Principal Crystallographic Axes Research Articles

Magnetic-field-controlled growth of magnetoelastic phase domains in FeRh

Magnetic phase transition materials are relevant building blocks for developing green technologies such as magnetocaloric devices for solid-state refrigeration. Their integration into applications requires a good understanding and controllability of their properties at the micro- and nanoscale. Here, we present an optical microscopy study of the phase domains in FeRh across its antiferromagnetic–ferromagnetic phase transition. By tracking the phase-dependent optical reflectivity, we establish that phase domains have typical sizes of a few microns for relatively thick epitaxial films (200 nm), thus enabling visualization of domain nucleation, growth, and percolation processes in great detail. Phase domain growth preferentially occurs along the principal crystallographic axes of FeRh, which is a consequence of the elastic adaptation to both the substrate-induced stress and laterally heterogeneous strain distributions arising from the different unit cell volumes of the two coexisting phases. Furthermore, we demonstrate a magnetic-field-controlled directional growth of phase domains during both heating and cooling, which is predominantly linked to the local effect of magnetic dipolar fields created by the alignment of magnetic moments in the emerging (disappearing) FM phase fraction during heating (cooling). These findings highlight the importance of the magnetoelastic character of phase domains for enabling the local control of micro- and nanoscale phase separation patterns using magnetic fields or elastic stresses.

Magnetic Phase Diagram of van der Waals Antiferromagnet TbTe3.

Terbium tritelluride, TbTe3, orders antiferromagnetically in three steps at TN1 = 6.7 K, TN2 = 5.7 K, and TN3 = 5.4 K, preceded by a correlation hump in magnetic susceptibility at T* ~8 K. Combining thermodynamic, i.e., specific heat Cp and magnetization M, and transport, i.e., resistance R, measurements we established the boundaries of two commensurate and one charge density wave modulated phases in a magnetic field oriented along principal crystallographic axes. Based on these measurements, the magnetic phase diagrams of TbTe3 at H‖a, H‖b and H‖c were constructed.

The role of the solidification structure on orientation-dependent hardness in stainless steel 316L produced by laser powder bed fusion

Owing to the rapid cooling rates and directional thermal gradients involved, fusion-based additive manufacturing (AM) processes yield complex, fine solidification structures that impart anisotropic mechanical properties in materials, such as stainless steel 316L (SS316L). In this work, we present a comprehensive study of the mechanical anisotropy of SS316L produced by laser powder bed fusion using instrumented nanoindentation. We produce and test near-single crystal samples oriented along the three principal crystallographic axes—namely ⟨100⟩, ⟨110⟩, and ⟨111⟩—using a Berkovich indenter. We find that the ⟨111⟩ and ⟨100⟩ orientations exhibit the highest and the lowest hardness, respectively. To decouple the contributions of grain orientation and solidification structure to the alloy's mechanical anisotropy, we compare our experimental results against crystal plasticity finite element (CPFE) simulations. We ascribe the hardness anisotropy in SS316L to the cell spacing along the slip direction (CSSD), which is a novel metric that we introduce to account for the role of the solidification structure on plasticity. Our work provides a universal pathway to understanding the microstructure-property relationships in cubic metallic materials that exhibit solidification structures,such as those commonly imparted by fusion-based AM.

Allanite at high temperature: effect of REE on the thermal behaviour of epidote-group minerals

The thermal behaviour of a natural allanite-(Ce) has been investigated up to 1073 K (at room pressure) by means of in situ synchrotron powder X-ray diffraction and single-crystal neutron diffraction. Allanite preserves its crystallinity up to 1073 K. However, up to 700 K, the thermal behaviour along the three principal crystallographic axes, of the monoclinic β angle and of the unit-cell volume follow monotonically increasing trends, which are almost linear. At T > 700–800 K, a drastic change takes place: an inversion of the trend is observed along the a and b axes (more pronounced along b) and for the monoclinic β angle; in contrast, an anomalous increase of the expansion is observed along the c axis, which controls the positive trend experienced by the unit-cell volume at T > 700–800 K. Data collected back to room T, after the HT experiments, show unit-cell parameters significantly different with respect to those previously measured at 293 K: allanite responds with an ideal elastic behaviour up to 700 K, and at T > 700–800 K its behaviour deviates from the elasticity field. The thermo-elastic behaviour up to 700 K was modelled with a modified Holland–Powell EoS; for the unit-cell volume, we obtained the following parameters: VT0 = 467.33(6) Å3 and αT0(V) = 2.8(3) × 10–5 K−1. The thermal anisotropy, derived on the basis of the axial expansion along the three main crystallographic directions, is the following: αT0(a):αT0(b):αT0(c) = 1.08:1:1.36. The T-induced mechanisms, at the atomic scale, are described on the basis of the neutron structure refinements at different temperatures. Evidence of dehydroxylation effect at T ≥ 848 K are reported. A comparison between the thermal behaviour of allanite, epidote and clinozoisite is carried out.

Tuning Magnetic and Transport Properties in Quasi-2D (Mn1−xNix)2P2S6 Single Crystals

We report an optimized chemical vapor transport method to grow single crystals of (Mn1−xNix)2P2S6 where x = 0, 0.3, 0.5, 0.7, and 1. Single crystals up to 4 mm × 3 mm × 200 μm were obtained by this method. As-grown crystals are characterized by means of scanning electron microscopy and powder X-ray diffraction measurements. The structural characterization shows that all crystals crystallize in monoclinic symmetry with the space group C2/m (No. 12). We have further investigated the magnetic properties of this series of single crystals. The magnetic measurements of the all as-grown single crystals show long-range antiferromagnetic order along all principal crystallographic axes. Overall, the Néel temperature TN is non-monotonous; with increasing Ni2+ doping, the temperature of the antiferromagnetic phase transition first decreases from 80 K for pristine Mn2P2S6 (x = 0) up to x = 0.5 and then increases again to 155 K for pure Ni2P2S6 (x = 1). The magnetic anisotropy switches from out-of-plane to in-plane as a function of composition in (Mn1−xNix)2P2S6 series. Transport studies under hydrostatic pressure on the parent compound Mn2P2S6 evidence an insulator-metal transition at an applied critical pressure of ~22 GPa.

Removing the orientational degeneracy of the TS defect in 4H–SiC by electric fields and strain

We present a photoluminescence (PL) study of the recently discovered TS defect in 4H silicon carbide. It investigates the influence of static electric fields and local strain on the spectral properties by means of low temperature (≈4 K) ensemble measurements. Upon application of static electric fields exerted by graphene electrodes, line splitting patterns are observed, which are investigated for four different angles of the electric field with respect to the principal crystallographic axes. More detailed information can be gained when additionally the excitation polarization angle is systematically varied. Altogether, the data allow for extracting the direction of the associated electric dipole moments, revealing three distinct orientations of the underlying TS defect inside the crystal’s basal plane. We also present three so far unreported PL lines (836.7 nm, 889.7 nm, 950.0 nm) as candidates for out-of-plane oriented counterparts of the TS lines. Similar to symmetry breaking by the electric field applied, strain can reduce the local symmetry. We investigate strain-induced line splitting patterns that also yield a threefold directedness of the TS lines in accordance with the Stark effect measurements. The response to both electrical and strain fields is remarkably strong, leading to line shifts of ±12 meV of the TS1 line. Combining our findings, we can narrow down possible geometries of the TS defect.

Signature of anisotropic exchange interaction revealed by vector-field control of the helical order in a FeGe thin plate

The authors demonstrate the vector-field control of the magnetic screw axis in a chiral helimagnet and show that the spiral period varies the orientation of the screw axis with respect to the principal crystallographic axes.

Anisotropy in the hardness of single crystal tungsten before and after neutron irradiation

In this work, the hardness of single crystal tungsten (W) after low, medium and high temperature neutron irradiation, reaching up to 1200°C, is studied. Micro-hardness tests with Vickers pyramid indenter are performed on reference and neutron irradiated samples by varying the orientation of the indenter on the single crystal tungsten contact surface. Due to the availability of multiple slip systems, the anisotropy of the hardness is characterized to allow the construction of uncertainty bands as well as dependence of the absolute value of the hardness on the orientation of the indenter wedges and principal crystallographic axes of the crystal. The applied neutron fluence and flux is representative for the ITER reactor, where tungsten is selected as armour material for plasma facing components. The neutron irradiation is performed in the BR2 reactor with mixed neutron spectrum up to 1 dpa (end of life fluence for ITER) but with appropriate measures to reduce the thermal neutron flux, such that the spurious transmutation into rhenium is reduced. The hardness study is accompanied with a detailed microscale examination to deduce the true indenter surface area. As a result, the true values of the hardness accounting for the pile-up effects are obtained as a function rotation angle of the indenter. The variation of the hardness as a function of indenter orientation before and after irradiation is discussed based on the indenter-slip system geometry. A simple but efficient methodology is proposed to deduce the true hardness and its angle-dependent variation for single crystal tungsten.

Thermal expansion of martensite in Ti29.7Ni50.3Hf20 shape memory alloy

Thermal expansion of martensite in Ti29.7Ni50.3Hf20 alloy was investigated by in situ neutron diffraction. It is found that the martensite exhibits a strong anisotropy in thermal expansion. The principal crystallographic axes and the coefficients of thermal expansion were determined.

Modulation of Jahn-Teller Mn3+ ion on anisotropy and high field magnetic diagram of Sm(Fe, Mn)O3

SmFeO3 and SmFe0.9Mn0.1O3 single crystal samples grown with a floating zone technique have been investigated under static and pulsed high magnetic fields along all principal crystallographic axes. Comprehensive investigation on magnetization (behavior) show that the spin switch transition and spin reorientation transition among the Sm3+ and Fe3+/Mn3+ sublattices is highly anisotropic. Especially, with the applied magnetic field along a-axis, a field induced multi-step transition was observed in SmFeO3 around compensation temperature (TComp1 ~ 3.9 K), which was not observed in Mn doped SmFe0.9Mn0.1O3 (TComp2 ~ 9.3 K). The experimental results show that the Jahn-Teller (J-T) Mn3+ ions has an important effect on anisotropy and affects the spin-reorientation and high field magnetization behavior. The study provides a clear picture to show the dominate effects between rare earth ions and transition metal ions on the complicated magnetization behavior.

Mg diffusion in forsterite from 1250–1600 °C

Abstract 26Mg tracer diffusion coefficients were determined in single crystals of pure synthetic forsterite (Mg2SiO4). Isotopically enriched powder sources both acted as the 26Mg source and buffered the activities of silica (aSiO2) at forsterite + protoenstatite (Mg2Si2O6) (high aSiO2) and forsterite + periclase (MgO) (low aSiO2). Experiments were conducted at atmospheric pressure between 1250 and 1600 °C, and at oxygen fugacities (fO2s) between 10–12 bars (CO-CO2 mix) and 10–0.7 bars (air). The resulting diffusion profiles were measured along the three principal crystallographic axes (a, b, and c; ||[100], ||[010], ||[001]) using laser ablation–inductively coupled plasma–mass spectrometry (LA-ICP-MS), with a quadrupole mass spectrometer. These measurements were corroborated by ion microprobe using the sensitive high resolution ion microprobe-reverse geometry (SHRIMP-RG) instrument. Mg tracer diffusion is anisotropic, with D[001] > D[010] > D[100], the difference in diffusion coefficients varying by about one order of magnitude at a given temperature with crystallographic orientation. Diffusion is faster in protoenstatite-buffered than periclase-buffered conditions, again with around one order of magnitude difference in diffusivity between buffering conditions. There is no apparent effect of fO2 on diffusion. A global fit to all data, including data from Chakraborty et al. (1994) and Morioka (1981) yields the relationship: log 10 D = log 10 D 0 ( m 2 s - 1 ) + 0 . 61 ( ± 0 . 03 ) log 10 a SiO 2 + - 359 ( ± 10 ) kJ / mol 2 . 303 R T where log10D0 is –3.15 (±0.08), –3.61 (±0.02), and –4.01 (± 0.05) m2 s–1 for the [001], [010], and [100] directions, respectively (1 s.d.). The LA-ICP-MS technique reproduces diffusion coefficients determined by SHRIMP-RG, albeit with slightly different absolute values of isotope ratios. This shows that LA-ICPMS, which is both accessible and rapid, is a robust analytical method for such tracer diffusion studies.

Element-specific soft x-ray spectroscopy, scattering, and imaging studies of the skyrmion-hosting compound Co8Zn8Mn4

A room-temperature skyrmion-hosting compound Co$_8$Zn$_8$Mn$_4$ has been examined by means of soft X-ray absorption spectroscopy, resonant small-angle scattering and extended reference holography. An element-selective study was performed by exciting the $2p$-to-$3d$ transitions near Co and Mn $L_{2,3}$ absorption edges. By utilizing the coherence of soft X-ray beams the element-specific real-space distribution of local magnetization at different temperatures has been reconstructed using iterative phase retrieval and holography with extended reference. It was shown that the magnetic moments of Co and Mn are ferromagnetically coupled and exhibit similar magnetic patterns. Both imaging methods provide a real-space resolution of 30 nm and allowed to record a magnetic texture in the temperature range between $T\,=\,20$ K and $T\,=120\,$ K, demonstrating the elongation of the skyrmions along the principal crystallographic axes at low temperatures. Micromagnetic simulations have shown that such deformation is driven by decreasing ratio of symmetric exchange interaction to antisymmetric Dzyaloshinskii-Moriya interaction in the system and effect of the cubic anisotropy.

Melt transport and mantle assimilation at Atlantis Massif (IODP Site U1309): Constraints from geochemical modeling

Olivine-rich troctolites (>70% olivine) reveal that extensive melt impregnation of pre-existing olivine-rich lithologies participate to the building of slow spread oceanic crust. To constrain their origin and their impact on the structure and geochemistry of oceanic crust, we realized a multi-scale petro-structural, geochemical, and numerical modeling study of olivine-rich troctolites drilled at IODP Hole U1309D (Atlantis Massif, Mid-Atlantic Ridge 30°N). Discrete intervals of olivine-rich troctolites display sharp to diffuse contacts with neighboring troctolites or gabbros. Their texture is characterized by plastically deformed (high temperature imprint), corroded coarse-grained to undeformed fine-grained olivine embayed in poikilitic clinopyroxene and plagioclase. Olivine crystallographic preferred orientations show weak [001] clusters. Olivine has variable major and minor element compositions, but similar fractionated REE (DyN/YbN = 0.04–0.11). We distinguished three types of olivine-rich troctolites based on microstructure, texture and mineral composition. Olivine-rich troctolites 1 and 2 display sharp contacts with adjacent lithologies. Type 1 has modal olivine <75%, occurring mainly as single rounded grains with primitive compositions (Mg# = 85–86), and associated with high Mg# clinopyroxene. Type 2 has higher olivine modes (>75%), dominantly forming aggregates, showing more evolved compositions (Mg# = 83–84) and associated with slightly lower Mg# clinopyroxene. These variations of olivine modes and compositions are in contrast to common trends of magmatic crystallization that predicts decreasing modal olivine with melt differentiation towards evolved compositions. Type 3 has diffuse contacts with gabbroic veins and modal olivine overlapping those of types 1 and 2. Chemical traverses along principal crystallographic axes of olivine are flat, suggesting local equilibrium between olivine and neighboring phases. Mineral modes and compositions, together with textures and microstructures, suggest that olivine-rich troctolites formed after melt-rock interactions in a reactive porous flow process. Their compositions are best modeled by percolation of primitive MORBs into Hole U1309D impregnated and compositionally heterogeneous harzburgites, triggering orthopyroxene dissolution, followed by olivine assimilation and concomitant crystallization of clinopyroxene and plagioclase. Modeling shows that Ni variations in olivine at constant Mg# are mantle inherited. Compositions of olivine-rich troctolite 1 are fitted assuming higher olivine assimilation (Ma = 0.06–0.13) in contrast to olivine-rich troctolites 2 and 3 (Ma = 0.01–0.02). Olivine-rich troctolite 3 was ‘buffered’ by crystallizing reacted melts, progressively more evolved as temperature decreased during a late stage process. We interpret olivine-rich troctolites from the Atlantis Massif as marking local assimilation of harzburgitic mantle into the gabbroic sequence during a period of enhanced magmatism at depth. Our study shows that the distribution and variable compositions of olivine-rich troctolites result from the incipient stages of this process when local spatial variations in mantle rock permeability, probably related to pyroxene distribution, controlled in turn melt transport and mantle-melt interactions.

Magneto-crystalline anisotropy of NdFe0.9Mn0.1O3 single crystal

Our present study on oriented single crystal revealed huge magneto-crystalline anisotropy with respect to principal crystallographic axes, even several magnetic transitions were observed below TN = 748K (c-axis) at 700K (a-axis) as well 657K (b-axis). The spin reorientation of magnetic moment takes place in very narrow temperature range between 135K and 125K and is attributed to vanishing of ferromagnetic component aligned along b-axis. Measurements of magnetic isotherms trace the development of ferromagnetic component and revealed the intermediate temperature range between 120K and 20K which is characterised by zero ferromagnetic components in any principal crystal direction. The ferromagnetic component develops consecutive at low temperature below 20K along a-axis. Our study indicates completely different magnetic structure of NdFe0.9Mn0.1O3 below 135K in comparison with NdFeO3.

Magnetic structure of Cu2MnBO5 ludwigite: thermodynamic, magnetic properties and neutron diffraction study

We report on the thermodynamic, magnetic properties and the magnetic structure of ludwigite-type Cu2MnBO5. The specific heat, low-field magnetization and paramagnetic susceptibility were studied on a single crystal and combined with powder neutron diffraction data. The temperature dependence of the specific heat and the neutron diffraction pattern reveal a single magnetic phase transition at T = 92 K, which corresponds to the magnetic ordering into a ferrimagnetic phase. The cation distribution and the values and directions of magnetic moments of ions in different crystallographic sites are established. The magnetic moments of Cu2+ and Mn3+ ions occupying different magnetic sites in the ferrimagnetic phase are pairwise antiparallel and their directions do not coincide with the directions of the principal crystallographic axes. The small value of the magnetic moment of copper ions occupying site 2a is indicative of partial disordering of the magnetic moments on this site. The magnetization measurements show a strong temperature hysteresis of magnetization, which evidences for field-dependent transitions below the phase transition temperature.

Batisite, Na2BaTi2(Si4O12)O2, from Inagli massif, Aldan, Russia: crystal-structure refinement and high-temperature X-ray diffraction study

The crystal structure of batisite, Na2BaTi2 (Si4O12)O2, from the Inagli massif (Aldan, Yakutia, Russia) was refined to R 1 = 0.032 for 1449 unique observed reflections. The mineral is orthorhombic, Imma, a = 8.0921(5), b = 10.4751(7), c = 13.9054(9) A, V = 1178.70(13) A3. The mineral is based upon three-dimensional titanosilicate framework consisting of chains of corner-sharing MO6 octahedra (M = Ti, Nb, Fe and Zr) and vierer chains of corner-sharing SiO4 tetrahedra. Both chains are parallel to the a axis and are linked by sharing peripheral O atoms. The octahedral chains display disorder of M atoms and bridging O sites related to the out-of-center distortion of octahedral geometry around Ti4+ cations. Electron microprobe analysis gives SiO2 39.46, TiO2 24.66, BaO 21.64, Na2O 7.56, K2O 4.38, Fe2O3 0.90, ZrO2 0.66, Nb2O5 0.36, (H2O)calc 0.58, sum 99.76 wt%. The seven strongest X-ray powder-diffraction lines [listed as d in A (I) hkl] are: 8.39 (94) 011, 3.386 (56) 031, 3.191 (36) 123, 2.910 (46) 222, 2.896 (100) 024, 2.175 (45) 035, 1.673 (57) 055. The thermal behaviour of batisite in the temperature range from 25 to 950 °C was studied using high-temperature powder X-ray diffraction. The thermal expansion coefficients along the principal crystallographic axes are: α a = 14.4 × 10−6, α b = 8.7 × 10−6, α c = 8.4 × 10−6, α V = 31.5 °C−1 for the temperature range 25–500 °C and α a = 19.6 × 10−6, α b = 9.1 × 10−6, α c = 8.8 × 10−6, α V = 37.6 °C−1 for the temperature range 500–900 °C. The direction of maximal thermal expansion is parallel to the chains of both MO6 octahedra and SiO4 tetrahedra, which can be explained by the stretching of silicate chains due to the increasing thermal vibrations of the Ba2+ cations. At 1000 °C, the titanosilicate framework in batisite collapses with the formation of fresnoite, Ba2TiSi2O7O.

Magnetic field-temperature phase diagrams of multiferroic (Ni0.9Co0.1)3V2O8

We present macroscopic and neutron diffraction data on multiferroic lightly Co doped ${\mathrm{Ni}}_{3}{\mathrm{V}}_{2}{\mathrm{O}}_{8}$. The magnetic $H\ensuremath{-}T$ phase diagrams have been derived from magnetization and electric polarization measurements with field directions parallel to the principal crystallographic axes. While the phase diagram for $H\ensuremath{\parallel}b$ is very similar to that of the parent compound ${\mathrm{Ni}}_{3}{\mathrm{V}}_{2}{\mathrm{O}}_{8}$ for the commonly involved phases, the zero-field phases in ${({\mathrm{Ni}}_{0.9}{\mathrm{Co}}_{0.1})}_{3}{\mathrm{V}}_{2}{\mathrm{O}}_{8}$ show a stronger instability for applied magnetic fields along the $a$ or $c$ axis. Neutron single-crystal diffraction revealed the magnetic structure of the field-induced phase for $H\ensuremath{\parallel}c$ with a collinear spin alignment along the $a$ and $b$ axes for the two magnetically inequivalent sites. A pronounced irreversibility has been observed for the transition between the zero-field spin cycloid and the field-induced phase, which is manifested in a propagation vector change from $\mathbf{q}\phantom{\rule{0.28em}{0ex}}=\phantom{\rule{0.28em}{0ex}}(0.322 0 0)$ to $\mathbf{q}\phantom{\rule{0.28em}{0ex}}=\phantom{\rule{0.28em}{0ex}}(0.306 0 0)$, with slight modifications of the magnetic structure after reentering the zero-field phase. The reentrant phase is characterized by a significantly larger $b$ component of the cross-tie site spin, therefore showing remanent features of the high-field phase. For $H\ensuremath{\parallel}a$ the magnetization data reveal anomalies, one of which was proved to reflect a field-induced transition from the cycloidally to the sinusoidally modulated magnetic structure.

Travelling-solvent floating-zone growth of the dilutely Co-doped spin-ladder compound Sr14(Cu, Co)24O41

We present here crystal growth of dilutely Co-doped spin-ladder compounds Sr14(Cu 1−x, Cox)24O41 (x = 0, 0.01, 0.03, 0.05, 0.1) using the Travelling Solvent Floating Zone (TSFZ) technique associated with an image furnace. We carried out detailed microstructure and compositional analysis. The microstructure of the frozen-in FZ revealed two bands: a lower band consisting of well-aligned single-crystalline stripes of the phase Sr14(Cu, Co)24O41 embedded in the eutectic mixture of composition SrO 18% and (Cu, Co)O 82%; and an upper band consisting of a criss-crossed pattern of these stripes. These analyses were also employed to determine the distribution coefficient of the dopants in Sr14Cu24O41. The distribution coefficient turned out to be close to 1, different from Sr2CuO3 reported previously where Co tend to accumulate in the molten zone. Direct access to the composition of the frozen-in zone eliminated any previous ambiguities associated with the composition of the peritectic point of Sr14Cu24O41; and also the eutectic point in the binary SrO–CuO phase diagram. The lattice parameters show an anisotropic variation upon Co-doping with parameters a and b increasing, c decreasing; and with an overall decrease of the unit cell volume. Magnetic susceptibility measurements were carried out on the pristine and the Co-doped crystals along the principal crystallographic axes. The spin susceptibility of the x = 0.01 crystal exhibits a strong anisotropy, which is in stark contrast with the isotropic behaviour of the pristine crystal. This anisotropy seems to arise from the intradimer exchange interaction as inferred from the anisotropy of the dimer contribution to the susceptibility of the Co-doped crystal. The Curie-tail in the magnetic susceptibility of Sr14(Cu 1−x, Cox)24O41 (x = 0, 0.01, 0.03, 0.05, 0.1) crystals (field applied parallel to the ladder) was found to scale with Co-doping – the scaling is employed to confirm a homogeneous distribution of Co in a x = 0.1 crystal boule.

Possible Heavy Fermion State of the Caged Cubic Compound NdV2Al20

The magnetic susceptibility M/H, the magnetization M, and the specific heat C were measured for the caged cubic compound NdV2Al20 single crystal at temperatures down to 0.5 K in magnetic fields H along the three principal crystallographic axes [001], [101], and [111]. The electrical resistivity ρ was measured in the temperature range of 1.9–300 K. A ferromagnetic phase transition was observed at a Curie temperature TC of 1.81 K. The easy direction of magnetization was the [001] direction at low fields, and changed to the [101] direction above 2 T. On cooling below 2 K at zero field, the specific heat divided by temperature, C/T, resulted in a large electronic specific heat coefficient γ of about 2 J/(K2 mol). A large C/T of more than 1 J/(K2 mol) remained at 9 T below 2 K. The temperature dependence of ρ showed the −ln T dependence at around 10 K. These behaviors possibly originate from a heavy fermion state.

Magnetic and Thermal Properties of TmV2Al20 Single Crystals

The magnetization and specific heat of TmV2Al20 single crystals were measured in the temperature range from 0.5 to 300 K in external magnetic fields up to 7 T. TmV2Al20 was found to be paramagnetic above 0.5 K. Clear magnetic anisotropy was observed along the three principal crystallographic axes in the field above 1 T at 0.5 K. The magnetically easy axis is along the [100] direction, and the hard axis is along the [111] direction. On cooling below 2 K in zero external field, the magnetic part of specific heat divided by temperature, Cmag/T, increases up to 6 J/mol K2 near 0.6 K. The magnetic entropy in zero field reaches R ln 5 near 10 K, suggesting that the ground state of Tm3+ ions is a nonmagnetic doublet state with the first excited state of a magnetic triplet state nearby (a pseudo-fivefold degenerate state). The experimental results were reproduced by the crystalline electric field calculations, and an energy level scheme was proposed. The enhanced value of Cmag/T in the lowest temperature region i...