O. V. Melnikov

Magnetocaloric effect in La1?xAgyMnO3 (y ? x): direct and indirect measurements

For the first time the magnetocaloric properties of La0.9Ag0.1MnO3, La0.8Ag0.2MnO3, La0.85Ag0.15MnO3, La0.8Ag0.15MnO3 and La0.8Ag0.1MnO3 manganites have been investigated by direct and indirect measurement techniques. All samples showed almost the same relative cooling power (RCP). Temperatures of maxima of the magnetocaloric effect (MCE) are between a few degrees below freezing and the room temperature region. The compounds showed RCP values of about 100 J kg−1 at a field change of 2.6 T, which is about half the RCP of gadolinium. Because of considerable MCE and the Curie temperatures ranging from 269 to 303 K, these materials could be used as magnetic refrigerants for magnetic refrigeration in the sub-room and room temperature range.

Ag-doped manganite nanoparticles: New materials for temperature-controlled medical hyperthermia

The purpose of this study was to introduce newly synthesized nanomaterials as an alternative to superparamagnetic ironoxide based particles (SPIO) and thus to launch a new platform for highly controllable hyperthermia cancer therapy and imaging. The new material that forms the basis for this article is lanthanum manganite particles with silver ions inserted into the perovskite lattice: La(1-x)Ag(x)MnO(3+delta). Adjusting the silver doping level, it is possible to control the Curie temperature (T(c)) in the hyperthermia range of interest (41-44 degrees C). A new class of nanoparticles based on silver-doped manganites La(1-x)Ag(x)MnO(3+delta) is suggested. New nanoparticles are stable, and their properties were not affected by the typical ambient conditions in the living tissue. It is possible to monitor the particle uptake and retention by MRI. When these particles are placed into an alternating magnetic field, their temperature increases to the definite value near T(c) and then remains constant if the magnetic field is maintained. During the hyperthermia procedure, the temperature can be restricted, thereby preventing the necrosis of normal tissue. A new class of nanoparticles based on silver-doped manganites La(1-x)Ag(x)MnO(3+delta) was suggested. Ag-doped perovskite manganites particles clearly demonstrated the effect of adjustable Curie temperature necessary for highly controllable cellular hyperthermia. The magnetic relaxation properties of the particles are comparable with that of SPIO, and so we were able to monitor the particle movement and retention by MRI. Thus, the new material combines the MRI contrast enhancement capability with targeted hyperthermia treatment.

Solution to the bioheat equation for hyperthermia with La1−xAgyMnO3-δ nanoparticles: The effect of temperature autostabilization

This work aimed to analyze the possibility and performance of the temperature controlled hyperthermia based on AC heating of magnetic nanoparticles with low Curie temperature. Temperature dependence of dynamic magnetic susceptibility has been studied experimentally on fine powders of La0.8Ag0.15MnO2.95 in the frequency range of 0.5–2.0 MHz. Critical drop of the AC magnetic losses was found in the vicinity of the Curie point, TC = 42°C. The obtained data was used in the numerical analysis of the bioheat equations under typical conditions of the hyperthermia treatment. The mathematical model includes a spherical tumor containing magnetic particles and surrounded by concentric healthy tissue, with account made for the blood perfusion. The calculations performed for various AC power, tumor sizes and doping geometries predict effective autostabilization of the temperature at T ≅ TC inside the tumor and steep temperature profile at the interface with the healthy tissue.

Spin-polarized transport in the manganite La0.85Ag0.15MnO3

The low-temperature minimum of the resistivity of La0.85Ag0.15MnO3 is investigated in detail. Analysis of the experimental data shows that the observed low-temperature minimum of the zero-field resistivity and the large magnetoresistive effect, which increases with decreasing temperature, can be explained in a model of spin-polarized tunneling of charge carriers through grain boundaries.

Critical behavior of the specific heat of manganites La1−xAgxMnO3 (x=0.1,0.15,0.2) near the Curie point

An investigation of the critical behavior of the specific heat of the manganites La1−xAgxMnO3 ×(x=0.1,0.15,0.2) near the Curie temperature is carried out. The behavior of the universal critical parameters near the phase transition point is established. All of the samples studied correspond to the ferromagnetic Heisenberg 3D universality class of critical behavior, with the critical exponent α=−0.115, −0.106, and −0.106 for La0.9Ag0.1MnO3, La0.85Ag0.15MnO3, and La0.8Ag0.2MnO3, respectively. It is shown that the universality class of the critical behavior of the specific heat of the manganites La1−xAgxMnO3 is independent of the silver concentration.

Electrical and thermal properties of the manganite La0.8Ag0.15MnO3

A comprehensive investigation of the electro- and thermophysical properties of the manganite La0.8Ag0.15MnO3 is carried out over a wide temperature interval (4.2–350K) and in magnetic fields up to 26kOe. It is shown that the colossal magnetoresistance in a magnetic field of 11kOe amounts to 57%, and the effect is maximum at room temperature. The dominant mechanisms of current carrier scattering in the ferromagnetic and paramagnetic phases are established. An analysis of the data on the low-temperature heat capacity provides estimates of the electronic density of states at the Fermi level, NF=6.82×1024eV−1mol−1, and of the Debye temperature, θD=370K. The results of thermal expansion measurements are used to find the spontaneous magnetostriction. It is found that the phonon mechanism of heat transfer is dominant, and the local Jahn–Teller distortions are considered as the main mechanism of phonon scattering.

The evolution of magneto-transport and magneto-optical properties of thin La0.8Ag0.1MnO3+δ films possessing the in-plane variant structure as a function of the film thickness

Epitaxial La 0.8 Ag 0.1 MnO 3+δ films of different thicknesses (500-1000 nm) were grown on ZrO 2 (Y 2 O 3 ) substrates. Their optical, magneto-optical and transport properties were studied in order to clarify the effect of the epitaxial variant structure and Ag ion distribution on the conductivity, magnetoresistance and infrared magnetotransmission in these films. An original method was developed for separating MR contributions related to the colossal magnetoresistance near T C and the tunnelling magnetoresistance. It was established that in the La 0.8 Ag 0.1 MnO 3+δ films spin-polarization of electrons P reached ∼0.5. The transverse Kerr effect revealed the irregular distribution of Ag ions through the film thickness. The comparison of optical and electrical data implies lower silver content near the film-substrate boundary in relation to that in the domain volume.

Anisotropic magnetoresistance in epitaxial (110) manganite films

We report on measurements of anisotropic magnetoresistance (AMR) (∼ρ‖−ρ⊥) along two orthogonal directions ([001] and [1−10]) of a manganite (La0.95Ag0.05MnO3) epitaxial thin film grown on a (011) SrTiO3 substrate. We show that AMR along [001] is negative whereas along the [1−10] direction is positive at low temperature, changing to negative when approaching the Curie temperature. We argue that temperature dependent anisotropic spin-orbit coupling and spin-dependent scattering effects could be at the basis of these experimental results.

MOCVD of YBCO and Buffer Layers on Textured Ni Alloyed Tapes

A RTR MOCVD was used for the deposition of YBCO and various oxides. A new MOCVD technique enable us to coat the metal tape directly without formation of NiO. At a low oxygen partial pressure the buffer layers were grown on the metal tape with good in plane and out of plane texture. The texture of the MgO buffer layers depend on the surface of the alloyed Ni-tape. YBCO layers exhibit excellent out of plane texture with FWHM(005) = 1.4 - 3.5deg and good in plane texture of FWHM(103) = 5-7deg. On MgO buffered Ni5at%W the inductive measured jc was 0.3-0.7 MA/cm2 at 77 K.

Electrically conducting oxide buffer layers on biaxially textured nickel alloy tapes by reel-to-reel MOCVD process

Reel-to-reel MOCVD process for continuous growth of electrically conducting buffer layers on biaxially textured Ni5W tapes has been developed. The new buffer layer architechture is presented: 200 nm (La, Ba)2CuO4/40 nm (La, Ba)MnO3/Ni5W. Constituting layers with high structural quality have been grown on moving tapes (in plane FWHM ≤ 6° and out of plane FWHM ≤ 3°).