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Low temperature magnetic phase diagrams of dysprosium and gadolinium
Physica B 169 (1991) 469-470 North-Holland
LOW TEMPERATURE MAGNETIC PHASE DIAGRAMS OF DYSPROSIUM AND GADOLINIUM A.V.
Andrlanov,
Division University,
of
A.N.
Vasil’ev,
Yu.P.
Low Temperature Physics, Moscow, 119899, USSR
GaiduKov DePartment
of
Physics,
Moscow
State
electromagnetic-acoustic efficiency of field dependences of the The transformation In Gd and DY sini3le crystals have been studied. The sharp Peaks Phase magnetic corresPonding to different of the transformation ef f iclency In Particular, intensive excitation of longitudinal were found. transitions field-induced spin-reorientation the regions of waves occurs in ultrasonic transitions. The data enables to construct. H - T diagrams for GA and DY. 1.
INTRODUCTION spin the restructuring of A material magnetic SubSYStem of a caused by the external magnetic field usually temperature is the or bY magnetoelastic manifested in can interactions These interactions+ be studied using the effect of direct electromaBnetlc-acoustic transformation (EMAT) at the surface The medium (11. conducting of a principles of EMAT are as follows. magnetoelastic ef f iciencr of The strength depends on the interaction of external magnetic field; it can be field. magnetic by the rf modulated both the application of Therefore, constant magnetic fleld H and the althe field h to magnetic ternating the appearance of results in metal within displacements time-dependent leads to the skin layer, i.e. it the waves ultrasonic Of excitation the bulk of the into Propagating All Processes that occur in sample. the magnetic Structure of a Substance are accompanied DY sharp changes of EMAT efficiency (2). 2, EXPERIMENTAL The single crystals of Gd and DY had a rectangular form with the faces crysto the Principal Parallel axes (a and b are the tallographic c is the hexagonal axis). binary axes, The sample under investigation was inductance into a solenoidal Placed were applied coil to which rf Pulses with an amplitude of 2 KV, a duration frequency of Of 1 ps, and a modulated external magnetic field 10 MHz . The (H i 60 KOe) was directed parallel to the alternating one (h :: 100 Gel and crystallothe chosen Parallel to
graphic axis. The ultrasonic waves excited in the sample were detected by the same coil bY means of the inverse EMAT. The signal measured using the echo-technique was ProPortional to the square Of the amplitude of the excited sound. 3. Gd MAGNETIC PHASE DIAGRAMS Gd experiences a transition from collinear into the the Paramagnetic ferromagnetic state at TC = 290 K. In the temperature range from TC to TSF = 240 K the magnetization vector in this metal is Parallel to the hexagoaxis. the easy nal At T < TSF exists. magnetization axis cone The ultrasonic intensive excitation of taKes the waves in Gd Place at Paramagnetictemperature of the ferromagnetic transition. It occurs also at T ! TC In the regions of the field-induced spin-reorientation wall transition. The domain displacement Processes in Gd do not reveal themselves in EMAT (31. The H-T Phase diagrams of Gd are Presented in Fig. 1. The uPPer part of Fig.1 corresPonds to the H II a and configuration, its lower Part is the H II c configuration. for The square dots indicate the beginning of the intenslve EMAT, the circle dots indicate the end of it. In the coordinates of the external field and temperature, region I corresponds to the multidomain Phase, region II COrresPonds to the angular Phase (i.e. there is some angle between the magnetization vector M and vector Hl, and region III corresPonds to the collinear Phase (M II H). The theoretical curves were calculated using
A.V. Andrianov et al. I Magnetic phase diagrams of dysprosium and gadolinium
470
‘HEX KOe 10
5
200
100
0
T,
K
HINT KOe 20
10
01,
f
0
-
8
100
-
’
*
-
r
200
.
’
T,
*
K
FIGURE 1 the data on temPerature dependences of magnetization and magnetic anisotroPy coef f iclents. 4. Dy MAGNETIC PHASE DIAGRAMS DY experiences the transition from the Paramagnetic into the spiral SPin moments state with antiferromagnetic the Plane of the basal lying in = 180 K. structure at TN hexagonal (a*> basal Plane of a Application the an!T) in magnet. ic field Hl destroys thr state tif erromagnetic and 1+ structure, spiral spin the state with into a fan collaPses around oscillat inB moments magnetic The f leld dlrectlon. the magnetic thP transforms into st at e fan a t. state f erromagnet 1c rolllnear “n 2Hl. At TC 1 85 K, DY experiences H2
Into the easy-plane state. easll‘u find the values of t.he magnetic HZ(T) from field dewndences of EMAT as the field values where the sharp changes of the excitation efficiency occur (4). The H-T diagrams are Presented in Fie. 2. Its UPPer Dart corres?Xnds to t-he H II a conf lgurat ion and the lower Part 1s for the H II 5 conflguratlon !a 1.s the easy maSnetlsatlon axis In the tranSItIon ferromagnetic One can Hi(T) and
150
100
.‘I D
’
T,
K
FIGURE 2 basal The
Plane square Hi and
and dots
b
is the lndlcate
hard
one).
the values of the circle dots show the values of Hz In t,he coordinates of the internal f leld temperature, and redion corresponds t Cl I t. h e antlferroma&!netlc reglcn spiral Phase, t 0 the Phase, !I corresDonds angular region to t.h e III corresPc1nd.s fan Phase, and region !V corresponds to the collinear Phase iM II H). The existence of the angular Phase a? T < of the easy-plane TC 1s a consequence anisotroPy. crossed The dots in the lower Part of Fig. 2 is the interface between t_he angular and the fan Phases. REFERENCES (11 E.R, ration Physical Mason
191. (2) A.V.
Dobbs, Electromagnetic geneof ultrasonic waves, in: Acoustics, Vol. 10, ed. W.P. (Academic, N.Y., 1973) PP. 127-
Andrlanov. V.0. &chelnlKov PhYs. Sov. JETP 67 (1988) 588. :3+j ?V. Andrlanov, A.N. Vasil’ev et sov. Phrs. JETP Lett. 45 (1987)
%9. (4) A.V.
al
715
sov.
Andrianov, A.N Vasll’ev PhYS. JETP Lett. 45
et
(1989)
LOW TEMPERATURE MAGNETIC PHASE DIAGRAMS OF DYSPROSIUM AND GADOLINIUM A.V.
Andrlanov,
Division University,
of
A.N.
Vasil’ev,
Yu.P.
Low Temperature Physics, Moscow, 119899, USSR
GaiduKov DePartment
of
Physics,
Moscow
State
electromagnetic-acoustic efficiency of field dependences of the The transformation In Gd and DY sini3le crystals have been studied. The sharp Peaks Phase magnetic corresPonding to different of the transformation ef f iclency In Particular, intensive excitation of longitudinal were found. transitions field-induced spin-reorientation the regions of waves occurs in ultrasonic transitions. The data enables to construct. H - T diagrams for GA and DY. 1.
INTRODUCTION spin the restructuring of A material magnetic SubSYStem of a caused by the external magnetic field usually temperature is the or bY magnetoelastic manifested in can interactions These interactions+ be studied using the effect of direct electromaBnetlc-acoustic transformation (EMAT) at the surface The medium (11. conducting of a principles of EMAT are as follows. magnetoelastic ef f iciencr of The strength depends on the interaction of external magnetic field; it can be field. magnetic by the rf modulated both the application of Therefore, constant magnetic fleld H and the althe field h to magnetic ternating the appearance of results in metal within displacements time-dependent leads to the skin layer, i.e. it the waves ultrasonic Of excitation the bulk of the into Propagating All Processes that occur in sample. the magnetic Structure of a Substance are accompanied DY sharp changes of EMAT efficiency (2). 2, EXPERIMENTAL The single crystals of Gd and DY had a rectangular form with the faces crysto the Principal Parallel axes (a and b are the tallographic c is the hexagonal axis). binary axes, The sample under investigation was inductance into a solenoidal Placed were applied coil to which rf Pulses with an amplitude of 2 KV, a duration frequency of Of 1 ps, and a modulated external magnetic field 10 MHz . The (H i 60 KOe) was directed parallel to the alternating one (h :: 100 Gel and crystallothe chosen Parallel to
graphic axis. The ultrasonic waves excited in the sample were detected by the same coil bY means of the inverse EMAT. The signal measured using the echo-technique was ProPortional to the square Of the amplitude of the excited sound. 3. Gd MAGNETIC PHASE DIAGRAMS Gd experiences a transition from collinear into the the Paramagnetic ferromagnetic state at TC = 290 K. In the temperature range from TC to TSF = 240 K the magnetization vector in this metal is Parallel to the hexagoaxis. the easy nal At T < TSF exists. magnetization axis cone The ultrasonic intensive excitation of taKes the waves in Gd Place at Paramagnetictemperature of the ferromagnetic transition. It occurs also at T ! TC In the regions of the field-induced spin-reorientation wall transition. The domain displacement Processes in Gd do not reveal themselves in EMAT (31. The H-T Phase diagrams of Gd are Presented in Fig. 1. The uPPer part of Fig.1 corresPonds to the H II a and configuration, its lower Part is the H II c configuration. for The square dots indicate the beginning of the intenslve EMAT, the circle dots indicate the end of it. In the coordinates of the external field and temperature, region I corresponds to the multidomain Phase, region II COrresPonds to the angular Phase (i.e. there is some angle between the magnetization vector M and vector Hl, and region III corresPonds to the collinear Phase (M II H). The theoretical curves were calculated using
A.V. Andrianov et al. I Magnetic phase diagrams of dysprosium and gadolinium
470
‘HEX KOe 10
5
200
100
0
T,
K
HINT KOe 20
10
01,
f
0
-
8
100
-
’
*
-
r
200
.
’
T,
*
K
FIGURE 1 the data on temPerature dependences of magnetization and magnetic anisotroPy coef f iclents. 4. Dy MAGNETIC PHASE DIAGRAMS DY experiences the transition from the Paramagnetic into the spiral SPin moments state with antiferromagnetic the Plane of the basal lying in = 180 K. structure at TN hexagonal (a*> basal Plane of a Application the an!T) in magnet. ic field Hl destroys thr state tif erromagnetic and 1+ structure, spiral spin the state with into a fan collaPses around oscillat inB moments magnetic The f leld dlrectlon. the magnetic thP transforms into st at e fan a t. state f erromagnet 1c rolllnear “n 2Hl. At TC 1 85 K, DY experiences H2
Into the easy-plane state. easll‘u find the values of t.he magnetic HZ(T) from field dewndences of EMAT as the field values where the sharp changes of the excitation efficiency occur (4). The H-T diagrams are Presented in Fie. 2. Its UPPer Dart corres?Xnds to t-he H II a conf lgurat ion and the lower Part 1s for the H II 5 conflguratlon !a 1.s the easy maSnetlsatlon axis In the tranSItIon ferromagnetic One can Hi(T) and
150
100
.‘I D
’
T,
K
FIGURE 2 basal The
Plane square Hi and
and dots
b
is the lndlcate
hard
one).
the values of the circle dots show the values of Hz In t,he coordinates of the internal f leld temperature, and redion corresponds t Cl I t. h e antlferroma&!netlc reglcn spiral Phase, t 0 the Phase, !I corresDonds angular region to t.h e III corresPc1nd.s fan Phase, and region !V corresponds to the collinear Phase iM II H). The existence of the angular Phase a? T < of the easy-plane TC 1s a consequence anisotroPy. crossed The dots in the lower Part of Fig. 2 is the interface between t_he angular and the fan Phases. REFERENCES (11 E.R, ration Physical Mason
191. (2) A.V.
Dobbs, Electromagnetic geneof ultrasonic waves, in: Acoustics, Vol. 10, ed. W.P. (Academic, N.Y., 1973) PP. 127-
Andrlanov. V.0. &chelnlKov PhYs. Sov. JETP 67 (1988) 588. :3+j ?V. Andrlanov, A.N. Vasil’ev et sov. Phrs. JETP Lett. 45 (1987)
%9. (4) A.V.
al
715
sov.
Andrianov, A.N Vasll’ev PhYS. JETP Lett. 45
et
(1989)