M. Mihalik

An ac susceptibility study of spin dynamics in a super spin glass nanoparticle La0.7Ca0.3MnO3 system: simultaneous relaxation processes

In this paper, we present the results of a systematic study of nonequilibrium dynamics in a strongly interacting super spin glass (SSG) nanoparticle La0.7Ca0.3MnO3 system by alternating current (ac) susceptibility measurements. Cole?Cole analysis of the obtained data revealed the simultaneous existence of two separated relaxation processes, which can be assigned to the relaxation of different magnetic entities. Along with the expected relaxation of the collective SSG phase, the existence of individual, nonagglomerated particles, which do not take part in the collective phase and relax independently, was proposed. A full dynamical scaling analysis was performed in order to elucidate the nature of the transition to a low-temperature SSG state in the interacting La0.7Ca0.3MnO3 nanoparticle sample.

On the ferroelectric and magnetoelectric mechanisms in low Fe3+ doped TbMnO3

Abstract This work addresses the effect of substituting Mn 3+ by Fe 3+ at the octahedral site of TbMnO 3 on the magnetic phase sequence, ferroelectric and magnetoelectric properties, keeping the Fe 3+ concentration below 5%. The temperature dependence of the specific heat, dielectric permittivity and electric polarization was studied as a function of Fe 3+ concentration and applied magnetic field. From the experimental results a strong decrease of the electric polarization with increasing Fe 3+ substitution is observed, vanishing above a concentration of 4%. However, within this range, a significant increase of the magnetic sensitivity of the electric polarization is obtained by increasing Fe 3+ concentration. For Fe 3+ concentration above 4%, a non-polar phase emerges, whose spin structure prevents ferroelectricity according to the Dzyaloshinskii-Moriya model. The experimental results here reported reveal the crucial effect of B-site substitution on the magnetic phase sequence, as well as, on the polar and magnetoelectric properties, evidencing the important role played by the e g electrons on the stabilization of the magnetic structures that are suitable for the emergence of electric polarization.

Heat capacity, magnetic and lattice dynamic properties of TbMn1-xFexO3

The effect of substitution of Fe3+ ions by Mn3+ ions on crystal structure, lattice dynamic, heat capacity and magnetic properties in TbMn1-xFexO3 ceramics has been studied. X-ray powder diffraction and Raman spectroscopy revealed that lattice distortion can be mainly attributed to Jahn-Teller distortion and tilting of octahedrons for samples with x < 0.4; for higher Fe concentration, the distortions are dominated by the octahedra tilting with less contribution of the Jahn-Teller effect. The anomalies in heat capacity of parent compounds (TbMnO3 and TbFeO3), which are associated with magnetic transitions, are smeared out by ion substitution. Magnetization measurements indicate that magnetic ordering persists in whole concentration range. The butterfly-type magnetic hysteresis loops suggest that the magnetic ground state of the whole system is complex and thence interesting for next experimental and theoretical studies.

Pressure effect on magnetic properties of La0.67Ca0.33(Co x Mn1−x )O3 ceramics

In this communication, we compare effects of hydrostatic and chemical pressure on the magnetic properties of La0.67Ca0.33(Co x Mn1−x )O3 ceramics. For ceramics with x=0.03, the Curie temperature T C increases under hydrostatic pressure with a slope d T c/d p=+23.4 K/GPa. The saturated magnetization μs does not change with applied hydrostatic pressure. Chemical pressure was induced by substitution of Co for Mn. The substitution from x=0.03 to x=0.1 reduces the volume of the elementary cell by about 0.28%, but T C decreases from 203.4 to 167 K. The saturated magnetization μs is not affected by this substitution.

HIGH-FIELD MAGNETIZATION, LONGITUDINAL AND TRANSVERSE MAGNETORESISTANCE OF UIrGe

UIrGe crystallizes in the orthorhombic TiNiSi structure and undergoes an antiferromagnetic transition around 14.1 K. The low-temperature longitudinal magnetoresistance (I // B) exhibits a pronounced field-induced step at about 13 T (14 T) and a much weaker step at about 17 T (out of field range) for B // b axis (c axis). No transition was seen for B // a. Here, we report on the magnetization results in fields up to 38 T applied along the principle directions. In addition, we present new magnetoresistance results taken in the transverse (I ⊥ B)configuration in fields up to 18 T applied along the c axis. The data show intriguing differences in comparison to those taken in the longitudinal configuration. The results are discussed in terms of field-induced magnetic transitions and/or Fermi-surface changes.

Magnetic anisotropy in UNiGa determined by polarized neutrons

UNiGa crystallizes in the hexagonal ZrNiAl structure and orders antiferromagnetically (AF) below 39.3 K with the U moments oriented along the c-axis (easy-magnetization axis). There are four different AF phases in zero-field and two field-induced magnetic phases in UNiGa. A strong uniaxial anisotropy is encountered in this system. Whereas a ferromagnetic state can be induced by a magnetic field higher than 1.2 T applied along the hexagonal axis, a magnetic field applied in a perpendicular direction has no influence on the magnetic structure of UNiGa. To date, the magnetic anisotropy in UNiGa has been estimated from bulk magnetic studies, which allow only a qualitative estimate. Here, we report on an anisotropy study by a microscopic method using polarized-neutron scattering on a UNiGa crystal in a magnetic field applied along a direction not parallel to the easy-magnetization direction. The magnetic field forces the U moments to tilt away from the c-axis towards the field direction. The tilting angle is then a direct measure of magnetic-anisotropy energy and leads to a value that is in good agreement with the value derived from bulk magnetic measurements.

Raman spectroscopy of NdFeO3 at pressures up to 11 GPa

We report the theoretical and experimental study of evolution of the first-order Raman-active phonons in NdFeO3 with pressure up to 11u2005GPa at room temperature. With non-polarized light, we have observed 10 Raman-active modes. Our study confirmed no structural phase transition in the studied pressure range. We have calculated that weighted average Grüneisen parameter is ⟨γ⟩ u2009=u20091.19.

Magnetocaloric Effect of La 0.85 Ag 0.15 MnO 3 Under Pressure

Electrical resistance R, heat capacity C, ac susceptibility, and magnetic moment of orthorhombic La_0.85Ag_0.15MnO₃ ceramic were investigated in magnetic fields with flux density up to 5 T and in high hydrostatic pressures up to 0.9 GPa. Sharp lambda-like anomalies in R(T) and C(T) indicate ferromagnetic (FM)-paramagnetic transition. Magnetic field shifts these anomalies to higher temperature and smears them out confirming FM origin of the ordering. Magneto-resistance is negative and large reaching maximal value of about 70% for field with flux density of 5 T at the magnetic phase transition. The magnetic phase transition is accompanied with anomalies at 219.5 K in χ(T) and at 221 K in χ(T). The Curie temperature T_C increases with applied pressure with the rate dT_C/dp = 14.2 K/GPa. Magnetocaloric effect was evaluated from the magnetic entropy change ΔS, which was determined independently from heat capacity and magnetic moment measurements. The maximal values were obtained for μ₀AH = 5 T and both values -ΔS = 5.85 Jkg^-1K^-1 (heat capacity) and -ΔS = 5.80 Jkg^-1K^-1 (magnetic moment) are comparable. Hydrostatic pressure of 0.84 GPa leads to an enhancement of -ΔS approximately about 14%.

Electronic properties of Ce(Cu,Ga)/sub 2/

Ce(Cu/sub 1-x/Ga/sub x/)/sub 2/ compounds with x=0.0, 0.2, 0.4, 0.6, 0.75 and 1.0 were prepared and found to crystallize in the orthorhombic CeCu/sub 2/ structure up to the composition x=0.6, whereas for higher Ga content the hexagonal AlB/sub 2/ structure is formed. We report on specific-heat, electrical-resistivity and magnetic-susceptibility measurements. Furthermore, the specific heat was measured in magnetic fields up to 5 T and the development of the magnetic moments and the magnetocrystalline anisotropy were studied measuring the high-field magnetization in magnetic fields up to 35 T. For CeCu/sub 2/-based compounds, the high-field magnetization results reveal a decrease of the ordered moment with increasing Ga content, which can be understood in terms of an increased 4f-ligand hybridization. The strong magnetocrystalline anisotropy observed in all samples changes from uniaxial type for x/spl les/0.2 to multiaxial type for x>0.2. Specific-heat measurements reveal the temperatures of magnetic ordering first to decrease from 3.5 K for CeCu/sub 2/ to a temperature below 1.3 K for CeCu/sub 1.6/Ga/sub 0.4/ and then to increase again to 2.1 K for CeCu/sub 0.8/Ga/sub 1.2/. A development of Kondo-like behaviour was observed in the electrical resistivity. >

Raman spectroscopy and magnetic properties of KMCr(CN)6 under pressure

We study the effect of pressure on Raman spectra as well on magnetic properties of molecule-based magnets KNiCr(CN)6 and KMnCr(CN)6. The effect of pressure on the ν[C≡N] vibration band which is located in the 2100–2200u2005cm−1 spectral range is relatively weak. Hydrostatic pressure has small almost a negligible effect on the Curie temperature of ferromagnetic KNiCr(CN)6 while leads to a pronounced reversible Curie temperature increase occurrence of new magnetic phase under pressure in the case of KMnCr(CN)6. Applied pressure affects magnetization curves only marginally. All pressure-induced changes are reversible.