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)