Zbigniew Bukowski

Polska Akademia Nauk Instytut Niskich Temperatur i Badań Strukturalnych im. Włodzimierza Trzebiatowskiego Wrocław, ul. Okólna 2

Magnetyzm i nadprzewodnictwo w domieszkowanym EuFe2As2

Seminarium Wydziału Fizyki i Informatyki Stosowanej AGH Kraków 18-01-2019

Plan:1. Podstawowe właściwości EuFe2As2

2. Wzrost monokryształów z metalicznych topników3. Diagram fazowy EuFe2As2

• wpływ pola magnetycznego• wpływ ciśnienia

4. Podstawienia chemiczne w EuFe2As2• domieszkowanie dziurowe – K, Na• domieszkowanie elektronowe – La• podstawienia izowalencyjne – Ca, Sr, Ba• podstawienia izowalencyjne – P• podstawienia metalami przejściowymi – Co, Ni, Ir, Ru, Rh…

5. Nadprzewodnictwo i magnetyzm w EuFe2-xNixAs2 - wybrane przykłady

6. Spontaniczne worteksy7. Poszukiwanie nadprzewodnictwa w EuFe2-xNixAs2

2

Crystal structure of iron-based superconductors

KFe2As2

RbFe2As2

CsFe2As2

BaFe2As2

SrFe2As2

CaFe2As2

EuFe2As2

low-Tc superconductorsnonsuperconducting parent compounds

3

Magnetic structure of EuFe2As2

Xiao et al. PRB 80, 174424 2009

Fe2+ 3d itinerant electronsSpin Density WaveFe saturation moment of 0.988 µB

aligned along the long a axis.TSDW=190 K

localised Eu2+ 4f electrons, spin S=7/2 µeff= 7.94 µB

RKKY A-type antiferromagnetTN=19 K

Two magnetic sublattices

4

5

Single crystals grown from Sn flux

EuFe2As

26

Effect of magnetic field on SDW ordering

Tokunaga et al. J. Low Temp. Phys. 159 (2010) 601

Simple extrapolation suggeststhat an extremely high field (>500 T) is needed to suppress the AFM stateat low temperatures.

EuFe2As2SDW

7

Effect of magnetic field on magnetic order in EuFe2As2

Xiao et al.PRB 81, 220406R (2010)

• spin canting• metamagnetic transitions• field induced ferromagnetism

8

Kurita et al. PRB 83, 214513 (2011)

Pressure-suppressed SDW order

Persistent Eu2+ magnetic order

Pressure-induced superconductivity

Effect of pressure

9

PRB 84, 024502 (2011)

K. Matsubayashi et al., PRB 84, 024502 (2011)

Pressure induced ferromagnetism

Effect of pressure

10

Effect of pressure on EuFe2As2 crystal structure

Z. Yu et al., Sci. Rep. 4:172

Pressure induced tetragonal-”collapsed tetragonal” phase

transition 11

Effect of pressure on Eu-ion valence in EuFe2As2

X-ray absorption spectra

Kumar et al. Appl. Phys. Lett. 104, 042601 (2014)

Conversion of Eu2+ to Eu3+ under pressure

K, Na-substitutionAnupam et al. J. Phys.: Condens. Matter 23 (2011) 455702

Maiwald et al. PRB 85, 024511 (2012)

Eu1−xKxFe2As2

hole doping:

- SDW is suppresed- Eu2+ AF order disappears- appearence of superconductivity

Y.Qi et al. , New Journal of Physics 14 (2012) 033011

12

Effect of La substitutionM. Zhang et al., PRB 85, 092503 (2012)

La-substitution

Electron doping:

• SDW suppression• superconductivity

13

Dilution of Eu-sublattice with nonmagnetic ions

• Disappearance of magnetic order of Eu2+

• SDW order remains intact

Zapf and Dressel, Rep. Prog. Phys. 80 (2017) 016501

14

L. M. Tran et al. PRB 98, 104412 (2018)

15

Co-substitution:EuFe2-xCoxAs

2

Single crystals of EuFe2-xCoxAs2

grown from Sn flux

Electrical resistivity

16

A.Błachowski et al., Phys. Rev. B 84, 174503 (2011)

Mössbauer spectroscopy of EuFe2-xCoxAs2

Eu2+ moments rotate from ab-plane toward c-axis direction

long-range ferromagnetic order of the Eu2+ moments along the c directionTC = 17 K

no incommensurate magnetic reflections corresponding to the helical arrangement of the Eu2+ spins are observed

Antiferromagnetism of the Fe2+ moments still survives tetragonal-to-orthorhombic structural transition is observedtransition temperatures of the Fe spin-density-wave (SDW) order and the structural phase transition are significantly suppressed to TSDW = 70 K and TS = 90 K

Superconducting TSC=8 K

17Jin et al., Phys.Rev. B 88, 214516 (2013)

Magnetic structure of Eu(Fe0.82Co0.18)2As2(single-crystal neutron diffraction)

Effect of Co-doping on Eu2+ magnetic ordering in Eu(Fe1−xCox)2As2 single crystals

W. T. Jin et al., Phys. Rev. B 94, 184513 (2016)

Co concentration x

Neutron diffraction

A-type antiferromagnet canted AF ferromagnet

• ferromagnetic Eu2+ moment of 6.2μB purely along the c direction• Fe2+ moment is estimated to be 0.63(4) μB

18

Magnetic phase diagram of Eu(Fe1−xCox)2As2(Sn-flux-grown single crystals)

W. T. Jin et al., PRB 94, 184513 (2016)

suppression of SDW order

superconductivity coexistswith Eu ferromagnetism

superconductivity competeswith Fe SDW antiferromagnetic order

19

Hydrostatic pressure effects on the staticmagnetism in Eu(Fe0.925Co0.075)2As2

W. T. Jin et al., Scientific Reports | 7: 3532 |

20

• Suppression of SDW• Superconductivity• Canted AFM FM• Superconductivity coexisting

with ferromagnetism

V. K. Anand et al., PRB 91 094427 (2015)

The body centered tetragonal chemical and magnetic unit cell (space group I4/mmm).

Ferromagnetic Eu(Fe0.86Ir0.14)2As2

ferromagnetically coupled Eu moments are aligned along the c axis with a magnetic propagation wave vector k = (0, 0, 0) and ordered moment of 6.29(5) μB at 1.8 K.

21

Jiao et al., J. Phys.: Conf. Ser. 400 (2012) 022038

TSC =23 KMossbauer data indicate that the Eu2+ spins order ferromagnetically below 19.5 K with the moments tilted 20◦ from the c-axis.

Jiao et al., EPL, 95 (2011) 67007

F

Eu(Fe0.75Ru0.25)2As2 ferromagnetic superconductor

22

Cao et al. J. Phys.: Condens. Matter 23 (2011) 464204

Isovalent P-substitution EuFe(As1-xPx)2

23

Superconductivity induced by partial substitution of P into As positionsAFM FerromagnetismSuperconductivity coexists with ferromagnetism

Nandi et al., PRB 89, 014512 (2014)

Peculiar properties of Sn-flux-grown Eu(Fe0.81Co0.19)2As2

single crystals

Magnetic field enhancement of superconductivity ?!

25

0 2 4 6 8 100.0

1.0

2.0

3.0

4.0

5.0

5.5

5.3

5.6

Re

sis

tan

ce (

m

)

Magnetic Field (kOe)

3.0 K

5.0 K

5.3 K

5.5 K

5.6 K

H II ab

Peculiar properties of Sn-flux-grown Eu(Fe0.81Co0.19)2As2

single crystals

0 2 4 6 8 10

0.0000

0.0014

0.0028

0.0042

0.0056

N11.0M10.0

L9.0L8.0

K7.25K7.0

A6.75J6.5

A6.4A6.3

A6.2A6.1

K6.0A5.9

A5.8A5.7

A5.6A5.5

A5.4A5.3

A5.2A5.1

J5.0I4.75

H4.5F4.25

E4.0D3.75

C3.5

R (

)

Magnetic Field (kOe)

Resistivity „peak” most likely corresponds to the flux flow effect

0 2 4 6 8 10 12 14 16 18 20

0

10

20

30

40

50

60

70

H (

kO

e)

Temperature (K)

zero1

zero2

zero

midpoint

onset

Eu-8

EuFe2-x

CoxAs

2

Bukowski et al., (SCTE 2010 Annecy)

26

Peculiar properties of Sn-flux-grown Eu(Fe0.81Co0.19)2As2

single crystals

1 10 100

0.0000

0.0014

0.0028

0.0042

0.0056

G11.0

G10.0

G9.0

G8.0

G7.0

G6.0

5.5

G5.0

G4.0

G3.0

G1.9

R (

m

)

Magnetic Field (kOe)

Temperature (K)

27

W-H Jiao et al., npj Quantum Materials (2017) 2:50

Spontaneous vortex state in ferromagnetic superconductor

28

Peculiar properties of Sn-flux-grown Eu0.73Ca0.27(Fe0.87Co0.13)2As2

single crystals

Zero-resistance superconductivity is suppressed in antiferromagneticregion and coexists with field induced ferromagnetism

Search for superconductivity in Ni-substitututedEuFe2As2

29

Zhi Ren et al. PRB 79, 094426(2009)

Polycrystalline material

I Nowik et al. New Journal of Physics 13 (2011) 023033

Mössbauer studies of Eu(Fe0.9Ni0.1)2As2 and Eu(Fe0.89Co0.11)2As2, in particular the Eu negative quadrupole interaction and the tilting of Heff from the c-axis, are almost the same. This indicates a similar magnetic structureregardless of whether the system is normal conducting or SC

Anupam et al.

In EuFe1.9Ni0.1As2 in addition to FM transition, two more transitions wereobserved. = 3.5 K. The broad transition at Tpeak =11.5 K could be due to thetransition from FM to AFM state. The transition at Tg =3.5 K could be due to thespin glass ordering, which might arise due to the competition between FM and AFMordering and hence leads to the spin freezing at Tg.

Superconductivity not detected

Ni substitution in EuFe2As2

30

Single crystals of EuFe2-xNixAs2 grown from Sn flux( up to x=0.4)

Chemical composition-determined from EDS data

0 50 100 150 200 250 3000.0

0.2

0.4

0.6

0.8

1.0

x =

0.00

0.04

0.07

0.08

0.10

0.12

0.20

0.40

R/R

30

0

Temperature (K)

EuFe2-x

NixAs

2

0.0 0.1 0.2 0.3 0.4 0.53.904

3.906

3.908

3.910

3.912

3.914

3.916

3.918

Ni content x

a (

A)

EuFe2-x

NixAs

2

12.02

12.04

12.06

12.08

12.10

12.12

12.14

12.16

12.18

c (

A)

c

a

Lattice parameters

Electrical resistivity

31

0 5 10 15 20 25 30

k0

k50

k100

k500

k1000

k2000

k3000

k5000

k7000

H II ab

'

Temperature (K)

x= 0.08

0 10 20 30 40 50 60 70 80 90 1000

1

2

3

4

5

6

7

Temperature (K)

H II ab

M (

B/f.u

)

1 kOe

2 kOe

5 kOe

4 kOe

30 kOe

50 kO

90 kOe

EuNi-3_s5

x= 0.08

Magnetic properties of EuFe1.92Ni0.08As2

AC-susceptibility vs. Temperature in various magnetic fields

Magnetization vs. Temperature in various magnetic fields

32

0 5 10 15 20 25 30 35 400

2

4

6

8

10

H (

kO

e)

Temperature (K)

TN '

TC '

TC M(T)

EuNi-3_s5

H II ab

x= 0.08

-30 -25 -20 -15 -10 -5 0 5 10 15 20 25 30-7

-6

-5

-4

-3

-2

-1

0

1

2

3

4

5

6

7

H II ab

EuNi-3_s5

at. [

B/m

ag.a

tom

]

H (kOe)

x= 0.08

2 K

15 K

25 K

CAF

PFIF

HCr

Field –dependent magnetization in various temperatures

Magnetic properties of EuFe1.92Ni0.08As2

Absence of superconductivity above 1.8 K

33

0.0 0.1 0.2 0.3 0.410

15

20

50

100

150

200

T (

K)

X

EuFe2-X

NiXAs

2

SDW

CAF FM

0.0 0.1 0.2 0.3 0.40

2

4

6

8

10

12

14

16

Hcr (k

Oe

)

x

HcrIIc

HcrIIab

II c

II ab

EuFe2-x

NixAs2

Magnetic phase diagram of EuFe2−xNix2As2

Magnetism of Eu in EuFe2-xNixAs2 is very similar to that in EuFe2-xCoxAs2

and seems to be not responsible for the absence of superconductivity.

34

Search for superconductivity in EuFe2-xNixAs2 under high pressure

0.0 0.5 1.0 1.5 2.0 2.510

15

20

40

80

120

160

200

T (K

)

pressure (GPa)

0.0 0.5 1.0 1.5 2.0 2.5

10

15

20

40

80

120

160

200

0.0 0.5 1.0 1.5 2.0 2.5

10

15

20

40

80

120

160

2000.0 0.5 1.0 1.5 2.0 2.5

10

15

20

40

80

120

160

200

x=0.01

0.04

0.08

0.12

SDW

AF/F

no evidence of superconductivityunder pressure down to 2 K

Resistivity measured using piston-cylinder pressure cell

Magnetic field easily aligns Eu2+ spins along the direction of the applied field(field induced ferromagnetism)

Hydrostatic perssure, transition metal substitutions, and P substitution suppress SDW order, induce superconductivity and change magnetic order of Eu2+ moments from antiferro- to ferromagnetic

Superconductivity coexists both with AF and F order of Eu2+ system

35

Coexistence of superconductivity and magnetism, Zero-resistance as an effect of applied magnetic field, High anisotropy, Magnetic field sensitive electronic transport ,Spontaneous superconducting vortices,- potentially interesting for spintronics and other electronic applications

Doped EuFe2As2

Collaboration:

Presented unpublished results obtained in fruitfullcollaboration with:

Michał BabijLan Maria TranDaniel GnidaPiotr Wiśniewski

36