Stability of antiferromagnetism at high magnetic fields inMn3Si

Abstract

We report low temperature measurements of the specific heat, resistivity and magnetisation of the itinerant antiferromagnet Mn3Si. The unprecedented stability of the magnetic state to high magnetic field up to 14 T inferred from the invariance of these bulk properties is incompatible with itinerant magnetism expected of a conventional Fermi liquid.PACS numbers: 71.45. Lr, 75.50Ee, 75.40.Cx, 75.30.Fr Weakly magnetic transition metal compounds with small ordered moments and low transition temperatures are usually well described as a Fermi liquid with weakly exchange split Fermi surface, where special topological features of the Fermi surface are ignored [1]. It is in contrast still an open issue if magnetic metals with large ordered moments and small ordering temperature, that are more akin to local moment insulators, may also be described on the basis of Fermi liquid theory. Insight into this question may be sought in the dominant energy scales controling the magnetic ordering temperature T N of an itinerant antiferromagnet. In a Fermi liquid low ordering temperatures result from strong coupling of the magnetisation at ordering wave-vector Q with heavily damped spin fluctuations [1]. On the other hand, in the isotropic Heisenberg model low ordering temperatures result from weak exchange coupling of localized magnetic moments. The energy scale and nature of the magnetic ordering compared to the mode-mode or local moment coupling, respectively, are hence fundamental to magnetism in solids.The polarization of a magnetic state in a magnetic field allows to probe the relevant coupling strengths. In fact, a very large number of transition metal compounds are known in which ordering temperatures of order 20 K are related to a high sensitivity to magnetic field of a few T regardless of whether they are better described in terms of Fermi liquid theory or the Heisenberg model [2][3][4]. In this paper we report an experimental investigation in which we employ the effect of high magnetic field (µ B H ≈ k B T N ) on the bulk magnetisation M , specific heat C and electrical resistivity ρ of a cubic metallic antiferromagnet, Mn 3 Si, to study the strength of the coupling of the uniform mode (q = 0) with the ordering wave-vector Q. The observed complete absence of a field dependence is surprising, because it either suggests an isotropic Fermi liquid in which the mode-mode coupling is absent or an isotropic Heisenberg magnet in which the moment coupling is exceptionally strong, despite low T N . From either point of view the conceptual simplicity of Mn 3 Si challenges the present day understanding of metallic antiferromagnetism.Recent years have witnessed an increased interest in the magnetic and metallic properties of Heusler transition metal compounds [5-8] to which Mn 3 Si belongs. Ternary members of this class of materials display a wide variety of different behaviours such as disorder induced non-Fermi liquid [7,8], half-metallic magnetic [6] and semiconducting ground states [5]. High ferromagnetic ordering temperatures o...

Spin density wave order and fluctuations inMn3Si: A transport study

“…Our measurement resembles previous results on polycrystalline Mn 3 Si. 22 At temperatures higher than ∼ 200 K the resistivity approaches a linearly rising behavior with temperature, a typical characteristic of electron-phonon-scattering (expressed in the high temperature limit of the Grüneisen-Bloch 3). At T < T * the resistivity starts to decrease stronger and then crosses the extrapolated high temperature linear T -dependence close to T N .…”

“…In this case we find the transition temperature from the paramagnetic to the SDW region to be exactly at the peak temperature of the anomaly and thus T N ≃ 21.3 K, which agrees rather well with previous reports. 18,22 The entropy conserving construction would yield a somewhat higher T N around ∼ 24 K.…”

“…It resembles the behavior seen in earlier measurements on polycrystals. 22 In order to determine the magnetic ordering temperature we refrain from applying the entropy conserving construction. Instead of a smeared out and rather broad peak structure which one would expect for a canonical second order type transition, the anomaly possesses a characteristic λ-shape, which points towards strong fluctuations (inset of FIG.…”

“…26,27 Further theoretical work predicted two nesting vectors of which one corresponds to the experimentally found one. 28,29 Early publications concerning Mn 3 Si suggested it to be a possible candidate for half-metallic antiferromagnetism 22,[30][31][32] , which would represent a new paradigm of itinerant magnetism. However, experimental evidence for such a ground state remains elusive.…”

“…This concerns in addition to the well known quantities resistivity, Hall and Seebeck effects, also the Nernst effect, which came into focus recently because of its sensitivity to subtle Fermi surface changes and fluctuations. [10][11][12][13][14][15][16][17] In this paper we take the impact of SDW ordering on the transport coefficients under scrutiny by investigating the transport properties of the itinerant antiferromagnet Mn 3 Si which undergoes a SDW transition at about 25 K. [18][19][20][21][22] We study in particular the electrical resistivity, thermal conductivity, Hall, Seebeck and Nernst effects in the temperature range from 10 K up to 300 K. Clear anomalies are observed at the SDW transition which confirm it to be at ∼ 22 K and give strong evidence for a large fluctuation regime which extends up to ∼ 200 K in the resistivity, as well as the Seebeck and Nernst effects. We compare our results with other prototype SDW materials, viz.…”