Crystal and magnetic structure of CoxNi1-xMnGe system

Symmetry analysis in neutron diffraction studies of magnetic structures 1. A phase transition concept to describe magnetic structures in crystals

Magnetic and crystallographic nature of the compounds NiMnGe1−nSin (0 ≦ n ≦ 1) are studied in the temperature range from 80 to 1000 K by X-ray and neutron diffraction, magnetometric and DTA measurements. On the basis of these experimental data, crystallographic and magnetic phase diagram are constructed. The compounds have NiTiSi type structure at low temperatures and they transform into the Ni2In type structure at high temperatures. Magnetic and neutron diffraction measurement revealed the existence of three regions of different types of magnetic orderings: helicoidal (0 ≦ n ≦ 0.25), noncollinear (0.3 ≦ n ≦ 0.55), and ferromagnetic (0.6 ≦ n ≦ 1.0). The transition from antiferromagnetic to ferromagnetic phase implies the decrease of the MnMn distances.



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Crystal and magnetic structure of the NiMnGe1-nSin System

We investigate the structural conditions for metamagnetism in MnP and related materials using density-functional theory. A magnetic stability plot is constructed taking into account the two shortest Mn-Mn distances. We find that a particular Mn-Mn separation plays the dominant role in determining the change from antiferromagnetic to ferromagnetic order in such systems. We establish a good correlation between our calculations and structural and magnetic data from the literature. Based on our approach it should be possible to find Mn-containing alloys that possess field-induced metamagnetism and associated magnetocaloric effects.

Structurally driven metamagnetism in MnP and related P n m a compounds

Chiral magnets are promising materials for the realisation of high-density and low-power spintronic memory devices. For these future applications, a key requirement is the synthesis of appropriate materials in the form of thin films ordering well above room temperature. Driven by the Dzyaloshinskii-Moriya interaction, the cubic compound FeGe exhibits helimagnetism with a relatively high transition temperature of 278 K in bulk crystals. We demonstrate that this temperature can be enhanced significantly in thin films. Using x-ray scattering and ferromagnetic resonance techniques, we provide unambiguous experimental evidence for long-wavelength helimagnetic order at room temperature and magnetic properties similar to the bulk material. We obtain α
 intr = 0.0036 ± 0.0003 at 310 K for the intrinsic damping parameter. We probe the dynamics of the system by means of muon-spin rotation, indicating that the ground state is reached via a freezing out of slow dynamics. Our work paves the way towards the fabrication of thin films of chiral magnets that host certain spin whirls, so-called skyrmions, at room temperature and potentially offer integrability into modern electronics.

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H. Boller

Papers

Helimagnetism in MnP-type compounds: MnP, FeP, CrAs and CrAs1−xSbx mixed crystals