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A new layered triangular antiferromagnet Li4FeSbO6: spin order, field-induced transitions and anomalous critical behavior
(2013)
Zvereva, E. A.
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Savelieva, O. A.
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Titov, Ya D.
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Evstigneeva, M. A.
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Nalbandyan, V. B.
Structure, electrochemical, magnetic and resonance properties of new layered antimonate Li4FeSbO6 were comprehensively studied using powder X-ray diffraction, cyclic voltammetry, magnetic susceptibility, heat capacity, electron spin resonance and Mossbauer spectroscopy. In the crystal structure the iron ions form the triangular network within (LiFeSbO6)(3-) layers alternating with nonmagnetic lithium layers. The electrochemical activity studied implies an Fe3+/Fe4+ redox couple at 4.3 V (ox.) and 3.9 V (red.) thereby revealing that Li can be reversibly extracted. The long-range antiferromagnetic order was found to occur at the Neel temperature, T-N approximate to 3.6 K, confirmed both by the magnetic susceptibility data and specific heat ones. The effective magnetic moment is estimated to be 5.93 mu(B)/f.u. and satisfactorily agrees with theoretical estimations assuming high-spin configuration of Fe3+ (S = 5/2). In the magnetically ordered state, though, the magnetization demonstrates rather peculiar behavior. An additional anomaly on the M(T) curves appears at T-2 < T-N in moderate magnetic field. The positions of transitions at T-N and T-2 separate increasingly with increasing external field. Multiple measurements consistently demonstrated field-sensitive moving of magnetic phase boundaries constituting a unique phase diagram for the compound under study. The complex low-dimensional (2D) nature of magnetic coupling was confirmed by the dynamic magnetic properties study. Electron spin resonance from Fe3+ ions in paramagnetic phase is characterized by a temperature independent effective g-factor of 1.99 +/- 0.01. However, the distortion and broadening of the ESR line were found to take place upon approaching the magnetically ordered state from above. The divergence of the temperature-dependent linewidth is analyzed in terms of both critical behavior close to long-range magnetic order and the Berezinskii-Kosterlitz-Thouless (BKT)-type transition. Heat capacity measurements even at zero field manifested an appearance of the additional anomaly at temperatures below the Neel temperature. The temperature dependence of ESR intensity, linewidth and shift of the resonant field imply an extended region of short-range order correlations in the compound studied. The rich variety of the anomalies in magnetic and resonance properties makes this new antimonate a very interesting system to investigate the multiple phase transitions and competing exchange interaction due to the critical role of the layered structure organization accompanied by the frustration effects in triangular antiferromagnets.
Noncollinear ferrimagnetic ground state in Ni(NO3)(2)
(2014-10-10)
Volkova, O. S.
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Mazurenko, V. V.
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Solovyev, I. V.
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Deeva, E. B.
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Morozov, I. V.
Both spin-liquid and magnetically ordered phases of both half-integer and integer low-spin quantum magnets are of interest, since the magnetic structures found in the latter case usually have no classical counterparts. Such a magnetic structure was found in a combined experimental and theoretical study of the integer spin system Ni(NO3)(2). Our thermodynamic measurements have revealed a magnetically ordered phase with small spontaneous magnetization at T-C = 5.5 K. The magnetization saturation of about 2 mu(B) at low temperatures corresponds to the high-spin state (S = 1) of Ni2+ ions evidenced in L-2,L-3 edges in x-ray absorption spectroscopy spectra. We show that a consistent description of the available data is possible within a noncollinear umbrella-type ferrimagnetic ground state model for which both intra-and interlayer magnetic interactions should be antiferromagnetic. Such a scenario is suggested by the first-principles and model calculations.
Weak ferrimagnetism and multiple magnetization reversal in alpha-Cr(3)(PO(4))(2)
(2012-01-18)
Vasiliev, A. N.
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Volkova, O. S.
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Hammer, E.
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Glaum, R.
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Broto, J. -M.
The chromium(II) orthophosphate alpha-Cr(3)(PO(4))(2) is a weak ferrimagnet with the Curie temperature T(C) = 29 K confirmed by a lambda-type peak in specific heat. Dominant antiferromagnetic interactions in this system are characterized by the Weiss temperature Theta = 96 K, indicating an intermediate frustration ratio vertical bar Theta vertical bar/T(C) similar to 3. In its magnetically ordered states alpha-Cr(3)(PO(4))(2) exhibits a remarkable sequence of temperature-induced magnetization reversals sensitive to the protocol of measurements, i.e., either field-cooled or zero-field-cooled regimes. The reduction of the effective magnetic moment 4.5 mu(B)/Cr(2+), as compared to the spin-only moment 4.9 mu(B)/Cr(2+), cannot be ascribed to the occurrence of the low-spin state in any crystallographic site of the Jahn-Teller active 3d(4) Cr(2+) ions. X-ray absorption spectra at the K edge indicate divalent chromium and unravel the high-spin state of these ions at the L(2,3) edges. Weak ferrimagnetism and multiple magnetization reversal phenomena seen in this compound could be ascribed to incomplete cancellation and distortion of partial spontaneous magnetization functions of Cr(2+) in its six crystallographically inequivalent positions.
Weak ferrimagnetism and multiple magnetization reversal in alpha-Cr-3(PO4)(2)
(2012-01-18)
Vasiliev, A. N.
;
Volkova, O. S.
;
Hammer, E.
;
Glaum, R.
;
Broto, J. -M.
The chromium(II) orthophosphate alpha-Cr-3(PO4)(2) is a weak ferrimagnet with the Curie temperature T-C = 29 K confirmed by a lambda-type peak in specific heat. Dominant antiferromagnetic interactions in this system are characterized by the Weiss temperature Theta = 96 K, indicating an intermediate frustration ratio vertical bar Theta vertical bar/T-C similar to 3. In its magnetically ordered states alpha-Cr-3(PO4)(2) exhibits a remarkable sequence of temperature-induced magnetization reversals sensitive to the protocol of measurements, i.e., either field-cooled or zero-field-cooled regimes. The reduction of the effective magnetic moment 4.5 mu(B)/Cr2+, as compared to the spin-only moment 4.9 mu(B)/Cr2+, cannot be ascribed to the occurrence of the low-spin state in any crystallographic site of the Jahn-Teller active 3d(4) Cr2+ ions. X-ray absorption spectra at the K edge indicate divalent chromium and unravel the high-spin state of these ions at the L-2,L-3 edges. Weak ferrimagnetism and multiple magnetization reversal phenomena seen in this compound could be ascribed to incomplete cancellation and distortion of partial spontaneous magnetization functions of Cr2+ in its six crystallographically inequivalent positions.
Zigzag antiferromagnetic quantum ground state in monoclinic honeycomb lattice antimonates A(3)Ni(2)SbO(6) (A = Li, Na)
(2015-10-01)
Zvereva, E. A.
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Stratan, M. I.
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Ovchenkov, Y. A.
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Nalbandyan, V. B.
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Lin, J. -Y.
We present a comprehensive experimental and theoretical study of the electronic and magnetic properties of two quasi-two-dimensional (2D) honeycomb lattice monoclinic compounds A(3)Ni(2)SbO(6) (A = Li, Na). Magnetic susceptibility and specific heat data are consistent with the onset of antiferromagnetic long-range order with Neel temperatures of similar to 14 and 16 K for Li3Ni2SbO6 and Na3Ni2SbO6, respectively. The effective magnetic moments of 4.3 mu(B)/f.u. (Li3Ni2SbO6) and 4.4 mu(B)/f.u. (Na3Ni2SbO6), where f.u. is formula units, indicate that Ni2+ is in a high-spin configuration (S = 1). The temperature dependence of the inverse magnetic susceptibility follows the Curie-Weiss law in the high-temperature region and shows positive values of the Weiss temperature, similar to 8 K (Li3Ni2SbO6) and similar to 12 K (Na3Ni2SbO6), pointing to the presence of nonnegligible ferromagnetic interactions, although the system orders antiferromagnetically at lowtemperatures. In addition, themagnetization curves reveal a field-induced (spin-flop type) transition below T-N that can be related to the magnetocrystalline anisotropy in these systems. These observations are in agreement with density functional theory calculations, which show that both antiferromagnetic and ferromagnetic intralayer spin exchange couplings between Ni2+ ions are present in the honeycomb planes, supporting a zigzag antiferromagnetic ground state. Based on our experimental measurements and theoretical calculations, we propose magnetic phase diagrams for the two compounds.