Quantum Magnetization Plateau Research Articles

Neutron diffraction studies under zero and finite magnetic fields of the 12 quantum magnetization plateau compound Ni2V2O7

We performed powder neutron diffraction experiments on a $\frac{1}{2}$ quantum magnetization plateau compound ${\mathrm{Ni}}_{2}{\mathrm{V}}_{2}{\mathrm{O}}_{7}$ for magnetic fields in the range 0--10 T. The incommensurate magnetic structures with the propagation vector $({k}_{x}\ensuremath{\sim}0.45,0,0)$ were determined at 0 T and at 6.0 K (between ${T}_{\mathrm{N}1}=6.7$ K and ${T}_{\mathrm{N}2}=5.7$ K) and 2.3 K. Consequently, the Ni1 and Ni2 moments were disordered and ordered at 6.0 K, respectively, indicating a partially disordered state. The magnetic structure of Ni2 moments was a spin density wave structure with moments ordered parallel to the $b$ axis and perpendicular to the propagation vector. Both Ni1 and Ni2 moments exhibited ellipsoidal cycloidal incommensurate magnetic structures at 2.3 K. These moments lay in the $ab$ plane. The maximum magnitudes of Ni1 and Ni2 moments [1.62(16) and 2.50(6) ${\textmu{}}_{\mathrm{B}}$] at 2.3 K were sufficiently smaller and slightly larger than the value ($\ensuremath{\sim}2.2\phantom{\rule{0.28em}{0ex}}{\textmu{}}_{\mathrm{B}}$) expected from the classical picture. Further, we evaluated the field-induced magnetic moments as follows: ${m}_{1}=0.3$ and ${m}_{2}=1.9\phantom{\rule{0.28em}{0ex}}{\textmu{}}_{\mathrm{B}}$ at Ni1 and Ni2 sites, respectively, at 10 T and 1.9 K, where the $\frac{1}{2}$ quantum magnetization plateau was observed. The results indicating both the ordered moment at 0 T and the field-induced moment at 10 T being small and large at Ni1 and Ni2 sites, respectively, were consistent with results expected in the $\text{dimer}+\text{monomer}$ model that was proposed by J. J. Cao et al. [Phys. Rev. B 106, 184409 (2022)].

Absence of magnetic order and quantum magnetization plateau in spin-1/2 tetramer compound K2Co2Mo3O12

A Seff = 1/2 tetramer antiferromagnet K2Co2Mo3O12 has been synthesized and its structure and magnetism are investigated. The magnetic susceptibility and electronic spin resonance show that the compound has no long-range order down to 0.5 K, although there is a large negative Curie-Weiss temperature. The high-field magnetization curve at 2 K measured up to 30 T exhibits two magnetic transitions at Hc1 = 4.4 T and Hc2 = 8.7 T, which are associated with 1/2 quantum magnetization plateau. The magnetization process can be well fitted by isolated Co4 tetramer model with anisotropic exchange interactions and g-factors. Thus, the title compound should be described as a weakly interacting spin-1/2 tetramer antiferromagnet with strong anisotropy of exchanges.

Syntheses, Structure, and 2/5 Magnetization Plateau of a 2D Layered Fluorophosphate Na3Cu5(PO4)4F·4H2O

A new two-dimensional (2D) fluorophosphate compound Na3Cu5(PO4)4F·4H2O with a Cu5 cluster has been synthesized using a conventional hydrothermal method. The compound crystallizes in the orthorhombic crystal system with space group Pnma. The 2D layered structure is formed by cap-like {Cu5(PO4)4F} building units consisting of a Cu4O12F cluster plus a residual cap Cu2+ ion. Magnetic susceptibility exhibits a broad maximum at T2 = 19.2 K due to low-dimensional character followed by a long-range antiferromagnetic ordering at T1 = 11.5 K, which is further confirmed by the specific heat data. High-field magnetization measurement demonstrates a 2/5 quantum magnetization plateau above 40 T. The ESR data indicate the presence of magnetic anisotropy, in accordance with the 2D structure of the system.

Magnetic properties of the antiferromagnetic spin- tetramer compound CuInVO5

We measured the temperature dependence of the magnetic susceptibility and specific heat and the magnetic-field dependence of the magnetization of CuInVO5. An antiferromagnetically ordered state appears below TN = 2.7 K. We observed a quantum magnetization plateau above 30 T at 1.3 K. The probable spin model for CuInVO5 is an interacting spin- tetramer model. We evaluated the values of the intratetramer interactions as J1 = 240 ± 20 K (antiferromagnetic) and J2 = −142 ± 10 K (ferromagnetic) and the value of the effective intertetramer interaction as Jeff = 30 ± 4 K. The ground state of the isolated spin tetramer with the J1 and J2 values is spin singlet. The shrinkage of ordered magnetic moments by quantum fluctuation can be expected. Longitudinal-mode magnetic excitations may be observable in CuInVO5.

Magnetism of the antiferromagnetic spin-12tetramer compoundCuInVO5

We measured the temperature dependence of the magnetic susceptibility and specific heat and the magnetic-field dependence of the magnetization of CuInVO$_5$. An antiferromagnetically ordered state appears below $T_{\rm N} = 2.7$ K. We observed a $\frac{1}{2}$ quantum magnetization plateau above 30 T at 1.3 K. We show that the spin system consists of antiferromagnetic spin-$\frac{1}{2}$ tetramers with $J_1 = 240 \pm 20$ and $J_2 = -142 \pm 10$ K for the intratetramer interactions.

Direct Observation of the Ground State of a 1/3 Quantum Magnetization Plateau in SrMn3P4O14 Using Neutron Diffraction Measurements

We can directly investigate the ground state in magnetization-plateau fields (plateau ground state) using neutron diffraction measurements. We performed neutron diffraction measurements on the spin-5/2 trimer substance SrMn$_3$P$_4$O$_{14}$ in magnetization-plateau fields. The integrated intensities of magnetic reflections calculated using an expectation value of each spin in a plateau ground state of an isolated-trimer model agree well with those obtained experimentally in the magnetization-plateau fields. We succeeded in direct observation of a plateau ground state in SrMn$_3$P$_4$O$_{14}$.

Magnetism of SrM 3P4 O 14 (M 2+ = 3d Ions) investigated using neutron-scattering measurements

The substances SrM3P4O14 (M = Mn, Fe, Co or Ni) have the same crystal structure. However, the magnetism of SrMn3P4O14 differs qualitatively from that of the other substances. We determined the magnetic structures of SrM3P4O14 (M = Mn or Co) by using neutron powder diffraction measurements. The spin system in SrMn3P4O14 can be regarded as a trimerized spin chain, which is consistent with the spin system inferred from the crystal structure and the appearance of the 1/3 quantum magnetization plateau. The spin system in SrCo3P4O14 is not a trimerized spin chain.

Magnetic Structure of SrCo3P4O14 Determined from Neutron Powder Diffraction Results

The spin system in SrCo 3 P 4 O 14 was reported to be a J 1 – J 1 – J 2 trimerized spin-3/2 chain. The J 1 and J 2 exchange interactions were antiferromagnetic and ferromagnetic, respectively. However, in spite of expectation for the trimerized spin chain, a 1/3 quantum magnetization plateau does not appear. To investigate the sign of exchange interactions, we determined the magnetic structure using neutron powder diffraction measurements. Both the J 1 and J 2 exchange interactions are ferromagnetic. The previously reported spin system is incorrect. Therefore, no 1/3 quantum magnetization plateau exists.

Experimental Realization of a Spin-1/2Triangular-Lattice Heisenberg Antiferromagnet

We report the results of magnetization and specific heat measurements on Ba{3}CoSb{2}O{9}, in which the magnetic Co{2+} ion has a fictitious spin 1/2, and provide evidence that a spin-1/2 Heisenberg antiferromagnet on a regular triangular lattice is actually realized in Ba{3}CoSb{2}O{9}. We found that the entire magnetization curve including the one-third quantum magnetization plateau is in excellent quantitative agreement with the results of theoretical calculations. We also found that Ba{3}CoSb{2}O{9} undergoes a three-step transition within a narrow temperature range.

Four Isomorphous Phosphates AM3P4O14 (A = Sr, Ba; M = Co, Mn) with Antiferromagnetic−Antiferromagnetic−Ferromagnetic Trimerized Chains, Showing 1/3 Quantum Magnetization Plateaus Only in the Manganese(II) System

The four new phosphates BaCo3P4O14 (1), SrCo3P4O14 (2), BaMn3P4O14 (3), and SrMn3P4O14 (4) were hydrothermally synthesized and characterized structurally and magnetically. They are isostructural with ANi3P4O14 (A = Ca, Sr, Pb, Ba), crystallizing in the monoclinic space group P2(1)/c. The CoO6 (or MnO6) octahedra share edges to from zigzag chains along the b axis, which are further interconnected by P2O7 groups into a three-dimensional structure. Preliminary magnetic measurements on powder samples indicate that 1, 2, and 4 are spin-canted antiferromagnets and 3 is a pure antiferromagnet at low field; long-range orderings were established respectively at T critical approximately 8.2 K for 1, 6.5 K for 2, and 2.6 K for both 3 and 4; field-induced spin-flop-like transitions occur respectively at Hc approximately 25 kOe for 1, 4 kOe for 2, 3 kOe for 3, and 0.7 kOe for 4. Interestingly, together with the known Ni analogues, they all apply the same antiferromagnetic-antiferromagnetic-ferromagnetic (AAF) trimerized chain model, whereas the 1/3 quantum magnetization plateau only appears in the Mn system. By qualitative analysis, we conclude that the appearance of quantum magnetization plateaus in the AAF chain compounds requires both good 1D characteristics and strong AF intrachain interactions.

Quantum magnetization plateau and sign change of the magnetocaloric effect in a ferrimagnetic spin chain.

The magnetocaloric effect in the $(5∕2,1)$ ferrimagnetic chain is investiagted using a finite-cluster solver with central spin selection to reduce finite-size effects. We found that an enhanced magnetocaloric effect occurs at the boundary of the ground-state magnetization plateau. The calculated magnetic Gr\uneisen parameter ${\ensuremath{\Gamma}}_{H}$ exhibits strong signatures of a field-induced quantum phase transition at the critical magnetic field ${H}_{c}$ destroying the plateau. We obtain the characteristic increase ${\ensuremath{\Gamma}}_{H}\ensuremath{\sim}{T}^{\ensuremath{-}1∕\ensuremath{\nu}z}$ near ${H}_{c}$ and the sign change ${\ensuremath{\Gamma}}_{H}\ensuremath{\approx}\ensuremath{-}{G}_{r}∕(H\ensuremath{-}{H}_{c})$, in accordance with scaling theory predictions.