We have investigated the crystal and magnetic structures of the trigonal iron-boracite Fe3B7O13X with X = OH by neutron diffraction. Neutron diffraction enables us to locate the hydrogen atom of the hydroxyl group and determine the magnetic ground st
ate of this member of the multiferroic boracite family. No evidence was found for a monoclinic distortion in the magnetic ordered state. The magnetic symmetry allows for magnetoelectric and ferroelectric properties. The N/eel tempera- ture TN of 4.86(4) K confirms the general trends within the boracites that TN decreases from X = I > Br > Cl > OH. Surprisingly while Fe3B7O13OH exhibits the largest frustration with $|theta/T_N| = 5.6$ within the Fe3B7O13X series, no reduction of the magnetic moment is found using neutron diffraction.
We performed neutron single crystal and synchrotron X-ray powder diffraction experiments in order to investigate the magnetic and crystal structures of the conductive layered triangular-lattice antiferromagnet PdCrO2 with a putative spin chirality, w
hich contributes to an unconventional anomalous Hall effect. We revealed that the ground-state magnetic structure is a commensurate and nearly-coplanar 120-degrees spin structure. The 120-degrees plane in different Cr layers seem to tilt with one another, leading to a small noncoplanarity. Such a small but finite non-coplanar stacking of the 120-degrees planes gives rise to a finite scalar spin chirality, which may be responsible for the unconventional nature of the Hall effect of PdCrO2.
Magnetism in SmPd2Al3 was investigated on a single crystal by magnetometry and neutron diffraction. SmPd2Al3 represents a distinctive example of the Sm magnetism exhibiting complex magnetic behavior at low temperatures with four consecutive magnetic
phase transitions at 3.4, 3.9, 4.3 and 12.5 K. The rich magnetic phase diagram of this compound reflects the specific features of the Sm3+ ion, namely the energy nearness of the ground-state multiplet J = 5/2 and the first excited multiplet J = 7/2 in conjunction with strong crystal field influence. Consequently, a significantly reduced Sm magnetic moment in comparison with the theoretical Sm3+ free-ion value is observed. Despite the strong neutron absorption by natural samarium and the small Sm magnetic moment (~ 0.2 {mu}B) we have successfully determined the magnetic k-vector (1/3, 1/3, 0) of the phase existing in the temperature interval 12.5 - 4.3 K. This observation classifies the SmPd2Al3 compound as a magnetically frustrated system. The complex magnetic behavior of this material is further illustrated by kinetic effects of the magnetization inducing rather complicated magnetic structure with various metastable states.
