Suppressed magnetic order and non-Fermi-liquid behavior in MnSi thin films under hydrostatic pressure

Abstract

In MnSi thin films the magnetic properties of the B20 compound are influenced by induced uniaxial anisotropy. In comparison to bulk MnSi the critical magnetic fields are enhanced and the Skyrmion phase is found to be enlarged within the magnetic phase diagram. Furthermore the ordering temperature depends on the film thickness reaching 43 K for films of around 10 nm and is considerably higher than in bulk crystals (T c,bulk = 29 K). In bulk MnSi the ordering temperature can be reduced by pressure, where at 1.46 GPa the magnetic order is completely suppressed and a non-Fermi-liquid behavior characterized by a T 3/2 law of the resistivity is observed. We present resistance measurements on MnSi thin films under applied pressure of up to 3.44 GPa. Qualitatively, the behavior is similar to bulk MnSi. However, the critical pressure is considerably enhanced to 3.1 GPa, which is assumed to be a consequence of strain. At high pressure non-Fermi-liquid behavior evidenced by a T 3/2 behavior of the resistance is observed up to T lin = 30 K, i. e., in a larger temperature range than for bulk MnSi. Uniaxial anisotropy might play an important role in this breakdown of Fermi-liquid behavior, since it stabilizes nontrivial spin structures.

Electronic transport in high magnetic fields of thin film MnSi

“…The lateral domain size is determined to the order of up to 100 nm, while the films are flat with a roughness ∼1 nm. The magnetic properties of the films have been established to fully correspond to those reported for instance in the [8,12,20], where evidence has been presented that tensile strain substantially affects the properties of thin film MnSi. To enable a direct comparison between MnSi thin films and MnSi bulk material regarding the magnetotransport properties the MnSi thin film samples were micro-structured by electron beam lithography (see [29]).…”

“…One way to test these notions would be-for instance-corresponding magnetoresistivity measurements under pressure on thin film MnSi. If the pressure scenario holds, we would expect a gradual transition of the magnetoresistive behavior of the films towards the bulk behavior with applied pressure [20].…”

“…For the high magnetic field studies, two epitaxial grown MnSi thin films (thickness sample #1: 10 nm; sample #2: 30 nm) were synthesized by molecular beam epitaxy on [111] Si-substrate as described previously [29]. Previously, we have extensively characterized thin films MnSi produced in this manner both structurally and magnetically by various experimental techniques such as RHEED, TEM, AFM, magnetization/susceptibility and resistivity [13,16,20,29]. Regarding their structural properties, the thin films form as layers of preferentially oriented MnSi domains, reflecting an island like growth process of the films.…”

“…This enhanced T N is attributed to the tensile strain in the MnSi film, exerted by the mismatch of the lattice parameters of MnSi and the underlying Si substrate. Effectively, it leads to a state of negative pressure in thin film material, with the bulk T N recovered if the films are pressurized [20].…”

MnSi nanostructures obtained from epitaxially grown thin films: magnetotransport and Hall effect

“…Initial studies established that MnSi thin films do show helical magnetic order, although for films thicker than ∼ 5 nm at temperatures significantly higher (T C up to ∼ 48 K) than in bulk material (T C = 29.5 K). This effect is attributed to tensile strain induced in MnSi thin films by the lattice mismatch with the Si substrate, effectively leading to a state of negative pressure [14,19,26]. As well, the suppression of the ordering temperature for films with less than 5 nm thickness can be understood in terms of the reduction of spin-spin interactions caused by the interface [19].…”