Enhanced low field magnetoresistance of Fe3O4 nanosphere compact

Abstract

Unusually large low field magetoresistance (LFMR), ~ 10 %, at 300 K has been observed with the sample of mono-dispersed Fe 3 O 4 magnetite nanospheres, ~ 200 nm, compactly cold-pressed and sintered at 800 o C. A detailed analysis on the transport and magnetic measurements indicates that the electron conduction is dominated by the spin-dependent scattering or tunneling at the grain boundaries. At low temperature, 140 K and 100 K near the Verwey transition, ~ 115 K, the LFMR (below 2 kOe) does a e-mail : cpchen@pku.edu.cn, Phone : +86-10-62751751, Fax : 86-10-62751615 2 not show any sign of dependence on the transition, and does not follow the variation of magnetization to reach the saturation region either. On the other hand, at 300 K, the MR saturates fast with the magnetization below 2 kOe. This temperature dependent property in LFMR is very likely attributed to the scattering or tunneling of the conduction electron passing through the grain boundary layer with spin disordered state.3

Large grain-boundary magnetoresistance in MnFe2O4 nanoparticle compact

“…While few reports were found in other ferrites, for example, giant MR were found in Zn 1Àx Ni x Fe 2 O 4 and (ZnFe) 3 O 4 -a-Fe 2 O 3 ceramic [12,13]. In our previous work, we have synthesized various monodisperse ferrites of 200-800 nm [14], and found enhanced LFMR of about 10% at RT in the compact of Fe 3 O 4 nanoparticles of 200 nm [9]. In this work, we further investigated the grain-boundary MR in another ferrite MnFe 2 O 4 nanoparticle compact.…”

“…In most cases, the grain boundary has been treated as an insulating barrier across which a spin-polarized tunneling of conducting electrons occurs. Till now, a lot of work has been carried out in a hope to optimize the devices to have a room temperature (RT) MR effect competitive with the giant MR multilayers [2][3][4][5][6][7][8][9][10][11][12][13]. However, a large MR could usually be obtained at high magnetic field or low temperature in the grain-boundary systems.…”

“…Up to now, studies of grain-boundary MR mainly focused on the magnetite Fe 3 O 4 [2][3][4][5][6][7][8][9][10]. This is because that magnetite is a good candidate to show the required properties for application due to its high Curie temperature and half metallic behavior [2,11].…”

Point-contact Andreev-reflection spectroscopy of doped manganites: Charge carrier spin-polarization and proximity effects (Review Article)

“…For example, magnetite, Fe 3 O 4 , is ferrimagnet with anomalously high Curie temperature ~ 850 K. The band-structure calculations (see, e.g., [30]) have predicted that Fe 3 O 4 is a half-metal with only one spin subband at the Fermi level. Experimentally, the spin-resolved photoemission on epitaxial thin films indeed indicated a spin polarization about 80% at room temperature [31] However, below a Verwey transition at about 120 K, single crystal Fe 3 O 4 shows a nonmetallic (polaronic) type of conductivity (see, e.g., [32]), and, in fact, the PCAR method cannot be used.…”

Excellent low-field magnetoresistance effect in Ga-doped MnZn ferrites

“…6 Among spinel ferrites, magnetite, Fe 3 O 4 , has been most extensively studied because it possesses a very high Tc (858 K) and a half metallic behavior. [7][8][9][10][11][12][13][14][15] Only a few reports are found for other spinel ferrites. [16][17][18] Unfortunately, however, the largest MR ratio ever reported for magnetite is only 1.2% in 1.5 kOe at RT.…”