 K for a field change of 90 kOe.