arXiv subjects

A. J. E. Lefering

Publications and source records attributed to A. J. E. Lefering.

4 recordsLinked to original sources

arXiv2018

New magnetic phase of the chiral skyrmion material Cu2OSeO3

The lack of inversion symmetry in the crystal lattice of magnetic materials gives rise to complex non-collinear spin orders through interactions of relativistic nature, resulting in interesting physical phenomena, such as emergent electromagnetism. Studies of cubic chiral magnets revealed a universal magnetic phase diagram, composed of helical spiral, conical spiral and skyrmion crystal phases. Here, we report a remarkable deviation from this universal behavior. By combining neutron diffraction with magnetization measurements we observe a new multi-domain state in Cu2OSeO3. Just below the upper critical field at which the conical spiral state disappears, the spiral wave vector rotates away from the magnetic field direction. This transition gives rise to large magnetic fluctuations. We clarify physical origin of the new state and discuss its multiferroic properties.

cond-mat.mtrl-sci↗

arXiv2016

Dissipation phenomena and magnetic phase diagram of Cu$_2$OSeO$_3$ below 50 K

The magnetic phase diagram of the chiral magnet Cu$_2$OSeO$_3$ has been investigated by dc magnetisation and ac susceptibility over a very large frequency range from 0.1 Hz up to 1 kHz and temperatures below 50 K. Qualitatively different phase diagrams have been obtained by applying the magnetic field along the easy $\langle100\rangle$ or the hard $\langle110\rangle$ crystallographic directions. Strong $χ"$ appears close to $B_{c2}$, but only below 30 K and is more pronounced when $B$ is applied along $\langle100\rangle$. In addition, the transition from the helical to the conical phase leads to two adjacent $B_{c1}$ lines below 50 K. The frequency dependence of $χ"$ indicates the existence of very broad distributions of relaxation times both at $B_{c1}$ and $B_{c2}$. The associated very long characteristic times eventually prevent the system from reaching thermal equilibrium at low temperatures and lead to thermal hysteresis.

cond-mat.str-el↗

arXiv2016

Magnetic relaxation phenomena in Cu$_2$OSeO$_3$ and phase diagram

We present an investigation of the magnetic field-temperature phase diagram of Cu$_2$OSeO$_3$ based on DC magnetisation and AC susceptibility measurements covering a broad frequency range of four orders of magnitude, from very low frequencies reaching 0.1 Hz up to 1 kHz. The experiments were performed in the vicinity of $T_C=58.2$ K and around the skyrmion lattice A-phase. At the borders between the different phases the characteristic relaxation times reach several milliseconds and the relaxation is non-exponential. Consequently the borders between the different phases depend on the specific criteria and frequency used and an unambiguous determination is not possible.

cond-mat.str-el↗

arXiv2015

First-order ferromagnetic transition in single-crystalline (Mn,Fe)2(P,Si)

(Mn,Fe)2(P,Si) single crystals have been successfully grown by flux method. Single crystal diffraction demonstrates that Mn0.83Fe1.17P0.72Si0.28 crystallizes in a hexagonal crystal structure (space group P-62m) at both 100 and 280 K, in the ferromagnetic and paramagnetic states, respectively. The magnetization measurements show that the crystals display a first-order ferromagnetic phase transition at their Curie temperature (TC). The preferred magnetization direction in is along the c axis. A weak magnetic anisotropy of K1 = 0.25x106 J/m3 and K2 = 0.19x106 J/m3 is found at 5 K. These values indicate a soft magnetic behaviour favourable for magnetic refrigeration. A series of discontinuous magnetization jumps is observed far below TC by increasing the field at a constant temperature. These magnetization jumps are irreversible, occur spontaneously at constant temperature and magnetic field, but can be restored by cycling across the first-order phase transition.

cond-mat.mtrl-sci↗