Electron Spin Resonance Linewidth Research Articles

Electron spin resonance study of Bi(1−x)CaxMnO3

The temperature dependent electron spin resonance (ESR) studies on Bi(1−x)CaxMnO3 (x=0.4, 0.45, and 0.5) having a triclinic structure were carried out to understand the spin dynamics, short-range magnetic interactions, and micromagnetic phase formation in these materials. The phase transition into charge-ordered (CO) state takes place at temperatures TCO=313K (for x=0.4 and 0.5) and at 317K (for x=0.45) samples. The data are explained in view of the existence of mixed valence clusters of Mn3+–Mn4+ ions coupled by strong short-range ferromagnetic (FM) double-exchange interactions in the paramagnetic state. The orbital ordering changes from FM to antiferromagnetic (AFM) type ∼190K (for x=0.4 and 0.5) and ∼180K (for x=0.45). The Néel Temperatures TN are 163K (for x=0.4 and 0.5) and 153K (for x=0.45). The temperature independence of ln (DI) double integrated intensity of the ESR resonance below 125K is ascribed to the existence of FM ordered microinhomogeneities embedded in the AFM ordered bulk sample. The TCO and TN values are found to be weakly dependent on the composition. The temperature dependence of ESR linewidth near TN has been analyzed in view of the spin-spin relaxation near magnetic critical points, as given by Seehra and Huber [AIP Conf. Proc. 24, 261 (1975)].

Magnetic interactions inα−NaMnO2: Quantum spin-2 system on a spatially anisotropic two-dimensional triangular lattice

The dc magnetization and the electron spin resonance (ESR) measurements have been performed on $\ensuremath{\alpha}\text{\ensuremath{-}}\mathrm{Na}\mathrm{Mn}{\mathrm{O}}_{2}$ polycrystalline sample, a quantum spin system on a frustrated two-dimensional (2D) triangular lattice with spatially anisotropic Heisenberg exchange. The former measurements reveal a realization of the high-spin state $(S=2)$ on magnetic ${\mathrm{Mn}}^{3+}$ sites. From the susceptibility curve, we have determined the nearest-neighbor antiferromagnetic exchange coupling constants (namely, in the preferably coupled spin chains, ${J}_{1}∕{k}_{B}=65\phantom{\rule{0.3em}{0ex}}\mathrm{K}$, and perpendicular to them, ${J}_{2}∕{J}_{1}=0.44$) by employing the finite-temperature Lanczos method. The dominant magnetic anisotropy term of the single-ion type, $D∕{k}_{B}=\ensuremath{-}4.1\phantom{\rule{0.3em}{0ex}}\mathrm{K}$, which establishes an easy-axis direction, is evaluated from the ESR linewidth. We find that the temperature dependence of the linewidth reflects the onset of short-range static spin correlations below room temperature.

Temperature dependence of the EPR lines in weakly doped LiNbO 3:Yb—possible evidence of Yb 3+ ion pairs formation

The electron paramagnetic resonance (EPR) studies of LiNbO 3 single crystal doped with 1 wt% of Yb 3+ are reported. To put the EPR results in perspective, a brief discussion of optical absorption spectroscopy investigations of LiNbO 3:Yb 3+ is provided. The temperature behavior of the EPR lines intensity and linewidth for LiNbO 3:Yb 3+ reveals antiferromagnetic coupling between Yb 3+ ions. The deconvolution of the EPR lines indicates that EPR signals arise from both the isolated Yb 3+ ions as well as the Yb 3+–Yb 3+ ion pairs; the latter signals dominate. Based on this indication, EPR spectra are interpreted using a spin Hamiltonian for the Yb 3+ dissimilar ion pairs. The negative sign of the isotropic parameter J confirms the existence of the antiferromagnetic interactions within Yb 3+–Yb 3+ pairs. The value of J obtained based on the proposed pair model, assuming the dipole–dipole interactions, is used to identify the positions of the Yb 3+–Yb 3+ pairs in the unit cell. Our results suggest the evenYb 3+– evenYb 3+ pairs are located at the neighboring Li + and Nb 5+ positions, whereas the pair axis is not parallel to the optical c-axis. Some alternative explanations of the observed EPR spectra are also considered.

Phase coexistence and magnetic anisotropy inLa1−xCaxMnO3(0<x⩽0.23)studied via electron spin resonance

We report an electron-spin-resonance (ESR) study of stoichiometric ${\mathrm{La}}_{1\ensuremath{-}x}{\mathrm{Ca}}_{x}\mathrm{Mn}{\mathrm{O}}_{3}$ for $0<x\ensuremath{\leqslant}0.23$. The room-temperature ESR linewidth shows a marked decrease with $x$ that is mainly due to the variation of the magnetic susceptibility and a much slower evolution of spin relaxation, associated with the interplay of crystal-field and superexchange interactions. In the canted antiferromagnetic regime, the ESR parameters show initially an $x$-dependent ferromagnetic (FM) behavior that evolves to antiferromagnetic in the vicinity of ${T}_{N}$, reflecting the development of spin canting. A weak ferromagnetic-resonance (FMR) mode is observed below ${T}_{N}$ that becomes enhanced near the phase boundary to the ferromagnetic insulating (FMI) phase. This mode persists at higher doping levels $(x\ensuremath{\leqslant}0.16)$ and is attributed to residual FM domains due to the release of crystal strain near the structural transformation at $T<100\phantom{\rule{0.3em}{0ex}}\mathrm{K}$. In the FMI regime, FMR measurements show strong uniaxial magnetic anisotropy up to $x=0.16$ with $K=(1--2)\ifmmode\times\else\texttimes\fi{}{10}^{6}\phantom{\rule{0.3em}{0ex}}\mathrm{erg}∕{\mathrm{cm}}^{3}$ at $100\phantom{\rule{0.3em}{0ex}}\mathrm{K}$. The temperature dependence of the magnetic anisotropy reveals power-law scaling with the magnetization, $K(T)\ensuremath{\propto}M{(T)}^{3}$, indicative of single-ion magnetocrystalline anisotropy and the persistence of orbital order in the FMI state. As the FM metallic phase is approached, the magnetic anisotropy decreases significantly and an additional FMR mode systematically emerges in the paramagnetic regime at $T\ensuremath{\lesssim}260\phantom{\rule{0.3em}{0ex}}\mathrm{K}$ for $x=0.19--0.23$. Its relative spectral weight grows with $x$ indicating an increase of the underlying FM fraction that correlates with the enhanced metallic behavior.

Soliton contribution to the electron paramagnetic resonance linewidth in a two-dimensionalantiferromagnet with a staggered field

In this paper we study the interactions between magnons and a solitonin a classical and isotropic two-dimensional Heisenberg antiferromagnetin the presence of a staggered field applied perpendicularly to theXY plane. The temperature dependence of the linewidth is calculated using the dynamic spincorrelation function derived from soliton–magnon scattering.

EPR Analysis of Spin Susceptibility and Line Width in the Hyperexpanded Fulleride (CH3NH2)K3C60

The electron paramagnetic resonance (EPR) technique is used to study the temperature evolution of the electronic and magnetic properties of the hyperexpanded fulleride (CH3NH2)K3C60 in the temperature range 4−294 K. Unambiguous signatures for the development of large internal magnetic fields and a transition to an antiferromagnetic ground state below TN = 11 K are provided by the temperature dependence of the spin susceptibility, the EPR line width, and the position of the EPR line. The EPR results in the paramagnetic regime are indicative of an insulating electronic state, with localized S = 1/2 moments on the C603- ions. The accompanying complex evolution of the spin susceptibility, EPR line width, and g-factor anisotropy furthermore reveals that effects of electronic origin (t1u orbital order−disorder transition, crossover from static to dynamic Jahn−Teller distortions) in the vicinity of the structural transformation are important for the understanding of the exchange interactions between the fulleride ions.

ESR and X-ray diffraction studies on thin films of poly-3-hexylthiophene: Molecular orientation and magnetic interactions

Poly-3-hexylthiophene (P3HT) thin films were investigated by X-ray diffraction (XRD) and electron spin resonance (ESR) to reveal the film structure and molecular organization. The XRD data showed a diffraction pattern with a plane separation between the planes containing thiophene rings of 16.0 Å. Comparison between the XRD patterns of powder and thin films of P3HT suggests that the main chains are folded on the substrate. Angular variation of the line position ( g-value) of ESR spectra revealed that thiophene ring of P3HT orients along the substrate normal axis. The ESR linewidth varied by the angular rotation, indicating the one-dimensional spin–chain interactions in the P3HT thin films with a linear network of spin–chains. An organic thin-film transistor (OTFT) with P3HT film as a channel layer was then demonstrated. The P3HT films showed conducting characteristics with holes as carriers. The OTFTs indicated a field-effect mobility of 4.93 × 10 − 3 cm 2/Vs and an on/off ratio of 73 in the accumulation mode.

Magnetic properties of frustrated Y-doped [formula omitted

We report temperature dependent magnetic susceptibility and electron spin resonance (ESR) measurements on single crystals of the frustrated antiferromagnet Gd 1 - x Y x InCu 4 ( x = 0 , 0.01 , 0.05 and 0.1). The magnetic susceptibility data revealed, as expected, a decreasing in the antiferromagnetic ordering temperature as function of the Y-concentration, while the high- T Curie–Weiss temperatures remain nearly unaffect by the doping. For T ≳ 100 K , a single Dysonian Gd 3 + ESR line with a nearly temperature independent g ∼ 1.989 ( 8 ) is observed, and its linewidth follows a Korringa-like ( Δ H / Δ T ∼ 0.75 ( 5 ) Oe / K ) behavior as a function of temperature. Below T ≈ 100 K both the ESR g-value and linewidth are affected by the presence of strong short-range magnetic correlation in the paramagnetic phase well above T N , consistently with the frustrated character of this compound. The role of chemical disorder and dilution effects induced by Y-doping in the properties of this highly frustrated material is discussed.

ZnO:Mn as a member of II-VI:Mn family

ZnO:Mn thin films are grown by the metal organic chemical vapor deposition technique. Mn (x) varies in the 0 < x < 0.44 range. Vegard's law has been verified for the lattice parameters. Electron paramagnetic resonance (EPR) measurements prove the substitutional incorporation of Mn2+ on zinc sites. The behavior of the EPR line width regarding temperature is discussed. All ZnO:Mn layers show antiferromagnetic interaction and a J(1)/k(B)=-15 K effective exchange constant. The optical band gap of ZnO:Mn increases with the manganese concentration. Raman spectroscopy reveals a Mn-related scattering band.

Electron spin resonance in YbRh2Si2: The role of the residual linewidth

We present electron spin resonance (ESR) investigations of the La-doped heavy fermion metal YbRh2Si2 and of undoped samples which differ in their low-temperature charge transport properties. The dilution of Yb by non-magnetic La leaves the temperature dependence of ESR parameters qualitatively unchanged. A comparison with various undoped samples shows that the residual, zero temperature ESR linewidth is a key parameter for the spin dynamics seen by the ESR active entities in YbRh2Si2.

Crystal Structure and Physical Properties of Conducting Molecular Antiferromagnets with a Halogen-Substituted Donor: (EDO-TTFBr2)2FeX4(X = Cl, Br)

The crystal structure and physical properties of radical ion salts (EDO-TTFBr2)2FeX4 (X = Cl, Br) based on halogen-substituted organic donor and magnetic anions are investigated, including the comparison with the isomorphous compounds (EDO-TTFBr2)2GaX4 with nonmagnetic anions. The crystal structure of these four salts consists of uniformly stacked donor molecules and tetrahedral counter anions, and the Br substituents of the donor molecules are connected to halide ligands of anions with remarkably short intermolecular atomic distances. These salts show metallic behavior around room temperature and undergo a spin-density-wave transition in the low-temperature range, as confirmed with the divergence of the electron spin resonance (ESR) line width. Although close anion-anion contacts are absent in these salts, the FeCl4 salt undergoes an antiferromagnetic transition at TN = 4.2 K, and the FeBr4 salt shows successive magnetic transitions at TN = 13.5 K and TC2 = 8.5 K with a helical spin structure as a candidate for the ground state of the d-electron spins. The magnetoresistance of the FeCl4 salt shows stepwise anomalies, which are explained qualitatively using a pi-d interaction-based frustrated spin system model composed of the donor pi-electron and the anion d-electron spins. Although on the ESR spectra of the FeX4 salts signals from the pi- and d-electron spins are separately observed, the line width of the pi-electron spins broadens under the temperature where the susceptibility deviates from the Curie-Weiss behavior, showing the presence of the pi-d interaction.

ESR study of the Prussian blue analogue Rb 0.8Mn 1.1[Fe(CN) 6]·D 2O

We performed electron spin resonance (ESR) studies of the mixed valence Prussian blue analogue, Rb 0.8Mn 1.1[Fe(CN) 6]·D 2O in a wide frequency (9.5–319 GHz) and temperature (3.5–300 K) interval. Evidence for the proposed high-temperature Mn 2+ ( S = 5 2 )–NC–Fe 3+ ( S = 1 2 ) to low-temperature Mn 3+ ( S=2)–NC–Fe 2+ ( S=0) internal charge transfer has been detected: a characteristic reduction of χ ESR T on cooling from room temperature to 100 K, a particular frequency dependence of the room temperature ESR linewidth, and the temperature dependence of the ESR linewidth. Short-range magnetic correlations, reflected in a large broadening and dramatic shift of the ESR signal develop just above T C=10 K. Below T C, both the linewidth and the shift in position mimic the temperature dependence of the order parameter. In a quench experiment T C was reduced by 3 K. The observed ferromagnetic ordering arises from Mn 3+ ( S=2) moments in the low-temperature electronic configuration.

ESR bottleneck effect in the heavy-fermion metal YbRh 2Si 2

An approach related to the bottleneck effect is proposed for an origin of the electron spin resonance (ESR) of a Kondo ion (Yb 3+) in the undoped Kondo-lattice systems YbRh 2Si 2 and YbIr 2Si 2. The effects observed for the effective ESR g-factor and the ESR linewidth in YbRh 2Si 2 are associated with the influence of the Kondo effect and the crystalline electric field splitting of the f-multiplet of ytterbium. A corresponding theory, which predicts the exchange-narrowed ESR linewidths in the temperature range 1–10 K, is discussed.

EPR study of local ordering in DMAAlS and DMAGaS crystals

X-band electron paramagnetic resonance (EPR) investigations of single crystals of Cr3+-doped dimethylammonium aluminium sulphate hexahydrate (DMAAlS) and dimethylammonium gallium sulphate hexahydrate (DMAGaS) are presented from room temperature down to liquid helium temperature. Both crystals undergo an order-disorder phase transition to ferroelectric phase at T C1 = 152 K and T C1 = 134 K, respectively. Additionally, DMAGaS undergoes a first-order transition into a low temperature non-ferroelectric intermediate phase at T C2 = 116 K and into a low temperature antiferroelectric phase at about T C3 = 60 K. The spin Hamiltonian parameters have been determined for all observed in both crystal phases. Remarkable EPR line width changes with observed triplets confirm the order-disorder character of the ferroelectric phase transition and demonstrate freezing-out of dimethyl ammonium reorientations, which is a primary reason for this transition. The doubled number of EPR lines in comparison to the paraelectric and ferroelectric phases in DMAGaS indicates a unit cell doubling in antiferroelectrics phase below 60 K.

Spatial Extent of Wave Functions of Gate-Induced Hole Carriers in Pentacene Field-Effect Devices as Investigated by Electron Spin Resonance

An electron spin resonance (ESR) method is applied to a pentacene field-effect device to investigate gate-induced hole carriers in such devices. Clear field-induced ESR signals are observed, demonstrating that all of the field-injected carriers have S = 1/2 spins. Anisotropic ESR signals due to unpaired pi electrons show the molecular orientation at the interface in the devices. The spatial extent of the spin density distribution (wave function) of the carriers is evaluated from the ESR linewidth, accounting for the hyperfine structure, to be of the order of 10 molecules.

Electron Spin Dynamics in (DMe-DCNQI)2M (M = Li1-x Cu x (x &lt; 0.14), Ag)

The quarter-filled π band systems, (DMe-DCNQI)2M(M=Li1−xCux(x ≤ 0.14), Ag) were systematically studied with electron paramagnetic resonance (EPR). The intercolumn spin hopping rate D⊥ in Li1−xCux-salt was obtained from the EPR linewidth. The temperature dependence of D⊥ can be understood with the hole soliton model which also explains the DC conductivity. The π − d mixing of the Cu-salt enhances both D⊥ and σ⊥ by103 times more than the Li-salt, which is consistent with the fact that the only Cu-salt has three-dimensional Fermi surface, but that Ag-salt is one-dimensional in spite of the mixing enhancement of D⊥ by 10 times more than the Li-salt.

Electron spin resonance linewidth, susceptibility, and conductivity in doped manganites

Analyses of the electron spin resonance (ESR) linewidths in manganites with ferromagnetic interactions arising from double exchange (e.g. La 1− x Ca x MnO 3) have generally followed either of two approaches. One approach, coming from general theories of spin relaxation, expresses the linewidth above the critical region in the form [( C/ T)/ χ( T)]Δ H( ∞), where χ( T) is the static spin susceptibility, C is the Curie constant and Δ H( ∞) is a material-dependent constant representing the limiting behavior of the linewidth at high temperatures, where χ( T)≈ C/ T. The other approach is based on the observation of a similarity between the temperature dependence of the linewidth and the high-temperature electrical conductivity, the latter being associated with the thermally activated hopping of small polarons. In this approach, the linewidth is fit to an expression of the form α+( β/ T)exp(− E a/ k B T), where α and β are constants and E a is identified as the polaron activation energy. In our work, we show that in La 0.75Ca 0.25 MnO 3 [ Tχ( T)] −1 is characterized by the same functional form as the linewidth with nearly identical values of the activation energy and the ratio α/ β. These results establish that the “thermal activation” component of the linewidth is associated with the static susceptibility. Using the susceptibility of La 0.67Sr 0.33MnO 3 as an example, we suggest this finding is indicative of a process where the Hund's rule correlations between the core spins and the spins of the e g polarons are disrupted by the random hopping of the polarons.

Electron spin resonance (ESR) in multiferroic [formula omitted

We report temperature dependent X-Band ( ν ∼ 9.4 GHz ) electron spin resonance (ESR) measurement in a single crystal of TbMnO 3 . A single Lorentzian ESR line with an isotropic g ∼ 1.96 was observed for T ⩾ 120 K up to 600 K. The ESR signal is attributed to the Mn 3 + ions in a insulator environment. For the three crystallographic axes the temperature dependence ESR linewidth shows a strong broadening as the temperature decreases due to the presence of short range magnetic correlations.

Electron Spin Resonance (ESR) and Microwave Absorption Studies in TbMnO$_3$Multiferroic Compound

We report temperature dependent X-Band (f~9.5 GHz) Electron Spin Resonance (ESR) and microwave absorption measurements in a single crystal of TbMnO <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">3</sub> . A single Lorentzian ESR line with an isotropic g-value g~1.96 was observed for Tges120 K up to 600 K. The ESR signal is attributed to the Mn <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">3+</sup> ions in a insulator environment. The temperature dependence of the ESR linewidth is investigated for the external field applied along the three crystallographic axes. For all direction the ESR linewidth show a strong broadening as the temperature decreases due to the presence of short range magnetic correlations. The microwave absorption around the ferroelectric transition T <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">lock</sub> ~27 K was investigated using a special cavity with a TE <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">103</sub> mode where the sample sits at the maximum microwave electric-field

Spin-flop and spin-Peierls transition in doped CuGeO 3

Ni ++ ions doped inorganic CuGeO 3 sample has been studied by using electron spin resonance (ESR) technique in the temperature range of 3–300 K. The ESR spectrum of Cu ++ ion has been observed to be strongly temperature dependent for inorganic spin-Peierls (SP) Cu 0.96Ni 0.04GeO 3 samples. The ESR line width and ESR amplitude exponentially vanishes below a critical temperature, T sp = 14 K. The one-dimensional (1D) antiferromagnetic (AF) spin chain formed of Cu ++ is broken by Ni ++ (spin-1) ion, giving uncoupled spins at the end of the chains that give extra contribution to the spectra at lower temperature and stabilizes a Néel state. The g-factor is much smaller than the expected value for isolated Cu ++ and Ni ++ ions and is much more anisotropic than for undoped samples [O. Yalçın, B. Aktaş, J. Magn. Magn. Mater. 258/259 (2003) 137 (reference therein)]. It is shown that the ground state of dimerized spins is singlet. The spin-flop (SF) phenomenon is obtained from AF state mixed condition and then ferromagnetic (FM) state. The spin-flop field slightly increases when increasing temperature in the temperature range 100–300 K. The SF transition is showed almost AF order for Cu 0.96Ni 0.04GeO 3.