Study of magnetoresistance of epitaxial magnetite films grown on vicinal MgO (100) substrate

Abstract

The magnetoresistance ͑MR͒ studies of magnetite thin films deposited on vicinal MgO substrates show an enhanced MR along the miscut direction as compared to the direction perpendicular to it. The MR anisotropy increases with the decrease in temperature and peaks at the Verwey transition. The increase in magnetoresistance and anisotropy behavior is attributed to the formation of a greater number of out-of-plane shifted antiphase boundaries due to the step edges on vicinal MgO substrates. These local electronic and spin structure modifications at the APBs introduce additional spin scattering and are responsible for the increase in MR along the miscut. © 2005 American Institute of Physics. ͓DOI: 10.1063/1.1850361͔ INTRODUCTIONRecently, there has been considerable interest in the growth of magnetic thin films on vicinal surfaces owing to the intriguing physics involved and technological potential. [1][2][3][4] The studies on vicinal surfaces have been carried out mainly to understand the effect of lateral modulation of the electronic structure induced by step edges on the magnetic anisotropies. 3,4 In our previous publication we haveshown that the growth of Fe on stepped Mo ͑110͒ substrates leads to the formation of self-assembled nanowedges of size 20-40 nm and a switching of the magnetic easy axis from along the step edges to direction perpendicular to them. 3There are few reports on the study of magnetoresistance properties of thin films grown on vicinal surfaces. EXPERIMENTThe Fe 3 O 4 thin films were grown on ͑100͒ oriented MgO single crystal substrates using an oxygen plasma assisted molecular beam epitaxy ͑MBE͒ system ͑DCA MBE M600, Finland͒ with a base pressure 5 ϫ 10 −10 Torr. Details of the film growth procedure are given elsewhere. 15 In situ reflection high energy electron diffraction ͑RHEED͒ was used to confirm epitaxial growth and also the growth mode. From the RHEED intensity oscillations it was found that the films grew in a layer-by-layer mode ͑at a rate of 0.3 Å / s. In the present study we report results obtained on two representative samples named, sample A and sample B, in which the MgO ͑100͒ substrates have nominal miscut of 0.5°͑±0.05°͒ and 2°͑±0.05°͒ along ͗011͘ directions. Structural characterization of the samples was performed using a high-resolution x-ray diffractometer ͑HRXRD, Bede-D1, UK͒. Miscut of the samples was determined from the variation in Bragg angle for the symmetric diffraction for different azimuth.Electrical resistivity and magnetoresistance ͑MR͒ measurements were carried out in the standard dc four probe collinear configuration. A variable field ͑up to 2 T͒ permanent magnet ͑Model: MM 2000 26.5-001, Multimag Magnetic Solutions Ltd., Ireland͒ was used to apply magnetic fields in the desired orientation. The MR is defined as;where R͑H͒ and R͑0͒ are the resistance of the sample with and without field, respectively. To determine the magnetoresistance anisotropy, the measurements were carried out by passing current in two directions, which are orthogonal to each other, i.e., a...

In-plane magnetic anisotropies inFe3O4films on vicinal MgO(100)

“…Also affected by the presence of APBs is the magnetoresistance ͑MR͒ behavior of the films. 19,20 To selectively extract the contribution of APBs to the MR, Arora et al 20 measured the MR in directions ͓011͔ and ͓011͔, parallel and perpendicular to the step edges formed by the epitaxial growth of Fe 3 O 4 films on vicinal ͑100͒ MgO substrates with miscut angles of 0.5°and 2°. They showed that the APBs would preferentially align parallel to the step edges and so were able to show that the observed anisotropy in MR could be attributed to the presence of the APBs.…”

Anomalous anisotropic magnetoresistance in epitaxialFe3O4thin films on MgO(001)

“…[7][8][9][10] The presence of APBs has a deleterious effect on the magnetic properties but they are beneficial in enhancing the magneto-resistance of films due to additional spin scattering they induce. 11,12 Magneto-transport studies in epitaxial magnetite films are mostly focused on the influence of APBs, disorder and strain. In a recent study, 13 we have shown that if these nano-scale defects in Fe 3 O 4 films are manipulated in an ordered fashion one can attain a sizable magnetoresistance.…”

Hybrid magnetic/semiconductor spintronic materials and devices

“…5 shows the in plane magneto-resistance (MR) measurements of a 4 nm thick Fe 3 O 4 /GaAs film with the magnetic field along the easy [0 1 1] and hard [0 1 1] directions. This anisotropic MR response along different directions has not been reported before in Fe 3 O 4 /MgO [26] and Fe 3 O 4 /Al 2 O 3 [27]. The MR along the hard axes initially decreases when the field is reduced and an increase through an abrupt irreversible jump is observed immediately when the field switches to opposite direction, then it reaches its maximum at the coercive field after which the MR is reduced with another abrupt jump.…”