arXiv subjects

Mirta Herak

Publications and source records attributed to Mirta Herak.

6 recordsLinked to original sources

arXiv2024

Properties of an organic model $S=1$ Haldane chain system

We present the properties of a new organic $S=1$ antiferromagnetic chain system $m$-NO$_2$PhBNO (abbreviated BoNO). In this biradical system two unpaired electrons from aminoxyl groups are strongly ferromagnetically coupled ($|J_\text{FM}| /k_B \gtrsim 500$ K) which leads to the formation of an effective $S=1$ state for each molecule. The chains of BoNO biradicals propagate along the crystallographic $a$ axis. Temperature dependence of the $g$ factor and electron paramagnetic resonance (EPR) linewidth are consistent with a low-dimensional system with antiferromagnetic interactions. The EPR data further suggest that BoNO is the first known Haldane system with an almost isotropic $g$ factor ($2.0023 \pm 2 \unicode{x2030}$). The magnetization measurements in magnetic fields up to $40$ T and low-field susceptibility, together with $^1$H nuclear magnetic resonance (NMR) spectra, reveal a dominant intrachain antiferromagnetic exchange coupling of $J_\text{1D}/k_B = (11.3\pm0.1)$ K, and attainable critical magnetic fields of $μ_0 H_\text{c1} \approx 2$ T and $μ_0 H_\text{c2} \approx 33$ T. These measurements therefore suggest that BoNO is a unique Haldane system with extremely small magnetic anisotropy. Present results are crucial for a future in-depth NMR study of the low-temperature Tomonaga-Luttinger liquid (TLL) and magnetic field-induced phases, which can be performed in the entire phase space.

cond-mat.str-el↗

arXiv2024

Spin-Reorientation-Driven Linear Magnetoelectric Effect in Topological Antiferromagnet Cu$_3$TeO$_6$

The search for new materials for energy-efficient electronic devices has gained unprecedented importance. Among the various classes of magnetic materials driving this search are antiferromagnets, magnetoelectrics, and systems with topological spin excitations. Cu$_3$TeO$_6$ is a material that belongs to all three of these classes. Combining static electric polarization and magnetic torque measurements with phenomenological simulations we demonstrate that magnetic-field-induced spin reorientation needs to be taken into account to understand the linear magnetoelectric (ME) effect in Cu$_3$TeO$_6$. Our calculations reveal that the magnetic field pushes the system from the nonpolar ground state to the polar magnetic structures. However, nonpolar structures only weakly differing from the obtained polar ones exist due to the weak effect that the field-induced breaking of some symmetries has on the calculated structures. Among those symmetries is the $PT$ ($\overline{1}'$) symmetry, preserved for Dirac points found in Cu$_3$TeO$_6$. Our findings establish Cu$_3$TeO$_6$ as a promising playground to study the interplay of spintronics-related phenomena.

cond-mat.str-el↗

arXiv2021

Control of a polar order via magnetic field in a vector-chiral magnet

Vector-chiral (VC) antiferromagnetism is a spiral-like ordering of spins which may allow ferroelectricity to occur due to loss of space inversion symmetry. In this paper we report direct experimental observation of ferroelectricity in the VC phase of $β$-TeVO$_4$, a frustrated spin chain system with pronounced magnetic anisotropy and a rich phase diagram. Saturation polarization is proportional to neutron scattering intensities that correspond to the VC magnetic reflection. This implies that inverse Dzyaloshinskii-Moriya mechanism is responsible for driving electric polarization. Linear magnetoelectric coupling is absent, however an unprecedented dependence of electric coercive field on applied magnetic field reveals a novel way of manipulating multiferroic information.

cond-mat.str-el↗

arXiv2018

Site-Specific Spin Reorientation in Antiferromagnetic State of Quantum System SeCuO$_3$

We report on the magnetocrystalline anisotropy energy (MAE) and spin reorientation in antiferromagnetic state of spin $S=1/2$ tetramer system SeCuO$_3$ observed in torque magnetometry measurements in magnetic fields $H<5$~T and simulated using density functional calculations. We employ simple phenomenological model of spin reorientation in finite magnetic field to describe our experimental torque data. Our results strongly support collinear model for magnetic structure in zero field with possibility of only very weak canting. Torque measurements also indicate that, contrary to what is expected for uniaxial antiferromagnet, in SeCuO$_3$ only part of the spins exhibit spin flop instead all of them, allowing us to conclude that AFM state of SeCuO$_3$ is unconventional and comprised of two decoupled subsystems. Taking into account previously proposed site-selective correlations and dimer singlet state formation in this system, our results offer further proof that AFM state in SeCuO$_3$ is composed of a subsystem of AFM dimers forming singlets immersed in antiferromagnetically long-range ordered spins, where both states coexist on atomic scale. Furthermore, we show, using an ab-initio approach, that both subsystems contribute differently to the MAE, corroborating the existence of decoupled subnetworks in SeCuO$_3$. Combination of torque magnetometry, phenomenological approach and DFT simulations to magnetic anisotropy presented here represents a unique and original way to study site-specific reorientation phenomena in quantum magnets.

cond-mat.str-el↗

arXiv2015

Torque magnetometry study of magnetically ordered state and spin reorientation in the quasi-one-dimensional $S=1/2$ Heisenberg antiferromagnet CuSb$_2$O$_6$

We present an experimental study of macroscopic and microscopic magnetic anisotropy of a spin tetramer system \cso using torque magnetometry and ESR spectroscopy. Large rotation of macroscopic magnetic axes with temperature observed from torque magnetometry agrees reasonably well with the rotation of the $\mathbf{g}$ tensor above $T \gtrsim 50$~K. Below 50~K, the $\mathbf{g}$ tensor is temperature independent, while macroscopic magnetic axes continue to rotate. Additionally, the susceptibility anisotropy has a temperature dependence which cannot be reconciled with the isotropic Heisenberg model of interactions between spins. ESR linewidth analysis shows that anisotropic exchange interaction must be present in \csos. These findings strongly support the presence of anisotropic exchange interactions in the Hamiltonian of the studied system. Below $T_N=8$~K, the system enters a long - range antiferromagnetically ordered state with easy axis along the $<\bar{1} 0 1>^*$ direction. Small but significant rotation of magnetic axes is also observed in the antiferromagnetically ordered state suggesting strong spin-lattice coupling in this system.

cond-mat.str-el↗

arXiv2014

Magnetic anisotropy of spin tetramer system SeCuO$_3$ studied by torque magnetometry and ESR spectroscopy

We present an experimental study of macroscopic and microscopic magnetic anisotropy of a spin tetramer system SeCuO$_3$ using torque magnetometry and ESR spectroscopy. Large rotation of macroscopic magnetic axes with temperature observed from torque magnetometry agrees reasonably well with the rotation of the $\textbf{g}$ tensor above $T \gtrsim 50$~K. Below 50~K, the $\textbf{g}$ tensor is temperature independent, while macroscopic magnetic axes continue to rotate. Additionally, the susceptibility anisotropy has a temperature dependence which cannot be reconciled with the isotropic Heisenberg model of interactions between spins. ESR linewidth analysis shows that anisotropic exchange interaction must be present in SeCuO$_3$. These findings strongly support the presence of anisotropic exchange interactions in the Hamiltonian of the studied system. Below $T_N=8$~K, the system enters a long - range antiferromagnetically ordered state with easy axis along the $<\bar{1} 0 1>^*$ direction. Small but significant rotation of magnetic axes is also observed in the antiferromagnetically ordered state suggesting strong spin-lattice coupling in this system.

cond-mat.str-el↗