As and Epitaxial-Growth MnSi Thin Films - OPUS Würzburg

Chapter 5
Basic properties of Ferromagnet
MnSi
Recent developments in the study of non-collinear spin structures, particularly MnSi,
have prompted the renewed interest in the study of these types of materials. They have
recently been the subject of several exploratory transport studies focusing on their unusual
magnetic behavior, existence of exotic magnetic states or spin structures ([Papp 09],
[Mueh 09])andastestbedforexistingtheoriessuchasthoseontheoriginoftheanomalous
Hall effect (AHE).[Naga 10] These developments have inspired the initial development of
in-house MnSi thin film growth in our group. In this chapter, we describe the basic
properties of the weak itinerant ferromagnet MnSi and state-of-the-art research on its
magnetic properties, particularly on its exotic magnetic structure.
5.1 Bulk properties of MnSi
Thought to be well-understood, interest in MnSi has grown in the recent years through
the observation of new exciting electronic and magnetic properties, particularly non-
Fermi liquid behavior under high pressure([Pfle 01]), presence of a Skyrmion lattice near
the ordering temperature T ord ([Pfle 10a]) and ultra-low current densities for spin-torque
applications using these exotic phases.([Joni 10], [Schu 12]) These interesting material
spintronic properties of MnSi are tied to the complex magnetocrystalline structure of the
material.([Ishi 77], [Naka 80], [Grig 06a])
The weak itinerant ferromagnet MnSi is a cubic helimagnet with non-centrosymmetric
B20 crystal structure belonging to space group P2 1 3 with distorted rock salt basis vectors
(u,u,u),( 1 +u, 1 −u,−u),(−u, 1 +u, 1 −u) and 2 2 2 2 (1 −u,−u, 1 +u) for the right-handed
2 2
form with u Mn = 0.137 and u Si = -0.155. For a left-handed structure, u is replaced by
1−u. The lattice constant is around 4.558 Å. The cubic crystalline structure is shown
55