Lattice collapse and quenching of magnetism in CaFe2As2 under pressure: A single crystal neutron and x-ray diffraction investigation
A. I. Goldman, A. Kreyssig, K. Prokes, D. K. Pratt, D. N. Argyriou, J. W. Lynn, S. Nandi, S. A. J. Kimber, Y. Chen, Y. B. Lee, G. Samolyuk, J. B. Leao, S. J. Po… 展开作者
A. I. Goldman, A. Kreyssig, K. Prokes, D. K. Pratt, D. N. Argyriou, J. W. Lynn, S. Nandi, S. A. J. Kimber, Y. Chen, Y. B. Lee, G. Samolyuk, J. B. Leao, S. J. Poulton, S. L. Bud'ko, N. Ni, P. C. Canfield, B. N. Harmon, R. J. McQueeney
备注：
List of authors in metadata and typos in labeling of inset in Fig. 1(a) corrected. One ref. added. No other changes
Single crystal neutron and high-energy x-ray diffraction have identified the phase lines corresponding to transitions between the ambient-pressure tetragonal (T), the antiferromagnetic orthorhombic (O) and the non-magnetic collapsed tetragonal (cT) phases of CaFe2As2. We find no evidence of additional structures for pressures up to 2.5 GPa (at 300 K). Both the T-cT and O-cT transitions exhibit significant hysteresis effects and we demonstrate that coexistence of the O and cT phases can occur if a non-hydrostatic component of pressure is present. Measurements of the magnetic diffraction peaks show no change in the magnetic structure or ordered moment as a function of pressure in the O phase and we find no evidence of magnetic ordering in the cT phase. Band structure calculations show that the transition results in a strong decrease of the iron 3d density of states at the Fermi energy, consistent with a loss of the magnetic moment.
The majority of the iron-based superconductors (FeSCs) exhibit a two-dimensional square lattice structure. Recent reports of pressure-induced superconductivity in the spin-ladder system, BaFe$_2$X$_3$ (X =S,Se), introduce a quasi-one-dimensional prototype and an insulating parent compound to the FeSCs. Here we report X-ray, neutron diffraction and muon spin relaxation experiments on BaFe$_2$Se$_3$ under hydrostatic pressure to investigate its magnetic and structural properties across the pressure-temperature phase diagram. A structural phase transition was identified at a pressure of 3.7(3) GP…
Magnetism in the insulating BaFe$_2$Se$_3$ was examined through susceptibility, specific heat, resistivity and neutron diffraction measurements. After formation of a short-range magnetic correlation, a long-range ordering was observed below $T_{\rm N}\sim 255$ K. The transition is obscured by bulk properties. Magnetic moments ($\parallel a$) are arranged to form a Fe$_4$ ferromagnetic unit, and each Fe$_4$ stacks antiferromagnetically. This block magnetism is of the third type among magnetic structures of ferrous materials. The magnetic ordering drives unusually large distortion via magnetoela…
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Single crystal neutron diffraction is used to investigate the magnetic and structural phase diagram of the electron doped superconductor Ba(Fe$_{1-x}$Co$_x$)$_2$As$_2$. Heat capacity and resistivity measurements have demonstrated that Co doping this system splits the combined antiferromagnetic and structural transition present in BaFe$_2$As$_2$ into two distinct transitions. For $x$=0.025, we find that the upper transition is between the high-temperature tetragonal and low-temperature orthorhombic structures with ($T_{\mathrm{TO}}=99 \pm 0.5$ K) and the antiferromagnetic transition occurs at $…
The properties of RbBi$_2$, a 4.15 K superconductor, were investigated using magnetic field, pressure and neutron diffraction. Under hydrostatic pressure, an almost 50 % reduction of T$_c$ is observed, linked to a low Debye temperature estimated at 165 K. The resistivity and magnetic susceptibility were measured on quenched and slow-cooled polycrystalline samples. The resistivity follows a low temperature power-law dependence in both types of samples, while the diamagnetic susceptibility, $χ$, is dependent on the sample cooling history. Slow-cooled samples have a $χ= -1$ while quenched samples…
This is the first report of the observation of the onset of excess volume and also of the strain along the a-axis near the magnetic ordering temperature in Ru-1222 superconductor, and indicates a coupling between the lattice and the magnetism in this system. Magnetization, magneto transport and thermoelectric power measurements being carried out on the same sample are also reported.
The distribution of chemically similar transition-metal ions is a fundamental issue in the study of herbertsmithite-type kagome antiferromagnets. Using synchrotron radiation, we have performed resonant powder x-ray diffractions on newly synthesized CoCu3(OH)6Cl2, which provide an exact distribution of transition-metal ions in the frustrated antiferromagnet. Both magnetic susceptibility and specific heat measurements are quantitatively consistent with the occupation fractions determined by resonant x-ray diffraction. The distribution of transition-metal ions and residual magnetic entropy sugges…
The title quasi-1D copper oxides (0=< x =<0.4) were investigated by neutron diffraction and magnetic susceptibility studies. Polyhedral CuO4 units in the compounds were found to comprise linear-chains at inter-chain distance of approximately 10 A. The parent chain compound (x = 0), however, shows less anisotropic magnetic behavior above 2 K, although it is of substantially antiferromagnetic (mu_{eff}= 1.85 mu_{B} and Theta_{W} = -46.4 K) spin-chain system. A magnetic cusp gradually appears at about 100 K in T vs chi with the Bi substitution. The cusp (x = 0.4) is fairly characterized by and th…
The crystal and magnetic structures of stoichiometric ZnCr2Se4 have been investigated using synchrotron X-ray and neutron powder diffraction, muon spin relaxation (muSR) and inelastic neutron scattering. Synchrotron X-ray diffraction shows a spin-lattice distortion from the cubic spinel to a tetragonal I41/amd lattice below TN = 21 K, where powder neutron diffraction confirms the formation of a helical magnetic structure with magnetic moment of 3.04(3) μB at 1.5 K; close to that expected for high-spin Cr3+. MuSR measurements show prominent local spin correlations that are established at temper…
Magnetism in the orthorhombic metal CaFe$_4$As$_3$ was examined through neutron diffraction for powder and single crystalline samples. Incommensurate (${\bm q}_{\rm m}\approx (0.37-0.39)\times{\bm b}^{\ast}$) and predominantly longitudinally ($\parallel b$) modulated order develops through a 2nd order phase transition at $T_{\rm N}=89.63(6)$ K with a 3D Heisenberg-like critical exponent $β=0.365(6)$. A 1st order transition at $T_2=25.6(9)$ K is associated with the development of a transverse component, locking ${\bm q}_{\rm m}$ to $0.375(2){\bm b}^{\ast}$, and increasing the moments from 2.1(1…
In order to investigate whether magnetism and superconductivity coexist in Co-doped SrFe$_2$As$_2$, we have prepared single crystals of SrFe$_{2-x}$Co$_x$As$_2$, $x$ = 0 and 0.4, and characterized them via X-ray diffraction, electrical resistivity in zero and applied field up to 9 T as well as at ambient and applied pressure up to 1.6 GPa, and magnetic susceptibility. At $x$ = 0.4, there is both magnetic and resistive evidence for a spin density wave transition at 120 K, while $T_c$ = 19.5 K - indicating coexistent magnetism and superconductivity. A discussion of how these results compare with…
It is widely believed that, in contrast to its electron doped counterparts, the hole doped compound Ba1-xKxFe2As2 exhibits a mesoscopic phase separation of magnetism and superconductivity in the underdoped region of the phase diagram. Here, we report a combined high-resolution x-ray powder diffraction and volume sensitive muon spin rotation study of underdoped Ba1-xKxFe2As2 (0 \leq x \leq 0.25) showing that this paradigm is wrong. Instead we find a microscopic coexistence of the two forms of order. A competition of magnetism and superconductivity is evident from a significant reduction of the …
FeVO$_4$ has been studied by heat capacity, magnetic susceptibility, electric polarization and single crystal neutron diffraction experiments. The triclinic crystal structure is made of \emph{S}-shaped clusters of six Fe$^{3+}$ ions, linked by VO$_4^{3-}$ groups. Two long-range magnetic ordering transitions occur at T$_{N1}$=22K and T$_{N2}$=15K. Both magnetic structures are incommensurate. That stable below T$_{N1}$ is collinear with amplitude modulated moments whereas below T$_{N2}$ the arrangement is non-collinear with a helicoidal modulation. Below T$_{N2}$, \fevo becomes weakly ferroelect…
Neutron diffraction was used to determine the crystal structure and magnetic ordering pattern of a La2CuO4 single crystal, with and without applied magnetic field. A previously unreported, subtle monoclinic distortion of the crystal structure away from the orthorhombic space group Bmab was detected. The distortion is also present in lightly Sr-doped crystals. A refinement of the crystal structure shows that the deviation from orthorhombic symmetry is predominantly determined by displacements of the apical oxygen atoms. An in-plane magnetic field is observed to drive a continuous reorientation …
A theory of Kondo lattices is applied to the crossover between local-moment magnetism and itinerant-electron magnetism in the t-J model on a quasi-two dimensional lattice. The Kondo temperature T_K is defined as a characteristic temperature or energy scale of local quantum spin fluctuations. Magnetism with T_N >> T_K, where T_N is the N\eel temperature, is characterized as local-moment one, while magnetism with T_N << T_K is characterized as itinerant-electron one. The Kondo temperature, which also gives a measure of the strength of the quenching of magnetic moments, is renormalized by the Foc…
The Fe1+xTe phase diagram consists of two distinct magnetic structures with collinear order present at low interstitial iron concentrations and a helical phase at large values of x with these phases separated by a Lifshitz point. We use unpolarized single crystal diffraction to confirm the helical phase for large interstitial iron concentrations and polarized single crystal diffraction to demonstrate the collinear order for the iron deficient side of the Fe1+xTe phase diagram. Polarized neutron inelastic scattering show that the fluctuations associated with this collinear order are predominate…
We studied the crystal structure and spin state of MnP under high pressure with synchrotron X-ray diffraction and X-ray emission spectroscopy. MnP has an exceedingly strong anisotropy in compressibility, with the primary compressible direction along the b axis of the Pnma structure. X-ray emission spectroscopy reveals a pressure-driven quenching of the spin state in MnP. Firstprinciples calculations suggest that the strongly anisotropic compression behavior significantly enhances the dispersion of the Mn d-orbitals and the splitting of the d orbital levels compared to the hypothetical isotropi…
Intra unit cell (IUC) magnetic order observed by polarized neutron diffraction (PND) is one of the hallmarks of the pseudogap state of high-temperature copper oxide superconductors. This experimental observation, usually interpreted as a result of loop currents, has been recently challenged based on lower statistics data. We here address the crucial issue of polarization inhomogeneities in the neutron beams showing that the original data had a much better reproducibilty. Within these technical limitations, we here propose a self-consistent analysis that potentially solves the controversy. We s…
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The structural and magnetic phase transitions have been studied on NdFeAsO single crystals by neutron and x-ray diffraction complemented by resistivity and specific heat measurements. Two low-temperature phase transitions have been observed in addition to the tetragonal-to-orthorhombic transition at T_S = 142 K and the onset of antiferromagnetic (AFM) Fe order below T_N = 137 K. The Fe moments order AFM in the well-known stripe-like structure in the (ab) plane, but change from AFM to ferromagnetic (FM) arrangement along the c direction below T* = 15 K accompanied by the onset of Nd AFM order b…
The interplay and coexistence of superconducting, magnetic and structural order parameters in NaFe{1-x}Co{x}As has been studied using SQUID magnetometry, muon-spin rotation and synchrotron x-ray powder diffraction. Substituting Fe by Co weakens the ordered magnetic state through both a suppression of T_N and a reduction in the size of the ordered moment. Upon further substitution of Fe by Co the high sensitivity of the muon as a local magnetic probe reveals a magnetically disordered phase, in which the size of the moment continues to decrease and falls to zero around the same point at which th…
Magnetization, neutron diffraction, and high-energy x-ray diffraction results for Sn-flux grown single-crystal samples of Ca(Co$_{1-x}$Fe$_{x}$)$_{y}$As$_{2}$, $0\leq x\leq1$, $1.86\leq y \leq 2$, are presented and reveal that A-type antiferromagnetic order, with ordered moments lying along the $c$ axis, persists for $x\lesssim0.12(1)$. The antiferromagnetic order is smoothly suppressed with increasing $x$, with both the ordered moment and Néel temperature linearly decreasing. Stripe-type antiferromagnetic order does not occur for $x\leq0.25$, nor does ferromagnetic order for $x$ up to at leas…
We report pressure tuned Raman and x-ray diffraction data of Bi1.98Sr2.06Y0.68Cu2O8 revealing a critical pressure at 21 GPa with anomalies in six physical quantities: electronic Raman background, electron-phonon coupling, spectral weight transfer from high to low frequency, density dependent behaviour of phonon and magnon frequencies, and a compressibility change in the c-axis. For the first time in a cuprate, mobile charge carriers, lattice, and magnetism all show anomalies at a distinct critical pressure in the same experimental setting. Furthermore, the Raman spectral changes are similar to…
Layered thallium copper chalcogenides can form single, double, or triple layers of Cu-Ch separated by Tl sheets. Here we report on the preparation and properties of Tl-based materials of TlCu2Se2, TlCu4S3, TlCu4Se3 and TlCu6S4, and compare to reports on layered ACu2nChn+1 materials with A = Ba, K, Rb, and Cs, and Ch = S, Se. Having no long-range magnetism for these materials is quite surprising considering the possibilities of inter- and intra-layer exchange interactions through Cu 3d, and we measure by magnetic susceptibility and confirm by neutron diffraction. First principles density-functi…
NiBi3 polycrystals were synthesized via a solid state method. X-ray diffraction analysis shows that the main phase present in the sample corresponds to NiBi3 in a weight fraction of 96.82 % according to the refinement of the crystalline structure. SEM - EDS and XPS analysis reveal a homogeneous composition of NiBi3, without Ni traces. The powder superconducting samples were studied by performing magnetic measurements. The superconducting transition temperature and critical magnetic fields were determinated as Tc = 4.05 K, Hc1 = 110 Oe and Hc2 = 3,620 Oe. The superconducting parameters were GL …
Within the BaFe2As2 crystal lattice, we partially substitute thallium for barium and report the effects of interlayer coupling in Ba1-xTlxFe2As2 crystals. We demonstrate the unusual effects of magneto-elastic coupling and charge doping in this iron-arsenide material, whereby Neel temperature rises with small x, and then falls with additional x. Specifically, we find that Neel and structural transitions in BaFe2As2 (TN =Ts= 133 K) increase for x=0.05 (TN = 138 K, Ts = 140 K) from magnetization, heat capacity, resistivity, and neutron diffraction measurements. Evidence from single crystal X-ray …
We present a detailed investigation of the electronic phase diagram of effectively charge compensated Ba1-xKx(Fe1-yCoy)2As2 with x/2 = y. Our experimental study by means of x-ray diffraction, Mössbauer spectroscopy, muon spin relaxation and ac susceptibility measurements on polycrystalline samples is complemented by density functional electronic structure calculations. For low substitution levels of x/2 = y \< 0.13, the system displays an orthorhombically distorted and antiferromagnetically ordered ground state. The low temperature structural and magnetic order parameters are successively redu…
Unlike the ferropnictide superconductors, which crystallize in a tetragonal crystal structure, binary FeAs forms in an orthorhombic crystal structure, where the local atomic environment resembles a highly distorted variant of the FeAs4 tetrahdedral building block of the ferropnictide superconductors. However, like the parent compounds of the ferropnictide superconductors, FeAs undergoes magnetic ordering at low temperatures, with no evidence favoring a superconducting ground state at ambient pressure. We employ pressure-dependent electrical transport and x-ray diffraction measurements using di…
We investigated the magnetism and superconductivity in as-sintered (AS) and oxidation annealed (OA) T*-type La$_{1-x/2}$Eu$_{1-x/2}$Sr$_x$CuO$_4$ (LESCO) with 0.14 $\leq x \leq$ 0.28 by the first comprehensive muon spin rotation/relaxation ($μ$SR), magnetic susceptibility, and electrical resistivity measurements. In OA superconducting samples, no evidence of magnetic order was observed, whereas AS semiconducting samples exhibited evidence of a disordered magnetic state in the measured temperature range between $\sim$4 K and $\sim$8 K. Therefore, the ground state in LESCO drastically varies wit…
The magnetic ordering and crystal structure of iron pnictide SrFeAsF was investigated by using neutron powder diffraction method. With decreasing temperature, the tetragonal to orthorhombic phase transition is found at 180 K, while the paramagnetic to antiferromagnetic phase transition set in at 133 K. Similar to the parent compound of other iron pnictide system, the striped Fe magnetism is confirmed in antiferromagnetic phase and the Fe moment of 0.58(6) uB aligned along long a axis. The thermal expansion of orthorhombic phase of SrFeAsF is also investigated. Based on the Grueneisen approxima…
Structure and composition of iron chalcogenides have a delicate relationship with magnetism and superconductivity. In this report we investigate the iron sulfide layered tetragonal phase (t-FeS), and compare with three-dimensional hexagonal phase (h-FeS). X-ray diffraction reveals the absence of structural transitions for both t- and h-FeS below room temperature, and gives phase compositions of Fe0.93(1)S and Fe0.84(1)S, respectively, for the samples studied here. The a lattice parameter of bigger than 3.68 A is significant for causing bulk superconductivity in iron sulfide, which is controlle…
We report $^{75}$As NMR studies on single crystals of rare-earth doped iron pnictides superconductor Ca$_{1-x}$Pr$_{x}$Fe$_{2}$As$_{2}$ ($x$=0.075 and 0.15). The $^{75}$As spectra show a chemical pressure effect with doping and a first order structure transition to the collapsed tetragonal phase upon cooling. A sharp drop of the Knight shift is seen below the structural transition, whereas $1/T_1$ is strongly enhanced at low-temperatures. These evidences indicate quenching of Fe local magnetism and short-range ordering of Pr$^{3+}$ moment in the collapsed tetragonal phase. The quenched Fe mome…
Among various parent compounds of iron pnictide superconductors, EuFe2As2 stands out due to the presence of both spin density wave of Fe and antiferromagnetic ordering (AFM) of the localized Eu2+ moment. Single crystal neutron diffraction studies have been carried out to determine the magnetic structure of this compound and to investigate the coupling of two magnetic sublattices. Long range AFM ordering of Fe and Eu spins was observed below 190 K and 19 K, respectively. The ordering of Fe2+ moments is associated with the wave vector k = (1,0,1) and it takes place at the same temperature as the…
Single crystals of K$_x$Fe$_{2-y}$Se$_2$ are prepared by quenching at various temperatures. The crystals obtained at higher quenching temperatures have a surface morphology with mesh-like texture. They show a sharp superconducting transition at $T_\rm{c}$ ~32 K with a large shielding volume fraction. On the other hand, the crystals prepared without quenching show an onset superconducting transition at ~44 K and a zero resistivity around ~33 K, and they possess island-like regions on the surface with a larger amount of Fe incorporation. In-situ high-temperature single crystal X-ray diffraction …
An extended investigation of the electronic phase diagram of FeSe$_{1-x}$ up to pressures of $p\simeq2.4$\,GPa by means of ac and dc magnetization, zero field muon spin rotation (ZF $μ$SR), and neutron diffraction is presented. ZF $μ$SR indicates that at pressures $p\geq0.8$\,GPa static magnetic order occurs in FeSe$_{1-x}$ and occupies the full sample volume for $p\gtrsim 1.2$\,GPa. ac magnetization measurements reveal that the superconducting volume fraction stays close to 100% up to the highest pressure investigated. In addition, above $p\geq1.2$\,GPa both the superconducting transition tem…
