Schottky Anomaly Research Articles

Neutron irradiation effects in chemical-vapor-deposited diamond

The structural disorder, heat capacity, resistivity, Hall effect, and magnetic susceptibility of polycrystalline chemical-vapor-deposited diamond irradiated with fast neutrons at temperature of $(325\ifmmode\pm\else\textpm\fi{}10)\text{ }\text{K}$ at high fluences $\ensuremath{\Phi}=(1--5)\ifmmode\times\else\texttimes\fi{}{10}^{20}\text{ }{\text{cm}}^{\ensuremath{-}2}$ were investigated. Despite a significant increase in unit-cell volume $(\ensuremath{\sim}4.5%)$, the crystalline structure remains stable in this fluence range. The irradiation results in a paramagnetic contribution to magnetic susceptibility and to a strong (by 4 orders of magnitude) increase in heat capacity at low temperatures $(Tl20\text{ }\text{K})$ due to electron contribution with a $T$ dependence characteristic of multilevel electron systems (the Schottky anomaly).

Measurements of magnetic susceptibilities, their anisotropies and crystal field investigations of monoclinic single crystals of Ho 2GeO 5

Monoclinic single crystals of Ho 2GeO 5 were grown by a flux technique. The molar principal susceptibilities ( χ 1 and χ 3) have been measured in the temperature range 300–13.5 K. The principal magnetic anisotropies ( χ 1– χ 2, χ 2– χ 3 and χ 1– χ 3) are obtained from the measured anisotropies in different modes of suspensions ( b-axis vertical, c-axis vertical and (1 0 0) plane horizontal) of the crystal. The molar principal susceptibility ( χ 2) is obtained from the observed values of the principal anisotropies. The observed principal susceptibilities together with their anisotropies are explained by invoking the crystal field interaction of the Ho 3+ ion with its diamagnetic neighbors in non-axial symmetry. The molar susceptibilities are correlated to the ionic values by finding out the proper orientation of the principal molar susceptibilities, i.e., crystal susceptibilities with respect to that of the ionic susceptibilities ( K x , K y and K z ). The electronic heat capacities are calculated from the crystal field analysis showing Schottky type anomalies.

Magnetocaloric and magnetotransport properties ofR2Ni2Sncompounds (R=Ce, Nd, Sm, Gd, and Tb)

We report a detailed magnetic, magnetocaloric, and magnetotransport study on ${R}_{2}{\text{Ni}}_{2}\text{Sn}$ compounds with different rare earths. The magnetic state of these compounds is found to be complex because of the coexistence of ferromagnetic and antiferromagnetic components. These compounds show phenomena such as multiple magnetic transitions, nonsaturation of magnetization, and metamagnetic transitions. Analysis of the zero-field heat capacity data shows that the magnetic entropy is less than the theoretical value, indicating the presence of some moment on Ni. Schottky anomaly is present in the magnetic heat capacity data of ${\text{Sm}}_{2}{\text{Ni}}_{2}\text{Sn}$. The temperature variation of magnetocaloric effect reflects the magnetization behavior. ${\text{Tb}}_{2}{\text{Ni}}_{2}\text{Sn}$ and to a less extent ${\text{Gd}}_{2}{\text{Ni}}_{2}\text{Sn}$ show oscillatory magnetocaloric effect. The variation of magnetocaloric effect is correlated with the ferromagnetic-antiferromagnetic phase coexistence. The electrical resistivity analysis has shown that the electron-magnon scattering is prominent at low temperature, while phonon scattering modified by the $s\text{\ensuremath{-}}d$ interaction is crucial at high temperatures. The magnetoresistance is very large in ${\text{Ce}}_{2}{\text{Ni}}_{2}\text{Sn}$ and shows a quadratic dependence on the field, implying the role of spin fluctuations in determining the transport behavior. Large magnetoresistance has been observed in other compounds as well.

Synthesis, chemical bonding and physical properties of RERhB 4 ( RE=Y, Dy–Lu)

The compounds of rare-earth metals with rhodium and boron RERhB 4 ( RE=Y, Dy–Lu) crystallize with the orthorhombic structure type YCrB 4 (space group Pbam, Pearson symbol oP24). The crystal structures of the compounds with RE=Y, Er, Tm and Yb were refined by using single-crystal diffraction data. Analysis of chemical bonding for YRhB 4 and YbRhB 4 was performed by electron localizability indicator and by calculation of quantum chemical charges (quantum theory of atoms in molecules). Boron and rhodium form the 3-D polyanion containing planar nets of three-bonded boron atoms interconnected by rhodium along [001]. The interaction of the RE species with the rhodium–boron polyanion is predominantly ionic. Magnetic susceptibility data of TmRhB 4 and YbRhB 4 showed that the RE species are in 4 f 12 (Tm) and 4 f 13 (Yb) electronic states, respectively. In the low-temperature region, the specific heat revealed a Schottky anomaly for TmRhB 4 while an antiferromagnetic transition is observed at 3.5 K for YbRhB 4. X-ray absorption measurement at the Yb L III edge for YbRhB 4 reveals the 4 f 13 state of ytterbium.

Low-temperature heat capacity of synthetic Fe- and Mg-cordierite: thermodynamic properties and phase relations in the system FeO-Al2O3-SiO2-(H2O)

The heat capacity of anhydrous low Fe-cordierite, Fe2Al4Si5O18, was measured for the first time between 5 and 300 K on a milligram-sized synthetic sample using low-temperature heat-pulse calorimetry. The C-p's of anhydrous low Mg-cordierite, Mg2Al4Si5O18, and a hydrous low Mg-cordierite of composition Mg1.97Al3.94Si5.06O18.0.625H(2)O, both previously studied by adiabatic calorimetry (Paukov et al., 2006, 2007), were also determined. At low temperatures around 10 K the C-p data for Fe-cordierite show a small feature that is interpreted as a Schottky anomaly. Using published DSC and adiabatic calorimetry results for anhydrous Fe-cordierite and Mg-cordierite and the results herein, Cp polynomials for both phases were calculated for use at T > 270 K. They are given by: C-p(Fe-Cd) = 91 1.1(+/- 9.7) - 5829.2(+/- 363) x T-0.5 - 13.9424(+/- 2.522) x 10(6) x T-2 + 1470.4(+/- 454.84) x 10(6) x T-3 and C-p(Mg-Cd) = 882.0(+/- 4.9) - 5155.8(+/- 167) x T-0.5 -20.7584(+/- 0.806) x T-2 + 2736.0(+/- 112.73) x 10(6) x T-3, respectively. The standard calorimetric entropy values at 298.15 K, SO, for anhydrous Fe-cordierite, anhydrous Mg-cordierite and hydrous Mg-cordierite are 460.5 +/- 0.5, 406.1 +/- 0.4 and 450.9 +/- 0.5 J/(mol.K), respectively. The latter two values are in good agreement with those determined by adiabatic calorimetry. The lattice (vibrational) and non-lattice contributions to the experimental C-p values for Fe-cordierite were separated by applying the Komada-Westrum model and the values S degrees(vib) = 447.7 J/(mol.K) and S-el(o) = 13.6 J/(mol.K) were obtained for the vibrational and electronic contributions to the standard third-law entropy. Thermodynamic calculations and analysis were carried out in the system FeO-Al2O3-SiO2 with and without H2O. A model C-p polynomial for hydrous Fe-cordierite, Fe2Al4Si5O18 center dot H2O, was derived as: C-p(hFe-Cd) = 967.3(+/- 9.7) - 6070.4(+/- 363) x T-0.5 - 13.9389(+/- 2.522) x 10(6) x T-2 + 1470.4(+/- 454.84) x 10(6) x T-3. The enthalpy of formation from the elements for both hydrous and anhydrous Fe-cordierite and the standard entropy for hydrous Fe-cordierite with one mole of H2O pfu were derived using the experimental phase equilibrium results of Mukhopadhyay & Holdaway (1994) on the reaction 3 Fe-cordierite center dot nH(2)O = 2 almandine + 4 sillimanite + 5 quartz + 3n H2O. For anhydrous Fe-cordierite Delta H-f(o) = -8448.26 kJ/mol was obtained and for hydrous Fe-cordierite, Delta H-f(o) = -8750.23 kJ/mol and S-o = 520.6 J/(mol.K). Phase relations in the FeO-Al2O3-SiO2-(H2O) systems at low pressures are analyzed and isohydrons for H2O in hydrous Fe-cordierite are modelled. H2O contents decrease with increasing temperature and increase with increasing pressure.

Magnetization and specific heat of DyFe3(BO3)4 single crystal

We present thermodynamic and magnetic studies of single crystalline DyFe3(BO3)4. The data indicate an easy axis antiferromagnetic order below TN~ 38 K which we attribute to the Fe subsystem. The Dy subsystem remains paramagnetic down to the lowest investigated temperatures of 2 K, but it is polarized by the Fe spins due to a f-d interaction. External magnetic field leads to a spin-flop transition in the iron subsystem as well as to superposed magnetization in the Dy subsystem. The repopulation of two low-lying Kramers doublets in Dy3+ ions results in well defined Schottky anomalies in specific heat and magnetization.

Spin gap inCeFe4Sb12studied by heat capacity and inelastic neutron scattering

The magnetic properties of the skutterudite compound $\mathrm{Ce}{\mathrm{Fe}}_{4}{\mathrm{Sb}}_{12}$ have been investigated by heat capacity and inelastic neutron scattering measurements. Heat capacity measurements reveal a broad peak centered at $125\phantom{\rule{0.3em}{0ex}}\mathrm{K}$, whose magnitude is much larger than that expected from a Schottky anomaly due to a cubic crystal electric field. At $5\phantom{\rule{0.3em}{0ex}}\mathrm{K}$, inelastic neutron scattering experiments clearly show the existence of a broad magnetic peak at $40(3)\phantom{\rule{0.3em}{0ex}}\mathrm{meV}$. The absence of quasielastic scattering at this temperature, together with the almost total account of the magnetic signal in the inelastic peak, shows that the excitation has a different origin than a splitting of the electronic levels due to crystal field potential. Instead, we propose a model in which the signal originates from inelastic excitations across two hybridization bands near the Fermi energy, usually referred to as a spin gap. A simple phenomenological two-level model can account for the peak in the specific heat, with a spin-gap energy of $36(2)\phantom{\rule{0.3em}{0ex}}\mathrm{meV}$, which is in very good agreement with the inelastic scattering data. Further, at $300\phantom{\rule{0.3em}{0ex}}\mathrm{K}$, the inelastic response becomes purely quasielastic, which is in agreement with the theoretical calculations. Interestingly, the spin-gap energy in $\mathrm{Ce}{\mathrm{Fe}}_{4}{\mathrm{Sb}}_{12}$ exhibits a universal scaling behavior with the Kondo temperature ${T}_{K}$. The relation between the spin-gap energy and the associated anomalies in the heat capacity or thermal expansion is discussed for a series of Ce- and Yb-based compounds.

Low-temperature heat capacity of sodium erbium molybdophosphate Na2Er(MoO4)(PO4)

Adiabatic calorimetry is used to measure the low-temperature heat capacity of Na2Er(MoO4)(PO4)from 6.41 to 347.87 K. Experimental data are used to calculate the thermodynamic functions of Na2Er(MoO4)(PO4), which at 298.15 K are as follows: C p 0 (298.15 K) = 243,3 ± 0.4 J/(K mol), S 0(298.15 K) = 312.8 ± 0.8 J/(K mol), H 0(298.15 K) − H 0(0 K) = 45280 ± 90 J/mol, and Φ0(298.15 K) = 136.1 ± 0.3 J/(K mol). A diffuse heat-capacity anomaly associated with splitting of the Stark levels (Schottky anomaly) is discovered in the low-temperature region.

Thermodynamic and optical properties ofNdCr3(BO3)4

We present magnetization and specific heat data as well as optical spectra of $\mathrm{Nd}{\mathrm{Cr}}_{3}{(\mathrm{B}{\mathrm{O}}_{3})}_{4}$ single crystals. At ${T}_{N}=8\phantom{\rule{0.3em}{0ex}}\mathrm{K}$, the magnetic and specific heat data imply long-range antiferromagnetic spin order of the ${\mathrm{Cr}}^{3+}$ subsystem. This observation is corroborated by the spectroscopic studies since in the ordered state the ${\mathrm{Nd}}^{3+}$ Kramers doublets are split by the internal staggered magnetic field. The splitting is also visible in a Schottky anomaly at the specific heat. In the spin-ordered phase, we find a staggered magnetic field at the Nd sites of $35\phantom{\rule{0.3em}{0ex}}\mathrm{kG}$ at $1.8\phantom{\rule{0.3em}{0ex}}\mathrm{K}$. The values ${\ensuremath{\lambda}}_{\mathrm{Nd}\text{\ensuremath{-}}\mathrm{Cr}}=3.9\phantom{\rule{0.3em}{0ex}}\mathrm{kG}∕{\ensuremath{\mu}}_{B}$ and ${\ensuremath{\lambda}}_{\mathrm{Cr}\text{\ensuremath{-}}\mathrm{Cr}}=29.4\phantom{\rule{0.3em}{0ex}}\mathrm{kG}∕{\ensuremath{\mu}}_{B}$ are obtained for the molecular-field constants of the Nd-Cr and the Cr-Cr interactions, respectively. The analysis of the magnetic susceptibility data points to the easy-plane type of the antiferromagnetic order. Several experimental manifestations of the low dimensionality of the title compound are mentioned.

Low-energy vibrational excitations ofMo6S3I6 nanowires revealed by low-temperature specific heat

We report on measurements of the low-temperature heat capacity ofMo6S3I6 nanowire-network samples in the form of a pressed pelletunder different conditions of annealing. In the temperature(T) rangeof liquid He4 and below, specific heat is dominated by three contributions: (i) phonons, forT>2 K, (ii) a nuclear hyperfine contribution, below 0.3 K, and (iii) a series of Schottky anomalies for2 K>T>0.1 K. In pristine samples, the phonon contribution varies asT2.6, which indicates a strongly anisotropic atomic structure. In the sample annealed at800 °C, this termvaries as T2.3, in agreement with a more one-dimensional (1D) structure, consistent with the transport properties.In comparison to other quasi-1D compounds, the departure from the 3D limit (corresponding to theusual T3 Debye law) is here very large, indicating a considerably loose interchain connection. Wediscuss the influence of stoichiometric disorder, especially the role of the position of theiodine atoms in the structure in both kinds of samples, the impact of topologicalimperfections and the possible origin of the observed Schottky anomalies.

Magnetic measurements and crystal field investigation on single crystals of Er(CF 3SO 3) 3·9H 2O

Single crystals of erbium tri-fluoromethanesulfonate (ErTFMS) were prepared from the slow evaporation of the aqueous solution. The principal magnetic susceptibilities perpendicular to the c-axis of the hexagonal crystal was measured down to 13 K. Principal magnetic anisotropy was also measured from 300 K down to 80 K which provides principal susceptibility parallel to the c-axis down to 80 K. A very good theoretical simulation of the thermal variation of principal magnetic susceptibilities of ErTFMS has been obtained with a crystal field (CF) of C 3h site symmetry, in which J-mixed eigenvectors and intermediate coupling effects have been used. No ordering effects were noticed down to the lowest temperature (13 K) attained, indicating the inter-ionic interaction to be of predominantly dipolar type. The g-values are found to be g ∣∣=8.86 and g ⊥=1.62, respectively. The Schottky anomaly in the electronic heat capacity at about 80 K has been computed from the Stark pattern. The thermal behavior of quadrupole splitting and hyperfine heat capacity were calculated from the CF analysis.

Magnetization and specific heat measurement of the Shastry–Sutherland lattice compounds: Ln 2BaPdO 5 (Ln = La, Pr, Nd, Sm, Eu, Gd, Dy, Ho)

Ln 2BaPdO 5 (Ln = La, Pr, Nd, Sm, Eu, Gd, Dy, Ho) all crystallizes in Nd 2BaZnO 5 structure which is proposed to have a Shastry–Sutherland (S–S) lattice of Ln 3+ ions. Ln 2BaPdO 5 (Ln = Nd, Sm, Gd, Dy, Ho) exhibits antiferromagnetic transitions at temperatures between 2 and 5 K. In addition, metamagnetic transitions have been observed for Ln 2BaPdO 5 (Ln = Nd, Dy, Ho) below 2 K. Specific heat of Ln 2BaPdO 5 (Ln = Ho, Dy) exhibits symmetric peaks at T N, and residual entropy below T N is negligibly small. On the contrary, specific heat of Ln 2BaPdO 5 (Ln = Nd, Sm, Gd) exhibits Schottky type anomalies followed by sharp peaks at T N, and residual entropy below T N is large. From these results, the applicability of the S–S model to Ln 2BaPdO 5 with various Ln 3+ ions is proposed.

Magnetic excitations and heat capacity of fayalite, Fe2SiO4

We have used inelastic neutron-scattering measurements to study the magnetic excitations in the antiferromagnetic and paramagnetic phases of polycrystalline fayalite, Fe2SiO4. Sharp, nondispersing excitations are found in the ordered state, at 3.3, 5.4, 5.9, and 11.4 meV, and are interpreted as arising from the spin-orbit manifold of the Fe2+ ions. These excitations are increasingly damped with increasing temperature, merging into a quasielastic continuum near the 65 K Neel temperature, although their energy does not vary with temperature. We have calculated the contribution of the heat capacity arising from these magnetic excitations and found that it compares favorably with the magnetic heat capacity deduced experimentally. Our analysis indicates that the M1 and M2 sites behave distinctly. The M1 site behaves quasi-locally and appears in the heat capacity as a Schottky anomaly that explains the shoulder in the heat capacity curve near 20 K, while the M2 site contributes predominantly to the critical lambda anomaly. The behavior of fayalite illuminates the nature of magnetic states in several related minerals, including others that also show shoulders and lambda anomalies in the heat capacity (tephroite), those that show only lambda anomalies (cobalt olivine and liebenbergite), and those that show only non-lambda anomalies (bronzite, anthophyllite, and almandine). We find no evidence to support the recent claim that some transition metal silicate and germanate olivines exhibit strong geometric frustration.

Crystalline Electric Field Effect and Magnetic Properties of CeRhSi3 Single Crystal

We have studied the crystalline electric-field effect of the noncentrosymmetric heavy-fermion antiferromagnet CeRhSi 3 by measuring the magnetic susceptibility χ( T ), specific heat C p ( T ) and inelastic neutron scattering. The 4 f level scheme determined from χ agrees with a magnetic excitation observed in the inelastic neutron spectra and the Schottky anomaly in the magnetic part of C p . Moreover, we have measured C p under various magnetic fields B up to 8 T and observed that the Neel temperature T N decreases proportionally to B 2 for B ∥ a -axis while the B dependence of T N is rather small for B ∥ c -axis. This anisotropic behavior suggests that the antiferromagnetically ordered moments lie in the tetragonal c -plane.

Magnetic properties of TbFe 3(BO 3) 4

Magnetization curves and temperature dependences of initial magnetic susceptibility of single-crystalline TbFe 3(BO 3) 4 are measured both along and perpendicular to the trigonal c-axis from 2 to 350 K. For T< T N=40 K, the spin-flop transition with small hysteresis and temperature-dependent magnetization jump is observed for H|| c. The H– T phase diagram is constructed. The highly anisotropic character of magnetic susceptibility is ascribed mainly to the Ising behavior of the Tb 3+ ion in the trigonal crystal field. The specific heat, measured up to 3 T at H|| c, is characterized by Schottky anomalies around 20 and 150 K associated with the change of occupation of excited energy levels of the Tb 3+ ion being split by f–d coupling and crystal field. All the properties and effects observed are described in the context of the unified approach, which is based on the mean-field approximation and crystal-field calculations. The main parameters of the compound are determined.

Magnetization and specific heat studies of RNi 4Ga (R [dbnd6]Sm, Gd and Tb)

In order to elucidate the anomalous magnetic properties in the ferromagnetically ordered state of SmNi 4Ga GdNi 4Ga and TbNi 4Ga, we have carried out a detailed study with magnetization and specific heat (SH) measurements. GdNi 4Ga shows the possibility of a filled 3d band and a helical spin arrangement below the ordering temperature. TbNi 4Ga shows a dominant crystal field effect resulting in a deviation of T C from the de-Gennes scaling and possible Schottky anomalies in the SH. SmNi 4Ga shows a large coercivity at low temperatures. A rough estimate of the domain wall thickness in SmNi 4Ga gives a value of 8 Å.

Magnetic properties of PrRhSn: A single-crystal study

A PrRhSn single crystal has been grown and investigated with respect to magnetic behavior. The magnetization and specific heat were measured as functions of temperature (range 2–300 K) and magnetic field (range 0–9 T) applied along the main crystallographic axes. A strong uniaxial magnetocrystalline anisotropy was observed with the c -axis as the easy magnetization direction. The transition temperature from paramagnetic to ferromagnetic state was determined to be T c = 2.85 ( 3 ) K . The specific heat data exhibit a Schottky anomaly just above T c . The anomaly is lifted to higher temperatures with an applied magnetic field along the c -axis yielding a considerable magnetocaloric effect.

Sm-based filled skutterudite [formula omitted] studied by specific heat

We report the specific heat C ( T ) of filled skutterudites SmOs 4 Sb 12 and LaOs 4 Sb 12 . The lattice specific heat of LaOs 4 Sb 12 has a contribution from characteristic low-energy phonon modes centered around ∼ 60 K . For SmOs 4 Sb 12 , considering the influence of a significant shift of the phonon modes toward low energy, we estimated the true electronic contribution in specific heat Δ C el . The obtained Δ C el / T in SmOs 4 Sb 12 steeply increases below 20 K without indicating a Schottky anomaly.

Specific heat of geometrically frustrated and multiferroicRMn1−xGaxO3(R=Ho,Y)

Specific heat measurements on single crystals of $R{\mathrm{Mn}}_{1\ensuremath{-}x}{\mathrm{Ga}}_{x}{\mathrm{O}}_{3}$ $(R=\mathrm{Ho},\mathrm{Y})$ have revealed that Ga doping raises the Mn-spin reorientation temperature ${T}_{\mathrm{SR}}$ while lowering the antiferromagnetic ordering temperature, ${T}_{\mathrm{N}}$, of the Mn spins and the Ho magnetic ordering temperature ${T}_{2}$. The variations of the calculated magnetic entropy with Ga doping show the existence of spin fluctuations above ${T}_{\mathrm{N}}$ in the geometrically frustrated Mn-spin system and a coupling between the ${\mathrm{Mn}}^{3+}$-ion and ${\mathrm{Ho}}^{3+}$-ion spins both at ${T}_{\mathrm{SR}}$ and ${T}_{2}$. The data also support Schottky anomalies in the specific heat of $\mathrm{Ho}{\mathrm{Mn}}_{1\ensuremath{-}x}{\mathrm{Ga}}_{x}{\mathrm{O}}_{3}$, which is dominated by crystalline electric fields but also affected by ${\mathrm{Mn}}^{3+}$-ion spin orderings. The large electronic contribution to specific heat of $\mathrm{Ho}\mathrm{Mn}{\mathrm{O}}_{3}$, $\ensuremath{\gamma}$, is suggested to be due to ${\mathrm{Ho}}^{3+}$ spin disorder.

Magnetic and transport properties of Yb 5T 4Ge 10 (T=Co, Rh, Ir)

The magnetic and transport properties of Yb 5T 4Ge 10 and Lu 5T 4Ge 10 (T=Co, Rh, Ir) have been investigated. All Yb compounds are metals with the paramagnetic state above 1.2 K. Some magnetic transition is commonly expected below 1.2 K from the result of the specific heat. Single crystal of Yb 5Rh 4Ge 10 has been grown by the Bridgman method. Magnetic susceptibility of Yb 5Rh 4Ge 10 shows a strong anisotropy with the easy-plane type within the c-plane. At 2 K, magnetization of Yb 5Rh 4Ge 10 for H∥ a gradually increases as increasing the magnetic field and saturates to a constant value of 4.5 μ B/f.u. in H = 5 0 kOe in contrast to magnetization for H∥ c, which keeps increasing to 0.9 μ B/f.u. in H = 5 0 kOe . The magnetic part of the specific heat for Yb 5Rh 4Ge 10 shows the Schottky anomaly centered at about 60 K due to the CEF effect, which acts on the eight-hold multiplet of Yb 3+ ion. Furthermore, a broad peak appears at low temperatures by the application of the magnetic field. Height of this peak is very low as compared to the Schottky peak expected for the two-levels split from the ground state doublet for five Yb 3+ ions in formula unit. The magnetic entropy gain in the magnetic field for Yb 5Rh 4Ge 10 at 300 K does not attain to 5 R ln8, therefore, there is a possibility that the mixed valence state consisted of three or four Yb 3+ ions among five Yb ions in formula unit is realized in all temperature range. A similar situation is found in Yb 5Co 4Ge 10 and Yb 5Ir 4Ge 10.