@article{nandi_observationof_2025,

title = {Observation of a gapped phase in the one-dimensional S = 1/2 Heisenberg antiferromagnetic chain Cu(Ampy)ClBr},

author = {S. Nandi and M. Jawale and S. Bachhar and Rahul Kumar and M. Schuller and R. Bag and J. Wilkinson and J. Sichelschmidt and A. Sundaresan and S. Haravifard and N. Büttgen and A. V. Mahajan},

url = {https://link.aps.org/doi/10.1103/mkdv-8m61},

doi = {10.1103/mkdv-8m61},

year  = {2025},

date = {2025-10-22},

urldate = {2025-10-22},

journal = {Phys. Rev. B},

volume = {112},

number = {13},

pages = {134437},

abstract = {Spin-1/2 Heisenberg antiferromagnetic frustrated spin-chain systems display exotic ground states with unconventional excitations and distinct quantum phase transitions as the ratio of next-nearest-neighbor to nearest-neighbor coupling is tuned. We present a comprehensive investigation of the structural, magnetic, and thermodynamics properties of the spin-1/2 compound, Cu(Ampy)ClBr(Ampy=C6⁢H8⁡N2=2 -(aminomethyl)pyridine) via x-ray diffraction, magnetization, specific heat, 1H nuclear magnetic resonance (NMR), electron spin resonance, and muon spin relaxation (𝜇⁢SR) techniques. The crystal structure features an anisotropic triangular chain lattice of magnetic Cu2+ ions. Our bulk and local probe experiments detect neither long-range magnetic ordering nor spin freezing down to 0.06 K despite the presence of moderate antiferromagnetic interaction between Cu2+ spins as reflected by a Curie-Weiss temperature of about −9 K from the bulk susceptibility data. A broad maximum is observed at about 9 K in magnetic susceptibility and specific-heat data, indicating the onset of short-range spin correlations. At low temperatures, the zero-field magnetic specific heat and the 1H NMR spin-lattice relaxation rate follow an exponential temperature dependence, indicating the presence of gapped magnetic excitations. Furthermore, persistent spin dynamics down to 0.088 K observed by zero-field 𝜇⁢SR evidences lack of any static magnetism.},

keywords = {},

pubstate = {published},

tppubtype = {article}

}

@article{seidov_griffiths_2025,

title = {Griffiths phase and magnetocaloric effect in ferromagnetic La_{0.7}Sr_{0.3}Mn_{0.9}Fe_{0.1−x}Zn_{x}O_{3} (x = 0.05, 0.075 and 0.1)},

author = {Z. Y. Seidov and I. V. Yatsyk and A. V. Shestakov and A. S. Ovchinnikov and F. G. Vagizov and V. A. Shustov and A. G. Badelin and V. K. Karpasyuk and M. J. Najafzade and I. N. Ibrahimov and H. -A. Krug von Nidda and R. M. Eremina},

url = {https://www.sciencedirect.com/science/article/pii/S0925838825044482},

doi = {https://doi.org/10.1016/j.jallcom.2025.182887},

issn = {0925-8388},

year  = {2025},

date = {2025-09-23},

urldate = {2025-09-01},

journal = {J. Alloys Compd.},

volume = {1040},

pages = {182887},

abstract = {The polycrystalline La0.7Sr0.3Mn0.9Fe0.1−xZnxO3 (x= 0.05, 0.075 and 0.1) have been investigated by means of electron spin resonance (ESR), magnetic susceptibility, magnetization, and Mössbauer measurements. Mössbauer studies for x = 0.05 indicate that Fe in these compounds is in the trivalent high-spin state. All compounds exhibits a paramagnetic to ferromagnetic transition at the Curie temperature TC. The Curie temperature TC decreases on increasing Zn content according to 278, 193 and 166 K for x = 0.05, 0.075 and 0.1, respectively. The existence of a Griffiths like phase is experimentally detected by means of magnetic susceptibility and ESR measurements and corroborated by theoretical modeling. We also observed a magnetocaloric effect with a maximum magnetic entropy change (textbarΔSMmaxtextbar) value occurring close to the Curie temperature TC, corresponding to textbarΔSMmaxtextbar = 2.9, 2.6 and 2.68 J/(kg K) under magnetic field change (ΔH) of 50 kOe for x = 0.05, 0.075 and 0.1, respectively. The relative cooling power values were found to vary between 0.25 and 0.31 kJ/kg.},

keywords = {},

pubstate = {published},

tppubtype = {article}

}

@article{gotovko_low-frequency_2025,

title = {Low-frequency dynamics of LiCu_{3}O_{3}: An antiferromagnet on a strongly depleted square lattice},

author = {S. K. Gotovko and A. G. Ivanova and P. S. Kudimkina and A. A. Bush and V. I. Kozlov and M. Hemmida and H. -A. Krug von Nidda and L. E. Svistov},

url = {https://link.aps.org/doi/10.1103/PhysRevB.111.064430},

doi = {10.1103/PhysRevB.111.064430},

year  = {2025},

date = {2025-02-28},

urldate = {2025-02-01},

journal = {Phys. Rev. B},

volume = {111},

number = {6},

pages = {064430},

abstract = {We present the study of low-frequency dynamics of LiCu3⁢O3 —an antiferromagnet on a strongly depleted square lattice. The crystal structure contains two types of square planes with different Li+ → Cu2+ substitution rates (20% and 40%). Recent nuclear magnetic resonance (NMR), magnetization measurements and neutron scattering experiments revealed the occurrence of antiferromagnetic order at Tc1=123K and the change of the magnetic state at Tc2≈30K. Electron spin resonance (ESR) intensity measurements confirmed that at Tc1=123K a magnetic phase transition of only a part of the sample occurs, while the rest of the sample remains paramagnetic. Supposedly, the order occurs in the magnetic planes with higher concentrations of magnetic ions. The ratio of ESR intensity values before and after the transition is in agreement with this suggestion. In the studied frequency and temperature range (18–140GHz, 30–300K) only one electron paramagnetic resonance (EPR) branch was observed. At temperatures T<30⁢K, the ESR branch acquires a gap which gradually increases with temperature decrease. The behavior of the observed gap in the magnetic resonance spectra indicates that this gap is, in fact, a pseudogap of exchange nature associated with finite-sized clusters of magnetic ions.},

keywords = {},

pubstate = {published},

tppubtype = {article}

}

@article{hemmida_role_2024,

title = {Role of magnetic anisotropy in the antiskyrmion-host schreibersite magnets},

author = {M. Hemmida and J. Masell and K. Karube and D. Ehlers and H. -A. Krug von Nidda and V. Tsurkan and Y. Tokura and Y. Taguchi and I. Kézsmárki},

doi = {10.1103/PhysRevB.110.054416},

year  = {2024},

date = {2024-08-08},

urldate = {2024-08-08},

journal = {Phys. Rev. B},

volume = {110},

number = {5},

pages = {054416},

keywords = {},

pubstate = {published},

tppubtype = {article}

}

@article{buttgen_magnetic_2024,

title = {Magnetic resonance in quantum spin chains with competing exchange interactions},

author = {N. Büttgen and H. -A. Krug von Nidda},

doi = {10.1088/1751-8121/ad5e4c},

year  = {2024},

date = {2024-07-18},

urldate = {2024-07-01},

journal = {J. Phys. A: Math. Theor.},

volume = {57},

number = {31},

pages = {313001},

abstract = {Based on a previous review on magnetic resonance in quantum spin chains (Krug von Nidda et al 2010 Eur. Phys. J. Spec. Top. 180 161–89) we report on further development in this field with special focus on transition–metal oxides and halogenides consisting of quasi one–dimensional spin systems, where both intra–and inter–chain exchange interaction may give rise to frustration effects and higher–order anisotropic exchange contributions like the Dzyaloshinskii–Moriya interaction become decisive for the formation of the magnetic ground state. Selected examples show how NMR and ESR contribute valuable information on the magnetic phases and exchange interactions involved: LiCuVO4 with competing nearest neighbour and next–nearest neighbour intra–chain exchange, LiCu2O2 with complex zig–zag chains, and Cs2CuCl4 where the chains form a triangular lattice with the inter–chain interaction weaker but of the same order of magnitude than the intra–chain interaction. The so called paper–chain compound Ba3Cu3In4O12, where each successive pair of CuO4 plaquettes is rotated by 90° with respect to its predecessor along the c–direction like in a paper–chain, provides an interesting topology of frustrated intra–chain exchange interactions. Finally, a few dimer systems are considered.},

keywords = {},

pubstate = {published},

tppubtype = {article}

}

@article{hirschberger_lattice-commensurate_2024,

title = {Lattice-commensurate skyrmion texture in a centrosymmetric breathing kagome magnet},

author = {M. Hirschberger and B. G. Szigeti and M. Hemmida and M. M. Hirschmann and S. Esser and H. Ohsumi and Y. Tanaka and L. Spitz and S. Gao and K. K. Kolincio and H. Sagayama and H. Nakao and Y. Yamasaki and L. Forró and H. -A. Krug von Nidda and I. Kézsmárki and T. Arima and Y. Tokura},

doi = {10.1038/s41535-024-00654-2},

year  = {2024},

date = {2024-05-23},

urldate = {2024-05-01},

journal = {npj Quantum Mater.},

volume = {9},

pages = {45},

abstract = {Skyrmion lattices (SkL) in centrosymmetric materials typically have a magnetic period on the nanometer-scale, so that the coupling between magnetic superstructures and the underlying crystal lattice cannot be neglected. We reveal the commensurate locking of a SkL to the atomic lattice in Gd3Ru4Al12 via high-resolution resonant elastic x-ray scattering (REXS). Weak easy-plane magnetic anisotropy, demonstrated here by a combination of ferromagnetic resonance and REXS, penalizes placing a skyrmion core on a site of the atomic lattice. Under these conditions, a commensurate SkL, locked to the crystal lattice, is stable at finite temperatures – but gives way to a competing incommensurate ground state upon cooling. We discuss the role of Umklapp-terms in the Hamiltonian for the formation of this lattice-locked state, its magnetic space group, and the role of slight discommensurations, or (line) defects in the magnetic texture. We also contrast our findings with the case of SkLs in noncentrosymmetric material platforms.},

keywords = {},

pubstate = {published},

tppubtype = {article}

}

@article{daul_heteropentanuclear_2024,

title = {Heteropentanuclear Ru(II)Cu(II)_{4} Kuratowski Complexes Assembled from a Ruthenium(II) Precursor Complex to Study Competing Exchange Interactions in M(II)(ta)_{2} Networks [ta(−) = 1,2,3-Triazolate]},

author = {W. G. Daul and M. Hirrle and B. Eisfeld and M. Kraft and H. -A. Krug von Nidda and D. Volkmer},

url = {https://doi.org/10.1021/acs.inorgchem.3c04478},

doi = {10.1021/acs.inorgchem.3c04478},

year  = {2024},

date = {2024-03-05},

urldate = {2024-03-01},

journal = {Inorg. Chem.},

volume = {63},

number = {11},

pages = {5027},

abstract = {We report a directed two-step synthesis toward pentanuclear Kuratowski complexes. First, six 5,6-dimethylbenzo[1,2,3]triazole ligands (Me2btaH) are coordinated to a single Ru(II) ion, providing a topologically ideal template for the addition of further metal ions. The synthesis and crystal structures of [RuCu4X4(Me2bta)6] [X = acetylacetonate (acac) and tris(3,5-dimethyl-1-pyrazolyl)borate (Tp*)] are described. Both represent new members of the family of so-called Kuratowski (K3,3) complexes. The coordination units feature triazolato-bridged metal-centered MM4 tetrahedra, which are known for frustrated magnetic interactions in both complexes and metal–organic frameworks. The novel Ru(II)-centered complexes were synthesized in order to investigate the influence of the presence or absence of a paramagnetic central metal ion in the Kuratowski complex. Superconducting quantum interference device and electron spin resonance measurements demonstrate that small deviations in bond lengths and valence angles can lead to the formation of pairs of magnetic exchange-coupled Cu(II) ions. Which Cu(II) ions pair up can be predicted in Jahn–Teller active compounds by the overlap of the respective orbitals. These data are compared with those gleaned for M(II)(ta)2 (ta = 1,2,3-triazolate) lattices, in which structurally similar MM4 tetrahedra constitute the secondary building units.},

keywords = {},

pubstate = {published},

tppubtype = {article}

}

@article{toth_broadband_2023,

title = {Broadband magnetic resonance spectroscopy in MnSc_{2}S_{4}},

author = {B. Tóth and K. Amelin and T. Rõõm and U. Nagel and A. Bauernfeind and V. Tsurkan and L. Prodan and H. -A. Krug von Nidda and M. Scheffler and I. Kézsmárki and others},

doi = {10.1038/s41598-023-37911-6},

year  = {2023},

date = {2023-01-01},

urldate = {2023-01-01},

journal = {Sci. Rep.},

volume = {13},

number = {1},

pages = {11069},

abstract = {Recent neutron scattering experiments suggested that frustrated magnetic interactions give rise to antiferromagnetic spiral and fractional skyrmion lattice phases in MnSc2S4. Here, to trace the signatures of these modulated phases, we studied the spin excitations of MnSc2S4 by THz spectroscopy at 300 mK and in magnetic fields up to 12 T and by broadband microwave spectroscopy at various temperatures up to 50 GHz. We found a single magnetic resonance with frequency linearly increasing in field. The small deviation of the Mn2+ ion g-factor from 2},

keywords = {},

pubstate = {published},

tppubtype = {article}

}