Influence of Stress and Defect on Magnetic Properties of Mn₃O₄ Films Grown on MgAl₂O₄ (001) by Molecular Beam Epitaxy

Abstract

Three single-crystal Mn 3 O 4 thin films were grown on MgAl 2 O 4 (001) substrates by plasma-assisted molecular beam epitaxy (PA-MBE). The films with different thicknesses are found to be compressed in the (001) plane and elongated in the perpendicular direction at different levels via in situ reflection highenergy electron diffraction (RHEED) and ex situ X-ray diffraction. Magnetic measurements indicate that either of the two thicker films owns smaller spontaneous magnetization, larger coercive force, and higher phase transition temperature than the bulk single-crystal Mn 3 O 4 material. On the contrary, it is noteworthy that the thinnest film exerts different characteristics with smaller coercive force and lower phase transition temperature than the bulk. The variation of magnetic properties for the films are proposed to be related to the combined effects of the lattice distortion under epitaxial stress, strain relaxation with the generation of defects and dislocations, and surface roughness, which could influence the magnetic anisotropy and the exchange interactions among the manganese ions in the films with different thicknesses on different levels.

Magnetic properties of Mn3O4 film with a coexistence of two preferential orientations

“…19 The peak fittings and detail analyses have been discussed in our previous work. 20 While the splitting value here between the Mn2p 3/2 and the Mn2p 1/2 level is 11.74 eV, and the M3s is 5.6 eV. Both of them are in accordance with the values of the well-defined stoichiometry Mn 3 O 4 materials in our previous reports and others.…”

“…Both of them are in accordance with the values of the well-defined stoichiometry Mn 3 O 4 materials in our previous reports and others. 20,21 Based on the above analyses, we have finally determined that the film grown on the Pt(111)//Si(100) substrate is a polycrystalline hausmannite Mn 3 O 4 with two preferred orientations coexistence and without any other impurity phases. It is quite different from the general polycrystals with various orientations and phases as well as the singlecrystal Mn 3 O 4 films reported in our previous works.…”

“…It is quite different from the general polycrystals with various orientations and phases as well as the singlecrystal Mn 3 O 4 films reported in our previous works. 10,20 In consideration of the special structure and phase, we have further investigated the magnetic properties of the film. Figure 3 shows the zero-field-cooled (ZFC) and field-cooledwarming (FCW) magnetization curves measured with a field of 50 Oe parallel to the film plane from 5 to 150 K. The ZFC curve gradually increases at low temperatures and reaches a maximum at around 42 K, while the FCW curve continues to decrease with increasing temperature.…”

“…Such a surface could induce local in-plane "magnetic poles" and ultimately affect the magnetizations and hysteresis loop shapes of the film on some level. 20 In order to further verify the above scenario, we have also investigated the magnetic properties of the Mn 3 O 4 film with two preferential orientations coexistence grown on MgAl 2 O 4 (MAO) substrate, as shown in Fig. 5.…”

Hooked on switch: strain-managed cooperative Jahn–Teller effect in Li0.95Mn2.05O4 spinel

“…23 However, with MgAl 2 O 4 as a substrate, the lattice mismatch is minimized and growth of the tetragonal Mn 3 O 4 phase has been observed with the c axis elongated in the direction perpendicular to the substrate surface. 24 Thus, the Jahn-Teller deformation-type control can be performed not only with temperature and pressure, as we present, but potentially also with the use of epitaxial strain.…”