arXiv subjects

Rahel Ohlendorf

Publications and source records attributed to Rahel Ohlendorf.

4 recordsLinked to original sources

arXiv2026

Probing multipolar order in the candidate altermagnet MnF$_2$ through the elastocaloric effect under strain

Altermagnets break a combination of time-reversal and rotational symmetries without generating a net magnetization. As such, the order parameter of $d$-wave altermagnets has the same symmetry as magnetic multipoles, and couples to the product of a magnetic field and uniaxial strain. We combine elastocaloric experiments, free-energy modeling, and first-principles calculations on MnF$_2$ to establish a thermodynamic probe of the predicted finite-temperature altermagnetic critical point. These results pave the way to explore altermagnetic quantum criticality in $d$-wave materials and beyond.

cond-mat.str-el↗

arXiv2023

Magnetic phase diagram and magneto-elastic coupling of NdB$_4$ studied by high-resolution capacitance dilatometry up to 35~T

We report high-resolution dilatometry studies on single crystals of the Shastry-Sutherland-lattice magnet NdB$_4$ supported by specific heat and magnetometry data. Our dilatometric studies evidence pronounced anomalies at the phase boundaries which imply strong magneto-elastic coupling. The evolution of the three zero-field phase transitions separating distinct antiferromagnetic phases at $TN=17.2$~K, $TIT=6.8$~K and $TLT=4.8$~K can thus be traced in applied magnetic fields which provides the magnetic phase diagrams for $B\parallel c$ up to 15~T and for $B\parallel [110]$ up to 35~T. New in-field phases are discovered for both field directions and already known phases are confirmed. In particular, phase boundaries between different phases are unambiguously shown by sign changes of observed anomalies and corresponding changes in uniaxial pressure effects. For $B||c$, we find a 1/4-magnetization plateau in addition to a previously reported plateau at 1/5 of the saturation magnetization. TN increases for $B\parallel c$ in fields up to 15~T implying that magnetic moments of the all-in/all-out structure in the high temperature AFM ordered phase are driven towards the $c$ axis in high magnetic fields. Uniaxial pressure dependencies ${\partial}T_{\mathrm{crit}}/{\partial}p_{\mathrm{c}}$ of the phase transition temperatures for magnetic fields and pressure applied along the $c$ axis are derived from the data.

cond-mat.str-el↗

arXiv2023

1/3 plateau and 3/5 discontinuity in the magnetization and the magnetic phase diagram of hexagonal GdInO$_3$

We report the high-pressure optical floating-zone growth of GdInO$_3$ single crystals and show its magnetic phase diagram down to the mK-regime as determined by magnetization measurements. The centered-honeycomb lattice structure shows considerable magnetic frustration ($\lvertΘ\rvert /T_{\rm N}\simeq 5$) and develops long-range magnetic order below $T_{\rm N}$~=~2.1 K from a short-range ordered paramagnetic phase. Concomitantly, a small net magnetic moment evolves at $T_{\rm N}$ which points along the crystallographic $c$ direction. Upon cooling, the net moment reorients at $T^{**}\simeq 1.7$ K and $T^{*}\simeq 1$ K. A broad 1/3 plateau indicative of the up-up-down ($uud$) spin configuration appears for $B||c$ but is absent for $B||ab$, thereby suggesting easy axis anisotropy. At $T=0.4$ K, a jump in magnetization at $\simeq 3/5$ of the saturation magnetization signals a discontinuous transition to a high field phase and we find evidence for a possible tricritical point. Small energy and field scales in the accessible regimes render GdInO$_3$ a prime example to study the phase diagram of a semiclassical frustrated hexagonal lattice in the presence of weak easy axis anisotropy of mainly dipolar origin.

cond-mat.str-el↗

arXiv2020

Magnetoelastic coupling and Grüneisen scaling in NdB$_4$

We report high-resolution capacitance dilatometry studies on the uniaxial length changes in a NdB$_4$ single crystal. The evolution of magnetically ordered phases below $T_{\rm N}$= 17.2~K (commensurate antiferromagnetic phase, cAFM), $T_{\rm IT}$= 6.8~K (intermediate incommensurate phase, IT), and $T_{\rm LT}$= 4.8~K (low-temperature phase, LT) is associated with pronounced anomalies in the thermal expansion coefficients. The data imply significant magneto-elastic coupling and evidence of a structural phase transition at $T_{\rm LT}$ . While both cAFM and LT favor structural anisotropy $δ$ between in-plane and out-of-plane length changes, it competes with the IT-type of order, i.e., $δ$ is suppressed in that phase. Notably, finite anisotropy well above $T_{\rm N}$ indicates short-range correlations which are, however, of neither cAFM, IT, nor LT-type. Grüneisen analysis of the ratio of thermal expansion coefficient and specific heat enables the derivation of uniaxial as well as hydrostatic pressure dependencies. While $α$/$c_{\rm p}$ evidences a single dominant energy scale in LT, our data imply precursory fluctuations of a competing phase in IT and cAFM, respectively. Our results suggest the presence of orbital degrees of freedom competing with cAFM and successive evolution of a magnetically and orbitally ordered ground state.

cond-mat.str-el↗