Crystals In High Magnetic Fields Research Articles

Grain boundary dynamics and selective grain growth in non-ferromagnetic metals in high magnetic fields

Abstract Grain boundary motion can be affected by a magnetic field if the anisotropy of the magnetic susceptibility generates a gradient of the magnetic free-energy density across the boundary. Due to this magnetic driving force, annealing of locally deformed single crystals in high magnetic fields results in growth selection. The character distribution of the boundaries connected to growth selection is found to be far from random. If a magnetic energy density gradient as a driving force is superimposed to a curvature driving force during grain growth, this biases the microstructure evolution with regard to grain size and crystallographic texture, as it is demonstrated on polycrystalline zinc and titanium. Analysis of individual orientation data reveals that the observed asymmetrical texture stems to a large extent from a difference in grain numbers of the individual texture components.

Specific Heat of the Kagome Antiferromagnet Herbertsmithite in High Magnetic Fields

Measuring the specific heat of herbertsmithite single crystals in high magnetic fields (up to $34$ T) allows us to isolate the low-temperature kagome contribution while shifting away extrinsic Schottky-like contributions. The kagome contribution follows an original power law $C_{p}(T\rightarrow0)\propto T^{\alpha}$ with $\alpha\sim1.5$ and is found field-independent between $28$ and $34$ T for temperatures $1\leq T\leq4$ K. These are serious constrains when it comes to replication using low-temperature extrapolations of high-temperature series expansions. We manage to reproduce the experimental observations if about $10$ % of the kagome sites do not contribute. Between $0$ and $34$ T, the computed specific heat has a minute field dependence then supporting an algebraic temperature dependence in zero field, typical of a critical spin liquid ground state. The need for an effective dilution of the kagome planes is discussed and is likely linked to the presence of copper ions on the interplane zinc sites. At very low temperatures and moderate fields, we also report some small field-induced anomalies in the total specific heat and start to elaborate a phase diagram.

Magnetostrictive properties of Tb0.2Gd0.8 single crystal in high magnetic fields

Temperature and field dependencies of the magnetostriction of the Tb0.2Gd0.8 single crystal were measured in strong magnetic fields up to 14 T in a temperature range of 4.2–300 K. The temperature dependencies of five magnetostriction constants λ1α,0, λ2α,0, λ1α,2, λ2α,2 and λγ,2 were determined, using Clark's theory for rare-earth hexagonal close-packed single crystals. Giant values of linear and volume magnetostriction due to forced magnetostriction were found in the Tb0.2Gd0.8 single crystal (λbc = 1.6 × 10−3) in the region of the Curie temperature (near room temperatures). It is shown that giant values of forced magnetostriction are caused by the sharp dependence of exchange interactions on interatomic distances along the hexagonal the c axis.

Optical spectroscopy study of Ca3(Ru0.91Mn0.09)2O7 single crystal in high magnetic fields

The magneto-optical spectrum, with magnetic fields up to 42 T, of double layered ruthenates Ca3(Ru0.91Mn0.09)2O7 (CRMO) single crystal is studied. Both the temperature and magnetic field induced insulator-to-metal transitions (IMTs) are observed via magneto-optical properties of the crystal. The critical magnetic field (H // c) of IMT for CRMO is found to be as large as 35 T at 5 K. The fine structure of optical spectra identified the antiferromagnetic/ferro-orbital-ordering configurations of Ru 4d orbitals at low temperatures. Meanwhile, the configuration of orbital polarization of such double-layer CRMO single crystal is discussed. These results suggest that the orbital degree of freedom plays an important role in the field induced IMT of multi-orbital system.

Magnetization, magnetic anisotropy and magnetocaloric effect of the Tb0.2Gd0.8 single crystal in high magnetic fields up to 14 T in region of a phase transition

The Tb0.2Gd0.8 single crystal magnetization, magnetic anisotropy and adiabatic temperature change ΔT dependencies on magnetic field and temperature have been studied in high magnetic fields (up to 14 T). In this work, we analyze experimental data within the framework of thermodynamic Landau theory for second order magnetic phase transitions to describe the relationship between the magnetization, adiabatic temperature change ΔT and magnetic field in the region of a phase transition. Moreover, it is proved that the Landau-Ginzburg equations are applicable in the case of high magnetic fields. Furthermore it is discovered that the adiabatic temperature change is proportional to the magnetic field with the relation ΔT ∼ (μ0H)2/5 in the region of high magnetic fields.

Bulk and in-gap states in SmB6 revealed by high-field magnetotransport

We report on temperature-dependent magnetotransport experiments of ${\mathrm{SmB}}_{6}$ single crystals in high magnetic fields up to 33 T. Above the low-temperature plateau region in the zero-field resistivity, we find two distinct gapped regimes. The first is characterized by a temperature-independent gap ${\mathrm{\ensuremath{\Delta}}}_{2}$ that closes in the presence of a high magnetic field while the second regime, above $\ensuremath{\sim}8\phantom{\rule{0.28em}{0ex}}\mathrm{K}$, features an energy gap ${\mathrm{\ensuremath{\Delta}}}_{1}$ that is temperature dependent. In the entire temperature range, we observe an overall negative magnetoresistance that does not depend on the orientation of the crystalline plane with respect to the applied magnetic field with a maximum value at $T\ensuremath{\sim}6.2\phantom{\rule{0.28em}{0ex}}\mathrm{K}$. The regime of in-gap states is characterized by a low mobility, an anomalously high carrier concentration, and an enhanced nonlocal resistance that exceeds the expected classical value for a two-dimensional metallic conductor. Overall, our data can be interpreted in terms of a transition from bulk to in-gap dominated transport, but evidence of topological surface states is not observed.

Multiferroic properties of an åkermanite Sr2CoSi2O7single crystal in high magnetic fields

The magnetic and dielectric properties of \aa{}kermanite Sr${}_{2}$CoSi${}_{2}$O${}_{7}$ single crystals in high magnetic fields were investigated. We have observed finite induced electric polarization along the $c$ axis in high fields, wherein all Co spins were forcibly aligned to the magnetic field direction. Existence of the induced polarization in the spin-polarized state accompanied with the finite slope in the magnetization curve suggests the possible role of the orbital angular momenta in the excited states as its microscopic origin. The emergence of the field-induced polarization without particular magnetic order can be regarded as the magnetoelectric effects of the second order from the symmetry point of view. A low magnetic field-driven electric polarization flip induced by a rotating field, even at room temperature, has been successfully demonstrated.

Angular Dependence of the High-Magnetic-Field Phase Diagram of URu2Si2

We present measurements of the magnetoresistivity RHOxx of URu2Si2 single crystals in high magnetic fields up to 60 T and at temperatures from 1.4 K to 40 K. Different orientations of the magnetic field have been investigated permitting to follow the dependence on Q of all magnetic phase transitions and crossovers, where Q is the angle between the magnetic field and the easy-axis c. We find out that all magnetic transitions and crossovers follow a simple 1/cos(Q) -law, indicating that they are controlled by the projection of the field on the c-axis.

Magnetization and specific heat of a UIrGe single crystal in high magnetic fields

The temperature and field dependence of the magnetization were measured on a single crystal of the antiferromagnet UIrGe in pulsed fields up to 51 T, and the specific heat in steady fields up to 18 T. At low temperatures, metamagnetic transitions are observed at critical fields Bc of 21 T and 14 T, applied along the b- and the c-axis, respectively. At 2 K, the magnetization jumps at Bc are 0.36 μB/U along the b-axis and 0.28 μB/U along the c-axis. The a-axis is the hardest magnetization direction with a weak linear magnetic response. Both along the b- and the c-axis, Bcdecreases with increasing temperature. Consistent with the magnetization, the sharp anomalies observed in the specific-heat obey the same dependence.

Magnetization of a Dy2Fe14Si3single crystal in high magnetic fields

The magnetization of a Dy2Fe14Si3 single crystal was measured at 4.2 K in pulsed fields up to 52 T along the principal axes. The compound is a ferrimagnet with TC = 500 K, has a spontaneous magnetic moment of 9 μB(at 4.2 K) and exhibits a very large magnetic anisotropy, ⟨100⟩ being the easy axis. In fields applied along the ⟨100⟩ and ⟨120⟩ axes, field-induced phase transitions are observed at 33 T and at 39 T, respectively. The c-axis magnetization curve crosses the easy-axis curve at 23 T. At higher fields, for all directions, the magnetization continues to increase due to further bending of the sublattice moments.

Grain boundary dynamics and selective grain growth in non-ferromagnetic metals in high magnetic fields

Abstract Grain boundary motion can be affected by a magnetic field if the anisotropy of the magnetic susceptibility generates a gradient of the magnetic free-energy density across the boundary. Due to this magnetic driving force, annealing of locally deformed single crystals in high magnetic fields results in growth selection. The character distribution of the boundaries connected to growth selection is found to be far from random. If a magnetic energy density gradient as a driving force is superimposed to a curvature driving force during grain growth, this biases the microstructure evolution with regard to grain size and crystallographic texture, as it is demonstrated on polycrystalline zinc and titanium. Analysis of individual orientation data reveals that the observed asymmetrical texture stems to a large extent from a difference in grain numbers of the individual texture components.

Weak ferromagnetic spin and charge stripe order inLa5∕3Sr1∕3NiO4

We present magnetization and specific heat data of a La5/3Sr1/3NiO4 single crystal in high magnetic fields. From the charge and spin stripe ordering temperatures, as well as a magnetic low temperature transition, we have constructed the electronic phase diagram for fields up to 14 Tesla. While the charge stripe ordering temperature TCO is independent of the magnetic field, there is a significant shift of the spin stripe ordering temperature TSO of about 1.5 K/ Tesla, if the magnetic fields are applied parallel to the NiO2-planes. The specific heat measurements indicate a large anomalous entropy change at TCO. In contrast, no significant entropy change is observed at the spin stripe transition. The high field magnetization experiments reveal the presence of in-plane weak ferromagnetic moments in the charge stripe ordered phase. From a phenomenological analysis, the magnetic correlation length of these moments is determined. We suggest that the weak ferromagnetism is due either to the presence of bond-centered charge stripes or to double exchange interactions across site-centered charge stripes.

Geometrical effect in magneto-Peltier cooling of single crystal Bi

The cooling temperatures of rectangular parallelepiped Bi single crystals with various widths W and thickness t were measured at 293 K as a function of electric current in the magnetic field B up to 2.17 T. The magnetic field was aligned along the thickness of a sample and the current flows along its length L through the copper leads soldered to both end surfaces of cross section (W×t), where W, t, and L are parallel to the binary, bisector, and trigonal axes of Bi single crystal, respectively. The thermoelement was not in contact with a heat sink. The cooling temperature at the cooled surface increased with increasing the magnetic field, and it depended strongly on the thickness rather than the width of the crystal in high magnetic fields. The largest maximum cooling temperature was achieved when a thermoelement has optimum dimensions so that no heat energy is generated at the cold side. The cooling temperature of Bi single crystal with optimum dimensions of L=15 mm, W=4 mm, and t=2 mm increased from 4.1 K in B=0 T to 8.5 K in B=+2.17 T, so that it exceeded maximum cooling temperatures of 5.7 K obtained for a typical Bi2Te3 and 5.2 K measured previously for a polycrystalline Bi in B=+2.17 T.

Exciton absorption spectra of MoS2crystals in high magnetic fields up to 150 T

We have measured the absorption spectra of a cleaned MoS2natural crystal in high magnetic fields up to 150 T in a Faradayconfiguration, and we have found Zeeman splitting and a diamagneticshift of the n = 1 A exciton band. The g-factor and thediamagnetic parameter are calculated to be -4.6 and 1.8×10-4 meV T-2, respectively.

Stray-field NMR imaging and wavelength dependence of optically pumped nuclear spin polarization in InP

One-dimensional NMR imaging experiments with micron spatial resolution are used to investigate the penetration depth and excitation energy dependence of optical pumping in Fe-doped semi-insulating InP crystals in high magnetic field at low temperature. The depth profile of ${}^{31}\mathrm{P}$ nuclear polarization revealed by NMR imaging is consistent with previous optical absorption measurements, while the efficiency of exciting nuclear polarization is found to be a complicated function of the excitation energy. This dependence is not explained by LO phonon emission by the photoexcited carriers. The optically pumped ${}^{31}$P NMR signal exhibits a maximum intensity with excitation several meV below the band gap, but this maximum is shown to be due to the dramatically increased absorption length of below-gap radiation. The efficiency of exciting nuclear polarization drops off quickly below the gap, and is about $\frac{1}{5}$ of its maximum value at the energy of greatest total NMR signal intensity.

Specific heat of a CeCoAl 4 single crystal in high magnetic field

The specific heat of a CeCoAl 4 single crystal has been studied in magnetic fields up to 17.5 T. In zero field, this compound has been found to order antiferromagnetically below the Néel temperature of about 13.5 K. The effect of the magnetic field is different when applied along the different main crystallographic axes. Along the a-axis, the Néel temperature decreases only slightly with increasing field. Along the b-axis, the Néel temperature decreases more strongly. Along the c-axis, a drastic change in the specific heat occurs in fields between 7–8 T which is attributed to a spin—flop transition.

Magnetic properties of Sc-substituted erbium iron garnet single crystals in high magnetic field

Magnetic properties of garnet single crystals Er3Fe5−zSczO12 (z=0.10 and 0.30) are reported under high magnetic field up to 264 kOe in the 2–320 K temperature range. Below the compensation temperature Tcomp (71 and 52 K for z=0.10 and 0.30, respectively), in the spontaneous state, the magnetic anisotropy is very weak for z=0.10 and more important for z=0.30. The “easy” axis is [100] for both Sc concentrations as in pure ErIG. These results are compared to Faraday rotation anisotropy. From the analysis of the temperature dependences of the spontaneous magnetizations, the molecular field coefficient Ndc related to the Fe–Er superexchange interactions has to be, as are Ndd and Nad, a function of z. In the high magnetic field and at low temperature, the onset of the usual canted magnetic phase takes place for H applied parallel to the “easy” [100] axis for both concentrations, whereas an unusual behavior is observed for z=0.30 and H parallel to [111] direction: below 30 K, three temperature dependent field induced transitions are observed.

Specific heat of DyCu 2 single crystals in high magnetic fields

Specific heat measurements on DyCu 2 single crystals in magnetic fields of 0, 1.7 and 4.0 T parallel to the a-direction were performed between 0.3 and 50 K. Various second order transitions due to the strong magnetic anisotropy of the compound were found in accordance with the phase diagram that was derived from magnetization and thermal expansion measurements. The nearly vertical phase transition lines at 5 K in the ferrimagnetic F1 phase and at 6 K in the ferromagnetic F2 phase can be confirmed by the present data. Moreover, the temperature dependence of the Ising-axis conversion field of DyCu 2 was complemented by specific heat and magnetocaloric investigations in fields parallel to the c-direction.

Study of the specific heat of a CeCoAl 4 single crystal in high magnetic fields

The specific heat of a CeCoAl 4 single crystal has been studied in magnetic fields up to 17.5 T. In zero field, this compound has been found to order antiferromagnetically below the Néel temperature of about 13.5 K. The effect of the magnetic field is different when it is applied along the different crystallographic axes. Along the a-axis, with increasing magnetic field, the Néel temperature slightly decreases and reaches a value of 12.7 K at 17.5 T. Along the b-axis, the Néel temperature decreases more strongly with increasing magnetic field. At 16 T, we found a value of T N of about 6.9 K. At 17.5 T, along the b-axis, we observed a rather broad peak in the specific heat which is associated with a transition from paramagnetism to ferromagnetic order. Along the c-axis, a drastic change in the specific heat occurs at a field between 7–8 T. At 7 T, the value of T N is about 9 K. At fields higher than 8 T, the specific heat is evidently characterised by a transition from paramagnetism to ferromagnetic order. The critical values of the magnetic field above which ferromagnetic order is formed at low temperature turn out to be consistent with the measurements of the magnetisation curves at 4.2 K.

Observation of coupled 4f-electron-phonon excitations in the Van Vleck paramagnet TmES in high magnetic fields

A model is proposed for explaining the anomalous behavior of the far-IR absorption spectra of the dielectric Van Vleck paramagnet thulium ethyl sulfate TmES. The good agreement obtained between the calculations and experiment on the basis of the idea of a resonance interaction between Tm3+ ions in one of the excited doublet states and optical phonons gives grounds for asserting that coupled 4f-electron-phonon excitations exist in TmES single crystals in high magnetic fields at liquid-helium temperatures.