Ground Kramers Research Articles

Heat capacity of a five-coordinated iron(III) complex with spin [formula omitted], bromobis ( N, N-dimethyldithiocarbamato) iron(III), between 0.4 and 300 K: New finding of a magnetic phase transition

The heat capacity of bromobis( N, N-dimethyldithiocarbamato)iron(III) was measured between 0.4 and 300 K. A phase transition from a ferromagnetic to a paramagnetic state was found at T c = (0.837 ± 0.005) K, and a Schottky anomaly arising from the zero-field splitting was observed around 9 K. The total magnetic entropy and enthalpy, including the phase transition and the Schottky anomaly, were (11.74 ± 0.01) J K −1 mol −1 and (92.0 ± 0.4) J mol −1, respectively. The entropy was only 1.8% larger than R ln 4 ( = 11.53 J K −1 mol −1), confirming that the spin manifold is really a quartet (intermediate spin S = 3 2 ). The transition entropy and enthalpy were estimated to be (6.05 ±0.01) J K −1 mol −1 and (5.77 ± 0.01) J mol −1, respectively. The transition entropy was only 5% larger than R ln 2. Since the ground spin states of the present compound are characterized by a zero-field splitting of the S = 3 2 state into two Kramers' doublets, the phase transition is concerned with only the ground Kramers' doublet. The entropy and enthalpy above T c, which is a measure of the short-range order, are large but relatively small compared with those of the ethyl-homologues. This fact suggests that the magnetic lattice dimension in the present complex is somewhat different from the ethyl-homologues from a thermodynamic point of view. The magnitude of the exchange interaction determined from the magnetic transition temperature for both the methyl- and ethyl-homologues is monotonically increased in the order Cl, Br and I. This implies that the halogen atom plays an important role in the intermolecular exchange interaction.

Magnetic and spectroscopic characterization of the high-spin (6A1) .dblharw. low-spin (2T2) transition in an iron(III) complex of pyridoxal thiosemicarbazone

The preparation and characterization of the new discontinuous ferric spin-crossover complex (Fe(HL)/sub 2/)Cl and the hydrated low-spin form of the complex (Fe(HL)/sub 2/)Cl/center dot/2H/sub 2/O are reported. In these complexes HL/sup /minus// is the deprotonated form of pyridoxal thiosemicarbazone (H/sub 2/L) acting as an ONS tridentate ligand. The magnetic moments for the spin-crossover complex show a thermal hysteresis, where with sample cooling the transition temperature is 245 K and with sample heating it is 256 K. Variable-temperature /sup 57/Fe Moessbauer and EPR data also provide evidence for the presence of a first-order phase transition in this complex. It is most likely that the cooperative (first-order) nature of this transition is due to the extended coupling of ferric complexes through intermolecular hydrogen-bonding interactions. EPR spectra of the two complexes in this study show that both have a single occupied d/sub xy/ orbital in the ground Kramers doublet. 39 refs., 3 figs., 2 tabs..

Paramagnetic resonance hyperfine structure of hexachloroprotactinate(IV).

Dirac scattered-wave calculations are presented for the ${\mathrm{PaCl}}_{6}^{2\mathrm{\ensuremath{-}}}$ cluster that models the ${\mathrm{Pa}}^{4+}$ impurity site in the octahedral ${\mathrm{Cs}}_{2}$${\mathrm{ZrCl}}_{6}$ lattice. The calculations predict a ${\ensuremath{\Gamma}}_{7u}$ ground state, and show fairly good agreement with the observed g tensor, $^{231}\mathrm{Pa}$ hyperfine interactions, and crystal-field splittings. The Zeeman and $^{231}\mathrm{Pa}$ hyperfine interactions are isotropic, arising from the large orbital contributions to the magnetic moment of the ground Kramers doublet. The amount of covalency is predicted to be about 3%, and the largest contribution to covalency comes from the chlorine 3${d}_{5/2}$ spinors (\ensuremath{\sim}2%).

An orbital model for the exchange interactions between low spin iron(III) and copper(II) ions

The effect of the quasi degenerate ground state of low spin iron(III) ion on the exchange interaction with an orbitally non-degenerate ion, such as copper(II), has been taken into account, using two formally different models which produce the same results when compared with the bilinear exchange spin hamiltonian. It is found that the four levels which originate from the interactions between the two ground Kramers' doublets are not generally grouped in a singlet and a triplet, but in a less regular fashion, due to the quasi degeneration of low spin iron(III). The model has been applied to some systems recently reported as mimicking the cyanide form of oxidized cytochrome oxidase.

The effect of the local zero field splitting of the nickel(II) ion on the E.P.R. spectra of exchange coupled copper(II) (S= 1/2)-nickel(II) (S= 1) pairs

The zero field splitting of the nickel(II) ion can have measurable effects on the E.P.R. spectra of heterodinuclear transition metal complexes. In this paper we will apply a simple method to calculate the g and A tensors of the ground Kramers doublet of copper(II)-nickel(II) exchange coupled pairs as a function of the spin hamiltonian parameters of the two isolated ions and of the exchange parameters. This model will be applied to reinterpret the E.P.R. spectra of some copper(II)-nickel(II) pairs.

Anomalousg-Value of a Cr-Trimer Complex, Cr-Propionate {Cr3O(C2H5COO)6(H2O)3}NO32H2O

Origin of anomalous g -shift observed in a Cr-trimer complex {Cr 3 O(C 2 H 5 COO) 6 (H 2 O) 3 }NO 3 2H 2 O is discussed. It is found that the Dzyaloshinsky-Moriya interaction in the trimer produces the in-plane g -shift for the triangular trimer plane. The g -shift in magnetic field H 0 is negative with the magnitude of (8/3) D z 2 /{( Δ E ) 2 -( g ⊥ 0 µ B H 0 ) 2 } where D z is the Dzyaloshinsky-Moriya interaction perpendicular to the trimer plane. g ⊥ 0 is in-plane g -value of each Cr 3+ ion, µ B is Bohr magneton and Δ E is the energy gap between the ground and first excited Kramers doublets splitted by the intra-trimer exchange interaction. The observed in-plane g -value 1.89 is well explained by introducing D z of 0.9 K in the trimer.

Single-crystal EPR study of bromobis (diethyldithiocarbamato) iron (III) diluted in the lattice of bromobis (diethyldithiocarbamato) arsenic (III)

The single-crystal EPR spectra of Fe(S2CNEt2)2Br diluted in As(S2CNEt2)2Br have been recorded at liquid–helium temperature. They display a typical rhombic pattern with g′X =3.07(2), gY =5.08(2), g′Z =1.95(2) in agreement with a ground Kramers doblet, ‖±〉≂‖S=3/2, MS =±1/2〉. The signals exhibit ligand hyperfine structure from the79,81 Br ions. Due to the overlapping of four, symmetry related signals, only a partial analysis of this hyperfine tensor was achieved. It was found that the ligand A-tensor anisotropy is not pronounced and that the magnitudes of the three principal components lie in the range 80–100×10−4 cm−1.

Optical detection of cross relaxation between rare-earth ions in lanthanum trichloride crystals

The dynamics of relaxation and interionic energy-transfer processes for ${\mathrm{Nd}}^{3+}$ and ${\mathrm{Er}}^{3+}$ ions, dilutely cosubstituted at ${\mathrm{La}}^{3+}$ sites in La${\mathrm{Cl}}_{3}$ single crystals, have been investigated in a series of optical-magnetic double-resonance experiments. These processes have been studied by measuring the effects of electron-paramagnetic-resonance absorption at microwave frequencies on the fluorescence radiation emitted during continuous Ar-ion-laser irradiation. In cases for which the ratio of the magnetic field energy splitting of the ground Kramers doublet of ${\mathrm{Er}}^{3+}$ to that of ${\mathrm{Nd}}^{3+}$ had values relatively close to \textonehalf{}, 1, 2, 3, or 4, the time for regaining steady-state-level populations after termination of microwave irradiation was markedly reduced compared with other ratios and was minimum at those particular values. This observation is interpreted as due to energy-conserving cross-relaxation processes involving several ${\mathrm{Nd}}^{3+}$ and ${\mathrm{Er}}^{3+}$ ions simultaneously.

Optical Investigations of YbCrO3. I. Optical Absorption Spectra of Yb3+Ion

The optical transition 2 F 7/2 → 2 F 5/2 of Yb 3+ in the antiferromagnet YbCrO 3 has been studied. The exchange splittings for the ground and excited Kramers doublets were observed in the antiferromagnetic state. From the analysis of the splitting of the ground Kramers doublet as a function of applied magnetic field, it is concluded that main Cr–Yb magnetic interactions are the Dzyaloshirnsky-Moriya antisymetric and the anisotropic-symetric exchange interactions, which cause the splittings of the Kramers doublets in the absence of the external magnetic field. Besides single-ion excitations, a cooperative transition corresponding to the simultaneous excitation of the 2 F 7/2 → 2 F 5/2 transition on a Yb 3+ ion and a spin flip of the ground doublet on its neighbouring Yb 3+ ion was observed.

High Field Transverse Magnetization of Ising Antiferromagnet CoCl2·2H2O

Transverse magnetization was measured on a single crystal of an Ising-like antiferromagnet CoCl 2 ·2H 2 O at 1.3 K using the high sensitive pick up coil system under a pulsed magnetic field up to 400 kOe. The antiferromagnetic-paramagnetic transition was observed at 162±5 and 370±15 kOe along the transverse principal x - and y -axes, respectively. These results have been well interpreted with the effective Hamiltonian for the ground Kramers doublet, together with the mixing matrix elements between the ground and excited states. Technical details of the magnetization measurement are also reported.

Cross-relaxation to (3d)1ions in ruby

Resonant cross-relaxation (RCR) and non-resonant cross-relaxation (NCR) measurements are reported on ruby crystals containing Ti3+ as an additional impurity, RCR is shown to be dominated by the Ti3+-lattice process. The temperature dependences of RCR and NCR both give values for the splitting between the ground and first excited Kramers doublets of Ti3+ which are less than that expected but possible reasons are put forward, RCR is also reported in ruby crystals containing V4+ and the results are explained in terms of NCR involving V3+ ions. It is concluded that the ion-lattice coupling is larger for V4+ than for Ti3+ but both are smaller than that for V3+. A table is given which lists all NCR and RCR measurements which have been carried out on all (3d)n ion impurities in ruby.

Mössbauer study of the Ising antiferromagnet DyPO4: Hyperfine parameters,g-factor anisotropy, and spin-lattice relaxation

M\"ossbauer spectroscopy of the 26-keV $\ensuremath{\gamma}$-ray transition in $^{161}\mathrm{Dy}$ was employed to study nuclear hyperfine interactions in Ising-like DyP${\mathrm{O}}_{4}$. Single-crystal and polycrystalline samples were studied over the temperature range $1.8\ensuremath{\le}T\ensuremath{\lesssim}300$ K, which included the N\'eel temperature ${T}_{N}=3.39$ K. For $0\ensuremath{\le}T\ensuremath{\lesssim}10$ K the spectra could be analyzed in terms of a "static" $S=\frac{1}{2}$ spin Hamiltonian $\mathcal{H}={A}_{z}{I}_{z}{S}_{z}+(\frac{{A}_{\ensuremath{\perp}}}{2})({I}^{+}{S}^{\ensuremath{-}}+{I}^{\ensuremath{-}}{S}^{+})+P[3{I}_{z}^{2}\ensuremath{-}I(I+1)]$. The measured components of the magnetic hyperfine tensor parallel and perpendicular to the tetragonal $c$ axis are, respectively, $\frac{{A}_{z}}{2}=\ensuremath{-}831\ifmmode\pm\else\textpm\fi{}4$ MHz and ${A}_{\ensuremath{\perp}}=\ensuremath{-}14\ifmmode\pm\else\textpm\fi{}5$ MHz. This is the first reported measurement of an ${A}_{\ensuremath{\perp}}$ term in M\"ossbauer studies of dysprosium compounds. Using the known ionic $g$-factor component, ${g}_{z}=19.32\ifmmode\pm\else\textpm\fi{}0.01$, we calculate $k=\frac{{A}_{z}}{2h{g}_{z}}=43.0\ifmmode\pm\else\textpm\fi{}0.2$ and hence ${g}_{\ensuremath{\perp}}=0.3\ifmmode\pm\else\textpm\fi{}0.1$. The ratio of quadrupole parameters for the excited and ground nuclear states of $^{161}\mathrm{Dy}$ is $\frac{{P}_{e}}{{P}_{g}}=0.986\ifmmode\pm\else\textpm\fi{}0.003$ with $\frac{{P}_{g}}{h}=60.3\ifmmode\pm\else\textpm\fi{}0.6$ MHz. For $T\ensuremath{\gtrsim}10$ K the spectra are relaxation broadened and can be described well using the time-dependent Hamiltonian $\mathcal{H}(t)=f(t){A}_{z}{I}_{z}{S}_{z}+P[3{I}_{z}^{2}\ensuremath{-}I(I+1)]$, where $f(t)=\ifmmode\pm\else\textpm\fi{}1$. These spectra were analyzed using a random-fluctuation stochastic model for $f(t)$ and incorporating the exchange splittings obtained from previous optical work on the ground Kramers doublet. The analysis then depends on a single relaxation parameter $\ensuremath{\Omega}(T)$. Between $T=16\mathrm{and}36$ K the relaxation is dominated by an Orbach spin-lattice process of the form $\ensuremath{\Omega}={\ensuremath{\Omega}}_{0}{e}^{\frac{\ensuremath{-}{\ensuremath{\Delta}}_{G}}{T}}$, where ${\ensuremath{\Delta}}_{G}\ensuremath{\simeq}70$ ${\mathrm{cm}}^{\ensuremath{-}1}$.

Magnetic Circular Dichroism of the Iron(III) Porphins

Abstract Magnetic circular dichroism (MCD) spectra were measured of some low-spin and high-spin Fe(III) porphins in a rigid matrix of polymethyl methacrylate(PMMA) for a variety of temperature. Some of the most prominent MCD, extrema of the low-spin Fe(III) porphins showed a remarkable enhancement of the intensity at reduced temperatures, while no appreciable increase was observed in the absorption intensity. The temperature dependence of the MCD dispersion of the low-spin Fe(III) porphins arises, in principle, from a change in the Boltzmann distribution between the ground Kramers doublet splitting in a magnetic field, however, the MCD enhancement observed in the Soret region can correctly be interpreted only when the excited states described by a product wave function of the porphin B state and the spin-orbit coupling substates of low-spin iron(III) d5 system are split by a configuration interaction with the “porphin to iron(III)” charge-transfer excited states.

A Mössbauer effect study of local moments of erbium in zirconium

By means of the Mössbauer effect, magnetic hyperflne splitting of dilute Er impurities in Zr has been observed in the paramagnetic state, without applied field. From analysis of the fully-resolved splitting seen at 4.2°K, we are able to determine the hyperfine coupling constants between the ground Kramers doublet of the electronic moment and the excited-state nuclear spin. By considering symmetry-imposed limits on the possible values of the electronic g tensor, we are able to show that the magnetic hyperfine coupling constant is at least 15 per cent larger than its value for Er in insulator hosts, which enhancement we attribute to conduction-electron effects. To our knowledge, this is the first measurement of such a conduction-electron contribution in a non-ferromagnetic system, as well as the first observation of magnetic hyperfine splitting in the zero-field paramagnetic state of a dilute alloy.

Mössbauer Effect ofEr166in Erbium Orthochromite

The hyperfine structure of the M\"ossbauer resonance in ErCr${\mathrm{O}}_{3}$ has been studied from 4 to 40\ifmmode^\circ\else\textdegree\fi{}K. At the lowest temperature, a well-resolved hfs pattern is obtained; from this the moment of the ordered ${\mathrm{Er}}^{3+}$ ion can be determined to be $6.2{\ensuremath{\mu}}_{\ensuremath{\beta}}$. At higher temperatures, relaxation effects smear the spectrum, and the data have been analyzed using a model in which the Kramers doublet which is the lowest Stark level of ${\mathrm{Er}}^{3+}$ is split by a molecular field coming from both the Cr and Er sublattices. Above the ${T}_{N}(\mathrm{Er})$, the relaxation rate follows an Orbach process, and below ${T}_{N}$ the rate is roughly constant, with $\ensuremath{\tau}\ensuremath{\approx}2\ifmmode\times\else\texttimes\fi{}{10}^{\ensuremath{-}10}$ sec. The first excited Stark level was found to lie about 47\ifmmode^\circ\else\textdegree\fi{}K above the ground Kramers doublet.

Exchange Contribution to the D-Parameter of Mn2+ in CoCl2·2H2O

The D -value of Mn 2+ in CoCl 2 ·2H 2 O has been obtained to be -0.13 cm -1 by Date and Motokawa. The large negative D value is reasonably explained by introducing an effective exchange interaction of general form between the Mn 2+ and the ground Kramers doublet of Co 2+ , taking account of the crystal symmetry. It is shown that the interaction -2 J x z s x S z -2 J y z s y S z is responsible for the negative D -parameter. The effective exchange interaction is derived from the nondiagonal exchange between Mn 2+ and Co 2+ with respect to the cobaltous orbits by projecting the exchange to the ground Kramers doublet.

Electronic Shielding Parameters and Anisotropic Mössbauer Patterns in Dysprosium Ethyl Sulfate

The M\"ossbauer effect of the 26-keV gamma transition in ${\mathrm{Dy}}^{161}$ was employed to study hyperfine interactions in single crystals of DyES at 4.2\ifmmode^\circ\else\textdegree\fi{}K. The Dy nuclei experience a magnetic hyperfine interaction ${g}_{0}{\ensuremath{\beta}}_{N}{H}_{\mathrm{eff}}$ of -446\ifmmode\pm\else\textpm\fi{}12 Mc/sec, with ${H}_{\mathrm{eff}}$ parallel to the $c$ axis of the crystal. The hyperfine field and M\"ossbauer patterns (parallel and perpendicular to the $c$ axis) are readily interpreted in terms of the symmetry of the hyperfine interaction from the ground Kramers doublet. The measurement of the electric quadrupole interaction is of interest because the $4f$ contribution to the electric field gradient (EFG) is often dominant in rare-earth ions; however, for the ground doublet of DyES, this gradient is very small. This fact allowed a simple and direct measurement of the lattice contribution to the EFG. From this result the ratio $\frac{(1\ensuremath{-}{\ensuremath{\gamma}}_{\ensuremath{\infty}})}{(1\ensuremath{-}{\ensuremath{\sigma}}_{2})}$ was found to be 262, where ${\ensuremath{\gamma}}_{\ensuremath{\infty}}$ is the lattice Sternheimer factor and ${\ensuremath{\sigma}}_{2}$ represents the shielding of the $4f$ electrons from the crystalline field. The resolution of the paramagnetic hyperfine spectra was interpreted to show that electronic relaxation times were longer than ${10}^{\ensuremath{-}8}$ sec.

Magnetic Hyperfine Interactions in Dysprosium Aluminum Garnet

The M\"ossbauer effect has been employed to investigate the magnetic hyperfine interactions of ${\mathrm{Dy}}^{161}$ in dysprosium aluminum garnet (DyAlG), which is paramagnetic (antiferromagnetic) above (below) 2.49\ifmmode^\circ\else\textdegree\fi{}K. At 4.2\ifmmode^\circ\else\textdegree\fi{}K a well-resolved paramagnetic hyperfine pattern was found that is consistent with the following interactions for the ground state of ${\mathrm{Dy}}^{161}$: ${g}_{0}{\ensuremath{\beta}}_{N}{H}_{\mathrm{eff}}=\ensuremath{-}769\ifmmode\pm\else\textpm\fi{}15$ Mc/sec and ${e}^{2}qQ=1480\ifmmode\pm\else\textpm\fi{}60$ Mc/sec. The magnetic interaction is in good agreement with the hyperfine interaction expected from the ground Kramers doublet of ${\mathrm{Dy}}^{3+}$. The excellent resolution of the 4.2\ifmmode^\circ\else\textdegree\fi{}K data allowed a more precise determination of the ratio of excited-state and ground-state moments to be obtained than has previously been reported; the ratios found were $\frac{{\ensuremath{\mu}}_{1}}{{\ensuremath{\mu}}_{0}}=\ensuremath{-}1.21\ifmmode\pm\else\textpm\fi{}0.02$ and $\frac{{Q}_{1}}{{Q}_{0}}=0.98\ifmmode\pm\else\textpm\fi{}0.03$. At 20\ifmmode^\circ\else\textdegree\fi{}K and above, the linewidths of the hyperfine lines increased owing to paramagnetic relaxation, and the data are compared with theoretical spectra whose shape is dependent on the electronic relaxation rate. The relaxation rates obtained in this manner are in approximate agreement with values extrapolated from reported electron-spin-resonance (ESR) measurements employing ${\mathrm{Dy}}^{3+}$ in the similar lattice YAIG. Although DyAlG undergoes an antiferromagnetic transition at 2.49\ifmmode^\circ\else\textdegree\fi{}K, data obtained with the sample at 1.9\ifmmode^\circ\else\textdegree\fi{}K yielded the same results as the 4\ifmmode^\circ\else\textdegree\fi{}K measurements. It is shown that the latter result is to be expected on the basis of available susceptibility and optical data.