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Hexagonal $\alpha$-Ru trichloride single crystals exhibit a strong magnetic anisotropy and we show that upon applying fields up to 14 T in the honeycomb plane the successive magnetic order at T1=14K and T2=8K could be completely suppressed, whereas in the perpendicular direction the magnetic order is robust. Furthermore, the field dependence of $\chi$(T) implies coexisting ferro- and antiferromagnetic exchange between in-plane components of Ru3+ spins, whereas for out-of-plane components a strong antiferromagnetic exchange becomes evident. Ru101 zero-field nuclear magnetic resonance in the ordered state evidence a complex (probably noncoplanar chiral) long-range magnetic structure. The large orbital moment on Ru3+ is found in density-functional calculations.

Physics

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Physical Review B - Condensed Matter and Materials Physics

Anisotropic Ru3+ 4d5 magnetism in the $\alpha$-RuCl3 honeycomb system: Susceptibility, specific heat and zero-field NMR anisotropic Ru3+4d5 magnetism in the ⋯ M. Majumder et al.

31P nuclear-magnetic-resonance (NMR) study in the trimer spin chain compound Ca3Cu2Ni(PO4)4 is performed in the presence of different external magnetic fields in the temperature range 4-300 K. The results suggest that the three magnon mediated scattering process which was the dominant contribution to 1/T1 in the pure compound Ca3Cu3(PO4)4, has negligible contribution in Ca3Cu2Ni(PO4) 4, with the two magnon mediated Raman process being dominant. The linear variation of nuclear spin lattice relaxation rate 1/T1T with the magnetic susceptibility $\chi$ indicates that the Q component of magnetic susceptibility $\chi$(Q) is nearly proportional to $\chi$, where Q is the antiferromagnetic wave vector. A change in the slope of 1/T1T with respect to $\chi$ near 15 K suggests a change in the antiferromagnetic spin fluctuation spectrum. Below 15 K, the spin diffusion mechanism governs the 1/T1 process. This could be a signature of the development of short range magnetic correlation or due to the contribution arising from the paramagnetic impurity spins. {\textcopyright} 2013 Elsevier B.V. All rights reserved.

Physica B: Condensed Matter

Low energy spin dynamics in trimer spin chain compound Ca 3Cu2Ni(PO4)4: 31P NMR study

75As and 31P NMR studies are performed in PrCoAsO and NdCoPO respectively. The Knight shift data in PrCoAsO indicate the presence of an antiferromagnetic interaction between the 4f moments along the c axis in the ferromagnetic state of Co 3d moments. We propose a possible spin structure in this system. The 75As quadrupolar coupling constant, $\nu$Q, increases continuously with decrease of temperature and is found to vary linearly with the intrinsic spin susceptibility, Kiso. This indicates the possibility of the presence of a coupling between charge density and spin density fluctuations. Further, the 31P NMR Knight shift and spin-lattice relaxation rate (1/T1) in the paramagnetic state of NdCoPO indicate that the differences of LaCoPO and NdCoPO from SmCoPO are due to the decrement of the interlayer separation and not due to the moments of the 4f electrons. The nuclear spin-lattice relaxation time (T1) in NdCoPO shows weak anisotropy at 300 K. Using the self-consistent renormalization (SCR) theory of itinerant ferromagnets, it is shown that in the ab plane, the spin fluctuations are three-dimensional ferromagnetic in nature. From SCR theory the important spin-fluctuation parameters (T0, T A, ) are evaluated. The similarities and dissimilarities of the NMR results in As and P based systems with different rare earths are also discussed. {\textcopyright} 2013 IOP Publishing Ltd.

Journal of Physics Condensed Matter

Local electromagnetic properties of magnetic pnictides: A comparative study probed by NMR measurements

We report resistivity, magnetization and 19F NMR results in a polycrystalline sample of SmFeAsO0.86F0.14. The resistivity and magnetization data show a sharp drop at 48 K indicating a superconducting transition. The nuclear spin-lattice rate (1/T1) and spin-spin relaxation rate (1/T2) clearly show the existence of a structural phase transition near 163 K in the sample, which also undergoes a superconducting transition. This finding creates interest in exploring whether this is unique for Sm based systems or is also present in other rare-earth based 1111 superconductors. {\textcopyright} 2013 IOP Publishing Ltd.

Evidence of a structural phase transition in superconducting SmFeAsO 1-xFx from 19F NMR

31P NMR has been done in the paramagnetic state of SmCoPO. Hisohf, Haxhf are 13.4 and -5.19 kOe/$\mu$B respectively have been estimated which indicates the nature of hybridization between P 2p orbitals with Co 3d orbitals. Anisotropic spin-lattice relaxation rate has been observed. In plane spin-correlations are 2D FM and out of plane spin correlations are AFM type. {\textcopyright} 2012 American Institute of Physics.

AIP Conference Proceedings

Anisotropic spin-fluctuations in SmCoPO: 31P NMR study

The effect of the substitution of one Cu2+ ion (S=1/2) by Mg2+ ion (S=0) on the magnetic property of the linear-chain spin trimer compound Ca3 Cu3 (PO4) 4 was studied using dc magnetic susceptibility in Ca3 Cu2 Mg (PO4) 4 together with those in Ca3 Cu3 (PO4) 4 and Ca3 Cu2 Ni (PO4) 4 for comparison. A remarkable difference is observed among the results obtained in the Mg and the Ni substituted compounds. A clear signature of the reduction in the net spin of the trimers in Ca3 Cu2 Mg (PO4) 4 was found below 65 K, which is compatible with the presence of the Cu2-Cu1-Mg trimers in the singlet ground state, together with those of the type Cu2-Cu1-Cu2 and Mg-Cu1-Mg in the doublet state. However, no signature of the reduction in the net spin of the trimers was observed in Ca3 Cu2 Ni (PO4) 4. This finding suggests that the type of trimers present in Ca3 Cu2 Mg (PO4) 4 and Ca3 Cu2 Ni (PO4) 4 are different. Furthermore, a singlet ground state is partially realized in a quantum spin trimer system Ca3 Cu2 Mg (PO4) 4. {\textcopyright} 2010 The American Physical Society.

Magnetic properties of the spin trimer compound Ca3 Cu 2 Mg ( PO4 ) 4 from susceptibility measurements

P 31 nuclear-magnetic-resonance (NMR) studies have been performed in trimer spin chain compound Ca3 CuNi2 (PO4) 4, in the temperature range 4-300 K. In the range 16-300 K, the spectrum corresponds to a typical overlap of two powder patterns, consistent with two inequivalent phosphorous sites, having different shift parameters. A comparison of the isotropic hyperfine field (H hf iso) and the axial part (H hf ax) obtained in the paramagnetic phase of Ca3 CuNi2 (PO4) 4, with those obtained in Ca3 Cu3 (PO4) 4, suggest a stronger interchain exchange interaction in Ca3 CuNi2 (PO4) 4, which is possibly the reason for the higher antiferromagnetic transition temperature in Ca3 CuNi2 (PO4) 4. The temperature dependence of the spin-lattice relaxation rate (1/ T1) shows a clear signature of long-range magnetic order in Ca3 CuNi2 (PO4) 4 below 16 K (TN). TN agrees quite satisfactorily with that obtained from the derivative of the molar susceptibility versus T plot. The NMR line shape below TN shows the signature of a considerable distribution of the internal magnetic field in the ordered state with the existence of two magnetic sublattices with opposite direction of polarization with respect to the direction of the external magnetic field. A comparison of the behavior of the 1/ T1 data in Ca3 CuNi2 (PO4) 4 with those in Sr3 Cu3 (PO4) 4 clearly suggests that the mechanism of the relaxation changes from a two magnon-mediated Raman process in the former to a three magnon-mediated process in the latter. {\textcopyright} 2010 The American Physical Society.

NMR study of a magnetic phase transition in Ca3 CuNi2 ( PO4 ) 4: A spin trimer compound

As NMR Investigation In An Itinerant Ferromagnet PrCoAsO

Detailed 27Al and 63Cu nuclear magnetic resonance (NMR) experiments have been performed in between 4.5 and 295 K on a polycrystalline sample of CeCu3Al2 which has a Kondo temperature ∼11K. The NMR spectral features and Knight shift measurements show that in this compound, Cu occupy both c and g lattice sites, while Al occupy only the g sites. From the temperature dependence of Knight shift (K), the hyperfine fields for 63Cu and 27Al at the g sites have been estimated as 2.02(5) and 1.67(5)kOe/$\mu$B, respectively and that for 63Cu at c sites as -3.83(5)kOe/$\mu$B. Nuclear spin-lattice relaxation time (T1) measurements indicate that though the relaxation process is governed by fluctuations of magnetic interaction, nuclear quadrupolar interaction also has a significant contribution, especially towards relaxation of 63Cu in both c and g sites. For 27Al, K and T 1 have yielded the effective 4f-spin correlation rate 1/$\tau$4f. The behavior of its temperature dependence indicates that at low temperatures in CeCu3Al2, the valence state of cerium might not be stable. {\textcopyright} 2010 Elsevier B.V. All rights reserved.

27Al and 63Cu NMR studies on intermetallic Kondo compound CeCu3Al2

The effect of interfacial hydrogen bonding on the behavior of the freezing/melting processes in two organic liquids, namely, ethylene glycol [(CH2OH)2] and isopropanol [CH3CH(OH)CH 3], confined in nanopores of ZSM-5 zeolite has been investigated using the positron annihilation spectroscopy (PAS) and nuclear magnetic resonance (NMR) techniques. Both liquids have intermolecular hydrogen bonding and feel attractive interaction toward the surface of the confining wall, resulting in an increase in the freezing/melting temperature while confined in nanopores. This observation differs from our earlier report on the behavior of benzene confined in ZSM-5 as well as in silica pores wherein a depression in freezing temperature was seen due to a weakly attractive/repulsive interaction between benzene and the pore surface. The measured S parameter, o-Ps lifetime and intensity profiles across the freezing point of ethylene glycol confined in ZSM-5 are seen to be different from those of isopropanol, signifying the difference in the behavior of phase transition in these two liquids under confinement. It is to be noted that, unlike isopropanol, ethylene glycol has strong intramolecular hydrogen bonding. This causes the difference in the fluid-wall interfacial interaction between ethylene glycol and isopropanol within the confinement. The phase-transition behavior of these two confined liquids was also investigated using the NMR technique by studying the spin-spin relaxation time (T2). The T2 process in ethylene glycol is expressed as a sum of at least two distinct components exhibiting Gaussian decay, whereas in isopropanol, T2 is expressed as a sum of three components showing Lorentzian decay. The transitions from one component to another were seen to be consistent with the positron annihilation spectroscopic observation. {\textcopyright} 2010 American Chemical Society.

Journal of Physical Chemistry C

Effect of interfacial hydrogen bonding on the freezing/melting behavior of nanoconfined liquids

L 139 a NMR study was performed in grain-aligned (c→|| H→0) sample of LaCoPO and polycrystalline LaFePO. Knight shift is isotropic and temperature independent in LaFePO. It is strongly temperature dependent and anisotropic in LaCoPO. The spin-lattice relaxation rate in LaCoPO clearly reveals the existence of three-dimensional spin fluctuations both in the paramagnetic and ferromagnetic state over and above the dominant two-dimensional spin fluctuations in the paramagnetic state, observed earlier from P 31 NMR measurements in the same oriented sample. The spin fluctuation parameters in LaCoPO determined from L 139 a NMR relaxation and magnetization data, using the self-consistent renormalization theory, are in close agreement and follow the universal Rhodes-Wohlfarth curve. {\textcopyright} 2010 The American Physical Society.

Electron spin dynamics in grain-aligned LaCoPO: An itinerant ferromagnet

We report (11)B and (195)Pt NMR Knight shift K and spin-lattice relaxation rate 1/T(1) in CePt(2)B(2)C in the range 4-315 K. The quadrupolar coupling constant, nu(Q) for boron nuclei is 790 +/- 10 kHz. The change of hyperfine field, H(hf), is observed below 30 K in the K versus susceptibility, chi, plot. The calculated value of H(hf) at the (11)B ((195)Pt) is 0.156 (6.86) kOe/mu(B) in the range 30-300 K and approximately 0 (0.22) kOe/mu(B) below 30 K. The 1/T(1) versus T curve shows some exotic behavior. The Ce 4f spin contribution to the nuclear relaxation rate (1/T(1f)) in each case is obtained by subtracting the T(1K)(-1) estimated from its La analog, i.e. LaPt(2)B(2)C. In the case of (11)B resonance, in the temperature range of 300-100 K, (1/T(1f)) is independent of T, suggesting a Curie-Weiss behavior of the imaginary part of the dynamic susceptibility. It then shows a slow but continuous increment in the range 100-70 K, indicating a signature of the development of short-range magnetic correlation among the Ce 4f spins. Below 70 K, this enhancement of 1/T(1f) is completely suppressed and it decreases sharply, indicating a suppression of the effect of magnetic correlation, due to the dominance of the Kondo effect over the RKKY interaction. 1/T(1f), follows approximately T(alpha), with an exponent alpha approximately 0.7 in the range 4-30 K for (195)Pt and in the range 8-30 K for (11)B resonance. This is a characteristics of a non-Fermi-liquid like behavior. However, in the case of (11)B, there is again a clear change in the slope of the 1/T(1f) versus T curve below 8 K, with the value of alpha = 1.0, as if the behavior of the conduction electrons approaches towards a Fermi liquid, when probed near the (11)B site.

Journal of Physics: Condensed Matter

11 B and 195 Pt NMR study of heavy-fermion compound CePt 2 B 2 C

dc magnetization and P 31 spin-lattice relaxation rate in the polycrystalline sample of LaCoPO suggest a spin-fluctuation dominated ferromagnetically ordered state. Moreover, NMR data clearly indicate a crossover from two-dimensional to three-dimensional spin fluctuations across TC. In contrast to isotropic hyperfine field, Hhf at the P 31 site in LaFePO, Hhf is anisotropic in LaCoPO. The data of spin-lattice relaxation rate also exhibit anisotropic spin fluctuation. The anisotropy vanishes near TC. {\textcopyright} 2009 The American Physical Society.