Upload
buitram
View
217
Download
0
Embed Size (px)
Citation preview
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