P.K. Chakrabarti

Magnetic studies on erbium bromate and the crystal field

Abstract Measurements of the principal magnetic susceptibilities of erbium bromate single crystals in the temperature range 300-15.5 K have been made. The anisotropy at 300 K is high (|ΔX/ X | = 0.15) and it increases very rapidly with decreasing temperature. The variation of X⊥ is nearly Curie-type down to the lowest temperature attained, whereas the X| versus T plot is nearly flat. Smooth variation of X⊥ down to 15.5 K does not indicate any structural phase transition of the crystal. The observed magnetic properties were analyzed for the first time invoking an effective electrostatic interaction of the Er3+ ion with its diamagnetic surroundings; the crystal field (CF) conforms to the approximate site symmetry of Er3+, i.e. D3h. The CF J-J mixing was included through term diagonalization and intermediate coupling effects were partly taken care of using appropriate reduced matrix elements. The computed values are in very good agreement with the corresponding observed values. Our computed values of X| in the range 60–500 mK reproduced the same sort of behavior as predicted by Simizu et al. in 1984. The thermal and hyperfine properties have been worked out.

Effect of multiferroic BiFeO3 nanoparticles on electro-optical and dielectric properties of a partially fluorinated orthoconic antiferroelectric liquid crystal mixture

The influence of multiferroic bismuth ferrite (BiFeO3) nanoparticles (NPs) on the electro-optical (EO) and dielectric properties of an orthoconic antiferroelectric liquid crystal (OAFLC) mixture is investigated in planar cells. It is shown that dispersion of NPs in OAFLC lead to modifications of response time, spontaneous polarization, rotational viscosity and voltage required for switching the molecules between two ferroelectric states in the antiferroelectric phase while the tilt angle remains almost the same after doping. The large electric field exerted by the NPs on LC molecules and probable charge transfer among them, causes weakening of the interlayer and intermolecular interactions of LC molecules in the antiferroelectric and ferroelectric phases, respectively.

The effects of crystal field on Tm3+ in Tm(BrO3)3 · 9H2O: An experimental and theoretical study

Abstract Crystals of thulium bromate enneahydrate were grown and the magnetic susceptibility χ ⊥ and the magnetic anisotropy Δχ(= χ ∥ − χ ⊥ ) were measured in the range 300-14 K and 300-80 K, respectively. χ ∥ and χ ⊥ show widely divergent thermal variation; the χ ∥ versus T plot is nearly flat compared to that of χ ⊥ · Smooth variation of χ ⊥ down to 14 K does not suggest any structural phase transition or symmetry breaking. Our observed data and that of Simizu et al . [ J. Appl. Phys 55 , 2333 (1984)] below 4 K were analyzed for the first time invoking an effective crystal field. Our theoretical values in general provide excellent agreement to the observed data. Very brief comment on the behavior of χ ∥ below 4 K by Simizu et al . is borne out qualitatively by our theory, but their absolute value seems abnormally high, which makes it suspect. The computed crystal field spectra led us to locate the peaks in the electronic heat capacity and to find the quadrupole splitting of the 8.42 keV nuclear excited state of 169 Tm; high magnetic field enhancement at the nucleus suggests complex Mossbauer spectra in the presence of a magnetic field perpendicular to the symmetry axis.

Magnetic susceptibilities, crystal field Stark energies, and hyperfine behavior of Sm3+ in hexagonal single crystals of Sm(CF3SO3)3⋅9H2O

Single crystals of samarium trifluoromethanesulfonate (SmTFMS) were prepared from the slow evaporation of the aqueous solution of SmTFMS. The crystals are elongated along the symmetry axis c of the hexagonal crystal. At room temperature, the c axis of the crystal sets parallel with the applied magnetic field which indicates that the susceptibility parallel to the c axis (χ∥) is greater than the susceptibility perpendicular to the c axis (χ⊥). χ∥ and χ⊥ were measured from 300 down to 14 K. Magnetic anisotropy (Δχ=χ∥−χ⊥) obtained from the values of χ∥ and χ⊥ was also checked by direct measurements of Δχ and both these results agreed very well. A crossover between χ∥ and χ⊥ has been observed at ∼56 K i.e., below this temperature χ∥<χ⊥. A good theoretical simulation of the observed magnetic data of SmTFMS has been achieved using the one-electron crystal field (CF) theory. Ordering effects in the observed magnetic data were not noticed down to the lowest temperature (∼14 K) attained, indicating the interionic ...

Single crystal magnetic properties and the crystal field interactions of Er3+ in ErVO4

Abstract Crystals of erbium vanadate were flux-grown and magnetic measurements carried out on the single crystals for the first time in the temperature range 300-13.2 K. At room temperature χ ∥ > χ ⊥ ; crossover in Δχ is observed at about 130 K. Our magnetic data and that of Kuse on crystal field excitations were analyzed invoking an effective crystal field of D 2d symmetry; the theoretical values provide an excellent agreement to the observed data. The principal susceptibility (χ ⊥ ) did not show any sharp change in its behavior down to 13.2 K, which rules out a structural or magnetic phase transition in this range. The computed Stark energies led us to locate a Schottky anomaly in the electronic heat capacity. The quadrupole splitting of 167 Er due to crystal field effects has been computed; the hyperfine heat capacity displays a sharp peak at about 4.8 mK.

Magnetic measurements and crystal field investigation of Tm3+ in Tm(CF3SO3)3⋅9H2O

Single crystals of thulium trifluoromethanesulfonate (TmTFMS) were grown and the principal magnetic susceptibility χ⊥ and magnetic anisotropy Δχ(=χ∥−χ⊥) were measured in the temperature range of 300–13.5K and 300–80K, respectively. Though the value of χ⊥ is found to rapidly increase with the decrease in temperature, the value of χ∥ slowly increases with the lowering of temperature down to ∼110K, below which it slowly decreases. The hexagonal crystal structure of TmTFMS is similar to that of the isostructural series of hydrated rare earth ethylsulfates and the non-Kramers Tm3+ ion occupies a site of C3h symmetry. Our observed magnetic data were analyzed using crystal field (CF) analyses where the Hamiltonian includes the atomic free ion and (CF) (one-electron) interaction terms. The computed and measured paramagnetic susceptibilities of TmTFMS agree well in the temperature range of our study. Smooth variation of χ⊥ down to 13.5K does not indicate any structural phase transition or symmetry breaking, at lea...

Studies of the magnetic behaviour of ErAl3(BO3)4 and the effects of the crystal field

Abstract Single crystals of ErAl 3 (BO 3 ) 4 were produced by flux growing techniques. The principal magnetic susceptibility, χ ⊥ , perpendicular to the symmetry axis of the crystal was measured in the range 300-14.2 K, and the principal anisotropy ( χ ∥ − χ ⊥ ) was determined from 300 to 77 K, which turned out to be negative throughout. A crystal field conforming to D 3 site symmetry (obtained from structural data) accounts very well for the observed thermal variation of the magnetic susceptibilities; this yields g factors, g ∥ and g ⊥ , of 2.32 and 8.95, respectively. The electronic heat capacity is computed, and shows a Schottky anomaly at around 45 K. Calculated quadrupole splitting of 167 Er due to crystal field effects shows a smooth decrease with decreasing temperature. The hyperfine heat capacity, contributed mainly by magnetic hyperfine splitting, displays a rounded maximum at about 8 mK.

Magnetic behavior of Ho3+ in HoAl3(BO3)4

Abstract Single crystals of HoAl 3 (BO 3 ) 4 were flux grown and their principal magnetic susceptibilities, parallel and perpendicular to the symmetry axis of the crystal, χ ‖ and χ ⊥ , measured in the range 300-14.5 K. The principal anisotropy χ ‖ - χ ⊥ turns out to be positive throughout. A theoretical analysis of the experimental results invoking the crystal field interaction of the Ho 3+ ion with D 3 site symmetry, obtained from structural data, provide an excellent explanation of the observed behavior of the ion over the entire temperature range in our study; this rules out exchange or dipolar effects of any significance down to 14.5 K. The energy level structure of this potential laser crystal for all the low lying multiplets of the ground term is given and the anomalies in the electronic heat capacity located. The quadrupole splitting of 165 Ho due to crystal field effects has been computed, which gives rise to a peak in the hyperfine heat capacity at about 5.5 mK.

XRD, HRTEM, Raman and magnetic studies on chemically prepared nanocrystalline Fe-doped gadolinium oxide (Gd1.90Fe0.10O3−δ) annealed in vacuum

Nanoparticles of Fe-doped gadolinium oxide (Gd1.90Fe0.10O3−δ) are prepared by a co-precipitation method. To obtain the desired nanocrystalline phase and to enhance the oxygen vacancy, the as prepared sample is annealed at 700 °C for 6 h in vacuum. The pure crystallographic phase is confirmed by Rietveld analysis of the X-ray diffraction (XRD) pattern. High resolution transmission electron microscopy (HRTEM) studies and Raman spectroscopy of the doped sample observed at room temperature also ruled out the presence of any unwanted impurity phase in the sample. XRD, HRTEM and Raman spectra of the sample confirmed the complete substitution of Fe-ions in the lattice of gadolinium oxide. The static magnetic measurements are carried out at different temperatures from 300 K down to 5 K by using a superconducting quantum interference device (SQUID) magnetometer. The onset of nonlinearity in the magnetization (M) vs. field (H) curve recorded at ∼20 K confirms the presence of magnetic ordering at and below ∼20 K. A clear hysteresis loop with a high value of magnetization (∼120.1 emu g−1) is observed at 5 K at an applied field of ∼5 T. The lack of saturation in the hysteresis loop at and below ∼20 K and good fitting of the M–T curve below ∼50 K by 3D spin wave model and Curie–Weiss law indicates the coexistence of paramagnetic (PM) and ferromagnetic (FM) phases. The observed magnetic phase transition is attributed to the substitution of Fe-ions in the Gd2O3 lattice, which is explained by oxygen vacancy mediated bound magnetic polaron model.

Microwave absorption and the magnetic hyperthermia applications of Li0.3Zn0.3Co0.1Fe2.3O4 nanoparticles in multi-walled carbon nanotubes matrix

Nanoparticles of Li0.3Zn0.3Co0.1Fe2.3O4 (LZC) were prepared by the sol-gel method and dried in a furnace at ∼200 °C. The dried sample was annealed at 500, 600, 700, and 800 °C for 5 h each. Rietveld analysis of X-ray diffraction patterns confirms the cubic Fd3̅m phase formation with lattice parameters ranged from 8.376 up to 8.390 Å and allows the crystallite sizes (dcryst) to be estimated. To enhance microwave (MW) absorption as well as the effectiveness for hyperthermia treatment, nanoparticles are taken in the matrix of multiwalled carbon nanotubes (MWCNTs) and the morphology of the so-prepared samples (LZC@MWCNT) was studied by scanning electron microscopy and transmission electron microscopy analyses. Both static and dynamic magnetic properties were investigated on the samples of LZC nanoparticles and compared to those of the samples of LZC@MWCNT. The samples annealed at 500, 600, and 800 °C are excellent candidates in cancer treatment as ac magnetic heating analysis shows that the hyperthermia temperature (42 °C) was successfully achieved for an applied ac magnetic field of 420 Oe and 300 kHz frequency. MW absorption study also reveals that the samples of LZC@MWCNT could be used as a potential MW absorbing material for which a maximum reflection loss (RL) of ∼-21 dB was achieved at a frequency of 15.27 GHz for only 1 mm layer thickness.