H. LI et al.: ANOMALOUS HALL EFFECT AND TRANSPORT PROPERTIES OF ULTRA-THIN Fe65Co35 FILMS
651–653
ANOMALOUS HALL EFFECT AND TRANSPORT PROPERTIES OF
ULTRA-THIN Fe
65
Co
35
FILMS
NEPRAVILEN HALLOV EFEKT IN TRANSPORTNE LASTNOSTI
ULTRATANKIH Fe
65
Co
35
FILMOV
Hui Li
*
, Yemei Han, Xianming Ren, Zhi Tao, Kailiang Zhang
School of Electrical and Electronic Engineering, Tianjin Key Laboratory of Film Electronic & Communication Devices, Tianjin University
of Technology, Tianjin 300384, China
Prejem rokopisa – received: 2019-10-29; sprejem za objavo – accepted for publication: 2020-03-23
doi:10.17222/mit.2019.259
We report on the preparation of nanoscale ultra-thin Fe65Co35 films of different thicknesses applied on Si/SiO2 substrates with
ion-beam deposition. Grazing incidence X-ray diffraction (GIXRD) was employed to characterize the microstructure of the
Fe65Co35 films. Magnetic hysteresis loops of the Fe65Co35 films indicate good soft-magnetic properties of the films. We
measured the transport properties of the films, and the behavior of resistance switching for more than an order of magnitude was
obtained. The measurement performed on the ultra-thin Fe65Co35 films reveal that the resistance-switching behavior is reversible
and the transformation occurs between two stable resistant states. The modulation can be attributed to the anomalous Hall effect
and the modification of the charge-carrier density at the interface.
Keywords: ferromagnetic film, resistance switching, anomalous Hall effect, carrier density
Avtorji v prispevku poro~ajo o ultratankih filmih Fe65Co35, razli~nih debelin in z razli~no nanostrukturo, ki so pripravljeni z
nanosom v ionskem curku. Za karakterizacijo Fe65Co35 filmov so uporabili difrakcijsko metodo obstreljevanja z rentgenskimi
`arki (GIXRD; angl: grazing incidence X-ray diffraction). Magnetne histerezne zanke izdelanih filmov dokazujejo njihove
dobre magnetne lastnosti. Izmerili so transportne lastnosti filmov in obna{anje med uporovnim preklapljanjem, ki je bilo za ve~
kot red velikosti ve~je. Na filmih izvedene meritve so pokazale, da je uporovno preklapljanje reverzibilno in pretvorba poteka
med dvema stabilnima uporovnima stanjema. Manipulacijo pripisujejo nepravilnemu Hallovemu efektu in modifikaciji gostote
nosilcev naboja na mejni ploskvi.
Klju~ne besede: feromagnetni film, uporovno preklapljanje, nepravilen Hallov efekt gostota nosilcev naboja
1 INTRODUCTION
In the field of spintronics, research on electronically
controlled magnetism has received much attention.
1
The
coupling of resistance switching and magnetism is a
typical example of electric control.
2
Under the action of
electric field, a dual control of resistance and magnetism
of a device is realized.
3
If resistance switching and mag-
netic switching are integrated in one device, the storage
density of data can be greatly improved, and a multilevel
storage of data can be realized.
4
In a recent study, N.
Spaldin et al.
5
explained the possibility of using an
electric field to directly adjust the magnetic properties of
magnetic materials. The results show that the magneto-
electric coupling effect can be realized without the need
of an insulating layer, and a metal non-volatile memory
can be constructed using the electromagnetic change of
the Fe film.
6
The Curie temperature of ferromagnetic
metals and some alloys is higher than room temperature,
7
and the direct modulation of magnetic properties with an
electric field is of great significance for the realization of
new memory devices.
8
However, due to the electrostatic
shielding of the metal under an electric field, the induced
charge of the metal surface prevents the electric field
from entering the inside of the conductor.
9
The electric
field can only exist at the atomic scale of the surface.
10
Therefore, in an ultra-thin ferromagnetic metal film, the
electric field may modulate the carrier density and
electron configuration of the film,
11
thus modulating the
macroscopic magnetic properties.
12
In this work, we
report on the fabrication of ferromagnetic structures con-
sisting of Fe
65
Co
35
thin films grown on Si/SiO
2
sub-
strates. We discuss the resistance-switching behavior and
transition mechanism of ferromagnetic metal films.
2 EXPERIMENTAL PART
An Fe
65
Co
35
alloy target was used and a thin film was
deposited on a SiO
2
/Si substrate using ion-beam depo-
sition. The film was deposited under a discharge voltage
of 60 V, acceleration voltage of 200 V and beam voltage
of 0.5 Kv. During the deposition process, argon gas was
continuously injected and its flow was maintained at
5.7 cm³/min. Thin films with thicknesses of (2, 5, 10, 15
and 20) nm were deposited. The microstructures of the
prepared films were characterized with grazing incidence
X-ray diffraction (GIXRD, BrookeD8, Advance). An
electron probe micro-analyzer (EPMA, JXA-8230) was
Materiali in tehnologije / Materials and technology 54 (2020) 5, 651–653 651
UDK 621.313.522.3:621.793.8:67.017 ISSN 1580-2949
Original scientific article/Izvirni znanstveni ~lanek MTAEC9, 54(5)651(2020)
*Corresponding author's e-mail:
740293354@qq.com (Hui Li)

used for the elemental-composition analysis. A vib-
rating-sample magnetometer (VSM, Lake Shore 7404)
was used to analyze the magnetic properties of the films.
A semiconductor device analyzer (B1500A) was used to
analyze the resistance-switching behavior. Transport
properties were measured using the physical-property
measurement system (ppms-9).
3 RESULTS AND DICUSSION
Figure 1 shows the grazing incidence XRD
diffraction patterns of the Fe
65
Co
35
films with different
thicknesses. Since the films were very thin, we used the
grazing incidence method to characterize the crystal
structure of the ultra-thin Fe
65
Co
35
films. The body-
centered cubic structure (bcc) of FeCo (110) was indexed
from the diffraction peak that appeared near 45°. By
comparison, it was found that as the thickness of the
films increases from 2 nm to 20 nm, the diffraction peak
near 45° becomes sharper, indicating that the film crys-
tallinity is increasing. In addition, the EPMA test result
showed that the Fe content in the Fe
65
Co
35
film was
about 65 %, and the Co content was about 35 %.
Figure 2 shows hysteresis loops for the Fe
65
Co
35
thin
films with thicknesses of (5, 10, 15 and 20) nm, while
hysteresis loops are absent in the 2-nm thin films due to
their thinness. It was found that with the increase in film
thickness, the saturation-magnetization intensity grad-
ually increased, and it was (0.76, 1.12, 2.01 and 2.11)
emu/mm
3
, for (5, 10, 15 and 20) nm Fe
65
Co
35
films,
respectively. The Fe
65
Co
35
films exhibited coercive-force
values of about (38, 41, 47 and 50) Gauss for (5, 10, 15
and 20) nm Fe
65
Co
35
films, respectively, confirming that
the prepared Fe
65
Co
35
films had good soft-magnetic
characteristics.
Curves I–V of the Fe
65
Co
35
thin films were obtained.
Figure 3 illustrates these curves of the Fe
65
Co
35
films
with thickness of (5, 10, 15 and 20) nm. The current as a
function of voltage no longer exhibits the proportional
relation behavior. For instance, for the 10-nm Fe
65
Co
35
films, when the sweep voltage is 150 mV, the current in-
creases steeply from 10 μA to above 110 μA, indicating
the presence of the low-resistance state, and as the
sweeping voltage increases to 200 mV, the current de-
creases sharply from 110 μA to about 10 μA, indicating
that the sample was switched to the high-resistance state
and the current changed substantially, proportionally to
the voltage. In this regime, the current voltage develops a
resistive switching behavior, producing more than an
order-of-magnitude change in the resistance. It should be
noted that the threshold voltage for the switch of the
low-resistance state to the high-resistance state increases
from 140 mV to about 300 mV when the film thickness
increases from 5 nm to 20 nm. When a Fe
65
Co
35
film is
in contact with Si, a depletion layer (barrier layer) of
carriers is formed on the surface of Si, a surface barrier
appears and a region with a rectifying effect is formed.
Its volt-ampere characteristic is similar to that of the p-n
junction, showing a non-linear state.
13
Figure 4 shows the Hall resistivity of the (5, 10, 15
and 20) nm Fe
65
Co
35
thin films at room temperature in
H. LI et al.: ANOMALOUS HALL EFFECT AND TRANSPORT PROPERTIES OF ULTRA-THIN Fe65Co35 FILMS
652 Materiali in tehnologije / Materials and technology 54 (2020) 5, 651–653
Figure 3: I–V behaviors of (5, 10, 15 and 20) nm Fe
65
Co
35
thin films
Figure 1: Grazing incidence XRD patterns for (2, 5, 10, 15 and
20) nm Fe
65
Co
35
thin films
Figure 2: Magnetization hysteresis loops of (5, 10, 15 and 20) nm
Fe
65
Co
35
films

relation to the applied magnetic field. The anomalous
Hall effect is observed for the Fe
65
Co
35
thin film. The
Hall resistivity to be maintained, RHall, is given by the
sum of the ordinary Hall effect (OHE) due to the Lorentz
force and the anomalous Hall effect (AHE), originating
from asymmetric scattering in the presence of mag-
netization.
14
It can be seen that the Hall resistivity rises
rapidly with the increase of the magnetic-field intensity,
which can be caused by the increase of the vertical
component of magnetization. When the magnetic field is
low, the abnormal Hall effect dominates. When magneti-
zation reaches saturation, the hall resistivity increases
linearly with a small slope and approaches saturation,
which is caused by the normal Hall effect.
15
In addition,
we measured the carrier density, Hall resistivity, Hall
coefficient and mobility of the films of different
thicknesses at room temperature as shown in Table 1.
Table 1: Summary of Fe
65
Co
35
thin films including thickness, tem-
perature, resistivity, coefficient, mobility and type
Thickness
(nm)
Density
(1/cm
3
)
Resistivity
( *cm)
Coefficient
(cm
3
/C)
Mobility
(cm
2
/V/S)
Type
5 1.13×10
19
3.30×10
1
2.28×10
–1
1.42×10
1
P
10 2.86×10
19
1.37×10
–2
2.20×10
–1
1.60×10
1
P
15 5.21×10
19
1.32×10
–3
1.03×10
–1
7.81×10
1
P
20 6.08×10
19
1.46×10
–3
1.20×10
–1
8.18×10
1
P
The research shows that in ferromagnetic metallic
systems, the change in magnetism is often related to the
carrier density.
16
Due to the anomalous Hall effect on the
surface of the Fe
65
Co
35
film, the surface carrier density of
the Fe
65
Co
35
film changed when the Hall-effect test was
performed, resulting in magnetic switching.
4 CONCLUSION
In summary, ultra-thin Fe
65
Co
35
metal films were
formed using ion-beam deposition on Si/SiO
2
substrates.
Under the action of an electric field, electrical-resistance
switching and magnetic switching occurred at the
nano-level of the surfaces of the Fe
65
Co
35
thin films. The
electric-field-modulated transport behaviors are
attributed to the density of the itinerant electrons in the
metals.
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H. LI et al.: ANOMALOUS HALL EFFECT AND TRANSPORT PROPERTIES OF ULTRA-THIN Fe65Co35 FILMS
Materiali in tehnologije / Materials and technology 54 (2020) 5, 651–653 653
Figure 4: Hall resistivity of (5, 10, 15 and 20) nm Fe
65
Co
35
thin films