DIFFERENTIAL SUSCEPTIBILITY X(T, H) OF THE MIXED MAGNETIC SYSTEM PdFeMn

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DIFFERENTIAL SUSCEPTIBILITY X(T, H) OF THE MIXED MAGNETIC SYSTEM PdFeMn

B. Verbeek, G. Nieuwenhuys, H. Stocker, J. Mydosh

To cite this version:

B. Verbeek, G. Nieuwenhuys, H. Stocker, J. Mydosh. DIFFERENTIAL SUSCEPTIBILITY X(T, H)

OF THE MIXED MAGNETIC SYSTEM PdFeMn. Journal de Physique Colloques, 1978, 39 (C6),

pp.C6-916-C6-917. �10.1051/jphyscol:19786407�. �jpa-00217877�

JOURNAL DE PHYSIQUE Colloque C6, supplément au n" 8, Tome 39, août 1978, page C6-916

DIFFERENTIAL SUSCEPTIBILITY X ( T , H > OF THE MIXED MAGNETIC SYSTEM PdFeMn

B.H. V e r b e e k , G . J . Nieuwenhuys, H. S t o c k e r and J . A . Mydosh.

Karmerlingh Onnes Labovatovivm dev Rijksuniversiteit, Leiden, The Netherlands.

Résumé.- Nous avons étudié l'influence d'un champ magnétique continu sur la susceptibilité d'un système magnétique mixte PdFeMn et on montre que cela donne un critère pour distinguer la transition ferromagnétique et la transition verre de spin dans la zone mixte.

Abstract.- The magnetic field dependence of the differential susceptibility of the mixed magnetic system PdFeMn provides an important criterion to define the spin glass and ferromagnetic transitions in the mixed region.

Competing magnetic interactions in insulating systems and binary rare-earth alloys result in dif- ferent magnetic phases and lead to interesting cri- tical properties /1,2/. Recently it has been found that some binary alloys with transition elements al- so exhibit such mixed (ferromagnetic -»• spin-glass) magnetic behaviour /3/. A further and better contro- llable example of this behaviour is found for the ternary : (Pd Fe ) Mn , 0<x<0.08, in

0 -9965 0-0035 1~X X

which the indirect giant moment ferromagnetism com- petes with direct antiferromagnetic interactions re- sulting in a spin glass transition. In a previous paper /4/ it was shown that for a composition range 4<x<6 at.% Mn this alloy exhibits a double magnetic transition. At high temperatures paramagnetism gives way to a ferromagnetic state, which is followed by

a spin glass phase at lower temperatures. The low field ac susceptibility offers a sensitive method to determine both types of magnetism, and in this paper we consider the effect of small applied dc magnetic fields, He x, on the temperature dependen- ce of the differential susceptibility.

The susceptibility was measured with a stan- dart mutual induction bridge operating at a frequen- cy of 210 Hz and an ac driving field of about 0.1 Oe. A superconducting solenoid produced the exter- nal dc magnetic fields (up to - 1 kOe) which were parallel to the ac driving field. The samples were spark cut in perfect spheres.

In figure 1 the temperature dependence of the susceptibility of binary PdFe 0.35 at.% is shown

Supported .by the Nederlandse Stichting voor Fun- damenteel Onderzoek der Materie (FOM - TON).

for various applied dc magnetic fields.

r \ \ V ^_

i i 0 T 5 10 K 15

Fig. 1 : Differential susceptibility of PdFe 0.35 at.% versus temperature. Curve (a) : He x = 0 Oe, curve (b) : He x = 50 Oe, curve (c) : He x = 75 Oe and curve (d) : He x = 150 Oe.

PdFe is a giant moment ferromagnet with y „ = 10 UR and exhibits the typical knee-like characteristic near the ferromagnetic transition-see curve (a).

At temperatures below T with H = 0 the suscepti- bility of the ferromagnetic alloy is determined by the demagnetization factor D (= 4.18 for a sphere) : Y = 1/D for T<T . Curve (d) is the result for

c

H = 1 5 0 Oe, which shows that the large ferroma-

ex ° gnetic signal has changed into a small peak at the

transition temperature T which can be explained by considering the magnetization curve M(H ) . The differential susceptibility x = AM/AH measures the slope of M(H ) . For H£ x = 0 and T<T , a spon- tanous magnetization appears with a very large

Article published online by EDP Sciences and available at http://dx.doi.org/10.1051/jphyscol:19786407

AM/AHac and x is thus limited by the D-factor. spin glass, and thus show that two independent or- However, if Hex # 0, the difference in the parama- dering mechanisms are present for this concentration.

gnetic and approximately saturated M(Hex) curve r e sults in a bump around Tc which has been observed in other ferromagnetic systems and is taken as a characteristic property of a ferromagnetic transi- tion 151. For intermediate fields, curve (b) and (c), there is this same bulge at T=Tc, but at lo- wer temperatures, the spontaneous (non uniform) magnetization overcomes the uniform field directed magnetization and a large x appears 161.

A paramagnetic to spin glass transition will occur in PdFeMn when the concentration of

is more than 7 at.%, characterized by the typical cusp in the susceptibility as shown in figure 2 -

curve (a) for the 8.1 at.% Mn ternary alloy.

Fig.

Differential susceptibility of

(PdFeo.3s)I-xMn, with x=8.1 at.%. Curve (a)

He,=

0

Oe, curve (b)

Hex=200 Oe and curve (c)

Hex=

500 Oe.

Here an applied field has a much less dramatic effect on the susceptibility signal. Clearly a rounding of the spin glass peak and a shift of the maximum to lower temperatures (as a result of the restraint on the spin glass transition from the field) determine the field dependence of the sus- ceptibility response of a spin glass transition.

The difference in the dc field dependence of the differential susceptibility of a ferromagnetic and spin glass transition can be directly applied to those cases where the two transitions in PdFeMn are very close to each other resulting in a large susceptibility peak for Hex

0 as shown in figure 3 by curve (a) for the E F e

6 at.% Mn. Due to the opposite field dependence a small applied ma- gnetic field is able to separate the single peak into the typical responses for ferromagnetism and

Fig. 3

Temperature dependence of the differential susceptibility of (PdFeo.35),- Mn with x

6 at.%.

Curve (a)

H

0 Oe, curve )CblX: H

50 Oe, curve (c)

H~~

100 Oe, curve (d)

200 Oe and curve (e) Hex

500 Oe .

References

/I/ Aharony, A. Proc. Conf. Magnetic Alloys and Oxides, Haifa, 1977, to be published in

Mag.

and Mat 1

978).

121 ~indglrd P.A., Phys. Rev. B14 (1976) 4074.

131 Mixed magnetism has been observed in &Fe

B.R. Coles, Sarkissian, B.V.B., and Taylor,R.H.

to be published in Phil. Mag. and Verbeek, B.H.

and Mydosh, J.A. to be published. Ferromagne- tism to mictomagnetism has been seen in FeAl by Shull R.D., Okamoto, H. and Beck, P.A. Solid State Commun. 0 (1976) 863. Other favorable systems include C F e , E C o and PtFe alloys at very low concentrations, Nieuwenhuys,

this con£ erence , ^{and CuNi} .

/4/ Verbeek, B.H., Nieuwenhuys,

Stocker, H.

and Mydosh,

Phys. Rev. Letters 40 ⁽¹⁹⁷⁸⁾

587.

151 Maartense, I. and Williams, G.,

Phys. F

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