Investigations on MnSb and related compounds with b8-type structures

Jakob Bouwma

Research output: ThesisThesis fully internal (DIV)

Abstract

This thesis describes investigations on phases with hexagonal B8-type structures in the systems Mn-Sb-Sn, Mn-Sb-Te, Mn-Cr-Sb and Mn-V-Sb. In -chapter 1 some general remarks are made on compounds with B8-type structures. The preparation of the samples, and the X-ray crystallographic investigations are described in chapter 2. Mnl+xSb forms continuous series of solid solutions (with B8-type structures) with Mn.l+xSn, with Crl+x Sb and with Vl+x Sb. The solubility of MnTe in Mnl+xSb is negligible. The homogeneity range of Mn1+X Sb 1- Sn y shifts gradually from 0 < x ~ 0. 25 for y=O to 0. 6 ~ x 0. 8 for y=1. The homogeneity ranges of Mnl+xSbi-Y Sr~ , (Mn, Cr)1+x Sb and (Mn, V)l+x Sb shift to metal-richer compositions with increasing temperature. The homogeneity range of the high-temperature phase Vi+x Sb is situated around the composition x=0. 40. In chapter 3 the results of measurements of the magnetization and the magnetic susceptibility are given. Mnl+x Sbj_ySny is ferrimagnetic. For a fixed Sb/Sn ratio, the magnetic ordering temperature TC and the spontaneous magnetization per gramatom Mn (Mgat) decrease with increasing Mn content. The largest values of Tc and Mgat are observed for compounds with y=0 (MnSb is ferromagnetic). The values of T, and Mgat decrease with increasing y for 0,<y 0.5 and increase again for 0.5 y <1,. For the ferrimagnetic compounds (Mn, Cr),+x Sb and (Mn, V) 1+X Sb, T cand the spontaneous magnetization per grammol decrease with increasing Cr/Mn and V/Mn ratios, respectively. V1.40Sb shows nearly temperature- independent (Pauli) paramagnetism (except -A low temperatures). In chapter 4 the neutron powder diffraction investigations of Mn 1.00 Sb and Mn 1.15 Sb are discussed. In Mn1.00Sb the magnetic moments (3. 79 ± 0. 03 9B at 4. 2 °K) are ferromagnetically aligned. The magnetic structure of Mn 1.15 Sb consists of two sublattices; the magnetic moments of Mn on the octahedral sites (3. 65 +_ 0. 07 aB at 4. 2 °K) are antiparallel to the moments of Mn on the interstitial, trigonal-bipyramidal sites (3. 0 t 0.4 µB at 4.2°K). The neutron-diffraction data reveal the turning of the magnetization from a direction perpendicular to the c- axis (low temperature) to a direction parallel to this axis (at higher temperatures). Zero-field nmr investigations are described in chapter 5. Mn 55 and Sb 123 resonance signals with frequencies of about 260 and 210-220 Mc/ s, respectively, have been observed at 4.20K in many of the investigated compounds. The signals of Mni.00Sb show a splitting due to the interaction of the nuclear quadrupole moments with the axially symmetric electric field gradients. Broad nmr signals with unresolved quadrupole splittings have been observed in compounds Mnl+xSbl-ySn Y with 0. 04 <x 0. 2 0, (Mn, V)l+x Sb with x=0. 20, (Mn, Cr),+x Sb with 0 < x < 0. 25 and in the tetragonal compound Mn2 Sb. No signals have been observed in compounds Nin Sb ~-Y Sn Y and 1+X (Mn, V)l+x Sb with x > 0. 20. Presumably, the atomic disorder of the non-stoichiometric B8-type compounds causes a spreading of the nmr signals over a broad frequency range. In chapter 6 the electronic structure of MnSb is discussed. Special attention is payed to the problem of the number of d electrons per Mn atom. Several models, i.e. a purely ionic description (d4), and ionic (d 3-5-4.5 ) and metallic (d5.5-6.5) band models, are discussed. From a comparison of the properties of MnSb with the properties of other Mn compounds and alloys, it is deduced that a metallic band model, with about six d electrons per Mn atom is preferable for MnSb.
Original languageEnglish
QualificationDoctor of Philosophy
Supervisors/Advisors
  • Haas, Cornelis, Supervisor
Publisher
Publication statusPublished - 1972

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