Magnetic order in the (La,Pr,Sr)2CuO4 system across the T'→O phase transition

Physica B 165&166 (1990) 1187-1188 North-Holland

MAGNETIC ORDER IN THE (La,Pr,Sr)2Cu04 SYSTEM ACROSS THE T'+O PHASE TRANSITION

Matthew J. ROSSEINSKY# and Kosmas PRASSIDES* :Inorganic Chemistry Laboratory, Oxford University, Oxford, UK School of Chemistry and Molecular Sciences, Sussex University, Brighton, UK

High resolution powder neutron diffraction has been used to study the magnetic The compositions La 1 . 4 _ X PrO. 6srXcu04 , x=o and 0.01 adopt the T'(Nd 2Cu0 4 ) type structure with a spin structure of the Cu sublattice identical to La Ni0 ; increased hole doping, as in 4 2 La1.37PrO.6srO.03cu04' leads to a first-order structural phase transition to the (K 2 NiF ) type structure and destroys the Neel state. 4

Bragg scattering in the La1.4_xPrO.6srXCu04 system.

°

The attempt to understand the transition

from

insulating

to

superconduct ing behaviour T

ceramic

materials

c exhaustive study of

metallic in

has

to

the highled

to

an

the structural and

magnetic properties of the CU0

factors

obtained

from Rietveld

refine-

ments of data of the same samples from D2b

(ILL)

and

Polaris

diffractometers

(ISIS, RAL). One magnetic peak was only observed for

the systems

wi th x=o and

layers 2 present in all these systems. A fascin-

0.01

ating contrast has been provided by the

the I4/mmm unit cell.

differing

cates a La Ni0 -type magnetic structure 2 4 with a spin direction (~~O) parallel to

behaviour

of

the

Neel

state

in

La Cu0 upon hole-doping and in 2 4 Nd Cu0 upon electron-doping 1 . We have 4 2 recently studied in detail the competition between the K NiF -type (O,T) and 2 4 the Nd Cu0 -type (T ' ) structures using 2 4 high resolution powder neutron diffra2 ction in the (La,Pr,Sr)2cu04 system Here we the

describe

magnetic

Cu0

and

its

the

determination

structure

of La 1 . 4 Pr O. 6 derivatives

hole-doped

4 La1.4_XPrO.6srXcu04' x=O.Ol, the T'+O phase transition.

Powder neutron diffraction ments were ter, K

ILL,

(A=2.52

of

performed

0.03

near

measure-

(D1B diffractome-

Grenoble) between 1.5 and 300 A)

with

nuclear

structure

a

h

that could be indexed as x

12

(~~1)

on

rotation of the basal plane of

the magnetic The values

of

This again indi-

propagation vector the

(~~O).

Cu staggered moment

and the Neel temperatures in La 1 . 4 Pr O . 6 Cu0 4 and Lal.39PrO.6srO.01Cu04' are estimated as 0.48(1) ].IB and 0.37(3) ].I B' and 210 and 180 K, respectively. No evidence is found for pr 3 + spin participation in the 3D LRO down to 1.5 K. Finally, in the

no magnetic peaks are present diffraction

profile

of

the

La1.37PrO.6srO.03Cu04 compound which adopts the orthorhombically distorted

K NiF structure down to 1.5 K. 2 4 The resul ts above may be compared to

those

0921-4526/90/$03.50 © 1990 - Elsevier Science Publishers B.V. (North-Holland)

already

obtained

for

the

M.J. Rosseinsky, K. Prassides

1188

Ln _ ce cu0 (Ln=Nd,Pr) and La _ 2 4 2 x x xSrXcu04 systems. The magnetic structure of Nd Cu0 is based on the La Ni0 4 2 2 4 type ordering described earlier (C'mm'm' space group) coupling

between

layers,

with

1

; it shows strong

the

Nd 0 2 2 Nd spin

the

and

Cu0 2

direction

parallel to the Cu one and a relatively high TN for Nd 3 + ordering. Successive magnetic at

2

phase

transitions

also

LRO

due

to

the

lanthanide

.

::0.2

iii 0.1

o o

state

due

to

ions

is

crystal-field

effects 4 .

On the other hand,

adopts

spin

a

structure

of

La cu0 _ 2 4 o the Cu

sublattice in which the spin direction (~, -~,

0)

1 ies

magnetic

perpendicular

propagation

Furthermore,

the

T'

to

the

(~~0)5.

vector structure

is

very

robust and the electrons do not show a pronouned effect

on the magnetic order

of

background;

the

Cu(II)

°

in

sharp

contrast, the holes in the structure very rapidly destroy the Neel state 6 ,7. We studied the

two

the competition between

structural

types

0 Itructure T'Itructure

1.92

1.94

250 K;

observed since pr 3 + possesses a singlet ground

near

the

lead

to

rhombically bond

ficantly the magnetic saturation moment of Cu of

23%

to 0.37(3) US' Le. a reduction upon

only

1%

hole-doping

in

La1.39PrO.6srO.01Cu04' This may be compared to the 12% reduction of the Cu moment

upon

3%

of

electron

doping

in

moment

with

distorted

lengths

ratio. LRO of

and

an

enlarged

(cia)

But

most important 1y, the 3D the Cu 2 + spins is destroyed at

the level of 3% doping.

In Figure 1, we

show the dependence of the Cu moment on formal Cu oxidation state for a variety of systems.

(1)

magnetic moment of 0.48(1) US' Holedoping of the T' -phase reduces signi-

2.04

K NiF 4 structure 2 with a collapse in the cu-O basal plane

REFERENCES

La -y Pr y Cu0 4 . The T'-compo2 sition La1.4PrO.6Cu04 shows identical magnetic behaviour to Pr Cu0 with no 4 2 Pr 3 + contribution to the LRO and a Cu 2 +

2.02

I d S r 2 + d op~ng . 1 evels ncrease the adoption of the ortho-

Nd 2Cu 0 41 '

ition

in

1.96 1.98 2.00 Cu oxidation Itate

FIGURE 1 Variation of Cu staggered formal Cu oxidation state

critical point of the T'+O phase trans-

2+

0

:>.

temperatures, due to 3 reorientation . Pr 2CuO 4 also

orders antiferromagnetically at

•

~ 0.4-;

intermediate

cu + spin no

occur

."1 1 1 t t"1 0.5

(2) (3) (4) (5) (6) (7)

M.J. Rosseinsky, K. Prassides and P. Day, J.Chem.Soc.,Chem.Commun. (1989) 1734. M.J. Rosseinsky, K. Prassides and P. Day, Physica C 161 (1989) 21. Y. Endoh et al. ,Phys.Rev.B 40 (1989) 7023; S. Stanthakumar et al. ,Physica C 160 (1989) 124. D.E. Cox et al. ,Phys.Rev.B 40 (1989) 6998; P. AIIenspach et al., Z.Phys.B 77 (1989) 185. D. Vaknin et al., Phys.Rev.Lett. 58 (1987) 2802. M.J. Rosseinsky and K. Prassides, Physica C 162-164 (1989) 522. R.J. Birgeneau, M.A. Kastner and A. Aharony,Z.Phys.B 68 (1987) 425.