Anomalous thermal expansion in the paramagnetic phase of dysprosium and terbium-50% holmium

The c-axis thermal expansion and expansion coefficients have been measured over the temperature range T_N < T < 273 K in single crystal dysprosium and terbium-50% holmium. The data show abrupt changes in the expansion coefficients at approximately 226 K in dysprosium and 250 K, 212 K and 196 K in terbium-50% holmium. Departures from lattice Grüneisen behaviour occur at temperatures well in excess of the Néel temperatures.     

Temperature and concentration dependences of thermal conductivity of solid solutions of gadolinium and dysprosium sulfides

Thermal conductivity of a number of solid solutions of gadolinium and dysprosium sulfides has been studied experimentally within the temperature range 80-400 K. The work offers the data on thermal conductivity coefficient and lattice thermal conductivity of the studied samples. It was found that replacement of gadolinium ions by dysprosium ions leads to significant decrease of the samples?? thermal conductivity and changes its temperature dependence character due to the resonance scattering of phonons by paramagnetic ions of dysprosium. Influence of this mechanism of phonon scattering conditions the area of anomalous change observed on the concentration dependence of thermal conductivity coefficient.     

Temperature dependence of the giant magnetostriction of submicrocrystalline dysprosium

The temperature dependence of the magnetostriction of Dy was measured in various structural states. A submicrocrystalline state was created by intense plastic deformation on Bridgman anvils. Intermediate-and large-grain states were obtained by annealing samples in a vacuum at 573 and 873 K respectively. In the large-grain state, plots of the magnetostriction versus temperature exhibit a kink at around 85 K, which is evidence of a magnetic phase transition from ferromagnetism to helical antiferromagnetism. In the submicrocrystalline state these curves have no kinks and decrease smoothly to zero at high temperatures. This is interpreted as the absence of helical antiferromagnetic order in the sample. Fiz. Tverd. Tela (St. Petersburg) 41, 1665–1667 (September 1999)     

Thermal expansion and relaxation of magnetostriction in a metastable state of dysprosium orthoaluminate

A study of thermal expansion and magnetostriction caused by the metamagnet phase transition in a rare earth sublattice was performed for a DyAlO₃ single crystal, which is the model object of a wide family of rare earth oxides with the structure of distorted perovskite. The sharp variation of the relative strains along the b axis 3.6 × 10⁻⁵ was found at T ≌ 2.18 K. The nature of the observed anomaly is caused by the occurrence of a metastable state of the magnetic subsystem achieved in the conditions of the experimental process. The relaxation of magnetostriction is studied and the exponential character is found. The possible mesoscopic nature of thermal and quantum mechanisms of magnetic relaxation is considered.     

Low temperature thermal expansion and magnetostriction of TmCd

Thermal expansion measurements in various external magnetic fields confirm the recently found Jahn-Teller transition in TmCd at 3.16 K. The tetragonal strain ?₃ at T = 0 K is found to be 0.62 × 10^?3. From magnetostriction data we determine a coupling constant g₀² = 0.4 × 10^?3 K which is in good agreement with the value found from ultrasonic experiments. In order to explain our magnetostriction results in the cubic phase, g₀ has to be taken negative.     

Dispersion relations and lattice thermal expansion of dysprosium

The lattice dynamics, second and third order elastic constants and the lattice thermal expansion of dysprosium have been calculated using Keating's approach. The ten third order elastic constants are calculated using four anharmonic parameters. The present model reproduces the measured pressure derivatives of the second order elastic constants of dysprosium well. The low and high temperature limits γ?_I and γ?_H of the lattice thermal expansion are evaluated and the agreement between the calculated γ?_H and that obtained from the thermal expansion and specific heat data is satisfactory.     

Interferometric measurements of the anomalous thermal expansion in single crystal dysprosium and 60% Gadolinium-Yttrium

An optical interferometer technique employed in the measurement of the c-axis thermal expansion in single crystal Dy confirms previous strain gauge observations that the expansion and Néel temperature are dependent on the internal strain in the crystal. The technique reveals that similar effects can be observed in single crystal 60% Gd-y although this material is less susceptible than dysprosium to internal strain produced by thermal cycling. The consequences of the deviations in c-axis expansion are discussed.     

Thermal expansion and ultrasonic attenuation anomalies in antiferromagnetic dysprosium and terbium-50% holmium

Anomalies in the c-axis thermal expansion of single crystal Dy and Tb-50% Ho have been observed at 113.0 ±1.0 K and 121.5 ±1.0 K respectively. In dysprosium this is accompanied by an anomalous increase in the attenuation coefficient, α₄₄, of 15 MHz ultrasonic shear waves propagated along the c-axis. In both materials the anomaly occurs when the helical turn angle, as measured by neutron diffraction, assumes a values of 30°. The observations are compared with a similar effect in holmium and discussed in terms of a model involving helical spin domains which may be commensurate, or otherwise, with the crystal lattice.     

Temperature dependence of thermal expansion coefficient of crystals with cubic syngony

A simple analytic temperature relationship for the thermal expansion coefficient of crystals with cubic syngony was obtained, and the thermal expansion coefficients of some crystals of this class were determined experimentally; the results agreed satisfactorily with the curve obtained from formulas (5) and (6). The temperature range from liquid nitrogen up to temperatures around 1000 ° K was investigated, and the results were compared with data given by other authors.     

Magnetocrystalline anisotropy and magnetostriction of Fe-Si-Al (Sendust) single crystals

The magnetocrystalline anisotropy constant, K₁ and the magnetostriction constants, λ₁₀₀ and λ₁₁₁ for the Sendust alloys were determined at 300 K in the composition region, 7.5–11.0 wt%Si, 4.0–7.0 wt%Al, bal. Fe. The line of K₁ = 0 in the Fe-Si-Al alloy system was found to lie around 7.0–9.5 wt%Si, 5.5 wt%Al, bal.Fe and 9.5 wt%Si, 5.5–7.0 wt%Al bal.Fe compositions. The line of λ_s = 0 was also determined as a function of Fe, Si and Al contents. Both lines of K₁ = 0 and λ_s = 0 intersect at the composition, 9.6 wt%Si, 5.5 wt%Al, bal.Fe. This alloy composition is close to those for alloys with high initial and maximum permeabilities. The line of K₁ = 0 determined by the present experiment is found to be different from that of Zaimovsky and Selissky. The line of λ_s = 0 is similar to their results.     

Derivation of magnetostriction constants for ferrite single crystals by ferromagnetic resonance

Anisotropic elastic stresses are used with discs. Formulas are derived for the saturation magnetostriction constants in terms of the observed shifts in the resonance field. Results are reported for manganese, lithium, and yttrium ferrites.     

Calculation of thermal stresses in profiled single crystals taking into account the temperature dependence of thermal expansion

Approximate expressions for stress tensor components in cylindrical and ribbon crystals are obtained taking into account the temperature dependence of the thermal expansion coefficient. These expressions are used for estimating the effect of the thermal expansion nonlinearity factor on the stress level. It is shown that the stresses emerging in linear temperature fields due to this factor are comparable with critical stresses for defect formation.     

Peculiarities of thermal expansion of layered crystals

Linear expansion coefficients parallel, α_□, and perpendicular, α_⊥, to layer plane of GaS, GaSe, and TlGaS₂ are investigated in the temperature range 5–300 K. Negative values of α_□ are observed in GaS and GaSe in the range of 30–50 K caused by negative Gruneisen parameters γ_□ in this interval. It is shown that negative α_□ in layer crystal can be due to TA_⊥ acoustic branch contribution to α_□.     

Thermal expansion of dysprosium tetraboride

The temperature variations of the interplanar spacings a(T) and c(T) in the crystal lattice of dysprosium tetraboride have been studied using X-ray diffraction in the temperature range 5?C300 K. Anomalous variations of a(T) and c(T) in the temperature range of magnetic transformations, anisotropy of the thermal expansion of DyB₄, and the monoclinic distortion of the crystal structure at low temperatures have been revealed. The magnitudes of the spontaneous magnetostriction, the thermal expansion coefficients ??a and ??c, and the exchange integrals Y _a and Y _c have been determined.     

Mechanical behaviour and fracture mechanism of flux grown holmium orthoferrite single crystals

Results of indentation induced microhardness and fracture studies on (110) and (001) planes of flux grown HoFeO₃ single crystals using a Vicker's hardness tester, in the load range of 10-100 g are presented. The variation of microhardness with load is found to be non-linear and is explained by using Hays and Kendall's law. The hardness results and the indentation-induced cracking yields the values of the yield strength, fracture toughness and brittleness index for (110) and (001) planes of HoFeO₃ crystals. Transition from Palmqvist to median crack systems takes place at higher loads for (110) plane of the crystal whereas (001) plane is characterized by Palmqvist cracks only.     

Analysis of thermal expansion of NaCl and KCl crystals

We derived new expressions for volume expansion ratio, thermal expansivity and higher order temperature derivative of volume with the change in temperature. The relationships are developed on the basis of suggestion made by Wang and Reeber [12]. We used a relationship demonstrating the temperature dependence of isothermal bulk modulus due to Srivastava et al. [13] to generate various other expressions. The model is applied on NaCl and KCl crystals. The superiority of the presented formulations over other identical formulations is shown. A close agreement between theory and experiment reveals the validity of the present work.     

Large magnetostriction and negative thermal expansion in the frustrated antiferromagnet ZnCr2Se4

A detailed investigation of ZnCr2Se4 is presented which is dominated by strong ferromagnetic exchange but orders antiferromagnetically at TN=21 K. Specific heat and thermal expansion exhibit sharp first-order anomalies at the antiferromagnetic transition. TN is shifted to lower temperatures by external magnetic fields and finally is fully suppressed by a field of 65 kOe. The relative length change DeltaL/L(T) is unusually large and exhibits negative thermal expansion alpha below 75 K down to TN indicating strong frustration of the lattice. Magnetostriction DeltaL/L(H) reveals large values comparable to giant magnetostrictive materials. These results point to a spin-driven origin of the structural instability at TN explained in terms of competing ferromagnetic and antiferromagnetic exchange interactions.