Study of magnetic and specific heat measurements at low temperatures in Nd 0.5Sr 0.5MnO 3, Nd 0.5Ca 0.5MnO 3 (original) (raw)
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Physical Review B, 2002
We studied the magnetization as a function of temperature and magnetic field in the compounds Nd 0.5 Sr 0.5 MnO 3 , Nd 0.5 Ca 0.5 MnO 3 and Ho 0.5 Ca 0.5 MnO 3 . It allowed us to identify the ferromagnetic, antiferromagnetic and charge ordering phases in each case. The intrinsic magnetic moments of Nd 3+ and Ho 3+ ions experienced a short range order at low temperatures. We also did specific heat measurements with applied magnetic fields between 0 and 9 T and temperatures between 2 and 300 K in all three samples. Close to the charge ordering and ferromagnetic transition temperatures the specific heat curves showed peaks superposed to the characteristic response of the lattice oscillations. Below 10 K the specific heat measurements evidenced a Schottky-like anomaly for all samples. However, we could not successfully fit the curves to either a two level nor a distribution of two-level Schottky anomaly. Our results indicated that the peak temperature of the Schottky anomaly was higher in the compounds with narrower conduction band. 60, 70, 65.40Ba, 74.25 Ha, Typeset using REVT E X
Schottky-like anomaly in the low-temperature specific heat of single-crystal NdMnO3
Solid State Communications, 2005
The specific heat of single-crystal NdMnO 3 was investigated from 2 to 20 K under different magnetic fields up to 8 T. All the specific heat data show a Schottky-like anomaly, which becomes more indistinctive as increasing magnetic field. The experiment data were successfully fitted by taking into account factors such as crystal-field splitting, the two-level Schottky anomaly, the lattice vibration, and type-A antiferromagnetic (A-AF) spin waves. It was found that the splitting of the ground state doublet of Nd 3C ion increases linearly with magnetic field. The above phenomena can be interpreted in terms of the model of unchanged effective molecular field at Nd 3C site caused by the ferromagnetic component of A-AF structure of Mn spins. This ferromagnetic component is likely caused by the GdFeO 3-type octahedron rotation. In addition, it was also found that the magnetic field increases the spin-wave stiffness coefficient, but reduces the Debye temperature.
Journal of Low Temperature Physics, 2011
The low temperature specific heat of the colossal magnetoresistance compounds (Nd x Y 1 − x) 2/3 Ca 1/3 MnO 3 (x = 0, 0.1) for 0.4 ≤ T < 2 K in magnetic fields up to H = 9 T has been studied. Applied magnetic fields lead to the drop of the low temperature specific heat by more than 2 orders, which implies a large magnetic contribution. Experimental data were successfully fitted by the sum of the hyperfine C hyp , the linear T-dependent C sg and the spin waves C sw contributions. The C sg attributed to the glassy state of the magnetic systems of the studied insulating compounds exponentially decreases with the increase of H up to ∼ 5 T. The C sw providing the best fitting of the experimental data is attributed to the ferromagnetic spin waves with pseudo gap (H) in the spin-wave spectrum which increases linearly with the increase of the applied magnetic field. The (0) ∼ 0.8 K is approximately the same for both compounds studied.
SCHOTTKY-LIKE ANOMALY IN THE LOW-TEMPERATURE SPECIFIC HEAT OF POLYCRYSTALLINE Y0.3Gd0.2Sr0.5MnO3
In this paper we have synthesis of a sample of Y0.3Gd0.2Sr0.5MnO3 by solid state ceramic route method. The structural and thermodynamic properties of polycrystalline samples of Y0.3Gd0.2Sr0.5MnO3 were measured in order to investigate the effect of higher magnetic moment ion Gd and divalent Sr over Y ion. The structural transition from hexagonal to orthorhombic is observed at very high doping of Gd ion. Low temperature specific heat measurements were performed at 2-300 K at three different applied magnetic fields, which reveals the signature of Schottky-like anomaly in the present sample.
Magnon-polaron and spin-polaron signatures in the specific heat and electrical resistivity of<mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" display="inline">mml:mrowmml:msubmml:mrow<mml:mi mathvariant="normal">Lamml:mrowmml:mn0.6</mml:ms...
Physical review, 2002
La0.6Y0.1Ca0.3M nO3, an ABO3 perovskite manganite oxide, exhibits a non trivial behavior in the vicinity of the sharp peak found in the resistivity ρ as a function of temperature T in zero magnetic field. The various features seen on dρ/dT are discussed in terms of competing phase transitions. They are related to the M n − O − M n bond environment depending on the content of the A crystallographic site. A Ginzburg-Landau type theory is presented for incorporating concurrent phase transitions. The specific heat C of such a compound is also examined from 50 till 200 K. A log-log analysis indicates different regimes. In the low temperature conducting ferromagnetic phase, a collective magnon signature (C ≃ T 3/2) is found as for what are called magnon-polaron excitations. A C ≃ T 2/3 law is found at high temperature and discussed in terms of the fractal dimension of the conducting network of the weakly conducting (so-called insulating) phase and Orbach estimate of the excitation spectral behaviors. The need of considering both independent spin scattering and collective spin scattering is thus emphasized. The report indicates a remarkable agreement for the Fisher-Langer formula, i.e. C ∼ dρ/dT at second order phase transitions. Within the Attfield model, we find an inverse square root relationship between the critical temperature(s) and the total local M n − O − M n strain.
NATIONAL CONFERENCE ON PHYSICS AND CHEMISTRY OF MATERIALS: NCPCM2020
Using a simple variational method, we have studied the zero field electronic specific heat (Cv) as a function of temperature of Anderson lattice model used for rare earth manganites doped with alkaline earths namely (where Re=La, Pr, Nd etc., and A= Ca, Sr, Ba etc.) which exhibit colossal magnetoresistance (CMR), metal-insulator transition & many other poorly understood phenomena. We have already used this variational method to study the zero field electronic & magnetic properties like electrical resistivity & magnetic susceptibility of doped CMR manganites. We have taken two band (l-b) Anderson lattice model Hamiltonian for manganites in the strong electronlattice Jahn-Teller (JT) coupling regime to study the temperature dependence of C vin these compounds. We have also observed the role of the model parameters e.g. local Coulomb repulsionU, strong ferromagnetic Hund's Rule coupling JH between eg& t2g spins & hybridization Vk between ℓ-polarons& d-electrons of the same spins on Cv&linear coefficient Cv/ T. We find from our results that as the temperature is lowered below a critical temperature Tc (˷ 100 K), there is an anomaly (sharp peak) in both Cv(T) &Cv/T beyond which it falls off for particular values of JH, V & doping values x resembling with the key feature of many CMR compounds La0.815 Sr0.185 MnO3 & Pr0.6-xBixSr0.4MnO3(x= 0.0-0.15). The observed low temperature peak in Cv(T) becomes progressively broader & shifts to higher temperature region on increasing Vk or JH or doping x value. The specific heat anomaly near Tc ˷ 100 K is related to magnetic ordering due to the paramagnetic-ferromagnetic transitions and magnetic inhomogeneity in these manganites.
Magnetothermopower in Nd1-xEuxNiO3 compounds
Journal of Applied Physics, 2007
We have measured magnetization M(T ,H), thermal conductivity κ(T ,H), and thermopower S(T ,H) of polycrystalline samples of Nd1-xEuxNiO3, 0⩽x⩽0.35, as a function of temperature and external magnetic field. The data indicate a metal-insulator (MI) transition in a wide range of temperature (200<TMI<325K). The magnetic susceptibility χ(T ) data, after the subtraction of the rare-earth contribution, exhibit a Curie-Weiss-like behavior at temperatures above TMI. Although a clear antiferromagnetic AF transition of the Ni sublattice is observed at TN⩽TMI, χ(T ) still increases down to 5K, suggesting a heterogeneous ground state. The thermal conductivity of the NdNiO3 compound is not affected by an external magnetic field of 90kOe in a wide range of temperature, and its temperature dependence below 15K is approximately quadratic, strongly suggesting the presence of disorder. S(T ) is negative above TMI and varies linearly with temperature. Below TMI, there is a minimum close to 120K, and S(T ) changes its sign at T ˜30K, indicating a competition between two types of charge carriers. A pronounced peak in S(T ) at TS˜20K is observed and the peak remains unaltered under magnetic fields up to 90kOe. However, its magnitude is enhanced by ˜25% with applied magnetic field, exhibiting a clear magnetothermopower effect. The combined results indicate a coexistence of ordered and disordered phases below TN and that an applied magnetic field is suitable for enhancing the thermoelectric properties close to TS.
Specific heat of single-crystalline Pr0.63Ca0.37MnO3 in the presence of a magnetic field
Physical Review B, 2001
We present the results of a study of specific heat on a single crystal of Pr0.63Ca0.37MnO3 performed over a temperature range 3K-300K in presence of 0 and 8T magnetic fields. An estimate of the entropy and latent heat in a magnetic field at the first order charge ordering (CO) transition is presented. The total entropy change at the CO transition which is ≈ 1.8 J/mol K at 0T, decreases to ∼ 1.5 J/mol K in presence of 8T magnetic field. Our measurements enable us to estimate the latent heat LCO ≈ 235 J/mol involved in the CO transition. Since the entropy of the ferromagnetic metallic (FMM) state is comparable to that of the charge-ordered insulating (COI) state, a subtle change in entropy stabilises either of these two states. Our low temperature specific heat measurements reveal that the linear term is absent in 0T and surprisingly not seen even in the metallic FMM state. 75.30.Kz 65.40.+g 75.30.Vn
Thermal relaxation in charge ordered Pr 0.63Ca 0.37MnO 3 in the presence of a magnetic field
Solid State Communications, 2001
We report observation of substantial thermal relaxation in single crystal of charge ordered system Pr0.63Ca0.37MnO3 in an applied magnetic field of H = 8T. The relaxation is observed when the temperature is scanned in presence of a magnetic field in the temperature interval TMH < T < TCO where TCO is the charge ordering temperature and TMH is charge melting temperature in a field. In this temperature range the system has coexisting charged ordered insulator (COI) and ferromagnetic metallic (FMM) phases. No such relaxation is observed in the COI state in H = 0T or in the FMM phase at T < TMH in presence of a magnetic field. We conclude that the thermal relaxation is due to two coexisting phases with nearly same free energies but separated by a potential barrier. This barrier makes the transformation from one phase to the other time-dependent in the scale of the specific heat experiment and gives rise to the thermal relaxation.
Journal of Experimental and Theoretical Physics Letters, 1999
An unusual temperature behavior of resistivity ρ(T, x) in La0.7Ca0.3M n1−xCuxO3 has been observed at slight Cu doping (0 ≤ x ≤ 0.05). Namely, introduction of copper results in a splitting of the resistivity maximum around a metal-insulator transition temperature T0(x) into two differently evolving peaks. Unlike the original Cu-free maximum which steadily increases with doping, the second (satellite) peak remains virtually unchanged for x < xc, increases for x ≥ xc and finally disappears at xm ≃ 2xc with xc ≃ 0.03. The observed phenomenon is thought to arise from competition between substitution induced strengthening of potential barriers (which hamper the charge hopping between neighboring M n sites) and weakening of carrier's kinetic energy. The data are well fitted assuming a nonthermal tunneling conductivity theory with randomly distributed hopping sites.