Magnetic properties of the Nd0.95Dy0.05Fe3(BO3)4 ferroborate with small substitution in the rare-earth element subsystem

The magnetic properties of a substituted Nd_0.95Dy_0.05Fe₃(BO₃)₄ ferroborate single crystal with competing Nd-Fe and Dy-Fe exchange interactions are studied experimentally and theoretically. A spontaneous spin-reorientation transition is detected near T = 4.3 K, and anomalies are observed in the low-temperature magnetization curves along trigonal axis c and in basal plane ab. The measured properties and the detected effects are interpreted in terms of a general theoretical approach, which is based on the molecular field approximation and crystal field calculations for a rare-earth ion. The experimental temperature dependences of the initial magnetic susceptibility in the range 2–300 K, the anomalies in the magnetization curves for B ‖ c and B ⊥ c in fields up to 1.5 T, and the field and temperature dependences of magnetization in fields up to 9 T are described. The effect of small substitution in the rare-earth subsystem on the magnetic properties is analyzed. The crystal field parameters and the parameters of the R-Fe and Fe-Fe exchange interactions are determined from the experimental data.     

Anisotropy of magnetic properties of a twin-free EuBaCo2O5.5 single crystal

The magnetic characteristics of a twin-free EuBaCo₂O_5.5 single crystal were studied. It is shown that Co ions exhibit an Ising-type behavior with an easy axis directed along the a axis in the temperature range from 2 K to T _c (250 K). As the temperature decreases from 300 K, a number of magnetic phase transitions occur under magnetic fields H ∥ a. In the range where antiferromagnetic ordering of Co³⁺ ions exists, metamagnetic transitions were observed to occur in fields whose values were dependent on temperature. The strengths of competing interactions in the crystal are estimated.     

Study and characterization by magnetophonon resonance of the energy structuring in GaAs/AlAs quantum-wire superlattices

We present the characterization of the band structure of GaAs/AlAs quantum-wire 1D superlattices performed by magnetophonon resonance with pulsed magnetic fields up to 35 T. The samples, generated by the ‘atomic saw method’ from original quantum-well 2D superlattices, underwent substantial modifications of their energy bands built up on the X-states of the bulk. We have calculated the band structure by a finite element method and we have studied the various miniband structures built up of the massesm_tandm_lof GaAs and AlAs at the point X. From an experimental point of view, the main result is that in the 2D case we observe only resonances when the magnetic fieldBis applied along the growth axis whereas in the 1D case we obtain resonances in all magnetic field configurations. The analysis of the maxima (or minima forB//E) in the resistivity ρ_xyas a function ofBallows us to account, qualitatively and semi-quantitatively, for the band structure theoretically expected.     

Magnetic phase diagram of MnBr24H2O

The magnetic phase diagram of the monoclinic antiferromagnet MnBr₂4H₂O (obtained from differential magnetization measurements) is presented for temperatures down to T = 0.3 K, and for applied magnetic fields parallel to the crystallographic axes a', b and c. For H∥c an unusual behaviour is observed below T ≈ 0.55 K where the antiferro-paramagnetic boundary apparently splits into three others. It is shown that our critical fields extrapolated to T = 0 are consistent with a recent theory proposed by Becerra and Ferreira.     

Magnetic structure of low-dimensional LiCu2O2 multiferroic according to 63,65Cu and 7Li NMR studies

The complex NMR study of the magnetic structure of LiCu₂O₂ multiferroic has been performed. It has been shown that the spin spirals in LiCu₂O₂ are beyond the ab, bc, and ac crystallographic planes. The external magnetic field applied along the c axis of the crystal does not change the spatial orientation of spirals in Cu²⁺ chains. A magnetic field of H ₀ = 94 kOe applied along the a and b axes rotates the planes of spin spirals in chains, tending to orient the normal n of spirals along the external magnetic field. The rotation angle of the planes of the magnetic moments are maximal at H ₀ ?? b.     

Magnetization anisotropy in the AFM and SDW phases of CeB6

The angular dependences of the magnetization and Hall resistance have been investigated by the method of the sample rotation in the magnetic field in the high-quality single-crystal samples in the paramagnetic and magnetically ordered phases of CeB₆ in the magnetic field up to 60 kOe. It has been shown that, as CeB₆ undergoes the transition from the antiferromagnetic modulated phase to the so-called antiferroquadrupolar phase, the easy-magnetization axis in the [110] plane changes from 〈100〉 to 〈110〉. The magnetic field dependences of the anisotropic component of the magnetization differ radically in these magnetically ordered phases. The analysis provides evidence in favor of the formation of a state with the spin density wave (SDW phase) in the temperature range T _N ≈ 2.3 K < T < T _Q ≈ 3.3 K in CeB₆.     

Ultrasonic attenuation determination of Hc1 and Hc2 for ErRh4B4 at 1.5 K

The attenuation coefficient of longitudinal sound waves propagating in ErRh₄B₄ has been measured as a function of applied magnetic field where the propagation direction (q) of the sound waves was oriented either parallel or perpendicular to H_applied. For both orientations there is evidence of a type II-1 superconducting transition at H_c1 for T ≈ 1.5 K. In addition, when q ⊥ H an increase in attenuation is evident at H_c2, which does not appear when q 6 H, consistent with theories developed by Tachiki et al. utilizing supercurrent screening of the internal magnetic fields.     

Magnetic-field and temperature effects on the optical properties of dicyano-2,2′-bipyridyl-platinum(II) single crystals

Studies of the polarized emission of [Pt(CN)₂(bipy)] single crystals as function of temperature (1.9 K ⩽ T ⩽ 295 K) and homogeneous magnetic fields (0 ⩽ H ⩽ 6 T), and the temperature dependence of the polarized absorption spectrum are reported. Raising the temperature from 1.9 to 7 K or increasing the magnetic field from 0 to 1 T results in a blue shift of ≈175 cm^-1 in the E ⊥ a polarized emission (E: electric field vector, a: crystallographic a axis). Between 1.9 and 295 K at H = 0) and between 0 and 6 T (at T = 1.9 K), the emission lifetime decreases by factors of ≈10³ and ≈10², respectively. The results are explained within the C'_2v symmetry of the single complex assuming a coupling between neighboring central ions.     

Magnetic phase transitions and phase diagrams of DyMn2Ge2

The experimental studies of magnetic phase transitions in the layered tetragonal intermetallic compound DyMn₂Ge₂ are continued. The existence of spontaneous phase transitions is confirmed by the results of measurements of the temperature dependences of lattice parameters and the initial magnetic susceptibility. The measurements in strong (up to 50 T) and ultrastrong (up to 150 T) fields revealed two new field-induced magnetic transitions. The inclusion of the exchange interaction between next-to-nearest layers of manganese and the crystal field effects for the rare-earth subsystem along with the antiferromagnetic exchange interaction of nearest Mn layers has made it possible to describe the magnetic properties of DyMn₂Ge₂ in a wide range of magnetic fields. The parameters of these interactions are determined from a comparison of the experimental and theoretical magnetization curves and H-T phase diagrams.     

Neutron diffraction study of multipole order in light rare-earth hexaborides

Multipole interactions are known to play a central role in the unconventional properties of light rare-earth hexaborides and especially of CeB₆. Substituting Pr at the Ce sites has the effect of enhancing exchange interactions and changing the symmetry of the local 4f charge distribution, while suppressing the octupole moment. The (T, H) magnetic phase diagrams of the Ce _x Pr_{1 − x} B₆ compounds display a large variety of ordered phases involving magnetic and/or charge degrees of freedom. Here we focus on the compound Ce_0.7Pr_0.3B₆, which is located slightly beyond the Pr concentration where the antiferroquadrupolar phase of pure CeB₆ is suppressed in zero field. The different magnetic structures have been characterized by neutron diffraction and their origin is discussed in connection with recent non-resonant X-ray results by Tanaka et al.      

Nuclear magnetic resonance in noncollinear antiferromagnet Mn3Al2Ge3O12

The ⁵⁵Mn nuclear magnetic resonance spectrum of noncollinear 12-sublattice antiferromagnet Mn₃Al₂Ge₃O₁₂ has been studied in the frequency range of 200–640 MHz in the external magnetic field H ‖ [001] at T = 1.2 K. Three absorption lines have been observed in fields less than the field of the reorientation transition H _c at the polarization h ‖ H of the rf field. Two lines have been observed at H > H _c and h ⊥ H. The spectral parameters indicate that the magnetic structure of manganese garnet differs slightly from the exchange triangular 120-degree structure. The anisotropy of the spin reduction and (or) weak antiferromagnetism that are allowed by the crystal symmetry lead to the difference of ≈3% in the magnetization of sublattices in the field H < H _c. When the spin plane rotates from the orientation perpendicular to the C ₃ axis to the orientation perpendicular to the C ₄ axis, all magnetic moments of the electronic subsystem decrease by ≈2% from the average value in the zero field.     

Magnetic Properties of Sm0.7Ho0.3Fe3(BO3)4

The magnetic properties of a ferroborate single crystal of substituted composition Sm_0.7H_0.3Fe₃(BO₃)₄ with competing Sm-Fe and Ho-Fe exchange interactions are studied. The measured properties and effects are interpreted in terms of a general theoretical approach based on the molecular field approximation and calculations using the crystal field model for a rare-earth ion. The experimental temperature dependences of the initial magnetic susceptibility in the temperature range 2?C300 K, the anomalies in the magnetization curves for B ?? c and B ?? c in fields lower than 1.2 T, and the field and temperature dependences of magnetization in fields lower than 9 T are described. The crystal field parameters and the parameters of the R-Fe and Fe-Fe exchange interactions are determined during the interpretation of the experimental data.     

High pressure-high field Mössbauer spectroscopy on pure and magnetically diluted europium-monochalcogenides

By simultaneously applying pressures up to 19.6 kbar and magnetic fields up to 13 T, the magnetic hyperfine (hf) fields of the Eu-monochalcogenides Eu X (X = S, Se, Te) and of the magnetic dilution system Eu_xSr_1-xS were studied using the ¹⁵¹Eu Mössbauer effect. Expected relations between the magnetic exchange interactions and the transferred hyperfine (thf) fields have been confirmed. The pressure dependence of the total hf field in the ferromagnetically saturated state of EuS, EuSe and EuTe has been shown to be due mainly to the pressure response of the thf field of the nearest Eu-neighbours. Except with EuO the thf fields of the next nearest Eu-neighbours and the Eu-core polarization field are nearly insensitive to pressure. The results are discussed in terms of the exchange model proposed by T. Kasuya.     

Galvanomagnetic properties of atomically disordered Sr<Subscript>2</Subscript>RuO<Subscript>4</Subscript> single crystals

The effect of neutron-bombardment-induced atomic disorder on the galvanomagnetic properties of Sr₂RuO₄ single crystals has been experimentally studied in a broad range of temperatures (1.7–380 K) and magnetic fields (up to 13.6 T). The disorder leads to the appearance of negative temperature coefficients for both the in-plane electric resistivity (ρ_a) and that along the c axis (ρ_c), as well as the negative magnetoresistance Δρ, which is strongly anisotropic to the magnetic field orientation (H ∥ a and H ∥ c), with the easy magnetization direction along the c axis and a weak dependence on the probing current direction in the low-temperature region. The experimental ρ_a(T) and ρ_c(T) curves obtained for the initial and radiation-disordered samples can be described within the framework of a theoretical model with two conductivity channels. The first channel corresponds to the charge carriers with increased effective masses (～10m _e , where m _e is the electron mass) and predominantly electron-electron scattering, which leads to the quadratic temperature dependences of ρ_a and ρ_c. The second channel corresponds to the charge carriers with lower effective masses exhibiting magnetic scattering at low temperatures, which leads to the temperature dependence of the ρ_{a, c}(T) ∝ 1/T type.     

Electron and nuclear magnetic resonances associated with magnetoelectric and antiferroelectric interactions in the exchange-noncollinear (“square”) chiral antiferromagnet Nd<Subscript>2</Subscript>CuO<Subscript>4</Subscript> and their behavior in chiral phase transitions

Experiments with the tetragonal antiferromagnet Nd₂CuO₄ in the temperature range 1.5 K < T < T _N = 245 K show that the magnetic moments of Cu²⁺ possess an exchange-noncollinear magnetic structure of the “square” type, which has the form of an exchange doublet whose components exhibit different chiralities (Γ₄ and Γ₅ phases). Between these phases, consecutive phase transitions Γ₄ ? Γ₅ ? Γ₄ with a change in chirality take place at temperatures T₁ = 30 K and T₂ = 70 K. The electron and nuclear magnetic resonances (natural frequencies and susceptibilities) associated with excitation of magnons (due to the magnetoelectric and antiferroelectric interactions) by an ac electric field E(t), as well as a variable magnetic field H(t) applied in the case of a constant electric field E⁰, are calculated. It is predicted that nuclear magnetic resonance is excited by an ac electric field at frequencies determined by hyperfine fields of the sublattices. The change in the resonance frequencies upon the above chiral phase transitions are analyzed (being first-order phase transitions, these transitions possess a number of features associated with the chirality of the magnetic structures).     

Anomalous magnetocaloric effect in van vleck paramagnet HoVO<Subscript>4</Subscript> near energy level crossing

The anomalous magnetocaloric effect in singlet rare-earth paramagnets near energy level crossing has been experimentally observed for the first time. The magnetization and differential magnetic susceptibility of Ho_{1 ? x} Y _x VO₄ crystals (x = 0, 0.5) measured along the tetragonal axis in a pulsed magnetic field with various change rates near the crossover field, dH/dt, from 3 × 10³ to 2.5 × 10² T/s are compared to the data in static magnetic fields down to 0.1 K. These data indicate the large negative magnetocaloric effect in the pulsed magnetic field, so that the crystal with the initial temperature T ₀ = 4.2 K is cooled much lower than 1 K. The experimental data are qualitatively described in the crystal field model with various interactions including hyperfine interactions and with the known interaction parameters.     

The influence of strong magnetic fields on position production in heavy-ion collisions

The strongest magnetic fields (|B|_max≈10¹⁵G) being accessible to experimental investigations are created transiently in collisions of very heavy ions. The possible interplay of these collisional magnetic fields with detected peak structures in spectra of emitted electron-position pairs is elucidated. As basis for a dynamical treatment we computed the adiabatic phase correlation diagram which exhibits no structures to cause the striking peaks. Relativistic two-centre continuum states for non-axial symmetric vector potentials are determined.     

Electronic structure and magnetic coupling properties of EuFe2P2: First-principles calculations

We have investigated the electronic structure and magnetic properties of EuFe₂P₂ using first-principles density functional theory within the generalized gradient approximation (GGA)+U schemes. Our calculated ground state magnetic configurations of EuFe₂P₂ is ferromagnetic which Eu²⁺ spins order along c axis. We argue that this kind of magnetic structure of Eu is determined by the indirect RKKY interactions between Eu and direct coupling interaction between Eu 4f with Fe 3d state by our spin-polarized density of states calculations. From the charge density and the Laplace charge density of EuFe₂P₂, we believe that the magnetic moment of Fe is determined by not only Fe-P coupling interactions but also Fe-Fe directly exchange interactions.     

Magnetic characteristics of PrCd single crystal

Magnetic measurements have been made along the [100], [110] and [111]-axes of PrCd single crystal in magnetic fields up to 70 kOe in the temperature range from 4.2 to 300 K. PrCd shows metamagnetism below T_t = 25 K in which two critical fields are observed in the magnetization processes along the [110] and [111]-axes and a critical field along the [100]-axis. The metamagnetic behaviour is interpreted by a noncollinear antiferromagnetic model with the Pr moments of ～ 2μ_B directed to the 〈111〉-axes.