DOPING IN NONCENTROSYMMETRIC CRYSTAL
STRUCTURESE . P L U N K E T T 1 , D . M . G A U T R E A U 2 , B . F . F U L F E R 3 , J . F .
D I T U S A 2 , D . P . Y O U N G 2
1Department of Physics, Applied Physics, and Astronomy, Rensselaer Polytechnic Institute, Troy, NY.2Department of Physics and Astronomy, Louisiana State University, Baton Rouge, LA.3Department of Chemistry, Louisiana State University, Baton Rouge, LA.
Introduction• Increasing demand for faster computers have forced approaching the limits of
traditional MOSFET devices.• One potential replacement technology requires magnetic semi-conductors.• Two systems with non-centrosymmetric structures were studied here,
and .• Pure barium copper germanate is an insulator and already has magnetic
phases.• Neither , an insulator, nor , a metal, display magnetic ordering, but
was discovered to be ferromagnetic. Thus, characterizing thenature of the magnetic structuring as a function of doping levels is of interest.
Figure 1(a):
Crystal structure, Space Group 113, P421mFigure1(b): Crystal structure, Space Group 198, P213
1(a) 1(b)
• This systems synthesis was not well reported.• After system was grown successfully, we attempted to dope it to
measure the electron transport properties.• It was determined that attempted doping at the copper site would
not be ideal, so we began with at the barium site.• Lanthanum shown to be ineffective, as it produced undesirable
phases. (Figure 2(a))• Nondoped samples showed good agreement with literature.[1](Figure
2(b))
25 30 35 40 452 (deg)
Rel
ativ
e In
tens
ity
TheoreticalUndopedx=.1x=.2x=.3x=.4
0 5 10 15 20 25 300.7
0.8
0.9
1
1.1
1.2
1.3
1.4
1.5x 10-4
Temperature (K)2(a) 2(b)
• Both and lack any magnetic ordering.• The system that combines the two was discovered to have ferro-
magnetic ordering at temperatures T < 20K• Systematic study of the system for various levels of doping began with
analysis of the purity of the polycrystalline samples produced, and the determination of the shift in lattice constant.
• XRD patterns were used to analyze purity (Figure 3(a)).• Shift in lattice parameter appears linear (Figure 3(b)).• Data on CoGe taken from reference [2]
0 5 10 15 20 25 30 35 40 45 500.46
0.465
0.47
0.475
0.48
0.485
0.49
Bulk percentage Co y (no units)
Latti
ce c
onst
ant a
(nm
)
DataLinear Fit
30 32 34 36 38 40 42 44 46 48 502 (deg)
Rel
ativ
e In
tens
ity
RuGex=.1x=.2x=.3x=.4x=.5x=.6Ru2Ge3
2 sin
/
3(a) 3(b)
• We measured the magnetic properties in a SQUID Magnetometer.
• This gave a preliminary look at how characteristics like the Curie Temperature, the Weiss Temperature, the Curie Constant, and the Saturated Moment vary as a function of doping.
Magnetic Characterization
0 5000 10000 15000 20000 25000 30000 35000 40000 45000 500000
100
200
300
400
500
600
700
Applied magnetic field H (Oe)
Mag
netiz
atio
n of
Mat
eria
l M (e
mu/
mol
)
5.81% Bulk Cobalt9.12% Bulk Cobalt11.32% Bulk Cobalt
20 30 40 50 60 70 80 90 1000
0.2
0.4
0.6
0.8
1
1.2
1.4x 10
-3
Temperature (K)
'
5.81% Bulk CobaltCurie-Weiss Fitx=9.12% Bulk CobaltCurie-Weiss Fitx=11.32% Bulk CobaltCurie-Weiss Fit
0 5 10 15 20 25 30 35 400
0.005
0.01
0.015
0.02
0.025
0.03
Temperature (K)
'
5.81% Bulk Cobalt9.12% Bulk Cobalt11.32% Bulk Cobalt
0 5 10 15 20 25 30 35 400
0.2
0.4
0.6
0.8
1
1.2
1.4x 10
-3
Temperature (K)
"
5.81% Bulk Cobalt9.12% Bulk Cobalt11.32% Bulk Cobalt
4(a) 4(c)
4(b)
Results
0 5 10 15 20 25 30 35 40 45 500
1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
Bulk Percentage Co y (unitless)
Tem
pera
ture
(K)
Curie TemperatureWeiss Temperature
0 5 10 15 20 25 30 35 40 45 500
0.2
0.4
0.6
0.8
1
1.2
1.4
Bulk Percentage Co y (unitless)
J
Saturated MomentFluctuating Moment
• The Curie Temperature was take to be the temperature of the highest measurement of the magnetic moment.
• The Saturated magnetic moment was taken from Magnetization at 5T and the equation
• The Weiss Temperature and Curie constant were taken from a fit of the data to the Curie-Weiss law.
• The Fluctuating moment was taken from the definition of the Curie Constant,
• Results indicate an itinerant mechanism, as well as decreases in the Curie and Weiss temperatures, with an apparent rapid increase at low doping levels.
5(a)
5(b)
Questions?
References:[1] H Hohl, A.P Ramirez, C Goldmann, G Ernst, E Bucher, Transport properties of RuSi, RuGe, OsSi, and quasi-binary alloys of these compounds, Journal of Alloys and Compounds, Volume 278, Issues 1–2, 1 August 1998, Pages 39-43, ISSN 0925-8388, http://dx.doi.org/10.1016/S0925-8388(98)00584-2. (http://www.sciencedirect.com/science/article/pii/S0925838898005842)[2]”Exploring the magnetic, thermodynamics, and electrical transport properties of MnGe and CoGe having the noncentrosymmetric B20 crystal structure” J. F. DiTusa, et al., (Preprint)