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The complex lanthanide doping of electron manganites results in enhancement of various phase separation effects in physical properties of these compounds. Selecting Ca0.8Sm0.16Nd0.04MnO3 as a model case we show that the first order structural phase transition from paramagnetic semi-metallic phase into anti-ferromagnetic semi-metallic phase at TS ~ 158 +- 4 K is marked by an abrupt decrease in magnetization, a step like anomaly DL/L = 10-4 in thermal expansion and large latent heat DQ = 610 J/mol. In a certain temperature range below TS, the high field magnetization exhibits hysteretic metamagnetic behavior due to field-induced first order transformation. ac-susceptibility, magnetization and resistivity data suggest rather a non-uniform state in Ca0.8Sm0.16Nd0.04MnO3 at low temperatures. The metal - insulator transition occurs at TMI ~112 +- 3 K, accompanied by a step-like increase in magnetization. These features could be ascribed to "sponging" of electrons from neighboring anti-ferromagnetic matrix by clusters undergoing the ferromagnetic ordering.

Measurements of magnetisation, magnetostriction and specific heat were performed on Nd 0.04 Sm 0.16 Ca 0.8 MnO 3 in order to investigate the influence of isovalent substitution in the rare-earth subsystem on spontaneous and field-induced magnetostructural transitions found earlier in electron-doped manganites Sm 1− x Ca x MnO 3 ( x =0.8, 0.85). It is shown that the temperature of the magnetostructural transition from the orthorhombic to the monoclinic phase, as well as the parameters of the magnetic subsystem in the orthorhombic phase, change non-significantly at partial substitution of Nd for Sm. However, this substitution strongly reduces the volume effect at the transition. Therefore, the volume anomaly at this magnetostructural transition appears to be quite sensitive to the ionic radius and/or the f-electronic state of the rare-earth metal.

The YbInCu 4 exhibits a first-order phase transition associated with a transformation of the valence state of the Yb ion. The effect of alloying on the valence transition in Yb 1− x Ce x InCu 4 (0⩽ x ⩽0.2) has been investigated by specific heat C measurements in the range 5–300 K. The C vs. T dependence in YbInCu 4 reveals sharp peak at T V =39 K. This peak shifts to higher temperatures with x and its shape gradually transforms to that of continuous phase transition. The specific heat measurements have also been made for nonmagnetic isomorphous compound YInCu. The comparison of YInCu 4 data with those of Yb 1− x Ce x InCu 4 allows an estimate of the value of entropy Δ S released at the phase transition. The Sommerfeld coefficient values in the Yb 1− x Ce x InCu 4 family of compounds were found increasing with Ce concentration.

The temperature dependences of the resistance and magnetic susceptibility are studied in gallium-doped lead telluride, which is characterized by a delayed photoconductivity effect, under various illumination conditions. After a sample is illuminated at low temperatures, the magnetic susceptibility is diamagnetic in the region of metallic delayed conductivity (for T

The metaloxide pyroxene compound NaVGe 2 O 6 containing isolated edge-sharing VO 6 ( S =1) chains undergoes a transition into a long-range antiferromagnetic state at T N =16 K. The broad maximum in the temperature dependence of magnetic susceptibility at T M =26 K indicates the low-dimensional character of magnetic subsystem. Even though the antiferromagnetic ordering is accompanied by a sharp peak of specific heat, significant magnetic entropy is released above the Neel temperature.

New metal oxide pyroxene compound NaVGe2O6 containing isolated edge-sharing VO6 (S=1) chains undergoes transition into a long-range antiferromagnetic state at TN=16 K. The broad maximum in the temperature dependence of magnetic susceptibility at TM=26 K indicates the low-dimensional character of the magnetic subsystem. Even though the antiferromagnetic ordering is accompanied by a sharp peak of specific heat, significant magnetic entropy is released above the Neel temperature.

The resistivity, magnetic susceptibility, magnetization, and the specific heat of electron-doped manganite Ca 0.85 Sm 0.15 MnO 3 were studied. The data obtained suggest that this compound undergoes a phase transition towards an insulating antiferromagnetic state at T C ∼115 K and displays negative magnetoresistance at T T C . The Debye temperature Θ D =575 K and the latent heat of the phase transition Q =493 J/mol were derived from the temperature dependence of the specific heat.

The transport, magnetic, and thermal properties of single crystal double-layer manganites of the Ruddlesden-Popper series (La1−z Prz)1.2Sr1.8Mn2O7 (z=0.1 or 0.4) were studied. The compounds exhibit the colossal negative magnetoresistance effect in the region of a transition into a ferromagnetic state. Upon the isoelectronic substitution of Pr3+ for La3+, the Curie temperature decreases, while the easy magnetization axis rotates from the ab plane to the c axis. The observed effect is related to a change in the occupancy of $$d{x^2-y^2} $$ and $$d{3z^2-r^2} $$ orbitals as a result of stretching of the MnO6 octahedra.

Low-temperature $(2\text{ }\text{K}\ensuremath{\le}T\ensuremath{\le}350\text{ }\text{K})$ heat capacity and room-temperature shear modulus measurements $(\ensuremath{\nu}=1.4\text{ }\text{MHz})$ have been performed on bulk ${\text{Pd}}_{41.25}{\text{Cu}}_{41.25}{\text{P}}_{17.5}$ in the initial glassy, relaxed glassy, and crystallized states. It has been found that the height of the low-temperature Boson heat capacity peak strongly correlates with the changes in the shear modulus upon high-temperature annealing. It is this behavior that was earlier predicted by the interstitialcy theory, according to which dumbbell interstitialcy defects are responsible for a number of thermodynamic and kinetic properties of crystalline, (supercooled) liquid, and solid glassy states.

Ferromagnetic Heusler alloys exhibiting martensitic transformations are known to change their shape in an external magnetic field. Magnetization, electric resistance, and specific heat as a function of temperature are examined in ${\mathrm{Ni}}_{54}{\mathrm{Fe}}_{19}{\mathrm{Ga}}_{27}$ single crystal. Structural transition appears as sharp anomaly in these dependencies. This points to an avalanchelike character of martensitic transformation. The jump in resistivity at the structural phase transition and the lower density of states at the Fermi level in the martensite phase supports the hypothesis of the Jahn-Teller origin of the martensitic transformation. Magnetic measurements show that transformation to the martensitic phase is accompanied by the increase of spontaneous magnetization and an increase of magnetocrystalline anisotropy. Magnetization increase is due to different Curie temperatures of austenite and martensite. These were determined from critical behavior using Arrott plot. Additional analysis of magnetic behavior indicates ferrimagnetic ordering in this nonstoichiometric compound. Intrinsic properties of the compound are analyzed with respect to both of the actuation modes possible in magnetic shape-memory alloys. However, neither a magnetically induced martensite transformation nor a magnetically induced reorientation of variants has been observed.

We report on the magnetic, magnetoelastic, as well as the specific heat measurements of the electron-doped manganite Ca 0 . 8 5 Sm 0 . 1 5 MnO 3 . The low-temperature monoclinic phase which is antiferromagnetic exhibits a first-order field-induced transition into the ferromagnetic state. This transition is accompanied by a strong decrease in volume. The latent heat calculated from the Clapeyron-Clausius equation coincides with that of the structural phase transition determined from the specific heat measurements. We thus deduce that the observed metamagnetic transition in Ca 0 . 8 5 Sm 0 . 1 5 MnO 3 is due to the field-induced structural transformation from the monoclinic phase to the orthorhombic phase.

At low temperatures some ionic, covalent and mixed bonding compounds, as well as semiconducting heterostructures and quantum wells exhibit persistent photoconductivity. This term is used to describe the striking observation that the conductivity of these compounds and/or structures is greatly enhanced by visible or infrared illumination and that the low resistance state is maintained for a long time after switching off the illumination. To describe this effect in variously doped ionic-covalent semiconductors the models of repulsive barrier for both electron emission and capture were introduced based primarily on the assumption of dopant’s displacement in the host’s crystal lattice. Here we report on the magnetic counterpart of this phenomenon, which however does not exactly meet the expectations based on transport measurements. It was found that the magnetic response of AIVBVI narrow-gap semiconductors doped with CIII impurities possesses features of both relaxation phenomena and light-induced phase trans...

In order to understand the electronic origin of the inverse magnetocaloric effect observed in a Ni–Co–Mn–In system we used a combination of indirect experimental probes as magnetization, resistivity and specific heat. The findings are compared with the band structure of isostructural Heusler alloys such as Ni–Mn–Ga. We suggest that the inverse magnetocaloric effect in Ni–Co–Mn–In originates from the high density of states close to Fermi energy. Within the austenite state this causes ferromagnetic band splitting. The structural change to the martensite allows an alternative way to reduce the high density of states at lower temperatures, which does not require band splitting and thus does not support ferromagnetic order.

The thermopower measurements of Yb1-xCexInCu4 alloys (x ≤ 0.2) were performed in a temperature range 4 − 170 K by the longitudinal steady-state four probe method. At TV~40 K, the intermetallic ternary compound YbInCu4 experiences an isostructural phase transition associated with the partial change in the valence state of the Yb ions. The thermopower S of YbInCu4 is negative. The valence transition is clearly seen in S vs. T dependence as a step-like anomaly at TV. The character of thermopower dramatically changes with Ce substitution. The thermopower of Ce-substituted compounds is positive and almost linearly increases at low temperatures, reaching maximum at T < TV. Then it decreases revealing minimum and rises again. Upon Ce substitution it became possible to observe the deep minimum in S(T) typical for Yb compounds.

The solid state memory effect, known as persistent photoconductivity is described in terms of electronic configurations of impurity centers in narrow-gap semiconductors. The studies of resistivity and magnetic susceptibility of compensated bulk single crystal PbTe:Ga present strong evidence that the dopant centers produce two types of electronic states: a shallow and delocalized paramagnetic level associated with the normal substitutional site configuration and a more localized non-magnetic level arising from a lattice distortion at or near the donor. The metastable properties of the impurity centers suggest a redistribution of electrons, 2Ga0 Ga+ + Ga-, where, rather than all donors being neutral, half the Ga atoms have two electrons and become negatively charged whereas the other half have none and are positively charged. The potential areas of application of these intelligent materials are discussed.© (1996) COPYRIGHT SPIE--The International Society for Optical Engineering. Downloading of the abstract is permitted for personal use only.