Single Crystals Of Tb Research Articles

Collapse of a region of the magnetic phase diagram of elemental terbium under a strain-induced Lifshitz transition

AC susceptibility and neutron scattering measurements are used to study the magnetic field-temperature magnetic phase diagram of a Tb single crystal under uniaxial tension along its hexagonal $c$ axis. An external magnetic field is applied in the basal plane. We focus on the region in the phase diagram that corresponds to the helical antiferromagnetic phase and find that this region collapses when the uniaxial tension is increased beyond a critical value as low as 600 bar. There are strong reasons to associate this collapse with an underlying Lifshitz transition in the Fermi surface of Tb's valence electrons. We use a finite-temperature ab initio theory to analyze our measurements, obtaining a pressure-temperature magnetic phase diagram in very good agreement with experiment. Our calculations indicate that short- and long-range magnetic order has a crucial effect on the Fermi surface nesting and consequent magnetism of Tb.

Characteristic Features of the Anomalous Magnetic Properties of Some Mixed Terbium–Yttrium Ferrite Garnets at Low Temperatures

This article is devoted to the experimental investigation of the occurrence of the so-called “low-temperature Belov point” T <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">B</sub> predicted previously for the mixed rare earth-yttrium iron garnet compounds RE <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">x</sub> Y <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">3-</sub> <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">x</sub> Fe <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">5</sub> O <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">12</sub> possessing or not a magnetic compensation point T <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">comp</sub> . Isothermal magnetizations MT(H) of two single crystals of Tb <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">x</sub> Y <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">3-x</sub> Fe <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">5</sub> O <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">12</sub> with rare-earth (RE) = Tb, and x = 1.98, 0.37, were measured in the 4.2-300 K range, using dc magnetic field H up to 100 kOe applied in one or more of the three main crystallographic directions. Anomalies are observed in the region of T <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">B</sub> <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">TbIG</sup> ≈ 58 K, the previous estimated value for TbIG (x = 3), in the temperature dependences of the paraprocess susceptibility χ <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">p</sub> , the parameter |b| of the bH <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sup> term of the quadratic expansion of MT(H) curves, and other pertinent magnetic characteristics. For x = 1.98 with T <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">comp</sub> = 137 K and when H is applied along (110), the χ <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">p</sub> - and |b|-maxima take place close to T <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">B</sub> <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">TbIG</sup> . The anisotropy of the χ <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">p</sub> -data gives evidence for a spontaneous noncollinear structure around the easy axis of magnetization (111) at 4.2 K. For x = 0.37 which has no T <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">comp</sub> point and when H is applied along (100), the χ <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">p</sub> - and |b|-maxima are clearly disturbed by the sign anomalies caused by the noncollinear structure instability mechanism due to the crossing of the Tb <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">3+</sup> levels at the critical point T* = 16 K and by the lower continuous change from the easy axis <;100> to a low-symmetry angular phase (uuw) due to the first spontaneous spin reorientation phase transition at T <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">SR1</sub> = 40 K. When x decreases from 3 to 0.37, it is found that despite different anisotropy effects of the Tb <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">3+</sup> ion, its magnetic moment m <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">Tb</sub> close to T <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">B</sub> <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">TbIG</sup> is practically constant (~4.99 in μ <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">B</sub> per Tb <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">3+</sup> ion).

Rotating-Sample Magnetometer for Measuring Crystal Field Parameters

A method of measuring crystal field parameters by means of a rotating-sample magnetometer is presented. The measurement is performed by registering 2nd, 4th and 6th harmonics of the signal that is proportional to magnetization change due to rotation of the sample in a magnetic field. Experimentally measured temperature dependence of the amplitudes of these harmonics is used to determine the crystal field parameters within the framework of the theoretical model proposed in [. The signal is detected by a digital lock-in amplifier, while temperature is controlled by a PID controller. The sample and pickup coils are located in the bore of a Halbach permanent magnet. The measurements are fully automated. Magnitude of the expected signal was estimated. Test measurements of magnetization of the Tb single crystal along a axis (in the easy crystallographic plane a-b) in the permanent magnetic field 2.7 T at room temperature were performed. The results show that sensitivity of the instruments and the proposed design of the equipment allows us to determine crystal field parameters of heavy rare-earth metals. Testing of the control software showed that computer-device communications and execution of the software blocks are correct.

Optical and thermal properties of crystalline Tb: KLu(WO 4) 2

A single crystal of Tb: KLu(WO 4) 2 with dimensions of 40 mm × 40 mm × 18 mm has been grown by the top-seeded solution growth (TSSG) method. The color of the crystal is brown. Absorption and fluorescence spectra were measured at room temperature. The measured specific heat is a little lower than that of Yb: KLW (0.365 J/g K) at 90 °C. The measured mean linear coefficients of thermal expansion are α a = 17.1643 × 10 − 6 K − 1 , α a ⁎ = 14.0896 × 10 − 6 K − 1 , α b = 8.7938 × 10 − 6 K − 1 , α c = 23.1745 × 10 − 6 K − 1 , α c ⁎ = 20.2866 × 10 − 6 K − 1 . The results indicate that the crystal has a large anisotropy. The refractive index was measured.

Temperature dependence of magnetic EXAFS for rare earth elements

A systematic study of the x-ray magnetic circular dichroism at the L3 edge is presented for Gd and Tb single crystals in the extended energy range (MEXAFS). The investigation of the dichroic signal in this energy range is especially interesting for rare earth metals because the relative intensity of the magnetic EXAFS to the near edge signal (XMCD) is much larger compared to 3d transition metals. This is because the MEXAFS for the rare earth elements is essentially proportional to the total 4f magnetic moment, whereas the XMCD is dominated by dipole transitions to the spin-dependent 5d densities of states only. The temperature dependence of the magnetic EXAFS originates both from spin fluctuations and lattice vibrations. We present a new procedure to separate these contributions by modeling the absorption coefficients μ+(E) and μ−(E) for right and left circularly polarized x-rays, by the energy shifted experimental spin-averaged spectra. The temperature dependence of the MEXAFS can then be described by a temperature-dependent energy shift ΔE(T) which is proportional to the temperature-dependent magnetization M(T). Furthermore, multiple and single scattering contributions in the MEXAFS are separated by comparison of the experimental data to ab initio calculations using the FEFF8 code.

Synthesis, structure, and magnetism of Tb 4PdGa 12 and Tb 4PtGa 12

Single crystals of Tb 4 MGa 12 ( M=Pd, Pt) have been synthesized. The isostructural compounds crystallize in the cubic space group Im 3 ¯ m , with Z = 2 and lattice parameters: a=8.5940(5) and 8.5850(3) Å for Tb 4PdGa 12 and Tb 4PtGa 12, respectively. The crystal structure consists of corner-sharing MGa 6 octahedra and TbGa 3 cuboctahedra. Magnetic measurements suggest that Tb 4PdGa 12 is an antiferromagnetic metamagnet with a Néel temperature of 16 K, while the Pt analog orders at T N = 12 K.

Elastic anomaly in Tb under uniaxial tension: Evidence of the change in the Fermi surface topology responsible for the magnetic ordering type

A single crystal of Tb was examined under uniaxial tension applied along the hexagonal axis by a x-ray dilatometry and resistive strain sensors. The experiment was carried out well above the magnetic ordering temperature.The strain-stress dependencies obtained exhibit the characteristic violation of linearity that is evidently due to the change in the Fermi surface topology caused by strain. This electron-topological transition is presumably responsible for the recently observed change in the magnetic ordering type in the same sample.

Quadrupolar and dipolar contributions to x-ray magnetic circular dichroism at the Tb L3,2 edges: Experiment versus theory

We investigate the x-ray magnetic circular dichroism (XMCD) at the L3,2 edges using a single crystal of Tb as a prototype system for a one-element magnet in order to ascertain the multipolar nature of the features in the dichroic spectra. The high resolution of the experimental data allows for a clear identification of the dipolar (E1: 2p→5d) and quadrupolar (E2: 2p→4f) transitions. On the basis of ab initio calculations we developed a simple procedure to extract the quadrupolar part by subtracting the derivative of the spin-averaged absorption spectra from the experimental XMCD data. The deconvolution has to be carried out before applying sum rules to determine 4f and 5d moments.

The magnetic characteristics of the Tb(Ni 1− xCo x) 2Ge 2 system

The compounds TbNi 2Ge 2 and TbCo 2Ge 2 both crystallize with the ThCr 2Si 2 structure. TbNi 2Ge 2 has a complex H– T phase diagram while TbCo 2Ge 2 has a much simpler, though disputed phase diagram. In order to investigate the effects on the magnetism of TbNi 2Ge 2 due to cobalt substitution, single crystals of Tb(Ni 1− x Co x ) 2Ge 2 with x ranging from 0 to 1 have been grown from a psuedoternary melt. We have traced the Néel and Weiss temperatures as a function of cobalt concentration, x. Close to x=0.5, the Weiss temperature is positive, indicating predominately ferromagnetic interactions (in contrast to x<0.4 and x>0.6 for which the Weiss temperatures are negative), χ( T≈ T N) is a maximum and the critical field for metamagnetism is a minimum. Nevertheless, the compound orders antiferromagnetically, similar to all other members of the dilution series.

Growth and spin reorientation transition of Tb(Fe,Ti) 12 single crystal

Single crystals of Tb(Fe,Ti) 12 have been grown by the Czochralski technique with cold crucible. Unknown solidifying property of Tb(Fe,Ti) 12 system has been defined as the peritectic. It usually generates a complex of α-Fe and TiFe 2 as non-host phases with a titanium content of 25 at%. Another important solidification behavior, segregation of titanium, is verified by chemical analysis. The segregation coefficient, k eff=0.92, is obtained by calculation based on a normal solidification model. Single crystalline samples of Tb(Fe,Ti) 12 compounds, without non-host phase impurities, and with precisely determined titanium concentration, have been used to measure a series of spin reorientation transition temperature ( T SR). The disputed T SR for TbFe 11Ti has been confirmed as 290 K. It has been found that the T SR is very sensitive to the Ti concentration in the samples. The mechanism for T SR being strongly affected by titanium and the possible reason for the uncertain value of T SR in the previous works are also discussed.

Tb magnetic moment behaviour in a Gd single crystal: nuclear orientation study

Low-temperature nuclear orientation has been used to study the behaviour of the Tb magnetic moment in a Gd + 1 at.% Tb single crystal. The -ray anisotropy of several lines was monitored in the temperature range of 5-50 mK and in the external magnetic field range of 0-8.5 T. The field was applied either along the a- or along the c-axis of the Gd single crystal. In the case of parallel to the a-axis the Tb magnetic moment was found to be almost aligned along even at very low fields, as expected because the hexagonal basal plane is an easy magnetization plane for the Tb ion in terbium metal. On the other hand, when is along the c-axis the Tb magnetic moment rotates very slowly towards the c-axis. Even at the Tb magnetic moment is not along the direction of . This is in contrast to the fast saturation of the gadolinium ions in pure Gd. Apparently, the Tb-Gd exchange interaction is in competition with the crystal field acting on the Tb ion in a hexagonal lattice, our data indicates that at along the c-axis the angle between the Tb magnetic moment and the applied field is of the order of .

Research of energy transfer in Y 2SiO 5Ce, Tb single crystals by time resolved luminescence spectroscopy

The energy transfer between the rare-earth ions in Y sSiO 5Ce, Tb crystals has been investigated with the use of the methods of luminescence spectroscopy with subnanosecond time resolution and excitation by pulsed synchrotron radiation (SR). Effective nonradiative energy transfer between Ce 3+ and Tb 3+-ions which is realized by the inductive resonance mechanism has been observed. The absolute constant of the energy transfer speed K t and the probability of transfer have been determined. A dependence of the energy transfer parameters on the SR-excitation density has been discovered and investigated. Increasing of the density of the SR-excitation by a factor of 10 results in the increase of K t from 4.8 × 10 8 up to 1.7 × 10 10mol −1 s −1.

Lattice location and magnetism of Fe and Sc impurities in Gd and Tb single crystals

We used the in-beam TD perturbed angular distribution (PAD) technique to investigate the magnetism and lattice location of dilute impurities of Sc and Fe implanted into single-crystal Gd and Tb host lattices. Sc is observed to implant on a unique site, which is almost certainly substitutional. The T = 0 hyperfine field B hf(0) is found to be −5.22(1) T in Gd host and −3.91(3) T in Tb host, both values being corrected for demagnetizing and Lorentz fields. At higher temperatures, the hyperfine fields deviate from the host lattice magnetization M(B,T); the local susceptibilities however follow Curie-Weiss laws similar to those of the hosts. Fe is found to implant onto two lattice sites, which can be identified by comparison with the similar host Y as substitutional and interstitial sites. The hyperfine fields are small and positive on both sites, but distinctly larger on the substitutional site. Again, Curie-Weiss behavior is found for the local susceptibilities up to 500 K in both hosts. Fe signals are unobservable below T C, probably owing to line broadening.

Precision measurement of theg-factor of the 2+ ?-vibrational state of160Dy and test of theF-spin purity

The rotations of the 392-966 keV and the 299–966 keV directional correlations of160Dy in the static hyperfine field of DyTb have been measured with high precision. A neutron activated Tb single crystal was used which was magnetized to saturation at 4.2 K by an external magnetic field of 4.5 T applied in the direction of theb-axis. The agreement of both rotations proves that the relaxation of the 4f-shell after theβ-decay takes less than 10 ps. A quantum mechanical calculation within the magnon model gave a relaxation time of the order of 1 ps. Theg-factor of the 2+γ-vibrational state was derived as $$g(2_\gamma ^ + ) = + 0.317(12)$$ and combining our results with Mossbauer data [24] on the magnetic splitting of the 2rot+ state in the same environment we obtain $$g(2_\gamma ^ + )/g(2_{rot}^ + ) = 0.82(3).$$ . The results are discussed within the Bohr-Mottelson model and finally within the IBM-2 model in terms ofF-spin purity.

Growth of Tb0.27DY0.73Fe2 magnetostrictive single crystals

Tb 0.27 DY 0.73 Fe 2 single crystal is a new kind of excellent magnetostrictive material with high λ s at room temperature. We have grown large-size Tb 0.27 DY 0.73 Fe 2 (Terfenol) single crystals completely without contamination using a magnetic levitation cold crucible CZ (Czochralski) technique. In the growth by this method, the starting materials Tb (99.95 wt%), Dy (99.98 wt%), Fe and Mn (99.99 wt%) are used to synthesize the precursor alloy. The weight of each loading is generally 80–100 g. A pulling rate of 1–10 mm/h and a rotation of 5–20 rpm are chosen. The single crystals of Tb 0.27 DY 0.73 Fe 2 grown under such conditions usually have a growth direction close to [112]. In order to improve the magnetostrictive properties of the Terfenol single crystal, Mn-doped alloy (Tb 0.27 DY 0.73 Fe 2−ϰ Mn ϰ ) single crystal is also prepared under similar conditions. The difference between the growth conditions is discussed also in this paper.

Static and dynamic properties of the high anisotropy ferrimagnets I. Experiment

Magnetization, differential magnetic susceptibility measurements and magnetic resonance study in the millimeter wave range are presented for single crystals of Tb x Y 3-x Fe5O 12 ( x

Nuclear orientation of 160Tb in Tb single crystal.

Nuclear orientation of {sup 160}Tb in a Tb single crystal has been carried out in order to obtain accurate values of multipole mixing ratios for 22 transitions in {sup 160}Dy. The experimental aspects are described in some detail as they form the basis for obtaining high quality data. Three different methods were used to extract the mixing ratios, and they are shown to agree very well. Our results for both {ital E}1/{ital M}2 and {ital E}2/{ital M}1 transitions are compared to other measurements. The signs and magnitude of the {ital E}1/{ital M}2 mixing ratios cannot be explained on the basis of Coriolis mixing of the {ital K}=0, 1, and 2 bands. Comparison of our results for the 299, 1178, and 1272 keV transitions with those from {gamma}-{gamma} directional correlation measurements indicate that some {ital E}3 admixture may be present in these transitions. The mixing ratios we obtained for the {ital E}2/{ital M}1 transitions are in reasonably good agreement with the predictions of the interacting-boson-approximation-1 model.

Magnetostriction in Tb&amp;lt;inf&amp;gt;.27&amp;lt;/inf&amp;gt;Dy&amp;lt;inf&amp;gt;.73&amp;lt;/inf&amp;gt;Fe&amp;lt;inf&amp;gt;2&amp;lt;/inf&amp;gt;: Evidence for a low-temperature transition

We report magnetostriction measurements on a single crystal of Tb <inf xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">.27</inf> Dy <inf xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">.73</inf> Fe <inf xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</inf> . Length changes parallel and perpendicular to a 111 direction were measured from 298 to 3.1K in magnetic fields from zero to 25kOe. The λ vs H curves show saturation at low fields above 280K; below 280K λ becomes progressively more difficult to saturate until approximately 65K at which temperature the magnetostriction begins to increase again. This upturn is taken as evidence for the existence, at low temperatures and low magnetic fields, of a non-colinear ferrimagnetic phase with the net moment in the (uuw) plane. The temperature and field dependence of λ is discussed by means of a Ginsburg-Landau model of the low temperature transition from a colinear, [100]-easy phase to the [uuw] phase.

Magnetoelastic coupling in dilute magnetic alloys

We present magnetostriction measurements on dilute magnetic alloys. Systematic investigation has been performed on monocrystals through the silver–rare earth and gold–rare earth series. The results present very different behavior from one RE to another, but we obtain a very good agreement with a single ion model; we deduce the magnetoelastic coupling parameters which appear to be quite constant along the series and clearly in contradiction with the prediction of a point charge model. Measurements on a (LaAg)Tb single crystal give similar results and we are able to explain some surprising observations obtained on polycrystalline (YPd3)RE alloys.

Magnetic Structure of Tb0.5Er0.5Alloy

Neutron diffraction studies on a single crystal of Tb 0.5 Er 0.5 alloy which had been considered to be a tilted helix structure from magnetization measurements, have been carried out at 4.2 K. It has been found that not only the fundamental satellites, but also the very weak 5th and 7th order harmonic satellites are observable at 4.2 K. From the analyses of the observed structure factors, the magnetic structure could be interpreted to be a homogeneous tilted helix with a tilt angle of 17° for both Tb and Er moments at 4.2 K. The appearance of the higher order satellites suggests a bunching state where the magnetic moments projected in the basal plane bunch about the easy directions. On the basis of the theory of Sherrington, the stability of tilted helical ordering in the ground state is briefly discussed.