A magnetic study of the CeScSi-type RZrSb compounds (R=Gd–Tm). Large coercive field at low temperature in TbZrSb and DyZrSb

X-ray single crystal refinement performed on the GdZrSb and HoZrSb compounds confirms the CeScSi-type structure for the RZrSb series. Spontaneous magnetization is detected for all the studied compounds (5 K (TmZrSb)<T_C<61 K (TbZrSb)). Both TbZrSb and DyZrSb compounds exhibit a second magnetic transition at low temperature (29 and 21 K, respectively). Large coercive field is measured for these last compounds below the second magnetic transition temperature.     

Magnetotransport properties of ferromagnetic LaMnO3+δ nano-sized crystals

Transport and magnetic properties of LaMnO_3+δ nanoparticles with average size of 18 nm have been investigated. The ensemble of nanoparticles exhibits a paramagnetic to ferromagnetic (FM) transition at T_C～246 K, while the spontaneous magnetization disappears at T≈270 K. It was found that the blocking temperature lies slightly below T_C. The temperature dependence of the resistivity shows a metal–insulator transition at T≈192 K and low-temperature upturn at T<50 K. The transport at low temperatures is controlled by the charging energy and spin-dependent tunnelling through grain boundaries. The low temperature I–V characteristics are well described by indirect tunnelling model while at higher temperatures both direct and resonant tunnelling dominates.     

Magnetic properties of RPdIn (R=Gd–Er) compounds

AC susceptibility and DC magnetization measurements were performed for the RPdIn (R=Gd–Er) compounds both in the paramagnetic and in the ordered state. In opposite to GdPdIn, which is a ferromagnet (T_c=102 K), the other samples show a complex ferrimagnetic behavior with the additional transition at T_t<T_c. In the high-temperature phase (for T_t<T<T_c), a ferromagnetic interaction dominates, while in the low-temperature phase (for T⩽T_t) antiferromagnetic interactions with the magnetocrystalline anisotropy, especially strong for TbPdIn, come into play. The ordering temperatures are T_c=70, 34, 25 and 12.3 K for Tb-, Dy-, Ho- and ErPdIn respectively, while transition temperatures are T_t=6, 14 and 6 K for Tb-, Dy- and HoPdIn respectively. TbPdIn reveals an additional transition at 27 K connected with the intermediate ferrimagnetic phase. The critical fields for the magnetization process of the low-temperature phase are high (52 and 150 kOe for TbPdIn and 32 kOe for DyPdIn at T=4.2 K) yet these values decrease remarkably with increasing temperature. Results of the study are compared with magnetic and neutron diffraction data hitherto available. We state that irreversibility of the zero-field cooled–field cooled magnetization is not connected with the spin-glass phase claimed elsewhere.     

Magnetic frustration in the antiferromagnetic Kondo lattice YbPtAl: Anomalous magnetic behavior at high pressures

We have investigated the magnetic and electronic properties of the antiferromagnetic Kondo lattice YbPtAl using the ¹⁷⁰Yb Mössbauer effect at ambient pressure (1.8<T<10 K), electrical resistance (1.8<T<300 K) and X-ray diffraction (T=300 K) techniques at high pressures up to 26 GPa. We find a complex magnetic state in YbPtAl at ambient pressure and an unusual volume-induced change of T_N. It is suggested, that the anomalous volume dependence of T_N is due to the interplay between frustrated anisotropic exchange interactions and magnetocrystalline anisotropy. The magnetic frustration originates from the topology of the crystal lattice.     

Effect of Cr substitution on the superconducting and magnetic properties of RuSr2Eu1.5Ce0.5Cu2O10−δ

In this paper we investigate the properties of polycrystalline series of Ru_1?xCr_xSr₂Eu_1.5Ce_0.5Cu₂O_10?δ (0.0 ? x ? 0.40) by resistivity, XRD and dc magnetization measurements. EuRu-1222 is a reported magneto superconductor with Ru spins magnetic ordering at temperatures near 100 K and superconductivity occurs in Cu–O₂ planes below T_c ? 40 K. The exact nature of Ru spins magnetic ordering is still being debated and no conclusion has been reached yet. In this work, we found the superconducting transition temperature T_c = 20 K from resistivity and dc magnetization measurements for pristine sample. DC magnetization measurements exhibited ferromagnetic like transition for all samples.     

Influence on magnetic properties of substitution of Co for Fe in TbFe11.3Nb0.7

The magnetic properties of Tb(Fe_1−xCo_x)_11.3Nb_0.7 compounds with x=0, 0.05, 0.1, 0.15, 0.2 and 0.3 have been investigated. All compounds studied crystallize in the ThMn₁₂-type of structure. Substitution of Co for Fe leads to a contraction of the unit-cell volume. The Curie temperature clearly increases with increasing Co content from 551 K for x=0 to 831 K for x=0.3. The magnetic moment of the transition-metal sublattice increases with increasing Co content from 22.2 μ_B/f.u. for x=0 to 23.1 μ_B/f.u. for x=0.3. As the temperature increases, a spin reorientation from easy-plane to easy-cone is found in all compounds investigated. The spin-reorientation temperatures T_sr have been derived from the temperature dependence of the magnetization in a low field and decrease monotonously with increasing Co content. The easy magnetization direction at room temperature has been determined by X-ray diffraction on magnetically-aligned powder samples. The influence of the substitution of Co for Fe on the magnetic anisotropy is discussed in terms of crystal-field theory.     

Magnetic properties of ball-milled Mn nanoparticles

Nanoparticles of Mn of sizes  < 500 Å were prepared by the ball-milling technique. The temperature dependence of the magnetic susceptibility χ showed systematic variation with particle size. Peaks observed in χ were attributed to the magnetic ordering of the oxides Mn₃O₄and MnO. Peaks found in ∂(χT) / ∂T were associated with the Neel temperature ofα -Mn. We estimated that our samples contain about 0.4% of Mn₃O₄. This low concentration of Mn₃O₄was not detected by X-ray diffraction experiments but contributed significantly to the magnetization measurements.     

Intrinsic pinning properties of FeSe0.5Te0.5

The intrinsic pinning properties of FeSe_0.5Te_0.5, which is a superconductor with a critical temperature T_c of approximately 14 K, were studied through the analysis of magnetization curves obtained using an extended critical state model. For the magnetization measurements carried out with a superconducting quantum interference device (SQUID), external magnetic fields were applied parallel and perpendicular to the c-axis of the sample. The critical current density J_c under the perpendicular magnetic field of 1 T was estimated using the Kimishima model to be equal to approximately 1.6 × 10⁴, 8.8 × 10³, 4.1 × 10³, and 1.5 × 10³ A/cm² at 5, 7, 9, and 11 K, respectively. Furthermore, the temperature dependence of J_c was fitted to the exponential law of J_c(0) × exp(?αT/T_c) up to 9 K and the power law of J_c(0) × (1 ? T/T_c)ⁿ near T_c.     

Magnetization anisotropy of the Tm- and Fe-subsystems in Tm2Fe17

Magnetic and neutron diffraction measurements were carried out in order to study the spontaneous and induced spin-reorientation (SR) transition of the “easy axis–easy plane” type in the poly and single-crystalline samples of the hexagonal Tm₂Fe₁₇. We have determined the temperature dependence of the lattice parameters and the angle between the c-axis and the magnetic moment of the Tm-subsystem. We also find that the SR transition is accompanied by a large (about 20%) magnetization change of the Tm subsystem. In order to induce such a SR transition with the external magnetic field, μ₀H_cr=5 T is necessary to be applied along the hard-magnetization direction (the a-axis) at 4.2 K. The H_cr value decreases with an increasing temperature. The magnetization measurements demonstrate that at 10 K the saturation magnetization along the easy-magnetization direction (the c-axis) is smaller than that along the hard-magnetization direction. Based on this observation, we believe that Fe-subsystem of Tm₂Fe₁₇ is likely to have magnetization anisotropy.     

The magnetization processes,spin reorientation transitions and magnetic domain structure in DyFe10CoTi single crystal

The tetragonal ThMn₁₂-type, single crystalline DyFe₁₀CoTi sample has been investigated by torque and magnetization measurements and observation of domain structure at various temperatures between 10–300 K and in magnetic field from B=0 to 0.15 T. These examinations showed that the magnetic structure of DyFe₁₀CoTi changes from “easy axis” (c-axis) type to conical at 225 K and to “easy plane” (ab plane) type at 100 K.     

Temperature dependence of the lattice parameters and magnetic properties of Er3Ir single crystals

Er₃Ir single crystals were grown by the Czochralski method from a levitated melt. The electrical resistivity thermal dependence exhibits ordering temperature of the erbium sublattice at 40 K and a spin reorientation process at 22 K. The DC and AC magnetic susceptibility show antiferromagnetic ordering in the form of an asymmetric peak. The magnetization in strong magnetic fields up to 140 kOe exhibits anisotropy. The lattice parameters’ thermal dependence of Er₃Ir and Er₃Ni show anisotropy and anomalous behaviour.     

Synthesis,characterization and magnetic properties of lightly doped La2−xSrxCuO4 (x = 0.04) nanoparticles

Lightly doped La_2−xSr_xCuO₄ (x = 0.04) nanoparticles with different particle sizes have been successfully prepared by a sol–gel method and characterized by X-ray diffraction (XRD), scanning electron microscopy (SEM), infrared transmission (IR) spectra and superconducting quantum interference device (SQUID) magnetometer. All samples are single phase and have an orthorhombic unit cell. As the particle size reduces, it is found that the IR band at around 685 cm⁻¹ corresponding to the in-plane Cu–O asymmetrical stretching mode shifts to higher frequency and the magnetization exhibits a large enhancement at low temperature. The magnetic susceptibility of all samples follows a modulated Curie law between ∼20 K and ∼100 K and the Curie constant displays a strong dependence on the particle size. It is suggested that as the particle size decreases surface effects should play an important role in the magnetic properties of the nanoparticles.     

Magnetic anisotropy and magnetostriction of Lu2Fe17 single crystal

The magnetic properties of Lu₂Fe₁₇ single crystal have been studied by means of magnetization, susceptibility and magnetostriction measurements. The unusual magnetic behavior with two magnetic phase transitions has been observed in magnetic fields up to 50 Oe. The magnetostriction of the Lu₂Fe₁₇ compound has the maximum at temperature T≈285 K at which the paraprocess makes the main contribution to the magnetization.     

Superparamagnetic properties of C60Co3 complexes

Preparation of fullerites containing cobalt and analyses of reactions based on semiempirical quantum calculations are described. The magnetic properties of thermally treated C₆₀Co₃ samples: Curie constant (C≈3500 emu K/mol Oe) temperature and field dependencies of magnetization and nonequilibrium effects of magnetization are interpreted in terms of superparamagnetic blocking model of the compound.     

Electrochemical and magnetic properties of Li4 / 3Mn2 / 3O2–LiCoO2 solid solution

The compounds Li_(4−x)/3Mn_2(1−x)/3Co_xO₂ (0 < x < 0.5) were prepared by the sol–gel technique. X-ray diffraction patterns of these compounds were identified as α-NaFeO₂ type layered structure, though some super-structure lines, related to the ordered array of Li and transition metal ions in the transition metal layer, were observed. The magnetic susceptibility exhibited an antiferromagnetic transition around 40 K for x < 0.2, however the specimens with x > 0.3 had no magnetic transition. The magnetic percolation may explain these magnetic variations. The electrochemical performances were evaluated for the compound of x = 0.5, and it was seen that the electrochemical properties were sensitive to the potential window. Additionally, it was also found that the discharge capacity strongly depended on the preparation temperature; it took a maximum value at the preparation temperature of 900 °C. The discharge capacity is sensitive not only to the cation mixing degree but also to the particle size.     

Magnetic properties and Verwey transition of quasi-one-dimensional magnetite nanowire arrays assembled in alumina templates

Magnetite (Fe₃O₄) has been successfully assembled into anodic alumina templates by an electrochemical method followed by a heat-treating process. Here, we report on the magnetic properties of these so formed nanowires and the Verwey transition measured by vibrating sample magnetometer and SQUID. A Mössbauer spectrum was collected to verify the magnetic orientation of the wires, and a tilt of the moment of 45° with respect to the wire axis was found. These wires show perpendicular magnetic anisotropy mainly due to the average easy axis of the grains pointing along the wire axis. The temperature dependence of the coercity, remanence, and the magnetization undergo a major change at 50 K, induced by the Verwey transition, which occurs at a temperature much lower than for bulk materials (120 K). The behavior of the magnetization in the vicinity of 50 K as well as its field-dependent properties was interpreted using the magneto-electronic model.     

Giant magnetic refrigerant capacity in Ho3Al2 compound

Magnetic properties and magnetocaloric effects (MCEs) of the intermetallic Ho₃Al₂ compound are investigated by magnetization and heat capacity measurements. Two successive magnetic transitions, a spin-reorientation (SR) transition at T_SR=31 K followed by a ferromagnetic (FM) to paramagnetic (PM) transition at T_C=40 K, are observed. Both magnetic transitions contribute to the MCE and result in a large magnetic entropy change (ΔS_M) in a wide temperature range. The maximum values of ?ΔS_M and adiabatic temperature change (ΔT_ad) reach 18.7 J/kg K and 4.8 K for the field changes of 0–5 T, respectively. In particular, a giant value of refrigerant capacity (RC) is estimated to be 704 J/kg for a field change of 5 T, which is much higher than those of many potential refrigerant materials with similar transition temperatures.     

57Fe Mössbauer spectroscopy and magnetization study of YFexAl12−x (4.4⩽x⩽5)

YFe_xAl_12−x in the composition range 4.4⩽x⩽5 was prepared by induction melting followed by annealing in vacuum at 1270 K. Magnetization data below 150 K show complex magnetic behaviour dependent on applied field, composition and temperature. The transition temperature T_c, corresponding to the main maximum of the magnetization vs. temperature curves and below which magnetic interactions are observed for a significant fraction of the Fe atoms in the Mössbauer spectra, decreases from 180 K for x=4 down to 100 K for 4.2⩽x⩽4.7 and rises again up to 160 K for x=5. The analysis of the spectra obtained at 5 K is consistent with full occupation of the 8f sites by Fe atoms and sharing of the 8j sites by Fe and Al as deduced from the Rietveld analysis of X-ray powder diffraction data. The Mössbauer spectra further show a dependence of magnetic hyperfine fields and isomer shifts on the crystallographic site and on the number of the Fe nearest neighbours similar to that observed in UFe_xAl_12−x (4⩽x⩽6) and RFe_xAl_12−x (R=Y, Lu, x=4, 4.2). The magnetic properties of the UFe_xAl_12−x and YFe_xAl_12−x series are compared and the magnetic interactions between the different Fe sublattices are discussed.     

Pressure effect on magnetic properties of RCo12B6 (R=Y,Ce) compounds

The effect of pressure on magnetic properties of YCo₁₂B₆ and CeCo₁₂B₆ was studied in temperature range 5–300 K at pressures up to 9 kbar. The Curie temperature T_C and spontaneous magnetization M_S decrease with pressure for both compounds. The decrease can be attributed mostly to the volume dependence of both, the Co magnetic moment and the exchange interactions. The hybridization of the p–d states as a consequence of small distances between the Co and B atoms can be one reason of the relatively low pressure effects (ΔT_C/Δp=?0.39±0.02 K/kbar, d ln M_S/dp=?0.0013±0.0002 kbar^?1) in YCo₁₂B₆. Higher volume sensitivity of magnetic properties of CeCo₁₂B₆ in comparison with YCo₁₂B₆ can be attributed to the pressure induced changes of the Ce f- and Co d-states.     

Magnetic ordering and the Kondo effect in the alloys,Ce2Co1−xPdxSi3

The compound Ce₂CoSi₃, crystallizing in a AlB₂-derived hexagonal structure, has been recently identified as a Kondo lattice with a non-magnetic ground state. Here, we report the influence of gradual replacement of Co by Pd on the magnetic behaviour in the pseudo-ternary solid solution, Ce₂Co_1−xPd_xSi_3, by magnetization (2–300 K), electrical resistivity (2–300 K) and heat-capacity (0.7–30 K) measurements to bring out a transformation from non-magnetic to magnetic ordering. Distinct features attributable to the existence of a competition between the Kondo effect and magnetic ordering with varying x and temperature are observed in the electrical resistivity data. The results reveal that small substitutions of Pd (x=0.2–0.3) are sufficient to induce magnetic ordering of the Ce ions at low temperatures. The strength of the Kondo interaction as indicated by the paramagnetic Curie temperature decreases monotonically with increasing Pd content. A notable finding is that there are qualitative changes in the isothermal magnetization data in the magnetically ordered state, as if there are modifications in the magnetic structure with changes in the Co/Pd composition. The importance of electronic structure relative to unit-cell volume in deciding magnetic characteristics of this class of compounds is brought out taking into account the trends in the magnetic behaviour of isostructural Ce compounds.