On the influence of 3d4 ions on the magnetic and crystallographic properties of magnetic oxides

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On the influence of 3d4 ions on the magnetic and crystallographic properties of magnetic oxides

John B. Goodenough

To cite this version:

John B. Goodenough. On the influence of 3d4 ions on the magnetic and crystallographic properties

of magnetic oxides. J. Phys. Radium, 1959, 20 (2-3), pp.155-159. �10.1051/jphysrad:01959002002-

3015500�. �jpa-00236008�

155

ON THE INFLUENCE OF 3d4 IONS ON THE MAGNETIC AND CRYSTALLOGRAPHIC PROPERTIES OF MAGNETIC OXIDES (1)

By ^{JOHN B.} GOODENOUGH (2).

Résumé.

Un interstice octaédrique ^{dans un} réseau des anions devient tétragonal ^{s’il est} occupé par ^un cation ayant ^la configuration électronique ^{externe 3d4.} Après ^{une courte} référence à

l’origine physique ^{de cet} effet, ^on l’illustre _par les propriétés cristallographiques ^de plusieurs oxydes

contenant les ions Mn3+. Une structure pour la phase orthorhombique ^de LiMnO2 ^est suggérée ^en

accord avec les diagrammes ^de rayon-x donnés dans la littérature. On démontre également que les cations 3d4 peuvent ^former simultanément des couples ferromagnétiques ^et antiferromagnétiques

avec des cations similaires si l’interstice local est tétragonal. ^{Cet effet est} illustré à la fois dans le réseau cubique simple des cations 3d4 et dans deux réseaux spinelles ^contenant dans les interstices

octaédriques des cations Mn3+. Trois couplages magnétiques différents entre deux ions Mn3+ sont

également ^{mis en} évidence. Cette propriété spéciale des ions 3d4 peut donner ^{lieu au} ferromagné-

tisme ou au ferrimagnétisme dans les réseaux perovskites ^{contenant des} cations Mn3+,

Abstract.

After a brief reference to the physical ^{basis for a} tetragonal distortion (c/a > 1)

of an octahedral anion interstice which is occupied by ^a cation with outer-electron configuration 3d4, the crystallographic properties ^{of several} Mn3+-containing ^{oxides are} given ^to illustrate the signifi-

cance of this effect for determining ^the crystalline symmetry. ^A structure for the orthorhombic

LiMnO2 phase ^is proposed which is consistent with the powder-pattern ^data reported in the lit- erature. It is also pointed ^out that 3d4 cations may simultaneously couple ferromagnetically ^and antiferromagnetically ^with similar cations if the local octahedron is distorted to tetragonal sym-

metry. This effect is illustrated in both the perovskite-type ^{and the} spinel-type ^{lattice. Also}

three different types of Mn3+ 2014 Mn3+ interaction are illustrated. It is pointed ^{out that the} magnetic properties ^{of several} Mn3+-containing, perovskite-type ^{oxides can be} interpreted ^{as due}

to this peculiar property of the Mn3+ ion.

JOURNAL PHYSIQUE 20, ^FÉVRIER 1959,

I. Crystallography.

^Until quite recently ^there

was considerable chemical opinion ^{that the exis-}

tence of cations with outer-electron config-

uration 3d4 is extremely ^rare. However, ^{in 1955}

it was pointed ^out [1, 2], ^{that the} interesting ^lattice

distorsions from cubic symmetry in certain man-

ganese-containing ^{oxides can be} understood if

Mn3+ (3d4) ^is present. ^{It was} shown that for a 3d4 cation in an octahedral anion interstice, ^{the rela-}

tive symmetries ^{of the d wave functions and the} near-neighbor ^{anions stabilize a} distortion of the local octahedron ^to tetragonal (c/a > 1) sym-

metry. ^{In the first} discussion of this effect, ^the

covalent-bond description ^{was used.} Recently

Dunitz and Orgel [3, 4], ^{and McClure} [5] ^{have used} ligand-field theory ^to supplement ^and strengthen

the theoretical argument. ^{Meanwhile several wor-}

kers have investigated ^{this effect} experimentally.

Although recent measurements [6] ^{of the low-} temperature ^lattice parameters ^{in the} system Fe3-xCrxO4 ^{can be} interpreted [7] by this model if

some Cr2+(3d4) ^{ions are} present, illustrations of this effect will be confined to a variety ^{of Mn3+ -con-} taining materials. The crystallographic ^{data for}

several spinel-type compounds ^and systems ^are (1) The research in this document ^was supported by ^the

U. S. Army, ^{U. S.} Navy, and U. S. Air Force under contract with the Massachusetts Institute of Technology.

(2) ^{Staff Member, Lincoln} Laboratory, Massachusetts Institute of Technology.

tabulated in Table I. In _every instance of tetra-

gonal (c/a > 1) symmetry, ^the tetragonal ^dis-

tortion can be attributed to the _presence of Mn3+(3d4) ^{ions on} octahedral sites iri excess of a

certain critical fraction, ^{this fraction} varying slightly ^{with the} type ^of other cation present.

This fraction also varies from one 3d4 cation to

another. It appears ^to decrease with increasing

ratio of 3d4-cation size to anion-interstice size.

Since the macroscopic distortion of the lattice

depends upon ^an ordering ^{of the c axes of the} individually ^distorted Mn3+-occupied octahedra, ^a martensitic, hysteretic phase change ^from tetrag-

onal to cubic symmetry ^{can be} expected ^at higher temperatures. ^{In the} high-temperature, ^cubic phase ^the Mn3+-occupied ^{octahedra are cubic.}

The Mn3+-occupied ^{octahedra are assumed to}

remain cubic even at low temperatures ^{unless the}

concentration of Mn3+ is sufficiently large ^that

there can be a cooperative distortion of octahedral sites to reduce the change in elastic energy relative

to the change ⁱⁿ electronic energy associated with

an octahedral-site distortion. In compositions containing nearly ^a sufficient number ^of Mn3+

cations for a cooperative distortion, ^{there is evi-}

dence [8] ^{that the} room-temperature ^cubic phase

contains regions ^{of local} distortion, ^{but no} long-

range order of the ^{c axes.} In Mn3O4 ^{the transition} temperature ^{is as} high ^{as 1 173 °C} [9]. ^{As the}

fraction of octahedral sites occupied by ^{Mn3+ ions}

Article published online by EDP Sciences and available at http://dx.doi.org/10.1051/jphysrad:01959002002-3015500

156

TABLE 1

R00M-TEMPERATbRE LATTICE PARAMETERS FOR SEVERAL MN3+-CONTAINING SPINELS

is decreased, ^the magnitude of the lattice distortion and the transition temperature ^{decrease. As illus-}

trated in Fig. 1, the transition temperature drops

off sharply ^at the critical Mn3+ concentration for a

cooperative distortion.

In a recent study ^{of the} systems ZnxGe 1-xMn 2O 4,

Zn.,Ge 1,CO 2- 21IMn 2110 4, ^and Li 1,Zn,,Mn 20 4,

Wickham and Croft [8] have shown that the

tetragonal distortions in these systems ^{cannot be} due to Mn2+ or Man4+ ions individually, ^{or to an} ordering of Mn2+ and lVIn4+ ions ; the distortions

can only be attributed . to the presence of Mn3+

ions. Further, they ^{find that the critical fraction}

of octahedral sites which must be occupied by ^{Mn3+ ions for a} cooperative distortion of the

Fie. 1.

Transition temperature ^{Tt for} martensitic tetra-

gonal-to-cubic phase change ^{in the} system

Zna:Ge -x[ CO20153Mn::]0 4.

(Af ter preliminary measurements by ^{D. G.} Wickham, and R. J. Arnott, ^Lincoln Laboratory, ^{M. I.} T.)

FIG. 2.

Saturation magnetization expressed ^{as the}

number of Bohr magnetons per molecule, nB, Curie

temperature, ^Tc, and lattice parameter for the sys- tem Co3-xMnxO4.

(After D. G. Wickham and W. J. Croft, ^Lincoln Laboratory Solid State Q. ^P. R., 1 May 1958.)

lattice is ~ 0.6 in these systems. Typical ^{of the} room-temperature crystallographic data is that of the system Co3-xMnxO4 ^{shown in} Fig. ^2.

If tbe ^{lVIn3+ ions form a} simple-cubic ^{array with}

anions on the cube edges, ^{the elastic} energy is minimized by ^{a différent} type ^of ordering ^{of the} elementary, tetragonal ^octahedra [2]. ^{This order-} ing ^{is shown} schematically ⁱⁿ Fig. ^{3 for the}

FIG. 3.

Ordering ^of dx2 orbitals for the compounds LaMn03, MnF3 and ordered CUC0304, ^In MnF3 ^the

Mn-F distance is 1. 9 A along a3 axis, 2.1 A and 1.8 A within the _a,-a2 plane, ^{the anion} shifting ^{in directions}

of arrows (but ^{also out of} a,-a2) plane [14].

Elementary ^{octahedra are not} tetragonal, but ratio of

long to average of short axes is

1.14.

perovskite-type compound LaMn03, ^{the com-} pound MnF3, ^{and the ordered} rocksalt-type ^com- pound Co3Cu04. ^Other factors, ^{such as ionic} size, also6contribute ^{to the} final lattice symmetry, ^but

this-ordering ^{of the} elementary ^octahedra produces

an axial ratio of the pseudocubic-cell edges ^of a3/aI = a3 ja2 ^1. Hepworth ^{and Jack} [10]

have recently ^{measured the anion} positions

in MnF3. Since the bonds in, ^the a1-a2 plane

can be coordinate covalent whereas those along

the _{a3 axis} can only ^be semicovalent, three ^cation-

anion distances would be expected instead of a

simple tetragonal distortion of the octahedra.

The three distances reported ^for IVInF3 give ^octa-

hedral axial ratios of 1.11 and 1.17, ^or an averaged value of ~ 1.14, ⁱⁿ good agreement ^{with the dis-}

tortions found in the spinels.

Several compounds ^{of the} type AM3+02 ^and AM3+S2, ^{where A} =Li, Na, ^or K, ^{and M3+ is a}

trivalent transition metal, ^{have been} studied, ^and

in many of these there is an ordering ^{of the cations}

into alternate (111) planes which distorts the l attice

to rhombohedral, ^or hexagonal, symmetry. ^The

crystal ^{structure of} NaNi02 ,is interesting ^{in that}

158

although ^this layer ^{structure occurs} above about 220 OC, ^{at lower} temperatures ^the lattice has mono-

clinic symmetry ^{due to the} formation of tetragonal

octahedra about the low-spin-state ^Ni3+ ions, thèse

distortions being quite analogous ^to those of Mn 3+-

occupied octahedral interstices [11, 12]. ^It might

be anticipated, therefore, ^that LiMn02 should form

a similar monoclinic structure. However, LiMn02

forms an orthorhombic unit cell containing ^two

formula weights ^of LiMnO2 [12, 13]. ^{With the aid}

of the powder-pattern data of Johnston and Heikes [13], ^a proposed ^{structure for this} as-yet-"

unidentified phase ^is given ⁱⁿ Fig. ^{4. In the} pro-

FIG. 4.

Proposed unit cell for LiMn02. Arrows indi- cate direction of shift (magnitude d) of oxygen ions from their ideal rocksalt positions. Coordinates through

manganese ^atoms indicate the coplanar directions of shorter Mn-0 bonding. The half-filled de ^orbitals

are oriented along ^the

^axis. Tetragonal ^octahedra

about the Mn3+ ions have an axial ratio of 1.15. Mn3+

and Li+ order in alternate pairs ^of (110) planes.

(Dimensions taken from powder data of Johnston and Heikes, J. Amer. Chem. Soc., 1956, 78, 3255.)

posed model, the distorted octahedra about a Mn3+

ion have ^an axial ratio ~ 1.15, which is similar to that exhibited in the spinels. ^{Since the} phase diagram [14] indicates that the distortion of the

elementaryoctahedral interstices occurs at temper-

atures which are high enough ^for considerable ion

mobility (> ⁸⁰⁰ OC), ^the LiMn02 phase ^{is one in}

which the Li ordering ^{minimizes the} elastic energy associated with the interstice distortions. In the

case of NaNi02, ^the transition temperature ^{is too}

low to permit ^{an ionic} rearrangement ^{to a similar} symmetry. ^This interpretation ^{also accounts for}

the sluggishness reported for the transition of

the LiMn02 phase ^{in the} compositional ranges of Liùmni_O ^{in which the} transition temperature

is 700 OC.

II. Magnetism.

^In magnetic ^{oxides the} pre- dominant magnetic interactions are indirect, ^an

anion playing ^{the role of} intermediary [14].

Although ^the exact nature of this interaction is not yet fully understood, simple symmetry ^consid-

erations plus ^{the fact that the} oxygen p orbital

responsible ^for the indirect interactions contains two electrons of opposite spin suggest ^the following generalization :

Indirect magnetic interactions between cations

on opposite ^{sides of an} anion are, if they ^involve

excited configurations ^{in which one of the anion}

electrons is preferentially stabilized in a cation- anion bond because ^of exchange effects, (1) ^anti- ferromagnetic ^{if the} anion p orbital predominantly overlaps ^{on each side either an} empty ^{or a half} filled cation orbital, (2) ferromagnetic ^{if the over-} lapped ^{cation orbital is} half filled on one side, completely empty ^{on the other.}

FIG. 5.

Schematic diagram for three different types ^of

indirect Mng+-Mn3+ magnetic interaction.

The 3d4 ions in octahedral interstices make a

particularly interesting study ^{since the anions} along

the c axis of a tetragonally ^{distorted interstice} overlap ^a half-filled dz2 orbital, ^those along ^{the a}

axes overlap ^a completely empty dZ2-11’l. ^orbital.

The consequences of this for three différent ^types

of Mn3+-Mn3+ interaction are shown schemat-

ically ⁱⁿ Fig. ^5. Illustrations of these three inter- actions can be found. In LaMn03, ^{the inter-}

actions within an al-a2 plane (see Fig. 3) ^are ferromagnetic, along ^the a3 axis they ^{are anti-} ferromagnetic [15]. ^{A similar} magnetic ordering

has recently been found in MnF3 [16]. ^{The ortho-}

rhombic compound LilVInfJ2 ^{has a} paramagnetic

159

susceptïbility corresponding ^{to a} high-spin-state, spin-only value, ^{and it has an} antiferromagnetic

transition at

300 OK [12]. ^{If the structure} pos- tulated in Fig. ^{4 is} correct, ^the predominant magnetic interaction is along ^{a chain of Mn3+ ions} coupled according ^to the third scheme of Fig. ^5.

This peculiar characteristic of the Mn3+ ion to

simultaneously couple differently ^{in différent direc-}

tions has several interesting consequences. ^{In a}

preliminary discussion of Mn3+-containing, perov- skite type compounds [2, 17], ^{it was sbown that}

this effect can be at least partly responsible ^{for the} particular variation of magnetization with compo- sition which is observed in these compounds. ^The

influence of this eflect on the magnetization ^{of the} tetragonal spinels ^{is of} equal significance.

The saturation magnetizations ^{at 4.2 OK for the} system Co3-xMnxO4 ^{shown in} Fig. ² give ^a striking

illustration. In this system the octahedral-site cobalt ions’are diamagnetic ^{Corn ions} [18]. Ideally

the compositional ^{formulae are}

C02+[Co ’II Mns+] O4 ^for 0 x ²

and Mn*2 C02+ [Mn’,’+] 04 ^{for x} > 2. As is to be expected, ^{the data} suggest ^{that the A-B} coupl- ing ^{is not} completely ^{ordered for} compositions

with x 0.5. With higher concentrations of manganese, however, Néel-type [19] coupling ^is expected ^so long ^{as the} lattice remains cubic. In

FIG. 6.

Schematic coupling ^{scheme for two différent} spinels : (a) is the Néel coupling commonly ^{found in}

cubic crystals ; (b) ^{is a} compromise ordering ^{scheme for}

a tetragonal spinel ^with magnetic ^{unit cell} along ^{c axis}

twice the crystalline ^{unit cell. The A-B} coupling ^is

assumed stable if antiferromagnetic along ^{the c} axis, ferromagnetic along ^{the a axis.}

the tetragonal lattice, however, ^the magnetic coupl- ing ^{between an A-site cation and} B-site Mn3+

cation should, by symmetry considerations, ^{be dif-}

ferent along ^{the c} axis than along ^{the a axes.}

Since it is not possible ^{to obtain a} cooperative arrangement ^{in the} tetragonal spinel lattice such that all A-B coupling along ^{the c} axis is of one

type, along ^{the a axes} another, ^some compromise

state must exist. In Fig. 6(b) ^the ferromag-

netic A-B interactions are .optimized ^{at the}

expense of only ^{a small} percentage ^{of " mis-} matches " in the antiferromagnetic, c-axis inter- actions. Since both sublattice A and sublattice B

are antiferromagnetic ^{in this} arrangement, ^{the net} magnetization ^{is zero.} According ^to Fig. 1, ^the

critical value of x for low-temperature, tetragonal symmetry ^is only ^{a little smaller than the room-} temperature ^{value so that the sudden decrease}

with ^x in the magnetization ^{at x ~} 1. 2, the ^Curie temperature varying relatively slowly ^with x, is

reasonably accounted for by ^the occurrence of such

an antiferromagnetic coupling ^{scheme in the} tetrag-

onal phase. ^The reappearance of ferrimagnetism

with the replacement ^{of A-site Co2+ ions} by

Mn2+ ions suggests that the covalent bonding

induced by ^the large ^{Mn2+ ion} causes some new,

compromise magnetic ^{order to} be achieved.

Recent measurements [20] ^{of the} magnetizations

of samples ^{over the} entire range of composition ⁱⁿ

the system MnxFe3-xO4 ^{show a similar behavior.}

For the _{range of} compositions ^{0 x} 2, ^the magnetic ^{data can be} interpreted by ^Néel coupling

and spin-only ^{cation moments} given the compo- sitional formula

Mni±vFE00FF+[Fcv+FEs-+-2vMn+Wl 0 (1 - y) ^x. However, compositions ^{with x} > 2

are tetragonal, ^{and the} magnetization drops ^off sharply ^to nearly ^{zero at x = 2.5.}

I am grateful ^{to K.} Dwight ^{and N.} Menyuk ^for making ^the liquid-helium magnetization ^measure-

ments reported ⁱⁿ Fig. 2, ^{and to} R. J. Arnott for a

helpful discussion of the powder-pattern ^{data for}

the compound LiMn02..

BIBLIOGRAPHY

[1] GOODENOUGH (J. B.) ^{and LOEB} (A. L.), Phys. Rev., 1955, 98, 391.

[2] GOODENOUGH (J. B.), Phys. Rev., 1955, 100, 564.

[3] ^DUNITZ (J. D.) ^{and ORGEL} (L. E.), ^J. Phys. ^Chem.

Solids, 1957, 3, ^20.

[4] ^DUNITZ (J. D.) ^{and ORGEL} (L. E.), ^J. Phys. ^Chem.

Solids, 1957, 3, 318.

[5] ^MCCLURE (D. S.), ^J. Phys. ^Chem. Solids, 1957, 3, 311.

[6] ^FRANCOMBE (M. H.), ^J. Phys. ^Chem. Solids,1957, 3, 37.

[7] GOODENOUGH (J. B.) (to ^be published).

[8] ^WICKHAM (D. G.) ^{and CROFT} (W. J.) ^J. Phys. ^Chem.

Solids, 1959, 4, ^351.

[9] ^MCMURDIE (H. F.), ^SULLIVAN (B. M.) ^{and MAUER} (F. A.), J. Research Nat. Bur. St., 1950, 45, ^35.

[10] ^HEPWORTH (M. A.) ^{and JACK} (K. H.), ^Acta Cryst., 1957,10, 345.

[11] ^DYER (L. D.), ^BORIE (B. S., Jr.) ^{and SMITH} (G. P.),

J. Amer. Chem. Soc., 1954, 76, 1499.

[12] ^BONGERS (P. F.), Thesis, ^{Univ. of Leiden,} July 4, 1957.

[13] ^JOHNSTON (W. D.) and HEIKES (R. R.), ^{J. Amer.}

Chem. Soc., 1956, 78, ^3255.

[14] ^KRAMERS (H. A.), Physica, 1934, 1, 182.

[15] ^WOLLAN (E. O.) and KOEHLER (W. C.), Phys. Rev., 1955, 100, ^545.

[16] ^WOLLAN (E. O.) (private communication).

[17] ^WOLD (A.), ^ARNOTT (R. J.) and GOODENOUGH (J. B.),

J. Appl. Phys., 1958, 29, ^387.

[18] ^CossEE (P.), ^{Rec. trav.} chim., 1956, 75,1089.

[19] ^NÉEL (L.), ^Ann. Physique, Paris, 1948, 3,137.

[20] ESCHENFELDER (A.), ^J. Appl. Physics, 1958, 29, ^378.