Crystal electric field effects in Pr0.5Sr0.5CoO3

The energy structure and temperature evolution of the magnetic excitation spectra of Pr_0.5Sr_0.5CoO₃ are studied by inelastic neutron scattering. The measurements are performed on a polycrystalline sample of Pr_0.5Sr_0.5CoO₃ and its non-magnetic analogue La_0.5Sr_0.5CoO₃ on the high intensity time-of-flight spectrometer IN4 (ILL, Grenoble) in the temperature range 10 K < T < 300 K. The crystal electric field parameters in Pr_0.5Sr_0.5CoO₃ are calculated and the splitting scheme of the 4f ground multiplet of Pr³⁺ ions is determined based on the experimental data.     

Charge ordering and structural transitions in Pr0.5Sr0.41Ca0.09MnO3

The structural and magnetic transitions in Pr_0.5Sr_0.41Ca_0.09MnO₃ have been investigated by neutron diffraction and electron microscopy. Two structural transitions, Imma to I4/mcm and I4/mcm to Pmmn, are observed by decreasing the temperature. Two magnetic transitions, from a paramagnetic insulating to a ferromagnetic metallic and from a ferromagnetic metallic to an antiferromagnetic insulating states at T_C=250 K and T_N=180 K, respectively, are also observed. The structures of these three forms have been determined from neutron powder diffraction data. The first important result concerns the low temperature antiferromagnetic CE type and charge ordered structure, which has been refined in the Pmmn space group, without any constraint. This structure is completely long range ordered, with two Mn-sites, Mn³⁺ in tetragonally elongated octahedra, and Mn⁴⁺, off-centered in nearly regular octahedra. The second important point concerns the abrupt character of the structural transition from the I4/mcm to the Pmmn structure, without any appearance of incommensurability. The magnetic and transport properties of this compound are compared with those of Pr_0.5Sr_0.5MnO₃.     

A study of the magnetic and dielectric properties of Y Fe0.5Cr0.5O3

Y Fe_0.5Cr_0.5O₃ ceramics have been synthesized by a conventional solid-state reaction. Powder X-ray diffraction shows that this compound possesses an orthorhombic structure with Pnma space group. It exhibits a high magnetic transition temperature at around 250 K with weak ferromagnetic behavior below this temperature. A dielectric relaxation following the Arrhenius law found in the Y Fe_0.5Cr_0.5O₃ compound can be attributed to the charge carrier hopping conduction.     

Evidence of glassy ferromagnetic phase and kinetic arrest of electronic phase in Sm0.35Pr0.15Sr0.5MnO3 manganites

The effect of doping of rare earth Pr³⁺ ion as a replacement of Sm³⁺ in Sm_0.5Sr_0.5MnO₃ is investigated. Temperature dependent dc and ac magnetic susceptibility, resistivity, magnetoresistance measurements on chemically synthesized (Sm_0.5−xPr_x)Sr_0.5MnO₃ show various unusual features with doping level x=0.15. The frequency independent ferromagnetic to paramagnetic transition at higher temperature (∼191 K) followed by a frequency dependent reentrant magnetic transition at lower temperature (∼31 K) has been observed. The nature of this frequency dependent reentrant magnetic transition is described by a critical slowing down model of spin glasses. From non-linear ac susceptibility measurements it has been confirmed that the finite size ferromagnetic clusters are formed as a consequence of intrinsic phase separation, and undergo spin glass-like freezing below a certain temperature. There is an unusual observation of a 2nd harmonic peak in the non-linear ac susceptibility around this reentrant magnetic transition at low temperature (∼31 K). Arrott plots at 10 and 30 K confirm the existence of glassy ferromagnetism below this low temperature reentrant transition. Electronic- and magneto-transport measurements show a strong magnetic field—temperature history dependence and strong irreversibility with respect to the sweeping of magnetic field. These results are attributed to the effect of phase separation and kinetic arrest of the electronic phase in this phase separated manganite at low temperatures.     

Pressure induced antiferromagnet-ferromagnet transition in La<Subscript>0.5</Subscript>Ba<Subscript>0.5</Subscript>CoO<Subscript>2.8</Subscript> cobaltite

The anion deficient cobaltite La_0.5Ba_0.5CoO_2.8 with theformal cobalt valence state close to 3+ has been studied as function of pressure up to6.5 GPa at different temperatures by neutron powder diffraction. At ambient pressure thecrystal structure of this compound has cubic symmetry (space group Pm3?m) and is found to become antiferromagnetic withT _N close to 250 K. Applied pressure inducesa gradual transition from the antiferromagnetic into a ferromagnetic state through a mixedmagnetic state. The transition is not accompanied by obvious changes in the macroscopiccrystal symmetry. It is suggested that the magnetic ground state strongly depends on theunit cell volume and that the transition is associated with a spin state crossover of thecobalt ions whereas the formal Co³⁺/Co⁴⁺ ratio is less importantthan expected following the double exchange scenario for the appearance offerromagnetism.     

Temperature dependence of coercivity and metamagnetism in Tb0.5Y0.5Ni

The temperature dependences of magnetic properties of the FeB structure compound Tb_0.5Y_0.5Ni are examined with the aim to elucidate the origin of intrinsic magnetic hardness in this compound. The easy a axis coercivity of an aligned powder sample is found to be strongly temperature dependent. A domain wall activation model is employed to obtain the parameters H₀(0)=30kOe, V_V(0)=0.24K^?1, and β=0.016K^?1, where H₀(0) is the coercive force at absolute zero, V_T(0) the domain wall activation parameter, and β the coefficient for the linear temperature dependence of the reduced anisotropy. From polycrystalline data, we find a strong temperature dependence of the c axis metamagnetic transition only for the ferromagnetic (F) to antiferromagnetic (AF) direction. From the relative constancy of the AF to F c axis metamagnetic transition compound to the a axis coercivity we conclude that the coercive force is not directly related to the local molecular fields as had been previously suggested.     

Structure and magnetization studies of Nd0.5−xPrxSr0.5MnO3 system

The structural and magnetic properties of Nd_0.5−xPr_xSr_0.5MnO₃ (x=0, 0.1, 0.2, 0.3, 0.4 and 0.5) system have been investigated. With the substitution of Pr in Nd_0.5Sr_0.5MnO₃, it shows a gradual structure transformation from the Imma orthorhombic symmetry to the tetragonal I4/mcm phase, and the crystallographic transition remains incomplete, even in Pr_0.5Sr_0.5MnO₃. A large bifurcation between zero-field-cooled (ZFC) and field-cooled (FC) susceptibility has been observed below Curie temperature (T_C), which is characteristic of coexistence of ferromagnetism (FM) and antiferromagnetism (AFM) at low temperature region. The magnetization of Pr_0.5Sr_0.5MnO₃ is larger than that of Nd_0.5Sr_0.5MnO₃, while Nd_0.5Sr_0.5MnO₃ with more CE-type AFM shows larger magnetization than Nd_0.3Pr_0.2Sr_0.5MnO_3, which mixed with CE-type (majority) and A-type (minority) AFM at low temperature, indicating that the magnetization of Nd_0.5−xPr_xSr_0.5MnO₃ system is affected by A-site disorder combined with orbital ordering of A-type AFM and CE-type AFM.     

High pressure effect on the crystal and magnetic structure of Pr0.1Sr0.9MnO3 manganite

The crystal and magnetic structure of Pr_0.1Sr_0.9MnO₃ manganite has been studied by the neutron diffraction at high pressures up to 5 GPa in the temperature range 10?C295 K. At normal pressure and decreasing temperature the appearance of the C-type (T _N = 220 K) and G-type (T _N = 180 K) antiferromagnetic states occurs, which is accompanied by a structural phase transition from the cubic structure (Pm $ \bar 3 $ m space group) to the tetragonal structure (I4/mcm space group). It is shown that the temperature of the transition to the C-type antiferromagnetic phase increases with pressure with the pressure coefficient dT _N/dP = 4.0(5) K/GPa and the temperature of the transition to the G-type antiferromagnetic phase weakly depends on pressure.     

Mössbauer study of the transition metal phosphorus trichalcogenide FePS3 and spin glass Mn0.5Fe0.5PS3

The transition metal phosphorus trichalcogenides MnPS₃ and the FePS₃ are CdCl₂ type layered compounds, where the transition metal ions form a hexagonal lattice. While these compounds order anti-ferromagnetically at low temperature, the magnetic structures are different. We have reported that these mixtures Mn_0.5Fe_0.5PS₃ is a spin glass with a glass transition temperature T _g=33.7 K. Then, in this work, we report that the results of the temperature variation of the ⁵⁷Fe Mössbauer spectra of FePS₃ and Mn_0.5Fe_0.5PS₃, in detail. In the anti-ferromagnetic state of FePS₃, the hyperfine magnetic field H _int increases with decreasing temperature and the Isomer shift I. S. increases slightly with decreasing temperature. However in Mn_0.5Fe_0.5PS₃, the two broadened peaks are observed and the two peaks became a single peak with decreasing temperature at about 50.0 K, which is higher than T _g=33.7 K. In the spin glass Mn_0.5Fe_0.5PS₃, the Mössbauer spectra suggest that the magnetic interactions exist far above T _g.     

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     

Effect of Mo doping on magnetic and transport properties of La0.5Sr0.5CoO3

The substitutional effect of Mo on the magnetic and transport properties of double exchange ferromagnets, La_0.5Sr_0.5Co_1−x Mo_xO₃ (0?x?0.2) has been investigated. Substitution of 10% Mo at the Co-site of La_0.5Sr_0.5CoO₃ decreases the Curie temperature by ∼60 K than that of the parent compound and the long-range ferromagnetic ordering disappears for x?0.2. The Mo-doped samples, however, undergo a transition from the parent metallic state to the insulating state below T_c. The insulating state is found to obey Mott's variable range hopping of conduction. The effect of Mo substitution is attributed to the factors namely, (i) the dilution of magnetic Co sublattice, (ii) the reduction of Co⁴⁺/Co³⁺ ratio resulting in a reduced carrier concentration and (iii) disruption of the intermediate spin structure of Co, namely Co³⁺: t_2g⁵e_g¹.     

半掺杂Sm0.5Ca0.5MnO3体系的电荷有序和再入型自旋玻璃行为

研究了半掺杂锰氧化物Sm_0.5Ca_0.5MnO₃体系的结构、输运和磁特性，结果表明，在半掺杂情况下，该体系呈现O′类正交结构，表明体系存在典型的Jahn-Teller效应畸变；输运结果在整个测量温区均呈现半导体导电行为，没有出现金属－绝缘体(M-I)转变和CMR效应；电荷有序转变发生在T=270K左右，反铁磁转变温度出现在200K附近，且表现出典型的再入型自旋玻璃(spin-glass)行为，自旋玻璃转变温度T_SG在4 关键词： 自旋玻璃 电荷有序 负磁化现象 多相竞争     

Successive structural phase transitions in Pr<Subscript>0.5</Subscript>Sr<Subscript>0.5</Subscript>CoO<Subscript>3</Subscript> in the range 10–1120 K

The crystal and magnetic structures of the Pr_0.5Sr_0.5CoO₃ metallic ferromagnet have been studied using neutron diffraction and synchrotron radiation. Successive structural transitions with the reduction of the crystal symmetry from cubic (space group Pm3m) to rhombohedral (\(R\bar 3c\), ～800 K), orthorhombic (Imma, ～300 K) and, then, to triclinic at ～120 K are detected during cooling from 1120 K. The transition from the orthorhombic system to a phase with a lower symmetry is characterized by a sharp change in the anisotropy of the unit cell, which indicates the partial ordering of the e _g orbitals of cobalt. The accompanying change in the interatomic distances and valence angles give rise to an anomaly in the temperature dependence of the magnetic susceptibility at T ≈ 120 K. The ordered magnetic moment μ_Co ≈ 2μ_B corresponds to the assumption of the intermediate spin state of Co³⁺ ions and the mixture of low- and intermediate-spin states of Co⁴⁺ ions.     

相分离Eu0.5Sr0.5MnO3体系中的场诱导磁相变及输运特性研究

研究了半掺杂相分离锰氧化物Eu_0.5Sr_0.5MnO₃样品的结构和电磁输运特性.在半掺杂情况下,该样品呈O′型正交结构,表明样品存在典型的Jahn-Teller畸变;在75 K附近样品的顺磁/反铁磁背景中开始出现铁磁相,在更低的温度42 K,4000 A/m磁场下M-T的场冷曲线和零场冷曲线出现明显分岔,样品的交流磁化率实部随温度的变化曲线中也在42 K观察到尖峰的出现,表现出团簇玻璃行为.在无外加磁场下该样品在 关键词： 多相竞争 半掺杂 铁磁团簇     

Magnetic and transport properties of Pr2Pd3Si5

We have investigated the magnetic and transport properties of a new ternary intermetallic compound Pr₂Pd₃Si₅ which forms in U₂Co₃Si₅-type orthorhombic structure (space group Ibam). At low field (0.01 T) magnetic susceptibility exhibits an abrupt increase below 7 K and peaks at 5 K, revealing a magnetic phase transition. The onset of magnetic order is also confirmed by well defined anomalies in the specific heat and electrical resistivity data. Apart from the sharp λ-type anomaly, magnetic part of specific heat also shows a broad Schottky-type hump due to crystal field effect. Magnetoresistance data as a function of temperature exhibits a pronounced peak in paramagnetic state which could be interpreted in terms of crystal field effect and short-range ferromagnetic correlations.     

Specific features of local structural,valence, and magnetic states of iron ions in the perovskite Bi0.5Ca0.5FeO3

The perovskite Bi_0.5Ca_0.5FeO₃ has been investigated using the Mössbauer effect at temperatures of 295 and 675 K. The measured temperature of the magnetic phase transition (Néel temperature) is T _N = 640 ± 10 K. Above the Néel temperature, there are two nonequivalent structural states of iron ions. In the perovskite Bi_0.5Ca_0.5FeO₃ at room temperature, there are seven most probable nonequivalent magnetic states of iron ions with significantly different values of the hyperfine interaction parameters. Four iron states correspond to Fe³⁺ ions in the octahedral oxygen environment, and three iron states correspond to Fe³⁺ ions in the tetrahedral oxygen environment.     

Neutron diffraction studies of the magnetic properties of Pr0.5Sr0.5Co1 ? x Mn x O3 solid solutions

The crystal structure and magnetic properties of a system of Pr_0.5Sr_0.5Co_{1 ? x} Mn _x O₃ solid solutions were studied by neutron diffraction and magnetization measurements. It is shown that, at a low manganese concentration, the structure can be described by the I/2a monoclinic space group; with increasing substitution level x the structure becomes orthorhombic. For x > 0.9 the crystal structure is tetragonal at high temperatures and the symmetry is lowered to orthorhombic with lowering the temperature. The substitution of cobalt for manganese leads to the destruction of long-range ferromagnetic order near x ?? 0.25. A transition from the high-temperature ferromagnetic phase to the A-type low-temperature antiferromagnetic phase is observed at x ?? 0.93 in the temperature range 110?C160 K.     

Effect of Ca doping on the magnetic properties of Nd0.5Sr0.5MnO3 studied by electron spin resonance

The magnetic properties of Ca-doped Nd_0.5Sr_0.5MnO₃ have been studied by electron spin resonance (ESR) and dc magnetization measurements. The antiferromagnetic order and charge order are found to occur separately at T_N=200 K and T_co=150 K, respectively. Compared to the undoped Nd_0.5Sr_0.5MnO₃, the ferromagnetic correlations are suppressed by doping of the small Ca²⁺ ion. In addition, the antiferromagnetic transition temperature is enhanced to 200 K, which can be explained by an increase of superexchange interaction between Mn³⁺ and Mn⁴⁺ ions as their distance decreases.     

XAFS studies of the local structure and charge state of the Pr impurity in SrTiO3

Solid solutions of (Sr_{1 ? x} Pr _x )TiO₃ have been studied using X-ray methods. It has been shown that, with an increase in the praseodymium concentration, the temperature of the structural phase transition to the phase with space group I4/mcm increases and, at x ?? 0.15, the structure at 300 K is tetragonal. X-ray absorption fine structure (XAFS) spectroscopy studies have revealed that Pr ions are predominantly in the charge state 3+ and occupy the Sr sites. No indications of the off-centering of Pr atoms at the Sr sites have been revealed. The local environment of Pr atoms is characterized by a strong relaxation of the oxygen atoms, the value of which corresponds to the difference between the ionic radii of Pr³⁺ and Sr²⁺. It has been found that, in the second shell, there occurs a significant repulsion of the Pr³⁺ and Ti⁴⁺ ions, which is responsible for the weak dependence of the lattice parameter in the solid solution on the praseodymium concentration.     

Effect of trivalent rare earth doping on magnetic and magnetocaloric properties of Pr<Subscript>0.5</Subscript>(Ce,Eu,Y)<Subscript>0.1</Subscript>Sr<Subscript>0.4</Subscript>MnO<Subscript>3</Subscript> manganites

Experimental studies of the structural, magnetic and magnetocaloric properties of the three compounds Pr_0.5X_0.1Sr_0.4MnO₃ (X = Ce, Eu and Y) are reported. Our samples were synthesized using the Pechini sol–gel method. X-ray powder diffraction at room temperature indicates that our materials crystallize in the orthorhombic structure with Pbnm space group. The compounds undergo a second-order magnetic transition from paramagnetic to ferromagnetic state around their own Curie temperatures T _C ~ 310, 270 and 230 K for X = Ce, Eu and Y, respectively. A considerable magnetocaloric effect (MCE) is observed around room temperature. The maximum values of magnetic entropy change ?S _max are 3.54, 3.81 and 2.99 J/kgK for the samples with X = Ce, Eu and Y, respectively, when a magnetic field of 5 T was applied. The relative cooling power (RCP) values for the corresponding materials are 246.60, 261.66 and 298 J/kg. It is shown that for Pr_0.5X_0.1Sr_0.4MnO₃ the exponent n and the magnetic entropy change follow a master curve behavior. With the universal scaling curve, the experimental ?S at several temperatures and fields can be extrapolated.