Studies of the incommensurate structures of B20 alloys

Abstract

The B20 structure is capable of supporting a long-range antiferromagnetic static spin density wave, and for transition metal silicides and germanides it has previously been found that the N6el temperatures, high field magnetizations and magnetic propagation vectors q all suggest a dependence on an electron concentration parameter. This relationship has yet to be confirmed.The present measurements from mixed alloys in the series CrSi/FeSi, CrSi/MnSi, CrSi/CoSi. MnSi/CoSi and CrGe/FeGe have extended the electron concentration range previously covered and the results support the suggested dependence. The q values are practically independent of temperature and the CrGe/FeGe display high N6eI temperatures comparable with that of FeGe. IC_ 1998 Elsevier Science B.V. All rights reserved. Ke3~t'ords:Antiferromagnetism; Dzyaloshinskii-Moriya interaction; Magnetic coupling -antiferromagnetic; Magnetic transitions Metallic alloys with the B20 (P213) crystal structure which lacks inversion symmetry have been found to support an antiferromagnetic static spin density wave at low temperatures probably through the operation of a Dzyaloshinskii-Moriya-type interaction I-l]. The periods of the magnetic structures observed are generally long and small-angle neutron scattering is an ideal technique for studying such systems. The variations with composition of the N~el temperatures, high-field magnetisations and propagation vectors q have previously been studied for a few such alloys and the similar form of all these has suggested a dependence on d-electron band filling [1,2]. Such at relationship has not yet been finally established and we have therefore fabricated a wide range of polycrystalline intermetallic silicides and germanides which span the electron concentration ranges of interest. We report the results of magnetization and SANS measurements carried out at Salford and RISO. respectively.Alloys have been prepared by argon arc melting from the mixed series CrSi/FeSi, CrSi/MnSi, CrSi/CoSi, MnSi/CoSi and CrGe/FeGe. The alloys were remelted *Corresponding author. Tel.: ÷ 44 16I 745 5259; fax: + 44 I61 745 5197: e-mail: j.g.booth@physics.salford.ac.uk. four or five times to ensure homogenisation, crushed into powder form and heat-treated in sealed ampoules. The silicides were heat treated at 825C for 24 h, quenched into water, and subsequent X-ray analysis indicated the B20 crystal structure, The germanides showed a two-phase structure after such treatment and it was necessary to heat these at 500-'C for 1 week before quenching to produce single-phase alloys. Magnetization measurements in fields up to 12 T were carried out on the Manchester/Salford VSM over the range 4-300 K. The SANS measurements were performed in the neighbourhood of the N6el temperatures over the low q range up to 0.10 k.-i.Typical results for the magnetization measurements as a function of field for the alloy Mno.95Cr0.osSi exhibiting long-range antiferromagnetism are shown in Fig. 1. In the antiferromagnetic regime the magnetization increases linea...

Evolution of magnetocrystalline anisotropies in Mn1−xFexSi and Mn1−xKindervater1, Adams2, Bauer3 et al. 2020Phys. Rev. B224170View full textAdd to dashboardCite

“…Likewise, early magnetization measurements and NMR in polycrystalline Mn 1−x Co x Si identified a suppression of the helimagnetic order with increasing cobalt content [82]. Subsequent small-angle neutron scattering in polycrystalline Mn 1−x Fe x Si and Mn 1−x Co x Si revealed a moderate reduction of the helical modulation length with increasing x without comparison between iron and cobalt doping [78,79].…”

“…The helimagnetic transition temperature in cubic chiral magnets responds sensitively to substitutional doping [78,79]. In turn, compositional changes represent an important tool when trying to identify the microscopic origin of the hierarchy of energy scales and the effects of fluctuations in cubic chiral magnets.…”

Generic Aspects of Skyrmion Lattices in Chiral Magnets

“…Doping with iron, cobalt, and nickel leads to an essentially identical modification of the magnetic behavior if scaled by the number valance electrons per formula unit75,89 . Doping with chromium, i.e., reducing the number of valance electrons, leads to a suppression of T c comparable to iron doping90 . This behavior is consistent with the notion that the main effects of chemical doping are due to a rigid shift the Fermi level, as recently inferred from a combined study of ab initio calculations and the electric transport properties in Mn 1−x Fe x Si ?…”

Evolution of magneto-crystalline anisotropies in Mn$_{1-x}$Fe$_x$Si and Mn$_{1-x}$Co$_x$Si as inferred from small-angle neutron scattering and bulk properties

“…The helimagnetic transition temperature in cubic chiral magnets responds sensitively to substitutional doping 77,78 . In turn, compositional changes represent an important tool when trying to identify the microscopic origin of the hierarchy of energy scales and the effects of fluctuations in cubic chiral magnets.…”

“…Likewise, early magnetization measurements and NMR in polycrystalline Mn 1−x Co x Si identified a suppression of the helimagnetic order with increasing cobalt content 81 . Subsequent small-angle neutron scattering in polycrystalline Mn 1−x Fe x Si and Mn 1−x Co x Si revealed a moderate reduction of the helical modulation length with increasing x without comparison between iron and cobalt doping 77,78 .…”