The magnetic structure of NiS2

S. Yano1, Chin-wei Wang1, Chun-Ming Wu1, J. S. Gardner, 1 Andrew Studer2, and Despina. Louca3

1National Synchrotron Radiation Research Center, Neutron Group, Hsinchu 30077, Taiwan

2 Bragg Institute, Australian Nuclear Science and Technology Organization,Lucas Heights, New South Wales, 2234, Australia

3University of Virginia, Department of Physics, Charlottesville, VA 22904, USA

AOCNS 2015 Manly, Australia 7/21/2015

The phase diagram of NiS2-xSex

Metal insulator transition is induced by Se doping or pressure

P.G. Nikolowitz et al. Phys. Rev. B. 77 (2008) 115135

T. Miyadai et al. JMMM 31-34 (1983) 337-338

M2 disappear at around x = 0.3M1 disappear between x = 0.6 and 0.8.

The magnetic structure of NiS2-xSex

M. Matsuura et al. PRB 68 094409 (2003)

AFM M1 k = (0 0 0); 1st order AFM M2 k = (1/2 1/2 1/2) 2nd order

NiS2 NiS2-xSex

NOMAD@SNS, ORNL, U.S.A

The neutron scattering experiment

The Nanoscale-Ordered Materials Diffractometer (NOMAD)

Purpose of the experiment1. Magnetic structure2. Local structure

Powder samples Temperature dependence

T = 2 to 150K NiS2-xSex

x = 0, 0.4, 0.6, 0.8

What is the magnetic structure M1 and M2 anyway?

Crystal structure symmetry (Space group)

Magnetic atoms

You have model??

2

2

, 2exp)()(69.2 3

iii

magFehklhklmag rQQsQQfFI

Find the default valuesGenerate random values for magnetic sites which show low χ2

Magnetic point group theory Model Free

You need constraints?

i

calci

obsi lkhFlkhF 22 )),,(),,((

The parameters are the number of magnetic atoms*3(x,y,z)

Neutron scattering intensities

Least square method

You got an answer!! Check your answers1. Agree with physical picture2. Add F=0 points as data, check χ2

3. Explain other experiment results?But, are you sure ??

S = Spinsq = The projection of Spins

QsQ i

1.0 1.5 2.0 2.5 3.0 3.5 4.0

-0.5

0.0

0.5

1.0

1.5

2.0

2.5

0.8 1.0 1.2 1.4 1.6 1.8

0.4

0.6

0.8

1.0

1.2

T = 2 K

Inte

nsity

(arb

. uni

ts)

N(222)

N(311)

N(220)

N(211)N(210)

N(200)

N(111)

M1+M2 phase

M2 phase

M1 phase

M2(1/2 1/2 3/2)

M1(110)M1(100)

M2(1/2 1/2 1/2)

Q (Å-1)

The powder neutron diffraction NiS2NiS2 Pa-3 (205) with Ni: 4a site(0 0 0)

The magnetic structure for M1

Ma Mb Mc

0.577 0.577 0.577

0.577 -0.577 -0.577

-0.577 0.577 -0.577

-0.577 -0.577 0.577

M1: Г1 𝟁1(Ni = 1.0 mB at NiS2

NiS2 Pa-3 (205) with Ni: 4a site(0 0 0)

To be compatible with M1, mM1i mM2i

Candidates for magnetic structure M2

k = (0 0 0) k = (1/2 1/2 1/2)

Ma Mb Mc

0.577 0.577 0.577

0.577 -0.577 -0.577

-0.577 0.577 -0.577

-0.577 -0.577 0.577

M1: Г1 𝟁1(Ni = 1.0 mB at NiS2

T. Miyadai et al. JPSJ 38, (1975) 115

1. The imaginary part of BV components2. M1 and M2 are normal to each other mM1i mM2j =0

Candidates for magnetic structure M2

M1(k = 000) M2(k = 0.5 0.5 0.5)

Г1 𝟁1 Г1 𝟁1

Г1 𝟁2

Г1 𝟁3

Г1 𝟁4

Г3 𝟁5

Г3 𝟁6

Г3 𝟁7

Г3 𝟁8

Ex.) Г1 𝟁1(M1) Г1 𝟁2(M2)

Ma Mb Mc

6 6 6

6 -6 -6

-6 6 -6

-6 -6 6

Ma Mb Mc

4.732 -4.732 0

2.732 -2.732 5.464

0.732 2.732 2

-2.732 0.732 -2

¿0Г1 𝟁2, Г1 𝟁4, Г3 𝟁6, or Г3 𝟁8 are possible.

SARAh, A. S. Wills, Physica B, 276 (2000) 680.

The magnetic structure in NiS2

Г1 𝟁2, Г1 𝟁4

Г3 𝟁6 Г3 𝟁8

Г1 𝟁2

Г1 𝟁4

Г3 𝟁6

Г3 𝟁8

The four magnetic domains in NiS2

S.Yano et al. PRB submitted (2015)

Experiments with a single crystal of NiS2

5*5*5 mm3

Wombat (ANSTO)

SIKA (ANSTO, NSRRC)

Single crystal data from Wombat

M1

M2

T = 60 K (Para)Nuclear reflections T = 35 K (M1 phase)Nuclear reflections with magnetic peak at k = 000 (ex. (001), (110)) T = 4 K (M2 phase)Nuclear reflections with magnetic peak at k = 0.5 0.5 0.5 (ex. (0.5 0.5 1.5)) and peak intensities at k = 000 are intensified.

The magnetic structure in NiS2

• 18 magnetic reflections

1 10 100 10001

10

100

1000

T = 4 K

Cal

clat

ed in

tens

ities

Observed intensities

The cold triple axis spectrometer SIKA

SIKA in User Program (2015, Mar) SIKA received operation license (2015, June) see more at P013, Guochu DengDon’t for get next proposal round (2015 September 15)

Located at ANSTO-Bragg institute

J1 = 0.050 meV J2 = 0.143 meVD = 0.163 meV

MnF2

28 29 30 310

1

2

3

4

(001) (110) In

tens

ities

(cou

nts/

mon

itor)

Temperature (K)

Critical scattering

1

2

3

4

(0.5 0.5 0.5)

0

1

2

3

4 (100) (011)

Inte

nsity

(cou

nts/

mon

itor)

25 30 35 40 455

10

15

20

(111) (200)

Temperature (K)

Background

M2

M2

M2

M1Background

Nuclear

M2 phase only @(0.5 0.5 0.5) with β = 0.223(29) @(1 1 1) with β = 0.219(54)@(2 0 0) with β = 0.227(37)

38 40

0.4

0.6

0.8

(001) 0.313 (71) (110) 0.252 (65)In

tens

ities

(cou

nts/

mon

itor)

Temperature (K)

M1

M2

28 29 30 310

1

2

3

4

(0.5 0.5 0.5) In

tens

ity (c

ount

s/m

onito

r)

Temperature (K)

28 29 30 31

5

10

15

20

(111) with (200)with In

tens

ity (c

ount

s/m

onito

r)

Temperature (K)

M. Matsuura et al. PRB 68 094409 (2003)

M1 β = 0.306(3) M2 β = 0.220(10)

M1 + M2 phasek = 0 0 0 @(1 0 0) β = 0.313(71) @(0 1 1) β = 0.252(65)k = 0.5 0.5 0.5@(1 0 0) with β = 0.194(53)@(0 1 1) with β = 0.246(50)

The magnetic structure with powder M1; the structure is : k = (0 0 0) and Г1 𝟁1

M2; the structure is k = (1/2 1/2 1/2) has four possible magnetic structures.

These two structure can coexist with mM1i mM2j We found the only 4 magnetic structure which might form domains couldn’t be distinguished by neutron scattering.

The magnetic structure with single crystal Wombat experiment

The powder model failed to explain 18 of magnetic scattering intensities from k = 0.5 0.5 0.5@ T = 4K

SIKA experimentThe order parameters tell me that we need to classify magnetic scattering intensities with new eyes.

Summary

And, the mission continues ……..